Charger from a computer's uninterruptible power supply circuit. A quick charger from a burnt-out UPS

UPS battery charger

I am publishing my article reader Alexander, who lives in Alexburg, or more precisely in Riga.

The article discusses in detail the principles of operation of batteries, the processes of charging and discharging, and provides ways to maximize the use of battery life.

There are very few such major works on the Internet now. Having seen the article, I realized that if properly prepared, it would be at least equivalent to a master’s thesis! I myself learned a lot of useful things from it, and I recommend it to my readers!

A LITTLE HISTORY or how it all started

In the early 2000s, I came across an old uninterruptible power supply BACK-UPS 600I from the Basurman manufacturer APC. I got it for free because its batteries were dead. Of course, I immediately tested it, bought batteries recommended by the Basurman manufacturer and “it worked for me”!

I wrote about such a UPS in an article about use.

I couldn’t be happier with him then. Of course, there is no light, but the computer and monitor are working.

But in one unfortunate moment my joy was ruined.

And who do you, Reader, think?.. Fucking hucksters. The first time I replaced two 6V/7Ah batteries with one 12V/7Ah it turned out a little cheaper. But when the battery died again within a year, I started thinking! Firstly, the battery had to be changed once every year or two. Secondly, I wanted the devices connected to the UPS to work not for a few minutes to “properly turn off the power,” but at least until the end of the calculation on the Premier line from Adobe.

This is where naughty thoughts began to arise in my mind: should I connect a 100-amp car battery (to be reliable) to my UPS. Moreover, the traders argued that only gel batteries should be used in the UPS, frightening with Great Punishments those who try to use much cheaper batteries for cars.

But I am a fairly literate person and have learned that you need to know the materiel! Otherwise, something might go wrong with the big bodabum! But you can’t trust traders. Therefore, I took up the study of materiel! As a result of my research, something that I am happy with to this day was born. Namely, I made it so that you can now connect a car battery to a UPS. That is, the UPS and the battery became friends.

INSTEAD OF A FOREWORD. Types of batteries

Uninterruptible power supplies (UPS) use gel batteries. And there are good reasons for this. I will not list them all, but I will explain the main ones. Imagine an office secretary with a twenty-kilogram battery in her hands. It's a funny sight, isn't it?..

There are not so many technically competent specialists who thoroughly know what electric current is. And specialists who know how a switching power supply works, how an inverter converts direct voltage into alternating voltage and even less. The average computer user is not interested in this. That's why gel batteries were created. Inside such a battery, of course, there is no hair gel or helium, as an inexperienced secretary might think from the name. Inside there is the same sulfuric acid and the same lead, as in a regular car battery that has been familiar to us for more than a century. Only there is still a fine mesh with very, very small cells made of non-conductive material, which holds the acid like a sponge in its pores. Also, such a battery does not require maintenance.

Imagine the same secretary with a hydrometer in her hands, with a jar of electrolyte and a bottle of distilled water on the table. UPS manufacturers strive to protect themselves from lawsuits and claims. Therefore, they use the safest batteries in their devices from the point of view of use by an inexperienced consumer. But we know the materiel :)).

I will not go into the weeds and touch in great detail on existing types of batteries, the issue of battery operation under different conditions (huge starting current, long-term load, constant undercharging, overcharging, electrolyte boiling off, deep discharge, operating temperature, etc.), although some -which of these concepts will be discussed in more detail further in the text. I simply guarantee and responsibly declare, based on my practical experience, that under certain conditions it is possible to use cheap starter batteries in a UPS instead of expensive gel ones! So, let's begin!

Battery THEORY. Required for studying!

Here I will only touch on the theory of MAINTAINED lead-acid starter batteries used in cars and produced in compliance with all technological production standards (in other words, not produced in the Chinese basement of Uncle Liao or in the janitor's room of the former house of Ippolit Matveevich in Stargorod). They are the cheapest but at the same time the most “knowledge-intensive” to operate.

If they are used and maintained correctly, but most importantly, charged correctly, they can last more than 15 years, or withstand more than FOUR HUNDRED 100% discharge-charge cycles or more than a THOUSAND 30-40% discharge-charge cycles! It's been tested, I guarantee!

The principle of operation of the battery

The battery has two extreme operating states - completely discharged and fully charged. Let me touch on these two states in more detail. Any car battery consists of 6 “cans”. This is slang for a vessel that contains plates and acid. The plates in these vessels are connected in series. Here is the first fundamentally important point. One “can” also has two extreme operating states - completely discharged with a voltage of 2.00 volts and fully charged with a voltage of 2.40 volts.

What's new in the VK group? SamElectric.ru ?

Subscribe and read the article further:

• The voltage of a completely discharged battery is 12.00 volts (6 x 2)
• The voltage of a fully charged battery is 14.40 volts (6 x 2.4)

How can this be, you ask? After all, the voltage on the battery is never more than 13 volts. And you'll be right. The voltage on a fully charged battery will be in the range of 12.75 - 12.80 volts with an electrolyte density of 1.26 g/cc and at a temperature of 25 degrees Celsius. But where does 14.4 volts come from?.. During charging and discharging, complex chemical processes occur in the battery, which last for some time after the charger or load is disconnected. This can be called chemical inertia. The density of the electrolyte changes accordingly.

The temperature in the battery can also be different (from -40 to +50). When some processes occur in the battery, all its indicators change. And they are interconnected. A voltage of 12.75 - 12.80 volts is the “rest voltage” of a fully charged battery. For a fully charged battery, the voltage will drop when a load is connected. When the load is turned off, the voltage will again tend to the same 12.75 - 12.80 volts. But since a certain amount of energy was given, the voltage (depending on this amount) will not rise to 12.75 - 12.80 volts.

The battery is considered discharged by a certain percentage. Accordingly, when charging, the voltage increases, and when charging stops (the processes inside the battery also stop), the voltage again tends to the resting voltage.

And here on the podium appears His Majesty Electric Current, measured in amperes. The greater the load current on the battery, the more energy the battery will release per unit time. And it will discharge accordingly. The battery's electrical capacity is usually written on it.

The electrical capacity of the battery is the product of the direct current of the battery discharge and the discharge time at the rated voltage (for a car battery this is 12 volts).

Accordingly, in an hour, a battery with an electrical capacity of 60 Ah can deliver 60 amperes with a voltage of 12 volts before it is completely discharged. In practice, it looks like this: if the battery is loaded with a current of 60 amperes for one hour, its voltage will drop from 12.75 - 12.80 volts to 12.00 volts. This is the fundamental basis of battery operation.

In practice, the battery has one very unpleasant feature. Self-discharge current. Moreover, this current increases if the battery is in the sun and the temperature of the electrolyte in it rises. But the battery capacity also increases accordingly. But in winter, the self-discharge current decreases. But the battery capacity decreases accordingly. Therefore, there are standards for the operation, storage, and preservation of batteries that take into account all these factors.

For a new battery with an electrical capacity of about 60 Ah, the self-discharge current at a temperature of 25 degrees Celsius usually does not exceed 20 milliamps. This means that at room temperature the battery can be discharged to half its electrical capacity in four to five months. As the battery ages and is used intensively, the self-discharge current increases with each discharge-charge cycle. When the battery is loaded, the self-discharge current and the load current are summed up. But what about 14.40 volts, YOU persistently ask again?... Here there is a second fundamentally important point.

Battery charging principle

There are two ways to charge the battery:

• DC charging
• Constant voltage charging

It is impossible to say which one is better. It all depends on what you want to achieve. Fast charging or full charging. I prefer to charge the battery using the second method. And then I will justify my position.

A DC charger is much simpler in design and cheaper to manufacture. A constant voltage charger is much more complex in design and more expensive to manufacture. Those who charged batteries with old Soviet chargers (by the way, very remarkable in their technical parameters and reliability of execution and operation) know the theory.

If the battery is completely discharged, unscrew the caps on the battery, connect the battery to the charger, draw a current of one tenth of the battery capacity and charge for 12 hours. After 12 hours, we reduce the current by half (to one twentieth of the capacity) and recharge for an hour or two, until the electrolyte begins to “boil”, turn off charging. Boiling of an electrolyte is the process of releasing hydrogen vapor from it. Ideally, the electrolyte should not boil. Because then you will have to take a hydrometer, measure its density and add distilled water. Therefore, you need to constantly reduce the current.

If the battery has lost its capacity due to harsh use, deep discharge or simply aging, it can be charged in a couple of hours. And the electrolyte will begin to boil an hour after connecting the charger.

Constant current charging means that the voltage increases while charging. And as soon as the voltage exceeds 14.40 volts, the electrolyte will boil anyway. What to do in this case?.. Option one is to monitor the charging process by constantly lowering the current, keeping the charging voltage at 14.40 volts. Option two is to use an automatic machine that monitors this itself. But it monitors the voltage, lowering the charge current as needed. This is charging in the second way - constant voltage.

The second fundamentally important point is the correct charging of the battery to ALL 100% of its electrical capacity:

YOU CAN FULLY CHARGE THE BATTERY (TO 100% OF ITS ELECTRICAL CAPACITY) WITHOUT BOILING OUT OF THE ELECTROLYTE ONLY WITH A VOLTAGE OF 14.40 VOLTAGES!

I prefer to charge the battery with a constant voltage of 14.40 volts. The reality is that charging a battery to 100% is quite difficult. When the battery has reached 95% of its capacity, its charging current is very small, and at 99% it is simply scanty and can be only 30 milliamps. I will note one detail - this is all on the verge of boiling the electrolyte. Theoretically, the electrolyte begins to boil at a charge voltage of 14.41 volts, provided that the battery is made perfectly, and does not boil at 14.40. In practice, it can be either 14.38 volts or 14.42. It all depends on the battery manufacturer and individually for each specific battery. But I hope you, dear reader, got the point.

The disadvantage of voltage charging is the charging time. Typically, the battery reaches its full charge capacity (100%) in more than a day. The charging current at the initial stage is very important here. You can charge at the initial stage with a current of one-fifth of the capacity. Then the charging time will be reduced. Same as battery life, but not significant. No one has canceled the charging theory. It is preferable not to exceed the charging current of more than one tenth of the battery capacity. The choice is yours, reader.

Can a car battery be used for a UPS?

And now we come to the crux of the matter. How to use a starter battery for a car in a UPS. My BACK-UPS 600I UPS fits this perfectly!

The very first UPSs from APC of the Back UPS series charged the battery exactly according to the principle of charging the battery with constant voltage. There is a microcontroller for controlling battery charging. The estimated battery capacity for my UPS is 7 Ah. The charge current is 350 milliamps at the initial stage. At the end, the current drops to 10 milliamps (in fact, to a current slightly higher than the self-discharge current). Newer UPSs charge differently. I tested the newer model Back-UPS CS 650 (I even wanted to buy it), but this iron beast keeps the voltage at 13.7 volts. When the charge current exceeds a certain parameter, this muck displays the Replace Battery icon on the front panel.

Of course, it can also be used with a car battery, but with a large-capacity battery there may be problems with undercharging. You will have to use external charging with it (I will discuss this issue below, in the Practice section). And the voltage of 13.7 volts is not enough to charge the battery 100%. Therefore, I don’t need such a UPS for nothing. But with my BACK-UPS 600I UPS you can use a battery of at least 150 Ah. Yes, if the battery is completely discharged, it will charge it with a current of 350 milliamps for several days. But it is guaranteed to charge 100%. But in order to save time, you can again get out of this situation using external charging.

PRACTICE charging the battery in a UPS. We study the materiel

So, Reader, we have come to the heart of the matter. I'm glad to present what my Back UPS 600I has become over 14 years of use. 9 of them I use it with lead-acid batteries for the car.

I hasten to immediately convince the skeptics with a fear of hydrogen. Both gas outlet holes on the sides of the battery were sealed with latex from a condom (if anything happens, it will simply inflate). The caps on the cans are also screwed tightly. But during 9 years of operation there were no incidents. Therefore, now they are filled with silicone glue. I use two batteries. The batteries are connected with a common minus and a switched plus. From the inside it looks like this:

On the front panel we see a digital voltmeter that shows a charge voltage of 14.44 volts and an ammeter that shows nothing. This is my standard operating mode. We'll find out why it doesn't show anything below.

Now again, just a little bit of history. What you, Reader, see in the photo below are my very first devices for monitoring UPS. This is a dial voltmeter with an extended scale (measures voltage from 10 volts to 15 volts) and an ammeter with a homemade shunt. I needed to see both the current when operating from the battery and the charging current. If you need to make the voltmeter show the voltage not from zero, but from the desired voltage, the scale can be stretched using voltage dividers; there are diagrams on the Internet.

They were made many years ago and served faithfully before Aliexpress became a symbol of the era. Then I got wonderful and, most importantly, very accurate instruments (an ammeter + a shunt for it and a voltmeter) at inexpensive prices. This is what the UPS looks like with the ammeter turned on:

It shows the charging current. As you can see, the current is not large - only 50 milliamps. This is the UPS battery charging controller. One detail is worth noting. Only after I installed a digital voltmeter of such accuracy did it become clear how the charge controller works. The dial voltmeter could not record this.

The charge voltage periodically varies from 14.37 volts to 14.47 volts and can be at the same level for half an hour or 30 seconds. The charging current depends on the connected battery. If a battery with a capacity of 17 Ah is connected, the charging current is within ten milliamps. But here it’s impossible to say for sure. This is on the verge of instrument error. Maybe 14 milliamps, maybe 6 milliamps. One thing I can say for sure is that it is different for batteries of different capacities.

But the ammeter is not as simple as it seems. The beauty of it is that it can show electrical current in two directions. It will show the charging current and discharge current but with a minus sign. Now I will connect a load of about 180 watts to take 20 amperes from the battery. You can immediately see how the voltage dropped and how the ammeter began to show battery discharge with a negative value:

I configured the UPS for myself based on the fact that I would draw no more than 20 amperes of current from the battery. A load of 90 watts from 220 volts loads the battery within 10-11 amperes. But in fact, I now have two servers on the UPS, a router and a switch. This whole facility consumes about 30 watts from 220 volts, and from the battery within 4-5 amperes. Battery 58 Ah.

It is guaranteed that all this can work without electricity for about 7-8 hours (depending on the load on the servers). As soon as the electricity goes out, I receive an SMS and I can turn off the servers remotely. But I don’t think this will be necessary. In seven hours I will appear and switch to the second battery :)), using a button manually. And while this is all working, I’ll remove the battery from the car and connect it instead of the first one. That's another 7-8 hours. Well, within a day the electricity supply will be restored for sure. So far there have been no such force majeure events. :)) Well, if they do, I’ll splurge on a 100 amp battery. True, you can’t put it in the car. By the way, this is one of the reasons why I don’t use a battery with a larger capacity than my car can “swallow.” Although, as you can see, Reader, the system allows you to use a battery with a capacity of at least 1000 Ah.

Well, the readings a couple of minutes after the UPS power switched back to 220 volts. As you can see, the voltage is 13.08 volts and the charging current is 140 milliamps:

Charge after a small discharge

The connection diagram allows you to INDEPENDENTLY charge one of the batteries while the other is in use. Once every six months I switch between batteries in order to somehow equalize the aging process of both batteries. Wires 6 sq. mm.

It is worth noting that when the length of the wires is more than a meter, you need to use a larger cross-section. For myself, I calculated that with an operating current from the battery of 12-15 amperes and a wire length of 40 centimeters, the voltage drops by 0.008-0.015 volts. This is about an extra 3-6 minutes of battery life. At 7 hours this is insignificant. Accordingly, the shorter and thicker the wires from the battery to the UPS, the better, especially at high load currents.

The wonderful battery selection switch button allows you to connect an external charger. Also, this key, with some skill, allows you to switch batteries while the UPS is running from the battery. This has also been verified. Modern switching power supplies for computers hold the load if the mains voltage is lost for 0.8 - 1.2 seconds. And this is just enough to quickly “switch” the key to another battery when the voltage on the battery drops to a critical level.

The ammeter and voltmeter draw very little current. If you turn off the display backlight LED, the devices consume about one milliampere (I even specifically measured how much the voltmeter consumes by calling up units on the display - this is a smaller number of LCD segments), the device consumed 900-odd microamperes at a supply voltage of 11.11 volts. With the LED on (when the display is lit) about 3 milliamps. And is it important. After all, it is connected to the battery directly. I generally made the ammeter switchable, because its power is connected to the 220 Volt output of the UPS. I want to clarify here. The ammeter's power supply must be galvanically isolated from the circuit in which it takes readings. Its supply voltage ranges from 6.5 volts to 15 volts. I haven't found a suitable power supply for it. As it turned out, a power supply with parameters of 6-12 volts, designed for a load of 10 milliamps, is not so easy to find. But I didn’t have the patience to do it myself. I really wanted to quickly connect it instead of the switch that was there before. So I took a 400 milliamp, 7.5 volt phone charger and connected it to the 220 volt UPS output and made it completely switchable. This is to reduce the load on the 220 Volt output of the UPS when it is running on battery power. The voltage and amperage control key turns off the ammeter completely, and the voltmeter turns off the backlight, minimizing battery energy consumption. Well, in general, that’s all the explanations for the UPS control keys.

CHARGING with an external charger

Now I want to separately touch upon the correct charging of the battery of my UPS. As I mentioned above, I will tell you why I prefer charging the battery with constant voltage. I’ll touch on this issue using my charging as an example. It looks like this:

Its diagram can be found in Radio magazine. Many thanks to my dad, who found it and then soldered it and the author of this development - M. Shumilov for a competent and very useful device made from a computer power supply. Charging is quite complicated to manufacture and configure. But after this process, it will delight you with its accuracy and ease of charging the battery at a guaranteed 100% capacity. The indicator shows, in addition to current, voltage and charging power, the watt-hours spent on charging. This is what it looks like from the inside:

Charge voltage 14.40 volts(adjusted during setup). Precisely so that it is not 14.39 and not 14.41! It is important. The charging current is limited to the range of the battery that you plan to charge. My current is limited to 6.5 amperes. For my needs this is the optimal current.

This type of charging can charge batteries with a capacity from 20 Ah to 80 Ah. Of course, you can also charge a 150 Ah battery. But charging time will be about two days. When the battery is connected, the voltage drops and the charging current is maximum. Here you should pay attention to the fact that if you do not limit the charging current, for the first few seconds it may be the same as the battery capacity. As the battery charges, the voltage tends to 14.40 volts and the charging current gradually decreases. As soon as the voltage rises to 14.40 volts, we can see one of the main parameters of the battery, which is not so easy to find out - SELF-DISCHARGE CURRENT. Using it you can find out how much the battery is worn out and what to expect from it in winter.

Another advantage of this charging method is that you will never overcharge the battery. It can stand on charge for at least 3 months. The electrolyte will never boil and it will be charged 100%. Unfortunately, industrial chargers of this type are very expensive, and the built-in ammeter with voltmeter is direct proof that the charging is really not hacky. Unlike the shitty Bosh and other Vart, where the control indication is carried out by LEDs that light up due to some case of flatulence from the manufacturer. Now I accurately and without any confusion explained the figure of 14.40 volts.

After the charging process, you need to wait about 2-6 hours (depending on the battery capacity) until the battery comes to a resting state. The voltage will be about 13 volts. And within a day or two (when all chemical processes inside stop completely), the battery voltage will drop to a voltage of 12.8 volts. The process of self-discharge will begin. Now, I hope, it has become clear why I plugged the holes in the battery and do not worry about harmful fumes during charging. Periodically, previously once every six months, now once every couple of years, I test and service the battery. I use a hydrometer to check the density of the electrolyte in the jars and its level. Well, accordingly, I recharge the backup battery with external charging.

ABOUT THE CHARGE TABLE and more

Now, perhaps, it is worth giving an explanation to the table, which characterizes the degree of charge and discharge of the battery. I explained everything about charging above. Now for an explanation of the discharge.

As you can see, I have noted that the battery is discharged to zero when the voltage on it drops to eight volts. This is a rather subtle and also important question. Let me immediately explain the term “deep discharge” that I use later in the text. The battery goes into a state of deep discharge when its resting voltage is below 11.35-11.40 volts. This is the upper limit of deep discharge. As I said above, after disconnecting the load, the voltage on the battery begins to increase. It is very important that after 2-6 hours, depending on the battery capacity, this voltage rises to 12.00 volts. This means the battery has not gone into a “deep discharge”. Although, in my experience, even if the battery is briefly discharged to 11.90 - 11.85 volts, nothing bad will happen if it is immediately put on charge. And manufacturers often write the short-term inrush current next to the capacitance. This current instantly sends the battery into a deep discharge, but, as you can see, the battery can withstand this and serves in the car for 5-6 years. When starting the starter in a car, the battery is loaded with currents of up to 200 amperes and the voltage drops to 9 volts. It is important how long the battery is under LOAD in a deep discharge.

The UPS manufacturer sets the lower shutdown threshold at full load on the battery. Therefore, in my case it is about 7.55 volts with a load of about 30-35 amps. I checked on a dead battery when I tested the entire system. At 7.55 volts, the UPS is completely disconnected from the battery and “goes out”. And 8 volts in my table is indicated for full load. This is a “memo to self.” I did not rely on 7.55 volts to leave some kind of safety buffer. In general, it is better not to let the battery discharge until the voltage drops to such a low level. The battery sags in voltage more under full load than under 50% or 30% load. As soon as the load disappears completely, the voltage on the battery rises abruptly and then continues to rise more and more slowly until the actual discharge voltage.

When I tested the UPS, with a 20-amp load on the battery, when the voltage dropped to 8 volts, I reduced the load to 9 amperes, the voltage instantly rose to 10.6 volts, while continuing to slowly decrease. This is calculated empirically. If you discharge the battery with a load of 10 amperes, then the lower value will not be 8 volts, like mine, but more (it can be 8.4 volts, for example, or 9.0 volts) - I repeat, this is calculated empirically. If the load on the battery from the UPS is 10-20% of the calculated value, accordingly the voltage “sags” less, but the load on the battery is longer lasting. And accordingly, the battery remains in a deep discharge under load longer. But this is already “killer” for the battery. Therefore, you need to try not to let the battery become deeply discharged and, if possible, if it comes to this, immediately charge it. And when, during a power outage, we try to disconnect some additional devices from the UPS, increasing the operating time of the UPS from the battery, thereby forcing the battery to work longer in a deep discharge. Therefore, this issue needs to be resolved more fundamentally, coming from the other side - connecting a 150-amp battery :)) and not letting it discharge below the voltage calculated for a certain amperage.

When I described the operating time of my consumers (router, servers and switch) as 7-8 hours, this is actually 2-3 hours the battery will work in a deep discharge. And accordingly, its life time will be reduced quite significantly, but not so much that it will no longer work. But buying a car battery with a capacity of 58 Ah (operating time 2-3 hours) for 32-34 euros is much more pleasant than a battery with a capacity of 7 Ah (operating time 5-10 minutes) for 18-20 euros. Feel and savor the difference;))… And the car battery is MUCH more durable, more serious and more reliable than the gel “battery” that comes “included” with the UPS. Direct proof is the service life of my battery :). Yes, and a gel “battery”, after working for 20-30 minutes in a deep discharge, actually dies immediately - the plates inside it begin to deteriorate and its electrical capacity drops significantly, unlike a car battery, where the loss of electrical capacity from working in a deep discharge for 2-3 hours is measured in percentages .

I would also like to draw the Reader’s attention to one point in the operation of this particular UPS. Comfortable operation with BACK-UPS 600I will be with a load of up to 200 Watts from a 220 volt AC network. Accordingly, about 25 Amperes will be drawn from the battery. At higher currents, the ceramic resistor starts to get very hot. If you want to provide autonomous power to electrical appliances up to 500 watts, you need a UPS designed for high power. And I would also like to draw your attention to the fact that the UPS-shek inverter over 800 volts operates from TWO batteries connected in series (12+12=24 volts) due to design features. I have not seen a kilowatt UPS powered by a single 12 volt battery.

PERHAPS, SELLERS OF SEALED, MAINTENANCE-FREE BATTERIES FOR UPS, AFTER READING EVERYTHING WRITTEN ABOVE, WILL NOT BE SATISFIED. I HAVE ONLY ONE ARGUMENT, BUT REINFORCED CONCRETE – IT’S ALL BEEN WORKING STABLE FOR MANY YEARS. THE LAST TIME I BUYED A BATTERY FOR A UPS SEVEN YEARS AGO (TWO PIECES), ONE IS STILL WORKING, THE SECOND IS NOW WORKING IN A CAR AFTER SERVING IN A UPS FOR FIVE YEARS.

From the blog administrator SamElectric.ru

The article will participate in an article competition, which will be held at the end of 2016. I remind you that the conditions of the competition, all articles and results are .

Download

• Theory and practice of using batteries. Types of batteries. The best thing you can read on the topic is: download.

An example of converting a UPS to a car battery

Reader BoB4uk I used the tips outlined in the article and assembled a similar device. More details in the comments around March 17, 2019.

UPS panel in different modes

We all know how unpleasant it is when the lights suddenly go out. This can happen at any time - at home or in the country. Residents of rural areas cannot be doubly envied, especially if at such moments the circulation pump is running. A sudden switching off of the lights can lead to the death of the future brood or the stopping of the heating pump.

There is an excellent solution to this problem - you just need to buy a car inverter from 12 to 220 V. However, their prices are very high; not every villager can afford to buy such an expensive item.

What to do - where can you inexpensively purchase an uninterruptible power supply for lighting a house, greenhouse, cottage, etc.? Of course, try making it yourself! And the Internet will help us with this.

It turns out that there is a simpler and cheaper solution - you just need to convert the uninterruptible power supply into an inverter.

For this purpose, we will need a working uninterruptible power supply from a computer, which can be bought for literally pennies at flea markets or through advertisements in local newspapers for the sale of used computer equipment. However, the uninterruptible power supply is not entirely suitable for our tasks and requires a little modification. Anyone who knows how to work with a soldering iron can handle this type of work without much difficulty.

Having converted the uninterruptible power supply to an inverter, at the output we get:

• Voltage regulator;
• Charger;
• and of course the inverter.

After our modification, if the uninterruptible power supply is 300 W, then you can load it with 200 W. Of course, the more powerful the uninterruptible power supply, the more you can increase the load on it.

In some UPS systems there are places where you can further increase the power. These places are called transistor switches. As soon as you solder them, the power of the uninterruptible power supply will increase.

Manufacturers sometimes do not solder such transistors in order to reduce the cost of the product. Transistors need the same rating as those installed.

You should also increase the cross-section of the wires from the board connector to the alligator battery.

From the secondary winding transformer to the board terminals,

you need to add one more wire in parallel to increase the cross-section.

The transformer had to be pried apart a little to get to the output of the secondary winding. There are three of these wires coming out.

To prevent the uninterruptible power supply from beeping every minute, we must remove the round beeper.

On the back wall I removed unnecessary connectors and left a hole for them to allow air to escape.

From these terminals we find two 220 volt power wires - the output from the board after the converter and we bring these wires out, we fix our socket.

Our uninterruptible power supply inverter is almost ready. To monitor the battery discharge of a car battery, you can build in a digital voltmeter. Just in case, I also connected a temperature sensor to monitor the temperature on the transistor switches. I attached the thermocouple from the multimeter to the radiator of the field operator’s transistor.

An important point: the inverter from an uninterruptible power supply must have a cold start - this is a function when it can be turned on without external power from a 220-volt household outlet. In some models, the cold start button is pressed twice at different intervals.

That's all the changes. You can take such an inverter with you on a trip - on a picnic, fishing, at home - through it you can connect lamps, a laptop, charge phones, flashlights, in the country and in the countryside - connect an incubator, greenhouse lighting, etc., but no more 70% of the power of our product.

For lighting it is better to use diode lamps; they have little draw and burn brightly. I also connected an 80 W soldering iron, even the TV works without problems.

Soldering with a technical hair dryer (03/04/2016). → An attempt to make a charger for external batteries from a UPS, using the APC BK500EI as an example.

As always, even in such a simple matter there are subtleties:
- earlier everyone assured me that the UPS can output 7A through the charging terminals. Even then I had doubts: the charging current, 10% of the capacity of the original 7Ah battery, was 0.7A. And so it turned out: the UPS is not able to supply more than 1.52A for a long time;
- the UPS terminals are energized even when turned off, the battery is always charged. Open circuit voltage is 13.5V;
- the plastic of the case is easily bitten off with 120mm nippers, burned, sawed out, drilled;
- batteries cannot be connected in parallel due to the exchange currents that arise between them (there are no restrictions, the current from a fully charged UPS battery to a discharged external battery can reach 20A or more). Plus, the resistance of two batteries in parallel is 2 times less than the resistance of a separate battery. As a result, the whole idea of ​​a charger from a UPS comes down to bringing the UPS terminals out through the side wall and a 50-100A switch (in a 1500VA UPS there can be currents of more than 100A when operating from the battery);
- with the price of the mass switch being 150-800 rubles, the idea itself has lost its practical meaning. The 14.4V/0.6A charger easily copes with the charge of the UPS battery (got from the echo sounder) - despite its cost of 200-300 rubles and its small dimensions. And since the voltage in the UPS is 13.5V, there is a 100% safe voltage range when purchasing a charger: V.

If the UPS is not used for its intended purpose (there are no consumers), then a charger is made from it simply:
- 2 holes are drilled in the side wall or along the front;
- RPI-P 1.5-7-0.8 terminals are inserted into the UPS terminals, the wires are led out and end with RPI-M 1.5-7-0.8 terminals (but better than RPPI-M 1.5-7-0.8).

Important! All articles on electronics on this site are made with practical experiments - and this determines the philosophy of electronics and electrical engineering: if you didn’t set up a practical experiment (bare theory) - sit and be silent in a rag, because the theory never coincides with the practice performed - and these inconsistencies are sometimes critical . This is me addressing the question of pseudo-electricians, advisers on general forums, like answers-ru. They give advice that makes your hair stand on end; at the same time they often refer to Ohm's law, which they themselves do not understand. Only practice leads to a correct understanding of Ohm's and Kirchhoff's laws; this realignment of the brain actually results.

Look, even with a regular UPS, how many subtleties have surfaced. And with car fuses - it’s generally the same...

(added 03/05/2016): There are some little things noticed when disassembling the APC UPS. The inside of the body has sharp parts; some places need to be sharpened with a file: this is the only way burrs pierce the skin. The UPS itself is 500VA, but the transformer inside is 430W. The board contains power terminals, RPI-P 1.5-7-0.8 were not even close.

If the UPS board breaks down specifically in the battery charging function, you can use this UPS as a surge protector for 4 “sockets”: with a 7A fuse and a convenient power button. And you can hide money inside the battery compartment: thieves, as a rule, do not carry cheap, heavy items.

The most important function performed by an uninterruptible power supply is the function of providing electricity to the load connected to it at the moment of loss of the mains supply voltage. As you know, for these purposes, any UPS includes a battery and an inverter, which converts the battery's direct current into the alternating current required to power the load. These components, of course, are the most important as part of any UPS, but without one more element it is impossible to imagine any uninterruptible power supply. This is a charger, which, by the way, accounts for a fairly high percentage of all UPS failures.

The main function of the charger included in the UPS is to charge the battery and further maintain this charge at the appropriate level. Functioning of the charger, i.e. The battery is recharged during those periods of time when there is mains supply voltage at the UPS input. Of course, the circuit design and main characteristics of the charger are determined by a number of parameters:

- type (class, topology) of an uninterruptible power supply (interactive, backup, ferroresonant, On-Line, etc.);

- UPS output power;

- the number of batteries included in the UPS;

- type of batteries used;

- UPS price;

- developer preferences.

It is the variety of factors influencing the choice of charger topology that has led to the fact that in modern uninterruptible power supplies we will find several completely different charger circuit design options.

An attempt to classify chargers has led to the fact that we propose to distinguish the following basic options for charger circuitry:

- linear voltage and current regulators;

- pulse DC-DC voltage converters;

- pulsed single-cycle voltage sources;

- push-pull bridge rectifier circuit combined with an inverter.

We do not claim completeness of the proposed classification, but our further review is intended to show with real examples that the circuit design options we have identified are used in the vast majority of modern uninterruptible power supplies.

Before moving on to a review of the circuit design features of various charger options, let’s say that the value of the charging voltage of the batteries, i.e. The output voltage of the charger depends, first of all, on the number of batteries in the UPS. This dependence is reflected in Table 1.

Table 1. Dependence of the charging voltage on the number of batteries

Number of batteries
	from 13.2V to 14V
	from 26.7V to 28.5V
	from 53.4V to 57.0V

The functionality of the charger and the correct formation of the voltage that charges the batteries can be checked as follows:

1. Connect the UPS to an alternating current network with a rated voltage (230V).

2. Open the cover covering the batteries and provide free access to the terminals on the batteries to which the wires (red wire and black wire) from the main board are connected. A similar procedure is very easy to perform in APC Smart-UPS devices. On other APC models and other manufacturers' UPS, you will have to consider how to provide access to the battery terminals.

3. Turn on the UPS and wait for the UPS self-test procedure to complete, which may take 8-15 seconds. After completing the self-test, the UPS switches to On-Line mode, which is usually indicated by the corresponding indicator (most often green).

4. Disconnect the black wire from the batteries, then the red wire.

5. Measure the DC voltage between the black and red wires.

6. The measured voltage is the charging voltage of the battery generated by the charger. The value of this voltage depends on the UPS model and the number of batteries used in that model. Typical values ​​of this voltage are presented in Table 1. But here you need to keep in mind that some cheap and primitive models of uninterruptible power supplies can turn off when the battery is disconnected.

7. If the measured voltage is not within the specified range, this indicates a malfunction of the UPS main board, and in particular a malfunction of the battery charging circuit.

In addition to the number of batteries, the charging voltage and charging current can also be influenced by factors such as:

- ambient temperature;

- battery charging method.

The voltage across a lead-acid battery cell is 2.2 V. Among all types of batteries, lead-acid batteries have the lowest energy density. There is no “memory effect” in them. Their long charge will not cause battery failure.

For the charging algorithm of lead-acid batteries, voltage limitation is more critical than charge current limitation. The charging time for sealed lead acid batteries is 12 – 16 hours. If the current is increased and multi-stage charging methods are applied, it can be reduced to 10 o'clock and less. But most UPS models do not go for such complications, preferring to use simpler battery charging schemes.

According to their purpose, lead-acid batteries, as well as other types of batteries (for example, nickel-cadmium), can be divided into two large groups:

1) Batteries for cyclic use, i.e. batteries used as the main source of power and characterized by repeated charge/discharge cycles.

2) Batteries operating in buffer mode, used in backup power supplies.

According to this division, the possible methods of charging batteries differ. For cyclic batteries, charging methods are used at a constant charge voltage and at constant charge voltage and current values. For buffer batteries, a two-stage charging method is used:

- firstly, the charging method at a constant charge voltage;

- secondly, the compensating charge method (jet or drop charging).

To charge buffer batteries, it is possible to use methods included in a two-stage charge as independent methods, i.e. they can be charged either by constant voltage or by the compensating charge method.

To better understand charger circuits, let's look at the basic methods of charging lead-acid batteries used in uninterruptible power supplies.

Constant voltage charging method

With this charging method, a constant voltage is applied to the battery terminals at the rate of 2.45 V per element at air temperature 20 – 25 °C, i.e. In this case, voltage must be applied to a battery with 6 cells (12-volt batteries) 14.7V. But this is in theory, in practice everything is somewhat different. The magnitude of this voltage may vary slightly for different types of batteries from different manufacturers. The technical documentation for rechargeable batteries clearly indicates the value of the charge voltage and information on its corrections for cases where the ambient temperature differs from normal ( 25°С). It should be noted that in real devices this voltage may also differ slightly, depending on what battery charging mode the UPS manufacturer decided to use. The service documentation for the UPS must provide information about the charging voltage for each specific uninterruptible power supply model. Similar data for UPS from a manufacturer such as APC is presented in table 2. But what should be in the sources of other models and other brands, unfortunately, can only be found out experimentally, working with absolutely serviceable devices.

Table 2. Charging voltage of some APC UPS models

ModelUPScompaniesAPC	Charger output voltage
Back-UPS 250EC/250EI	13 . 8 (±0.5) VDC
Back-UPS 400 EC/EI/MI	13 . 8 (±0.5) VDC
Back-UPS 600 EC	13 . 8 (±0.5) VDC
Back-UPS 200	from 13.75 to 13. 8 VDC
Back-UPS 250 (BK250)	13.76 (±0.2) VDC
Back-UPS 360/450/520	from 13.75 to 13. 8 VDC
Back-UPS 400/450 (BK400/450)	13.76 (±0.2) VDC
Back-UPS 600 (BK600)	13.76 (±0.2) VDC
Back-UPS 900/1250 (BK900/1250)	27.60 (±0.2) VDC
Back-UPS AVR 500I/500IACH	13.6 (±3%) VDC
Back-UPS PRO 280/300J/420	13.6 (±3%) VDC
Back-UPS PRO 500J/650	13.6 (±3%) VDC
Back-UPS PRO 1000	from 26. 7 to 28. 5 VDC
Back-UPS PRO 1400	13.6 (±3%) VDC
Smart-UPS 450/700	from 26. 7 to 28. 5 VDC
Smart-UPS 1000/1400	from 26. 7 to 28. 5 VDC
Smart-UPS 2200 RM/RMI/RM3U/RM3UI	from 53.4 to 57.0 VDC
Smart-UPS 3300 RM/RMI/RM3U/RM3UI	from 53.4 to 57.0 VDC
Smart-UPS 250 (1G and 2G)	from 20.4 to 21.2 VDC
Smart-UPS 370/400 (1G and 2G)	from 27.05 to 27.9 VDC
Smart-UPS 600 (1G and 2G)	27.60 (±0.2) VDC
Smart-UPS 900/1250 (1G and 2G)	27.60 (±0.2) VDC
Smart-UPS 2000 (1G and 2G)	55.1 (±0.55) VDC
Smart-UPS RM 700/1000/1400	27.60 (±0.27) VDC
Matrix-UPS	55.3 (±0.5) VDC

The charge is considered complete if the charge current remains unchanged for three hours. If you do not monitor the constant voltage on the battery, it may overcharge. As a result of electrolysis, due to the fact that the negative plates cease to actively absorb oxygen, the electrolyte water begins to decompose into oxygen and hydrogen, evaporating from the battery. The electrolyte level in the battery decreases, which leads to a deterioration in the chemical reactions in it, and its capacity will decrease and its service life will be shortened. Therefore, charging using this method must occur with mandatory control of the voltage and charging time, which will increase the battery life.

You should pay attention to this charging method as the simplest. Previously, in the domestic literature, when charging unsealed lead-acid batteries, it was considered normal to charge them with an initial current equal to 0.1C for 8 – 12 hours at charging voltage based on 2.4 V per battery cell.

Figure 1 shows, as an example, the charging characteristics of 12-volt lead-acid batteries discharged to 50% and 100%. The degree of discharge is determined by the end-of-discharge voltage on the battery.

Fig. 1 Charging characteristics of 12-volt lead-acid batteries

When charging with constant voltage, the charger must have a timer to turn off the battery at the end of charging or another device that monitors the time or degree of charge of the battery and issues a shutdown signal to the control device. This function in modern uninterruptible power supplies is performed by a microprocessor that monitors the battery charge. Limiting the charging time allows you to avoid both undercharging and overcharging. Please remember that interrupting the charge will shorten the battery life.

Do not charge a fully charged battery - overcharging may damage it. When using the battery cyclically, the charging time should not exceed 24 hours.

Two-stage charging method at constant charging voltage

The two-stage charging method at constant charging voltage, as its name suggests, occurs in two stages:

- charge first at a higher charge voltage;

- and then charge at a lower charge voltage (trickle or compensating charge).

The operation of the charger is explained by the charge characteristics graph (Fig. 2). Charging begins by applying increased charge voltage to the battery. In this case, the starting current of the charge is chosen, as a rule, equal to 0.15 C, and the time of the first stage of charging is about 10 hours. As the battery is charged, the charge current decreases, and when its value reaches a certain value, the charger will switch to low-current trickle charging mode (usually 0.05C).

Fig.2 Two-stage charging method at constant charging voltage

With a two-stage charge, the initial current of the first stage should not exceed 0.4C, and the jet charging current should not exceed 0.15C. Typical charge voltages at various ambient temperatures for a 12-volt battery are given in table 3.

Stagecharge	Typicalmeaningvoltagecharge, IN
	0° WITH	25°WITH	40°WITH
Basic	15.4	14.7	14.2
Compensatory	14.1	13.7	13.4

An important advantage of this method is the reduced battery charging time during the transition from operating mode to standby mode, to the state of trickle (compensatory) charging at a low charge current.

Compensating charge method

The compensating charging method, also called the trickle charging method, is usually used at the final stage of the charging process. However, it is also used as an independent charging method when charging lead-acid batteries operating in standby mode, i.e. as a backup power source. In such a source, in the event of a failure of the main source, the battery comes into operation. If its discharge was short-lived and the capacity decreased slightly, then a compensating charge of the battery will be sufficient for charging, which will ensure a gradual restoration of its working capacity. However, with a deep discharge, you will need to use another charger capable of providing a sufficiently high charging current. In the case of a deep discharge and subsequent jet recharging, sulfation of the battery plates may occur with all the ensuing consequences. The way out may be to prevent deep discharge, which is ensured by the UPS microprocessor that monitors the level of battery discharge.

When making a compensating charge, it should also be taken into account that long-term charging with slight fluctuations in the charge voltage significantly reduces the battery life. Therefore, its stabilization must be provided. It is desirable that the deviation of the charge voltage from the norm does not exceed ±1%. In addition, since charging characteristics are highly dependent on ambient temperature, the charger must have thermal compensation circuitry.

It cannot be argued that compensating charge is so useful for lead-acid batteries, because this method is usually used in two cases: when they are slightly discharged and for recharging charged batteries in order to compensate for their self-discharge.

For lead-acid batteries, undercharging is unacceptable, as this leads to sulfation of the negative plates. But equally, overcharging, which causes corrosion of the positive plates, is also unacceptable. During a compensating charge, if it lasts too long, the battery will begin to overcharge and, in addition, the electrolyte will boil.

So, from all of the above, we can conclude that the most common uninterruptible power supplies use the simplest charging methods - the constant voltage charging method and the compensating charging method.

It should also be noted that when choosing the value of the charge voltage, it is necessary to take into account the ambient temperature: at its high values, the voltage must be reduced slightly, and at low values, it must be increased. That is why good chargers designed for use in a wide temperature range have a special circuit that monitors the ambient temperature and ensures that the compensating charge voltage is set in accordance with its value.

In principle, we can talk about all the features of rechargeable batteries and their chargers for quite a long time, but let’s return to the topic of our publication and begin our acquaintance with practical options for chargers. But all the information provided here, we hope, will help our readers better understand everything that will be presented below.

Chargers based on linear voltage regulators

Chargers in the form of linear voltage regulators are very rarely used today by APC in their uninterruptible power supplies. Linear regulators were widely used in models of the first (1G) and second (2G) generations, and their use was most often typical for models with low output power.

As for other manufacturers, they still continue to use linear regulators as chargers, because... names This topology is the simplest both in design and in practical implementation.

The block diagram of a charger based on a linear voltage regulator is shown in Fig. 3, which demonstrates the simplicity of the circuit. A mandatory element of the circuit is a step-down low-frequency transformer. Which, by the way, can be used as the main power transformer of an uninterruptible power supply. In this case, the transformer has an additional step-down winding. This solution avoids the use of a separate transformer, which reduces both the cost and weight of the UPS.

Fig. 3 UPS charger architecture (linear regulator)

The conversion of alternating voltage to direct voltage is traditionally carried out by a rectifier based on a diode bridge, from which the rectified voltage is supplied to the regulator-stabilizer circuit.

The operating mode of the voltage regulator can be determined by two schemes:

- stabilizer current limiting circuit;

- thermal control circuit.

Both of these circuits are optional and their presence is typical for higher-class chargers. In the simplest chargers operating in constant voltage charging mode, they are most often absent.

The voltage regulator is turned on and off by a microprocessor (or another controller that performs the function of the main control chip of the UPS) using a signal ON/OFF. The charger is turned on and off by a microprocessor that analyzes the state of the battery charge level signal and the signal AC-OK(signal of the presence of alternating mains voltage at the UPS input).

The vast majority of UPS developers use the chip LM317 as the basis of a linear charging voltage regulator. This universal three-terminal positive voltage regulator IC allows the design of stabilizers with output voltages ranging from 1.2V before 37V and load current up to 1.5A. We will not dwell on the LM317 now, because anyone can find the most detailed information about it both via the Internet and in domestic reference books on foreign components. The only thing I would like to dwell on is the features of switching on the stabilizer and methods for programming the output voltage level.

The LM317 stabilizer is convenient because it requires only two external resistors to set the output voltage level. In addition, the instability of load current and voltage of the LM317 is much better than that of stabilizers with a fixed output voltage. LM317 has built-in overload protection circuit, current limiting circuit, overheating protection circuit, safe operating area failure protection circuit.

The configuration of external resistors and the direction of currents flowing through the terminals of LM317 are shown in Fig. 4. The stabilizer provides the reference voltage Vref = 1.25 V(voltage between output and control terminals). This reference voltage is applied to the current-driving resistor R1. The value of the output voltage is determined by formula (1):

Vout=Vref(1+R2/R1)+I ADJ R2 (1)

Fig.4 Stabilizer LM317

The current through the control terminal does not exceed 100 μA and in this formula is included in the term that determines the error. Therefore, when developing a stabilizer, the current I ADJ strive to minimize, and thus reduce as much as possible, variations in output voltage and load current. For this purpose, all current consumption flows through the output pin of the microcircuit, determining the minimum required load current. If the output load is not sufficient, the output voltage will increase. To prevent this phenomenon, a tracking circuit is introduced in chargers, which, when the output voltage increases (and this can occur as the batteries are charged), adjusts the values ​​of the resistive divider, and, in particular, the equivalent resistance of the resistor R2. An example of such a tracking link is presented in Fig.5. In the presented circuit, the output voltage sensor is a resistive divider R4/R5. An increase in output voltage causes the transistor to open Q1 and connecting a resistor R3 parallel to the resistor R2. As a result, the equivalent resistance of the resistor R2 decreases, which leads to a decrease in the output voltage. In a similar way, you can compensate for the charging voltage when the ambient temperature changes. To do this, instead of a resistor R5 It is enough to install a thermistor.

Fig.5 The tracking circuit prevents changes in output voltage and load current

None of the pins of the microcircuit must be connected to ground. The connection to ground is made through an appropriate divider. Therefore, this stabilizer is said to have terminal potentials that “float” relative to ground. As a result of this, voltages of several hundred volts can be stabilized using the LM317, provided that the permissible voltage difference between input and output is not exceeded (the maximum difference should not exceed 40V ).

It should be noted that the LM317 microcircuit is convenient for creating not only linear stabilizers with programmable output voltage, but also for creating simple adjustable switching stabilizers, although such a solution is practically not found in uninterruptible power supplies.

Connecting the control pin ADJ (pin 2) to ground leads to the fact that the output voltage of the stabilizer is set at the level 1.2 V, at which most loads begin to consume scanty current, i.e., in fact, the load is turned off. This is the principle used to turn the charger on/off. To do this, a transistor is introduced into the circuit, connected between the ground and the contact ADJ. The transistor is controlled by a TTL signal generated by the microcontroller Fig. 6.

Fig.6 Turning on/off the LM317 stabilizer

Opening the transistor shunts the ADJ pin to ground and turns off the charger. Locking the transistor allows you to turn on the charger and generate a voltage at the output of LM317, the value of which is set by an external resistive divider. The control pin can be shunted not directly to ground, but through a resistor ( Fig.7). In this case, not 1.2V, but a slightly higher voltage is formed at the output of the charger, however, still with a fairly low potential, which, in fact, corresponds to the cessation of operation of the charger.

Fig.7

In addition to the control transistor, the charger circuit often also has a current limiter, which turns off the LM317 stabilizer if the load current (in this case, the battery charging current) exceeds the set value. A version of a charger with a current limiter is shown in Fig. 8. This is exactly what chargers look like for the vast majority of PowerCom's uninterruptible power supply models. KING(family KIN) and model range Black Knight(family BNT). In this circuit, the magnitude of the current at which limitation occurs is determined, first of all, by the value of the resistor R3. Voltage drop across resistor R3 controls the transistor Q1. Resistor R3 with resistance 1 ohm sets current limit value 0.6A. And in principle, the value of the output current at which the limitation is carried out, i.e. The magnitude of the short circuit current (SC) is calculated using formula (2):

Ic = 600 mV / R3 (2)

Fig.8 PowerCom UPS charger of KIN/BNT families

This concludes our review of the features of the LM317 microcircuit and moves on to a review of practical charger circuits for various uninterruptible power supplies.

The only thing you can still pay attention to is that the LM317 microcircuit also has a domestic analogue - this is a stabilizer 142EN12, which is no different from it (neither in characteristics, nor in the type of case, nor in the internal circuit, nor in the application diagrams).

Fig.9 APC Back-UPS 600 UPS charger (chassis 640-0208E)

Figure 9 shows the first example of using the LM317 to build a charger. In this example, the input of the stabilizer is supplied with a rectified, but not smoothed, voltage obtained at the output of the diode bridge from the reduced AC mains voltage. As a result, at the output of the stabilizer, not a constant voltage is also formed, but “parabolas with cut off tops.” The parabola is limited at the stabilization voltage level, which is primarily set by resistors R9 And R11. More precise adjustment of this voltage is carried out by a divider R10/VR1. So the variable resistor VR1 allows you to adjust the output voltage of the charger. The output voltage of the charger is smoothed by an electrolytic capacitor C3.

Fig.10 UPS charger PowerCom KIN 800/1500AP

Figure 10 shows a diagram of the charger used in many models of the families KIN And BNT from PowerCom. This charger is built according to the classical scheme with current limitation. The output voltage of the charger is set by a resistive divider R7/R38. The current sensor that sets the current limit threshold is a resistor R51. Current sensor controls transistor Q8, with the help of which the stabilizer is blocked when the current exceeds the threshold value. The charger is turned on/off by a transistor Q10, which is controlled by a signal ON/OFF from the microprocessor.

Fig.11 UPS charger PowerCom KIN 425/625AP

Figure 11 shows another diagram of a charger for UPS from PowerCom. This circuit is also based on the classic circuitry of a current-limiting charger, but it provides for changing the operating modes of the charger. Changing operating modes, i.e. programming of the charger is carried out by a signal VOLT_SELECT , which is a discrete signal and is generated by the microprocessor. This signal changes the parameters of the resistive divider, which sets the output voltage of the stabilizer, and in particular changes the resistance of the “lower” resistor ( R2 in Fig. 4). Alarm setting VOLT_SELECT a high level causes the transistor to open Q12 and locking Q7. As a result, the “lower” resistor of the divider becomes the resistor R15. Setting the same signal VOLT_SELECT a low level causes the transistor to open Q7 and closing Q12, as a result of which the “lower” resistor of the divider becomes R17 with a different resistance value, which ultimately leads to a change in the output voltage of the charger.

The charger is turned on and off by a signal ON/OFF and a transistor Q18, when opened, the control output of the stabilizer LM317 ( pin 1) is shunted to ground. Current limitation, as usual, is carried out by a transistor Q19, which, in turn, is controlled by a current sensor - a resistor R35.

In the diagram shown in Fig. 11 you can also see the presence of a charger operation sensor, consisting of R53, R45 And C19. This sensor generates a signal CHRG_ON immediately as soon as the supply voltage of the primary network appears at the UPS input. This high level signal informs the microprocessor about the presence of mains voltage and the possibility of starting the battery charging process. It is based on this signal that the microprocessor sets the signal ON/OFF to a low level, which causes the charger to start. In principle, this sensor could be called a mains voltage presence sensor.

Fig. 12 Back-UPS 900/1250 UPS charger (chassis 640-0209)

The charger in Fig. 12 is designed to generate a powerful charging current for batteries. But since LM317 allows you to generate a current of only up to 1.5A, then to increase power, two stabilizers are installed in parallel ( IC12 And IC13), as a result of which the load current is divided approximately in half between these two microcircuits, i.e. This charger provides a charging current of up to 3A. The charging voltage is set by resistors R141, R142, R143 And VR6. As in one of the examples already discussed, the variable resistor VR6 allows for precise adjustment of the charger voltage. This operation is performed at the factory and can also be performed by service engineers when testing the UPS.

This scheme provides for a smooth start of the charger, i.e. The output voltage increases gradually - according to an exponential law. Smooth start is ensured by a circuit consisting of a transistor Q45 and integrating circuit R166/C48. At the moment the alternating voltage appears at the output of the step-down transformer T2, capacitor C48 discharged, causing the transistor Q45 turns out to be closed. Closed Q45“cuts off” the resistive divider (and, in particular, the resistor) from ground R142), which sets the output voltage of the charger. However, as the capacitor charges C48, transistor Q45 begins to open slightly, and the master divider is connected to ground. The voltage across the capacitor increases according to an exponential law, as a result of which the output voltage and current change according to the same law.

Transistor Q19 is a control transistor that is used to turn the charger on and off. The transistor is controlled by a signal ACFAIL , which is set to a high level at the moment of loss of mains voltage. Signal activation ACFAIL causes the transistor to open Q19 and turning off the charger.

In addition, this circuit provides both thermal compensation of the charging voltage and thermal protection. A thermistor is designed for these purposes. R161 and the transistor controlled by it Q18, which in turn controls the transistor Q19.

In addition to the LM317, chargers can also use integrated three-terminal stabilizers for a fixed voltage. These stabilizers have three terminals: input voltage, output voltage and ground. It is the relative “ground” that these stabilizers limit their output voltage. Of the variety of such microcircuits, the most suitable for building battery chargers are stabilizers based on 15 Volt. However, the tension 15V is redundant. Therefore, to reduce the value of the effective output voltage, these stabilizers are forced to operate in a conditional pulse mode. This mode implies that an unsmoothed rectified voltage is supplied to the input of the stabilizer. As a result, at the output of the stabilizer, “cut-off” signals are formed at the level 15 Volt parabolas, when smoothed, a voltage of about 14 Volt. An example of such a charger is shown in Fig. 13.

Every car owner at some point faces the question of how to charge a dead battery. He also appeared in front of me one day. And it happened, as always, unexpectedly, on a day off, in the village, and as luck would have it, no one nearby had anything similar to charging. I had to strain my brains and quickly make a simple but powerful charger from available materials. And the burnt UPS, an uninterruptible power supply for computers, helped me with this. Without going into deep details, I’ll just note that this device powers the computer from the built-in 12-volt battery in the event of a power failure in the outlet.

From a broken uninterruptible power supply we take the most important thing - a powerful transformer, which usually remains intact; we don’t need all the other spare parts from it.

So, to make a simple charger you will need:

1. Transformer from a burnt-out uninterruptible power supply
2. Diode bridge (rectifier) ​​2-4 pcs.
3. Capacitor 100...1000 uF with a voltage of at least 25 V
4. Medium-sized radiator
5. Plank, plywood, plastic
6. Thermal paste KPT-8
7. Tester
8. Soldering iron, pieces of wire

Using a tester, we determine the winding terminals that have a higher resistance (from 10 to 50 Ohms), this will be a 220 V network winding. The terminals of the 12V secondary winding are thicker, it is wound with a thicker wire, so the resistance of the secondary winding is almost zero.

The pins that went to the output connectors of the uninterruptible power supply will now be connected to the network, and the wires through which 12V was supplied from the board will be connected to the rectifier.

You will also need several rectifier diode bridges GBU406, GBU 605, GBU606, and a filter capacitance, a capacitor from 100 to 1000 uF for a voltage of at least 25V (from a burnt-out computer power supply). A small radiator for diodes will also come in handy. Of course, you can make a rectifier using ordinary diodes with a maximum current of at least 10 A and a reverse voltage of at least 25 V, but at that moment they were not at hand, and later I also used ready-made rectifier bridges, because they are convenient to mount on a radiator . The rectifier bridges are stacked, coated with heat-conducting paste and pressed to the radiator with a long bolt. All pins of the same name are connected in parallel. Pros with pros, cons with cons, etc.

A transformer, a radiator with diodes are attached to a suitable size wooden plank, plywood, or piece of plastic, the entire circuit is mounted, a cord with a plug from an old soldering iron is connected - and charging is ready!

The mounting options and layout of the charger components can be any, based on what is at hand.

With a rectified output voltage of about 18 V, the charger freely provides a current of up to 5 A. A regular battery is charged in an hour, a very low one - in 3...4 hours. Many motorists in our village now have such a charger.

Moreover, to better charge the batteries, I came up with the idea of ​​connecting the charger in pulse mode. Pulse, of course, is a strong word, it just means that it is connected to the socket through an electromechanical time relay.

This is a simple daily electromechanical relay, it comes from the Middle Kingdom and is sold in the store for 150 rubles.