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DIY do-it-yourself

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We make a powerful uninterruptible power supply based on a standard UPS by connecting two KAMAZ batteries to it. We also do automatic ventilation when switching to offline mode.

Such is the reality that Russian power grids force consumers themselves to take care of the stability of the electricity they receive. In our case, it is necessary to solve two important problems: a large voltage drop (typical for the hot / cold season, when air conditioners / electric heaters turn on) and a complete blackout (“knocking out” of machines, accidents at substations, etc.).

If the first problem is easily solved by installing an autotransformer, which allows to obtain a stable voltage of 220 volts at the output, the second requires the organization of an uninterruptible power system, designed for a long period of battery life.

To organize uninterrupted supply of a country house or a garage, you can use the modernization of computer UPSs (uninterruptible power supply). After two years of operation in any UPS, internal batteries degrade. An uninterruptible power supply with non-working batteries was repeatedly observed on the radio market at a symbolic price of 1000 rubles.

For a long battery life, an uninterruptible power supply must be connected to a large capacity battery. The best option would be starter batteries from KAMAZ - 140 Ah batteries. Since most powerful uninterruptible power supplies use batteries with a total voltage of 24 volts, we need a pair of rechargeable batteries connected in series. The duration of the battery life will depend on the condition of your batteries.

First of all, we take out and throw out the faulty battery. For the convenience of connecting an external high-capacity battery, we need to make contact clips (preferably red and black colors, indicating plus and minus, respectively). To do this, we make two holes on the front panel of the uninterruptible power supply unit, fix the contact clamps and solder the wires to them, which fit the internal battery.

Continuous operation in the state of converting battery energy to a voltage of 220 volts is accompanied by large heating. To prevent premature failure, it was decided to install two ordinary fans with a size of 80x80x25 mm on the ventilation grill.

Fans are connected in series. To start the fans in conversion mode, we use an LED that indicates the operation of the uninterruptible power supply from the battery. We solder the LED leads to the windings of a small relay. We solder the wire from the incoming plus of our battery to one of the relay contacts. To the second - the free red wire of the fan. Solder the free black wire of the fan to the incoming minus of the battery.

Everything! Now, when the uninterruptible power supply enters the operating mode from the battery, cooling will automatically turn on.

How to make an uninterrupted do-it-yourselfer?

Provide uninterrupted power to appliances for quite some time only devices based on powerful and capacious batteries can be used, for which you need to use a charger of the appropriate power and an inverter that converts direct voltage to standard 220 V. It is the inverter that will be the most difficult to make, because whether it produces a pure sine or a meander types - it depends on which devices can be powered from the kit received. Some devices do not accept pulsed voltage with a large number of high-frequency harmonics - this must be taken into account when planning the creation of a UPS.

Most users prefer to use a ready-made factory assembled inverter, since it is quite difficult to provide the necessary frequency for the home and all consumers.

What is required?

Do-it-yourself UPS in the first place need batteries from a powerful car - KamAZ or other similar truck. You must use a pair of 12 V batteries, connected in series and having a capacity of 190 Ah. Small-capacity devices charge faster, but are more demanding on the charging mode and painfully react to overcharging. In addition, you need a charger with sufficient power, and an inverter.

Of all these components, batteries will definitely be bought, and since they still have to be spent on them, it is better to buy new ones, not used ones. The charger can be assembled independently, like the inverter, although experts say that the result will in any case be inferior to the factory models due to the low quality of parts and accessories.

Safety Rules and Important Tips

First of all, you must follow the safety rules when working with electrical appliances and with live installations. If produced assembly of the entire UPS or individual components do-it-yourself, safety rules when working with heating appliances are added to the list of common requirements. Working with a soldering iron requires caution; the best option is to use a soldering station with a hood and a special safe stand.

An important point is the use of a sufficiently thick connecting wire. If its cross-section does not comply with the established standards, the wire will become very hot and may melt, which will cause the kit to stop working and create a fire hazard.

It is recommended to use a copper stranded wire with a cross section of 12 mm2 (“pigtail”), which can withstand current up to 100 A.

Step-by-step algorithm of actions

In order to make an uninterruptible do-it-yourselfer, you need to perform a certain sequence of actions. First of all, you need to decide which nodes will be created independently, and which are better to purchase in finished form. Then you need to acquire the necessary components, elements and parts of the kit, purchase batteries. It is not recommended to start assembly without them, since the charger must exactly match the battery specifications.

Schemes and explanations

Consider the structural diagram of the UPS.

Here, the inverter and the filter of higher harmonics are presented as two different units, although in practice they are often combined into one unit.

First, the converter (another name for the inverter) receives a constant voltage of 12 V from the batteries, turning it into a pulsed alternating voltage (meander) of 310 V. Then, with the help of a higher harmonic filter, the excess is cut off, bringing the signal shape to a sinusoid with an amplitude of 220 V. An important moment - the voltage of the charger for these batteries should be 28.8 V. This value allows you to fully charge the batteries without the risk of overcharging, boiling out or battery failure.

Uninterruptible power supply is provided by switching from the mains source to the UPS, produced when the mains voltage changes - when it drops or completely disappears. Some devices also cut off power surges, transferring consumer power to the UPS until the mains voltage returns to normal.

To switch the power, a relay is used, to which voltage is constantly supplied from the network.

Possible problems and nuances

Power supply accompanied by strong heating of parts and requires quality cooling. For this, a fan of the appropriate size is usually used (sometimes a computer cooler is suitable, less often it is necessary to install larger samples). A common mistake is to connect the fans to the batteries (output terminals). When the kit goes to stand-alone mode, the fans continue to work, contributing to the discharge of the battery, although in this mode they are not needed. The condition of the fans must be constantly monitored, they are the weakest link in the entire system and often fail, leaving the power supply unit without cooling, which should not be allowed.

Care must be taken to ensure that the batteries are connected correctly. Serial connection provides a uniform load and the same charge, while in parallel only one battery works, which contributes to its early failure.

A self-made uninterruptible power supply is easier to repair or upgrade.

In addition, such a kit can be used in conjunction with solar panels or a wind generator, which significantly expands the capabilities of the UPS and brings it to an autonomous level of functioning.

Having converted the uninterruptible power supply to the 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 it can be loaded with 200 W power. Of course, the more powerful the uninterruptible power supply, the more you can increase the load on it.

In some uninterruptible systems, there are places where you can additionally increase power. These places are called transistor switches. It is worth soldering them, as the power of the uninterruptible power increases.


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

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


From the secondary transformer to the terminal board,


you need to add another wire in parallel to increase the cross section.

The transformer had to be cracked a bit to get to the output of the secondary winding. Three wires come out of these wires.


So that the uninterruptible squeak does not squeak every minute, we must drink a round squeaker.



Further in the case, I drilled a hole for the fan using plaster or wood, and placed it so that it blew on the keys of transistors and radiators.




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



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

Our uninterruptible inverter is almost ready. A digital voltmeter can be integrated to control the discharge of the car battery. Just in case, I also connected a temperature sensor to control the temperature on transistor switches. A thermocouple from a multimeter was mounted on the radiator of a fieldwork transistor.


An important point: the inverter from the uninterruptible power supply must have a cold start - this is a function when it can turn on without external power from a 220-volt household outlet. On some models, the cold start button has a double tap at different time intervals.


That's all the alterations. 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% power from our product.

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

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