Inverter from an uninterruptible power supply
In everyday life, sometimes there is an urgent need for uninterrupted power to various devices. This can be emergency lighting, incubators, aquarium equipment or a simple amplifier, with which the company broke out in nature. Modern budget computer uninterruptible power supplies are able to work no more than half an hour from off-line power, and those that can and are specifically designed for this purpose, are worth quite a bit more money. Automotive output inverters do not always produce a frequency of 50 Hz. If you need autonomy for a few hours, then the thought immediately comes to mind, whether it is possible to power the UPS from an ordinary car battery. To this question, and we will try to give an answer today, let’s make an inverter from the UPS with our own hands.
Inverter from an uninterruptible power supply
For the conversion into an inverter, we chose UPS Mustek Power Must 800 USB (board number 098-17615-00-S1), this UPS is as if created for what would be his conversion, especially the load of 500 watts for household purposes is not so small.
The conversion of the UPS for a car battery will be broken down into several steps:
- Disabling the Green Power function
- Active cooling system installation
- Real tests
Green Power in the UPS – some tricky chip that does not allow the UPS long enough to work on battery power. In different devices it is manifested and implemented in different ways, in some it turns off the UPS, which runs without load after 5-10 minutes, in other devices Green Power does not allow the UPS to run more than 25-30 minutes, regardless of its load. Sometimes this function can be disabled with a special resistor, but sometimes the process of disconnection is written in the microcontroller UPS, and there is nothing that can help it.
The first thing we do is to open the case and take a picture of its insides, it should be done so that in the future there would be no questions, what and where to connect when reassembling.
After that, unplug all the wires and take out the control board, board number 098-17615-00-S1.
If you take a closer look at the board, you can see that it has tables that change the modes of the UPS.
We are interested in the resistor R15A, which is responsible for the Green Power function. We carefully unsolder the resistor from the board, and for those who like silence we can also do a little manipulation with the boozer. If you want to get rid of all the squeaks, which the UPS can unsolder jumper JP82 or unsolder the boozer, and for those who want to muffle the sound is enough to solder a small resistor of 100-300 ohms, instead of this jumper.
The next step is to install a 80mm fan and make some modifications to the UPS enclosure.
The fan will fit nicely to the plastic jumpers which are already in the case.
As you can see the fan is in the middle of the case, so it can blow air not only through the transformer, but also through the heatsinks of the transistors on top of the case.
You can think of a lot of ways to power a UPS fan. But we have chosen the simplest and easiest to replicate. The fan can be powered from the front panel board, which has a power button and LEDs. Put the button on the position off and use a tester to test the connector pins, find out where plus and minus comes from the battery (in our case it is pin 7 – plus, 5 – minus). Already on the track or with a tester trace plus battery to the power button and after the button (it returns through pin 8 on the board). So, the fan power can be taken from the pins: 5 – minus ; 8 – plus . In this case, the fan will work at full power when the power button will be on, i.e. when working from the network (charging) and when working with the battery.
The next step will be a slight modification of the case. The first thing to do is to make holes for the fresh air intake to the fan. If you pity to spoil the front panel, you can make holes in the bottom, the height of the legs will allow a small stream of air to pass quietly.
Also I was a bit surprised by the decorative plastic covers which have holes for ventilation, but there are no holes in this area in the case itself. This is all solved with a small drill bit and a drill.
The last step before reassembly will be the fixing of the transformer. When carrying the UPS without the regular battery, the transformer literally walks in its seats, it can easily jump out of them and damage the main board.
Now connect the wires with terminals, instead of the regular battery. It is better to put on special silicone caps for extra insulation. The wire for connecting the car battery to the UPS should be as large as possible, and the wire itself should be as short as possible.
And so, let’s drive and test our inverter from the UPS.
As you can see it is not difficult to make an inverter from the UPS, now it is time for the real tests. The UPS is idle, the current consumption is about 1 A.
Putting a laptop on charge, the current consumption rose to 5 A.
UPS loaded by a 60 W light bulb, current consumption is about 8 A.
By the way, the charging current does not rise above 1 A, with the charge gradually decreases.
The charging voltage of the UPS is 13.7 V.
It is not difficult to guess that the more capacity of your battery, the longer this inverter from the UPS will work, but also to charge from the mains will also be quite a long time.
The screenshots and pictures below are for the 098-17615-00-S1 from the Mustek Power Must 800 USB UPS. If you modify any other UPS, it is possible that these recommendations will only partially remain valid, because the design and schematics will be different. It is important to carefully read the markings and tables on the circuit board, follow the manufacturer’s recommendations and do not try to experiment without knowledge and skills, because it is possible to destroy not only the UPS, but also the equipment connected to it. The main thing to remember is that there is a life-threatening voltage when the UPS is operating.
Can I connect a car battery to the UPS?
Opinions on this matter are twofold, but radically different. Often, according to different reviews, car batteries are quite able to cope with this task and work stably. The main problems: the gases that will be released when charging the battery and overheating of the transformer, power keys. It is possible to get rid of the last problem, at least partially, by using additional fans, etc. But no one can get rid of the gases during charging. Charging releases not only explosive hydrogen, but also other gases, and they are far from vitamins. If an inverter from an uninterruptible power supply is used in a car, then this question disappears on its own. It is also important to remember that the network charging the battery is quite a small current and the charging process can stretch for a long time, you can safely get away from this if you charge the battery separately from the UPS, for example, for this purpose you can use a home-made charger from a computer power supply unit. Whether to use a car battery in the UPS must be decided solely by you.
How to make an inverter from the uninterruptible power with their own hands?
When you go to the countryside, where we do not provide the usual 220 V, we think about buying an inverter. The cost stops us. But when you know how to work the soldering iron and can figure out where in the device or device plus and minus, you can solve a simple problem: make an inverter from an uninterruptible power supply with your own hands. If the UPS connected to a 220 V mains supply provides power to 12 V devices, then is it impossible to achieve the opposite effect: to get 220 V from 12 V? With the appropriate modification of the design, nothing is impossible.
The proposed variant is designed to use a car battery as the main power source. Without a minimum knowledge of electrical engineering, it is undesirable to undertake the construction of an inverter.
What are the modifications that make it possible to obtain an inverter from an uninterruptible power supply, usually with used batteries?
Let’s consider the process of reconstruction in general terms, paying attention to the moments critical for the future operation of the inverter, since UPSs of different companies and models have design differences.
Modeling an inverter from a UPS
In the process of transformation you will have to disassemble UPS, remove surplus parts, modify the construction, check and assemble. You will need a standard set of installer’s tools: soldering iron, screwdrivers, wire cutters, tester. Spare parts that are not present in the disassembled unit will also be useful: wire with a cross section of 4 sq. mm, connectors, a pair of familiar crocodile or wire with a car cigarette lighter plug, overhead socket, cooler, protective grid, fasteners, tape. You may want to prepare a drill in advance to work with the case.
Carefully disassemble the case and take out the battery. If the manufacturer provides for the disassembly of the case into individual panels, it is worth doing it: it will be more convenient to work. It is easier to start with the installation of the input, i.e. 12 V supply. Directly on the board to determine the plus and minus, then solder or put on the appropriate connectors red to plus, black to minus that will go to the cigarette lighter or directly to the battery terminals.
Now we are working on the output. Wires, which led to the three-pin connector supply to the UPS 220 V, unsoldered or disconnected. In their place mount wires of required length (for remote socket – about 70 cm, if the socket is planned directly on the case – 20-30 cm). Bring the wires to the socket.
The rough model is ready. You can’t operate it, but you can check it. Without assembling the case (it is to be worked with), we connect to the battery and measure the voltage in the socket. You should get about 160-180 volts.
If the system is silent, maybe the converter board in the old UPS is not working.
Final assembly
It remains to include the working circuit into the device, changing and augmenting the design at the same time.
First of all we need to remove all extra connectors, buttons with the corresponding wires, and the signal speaker. Free space for the installation of one or two coolers. Their installation will protect the device from overheating. It is logical to build a through-ventilation. To get air into the case you will have to drill holes or cut windows. Cut holes should be covered with a protective mesh to prevent dust and dirt from getting in. The coolers are connected to the 12-volt line.
All connections are checked, wires are placed inside the case, and if necessary, secured. Make sure that the fans are tightly seated. Sometimes after the removal of the original batteries transformer is weakly fixed, so you need to further strengthen it, for example, a retaining plate (not metal).
Provide for fixing a socket on the body or drill an additional hole for the output wires.
It is not bad to install a separate switch: rather, to protect the car battery from complete discharge, in case you forget to disconnect. You can also design an electronic circuit that triggers at a given level of charge.
Advantages of a homemade inverter
As a sample uninterruptible power supplies were considered a relatively simple, budget-friendly design, when, based on cost considerations, instead of replacing the batteries that have expired, you buy a new power supply. In this case, you really get almost free inverter with good technical characteristics.
If the original uninterruptible power supply gave 500 W to the connected equipment, then theoretically it will give the same amount in the form of an inverter. Practically this value is less. But, for example, the total load of 350-400 W it can easily handle. The limitation is the time for which the battery charge is enough. Taking into account the current trend to reduce the energy capacity of the used devices, in the absence of electricity and will not remain without light, and mobile devices will recharge.
It is possible to use power tools. This is convenient when there is no electricity in the country house, but it is necessary to do the wiring. By hand you can, but it is much more difficult.
On the weight of the resulting device there is no point in stopping: a car of 3-5 kg is not an obstacle.
But with frequent use of inverter it is necessary to remember to charge the battery or have a spare one.
So, it makes sense to take out of the closet or garage, written off because of failure uninterruptible power supply, modify it slightly and get serviceable converter of direct current of 12 V to alternating current of 220 V.
