help me out with this transformer... I don't know about the connection?

this transformer is from 600VA UPS(220v supply)(using 12v battery). On primary side their are 4 wires and on secondary two wire. output on primary for the following : black- green=6.5Vac      black-blue=9Vac          black-yellow=7.7Vac......now how can I get 12V from this...?? help me....I want to use this as my power supply for charging batteries....  

Picture of help me out with this transformer... I don't know about the connection?
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iceng2 years ago

What were you feeding the Secondary side of transformer ?


Hey, wow! The lightbulb-as-current-limiter trick. This is good advice. +1

And as you load the secondary the lightbulb gets brighter.

tajeshwar28 (author)  iceng2 years ago

hey sorry their is little mistake... output is on secondary side... that is the two thich wire....and input to primary is 220V ac

Shimonek2 years ago

You probably won't be able to get 12 volts from this transformer, but there is a slight chance.

Since you can measure voltage between the black and each of the colours
you know that your secondary is a single continuous winding. You have a
wire attached to each end of the secondary winding and two in the middle
somewhere. If your transformer is laid out like this: Black~Green~Yellow~Blue, you won't reach 12 volts. If your transformer were laid out like this: Green~Black~Yellow~Blue, you would be able to get > 9 volts between Green and Blue.

You need to determine how your transformer is laid out. Try this: Measure the resistance between the black wire and each of the coloured wires and record each value. Now measure the resistance between the green wire and each of the others. Repeat for the blue and yellow. The combination with the highest resistance will have the largest number of windings. If this turns out to be black/blue you don't have enough secondary windings to get to 12 volts.

If you find a combination that has a higher resistance than Black/Blue measure the voltage between those two wires. If by chance it is close to 12 volts then go with it. If its much higher than 12 volts you have more work to do. Take your resistance measurements using the black wire and make an educated guess about the winding layout. For example, if I measured 1 ohm between Black/Green, 2 ohm between Black/Yellow and 3 ohm between Black/Blue, I would guess that the transformer were laid out as follows:


Calculate the individual winding resistances from your assumed layout using the formula Black/Green + Green/Yellow = Black/Yello or 1 + Green/Yellow = 2. Therefore, Green/Yellow = 2 - 1 = 1 ohm. Now use the other sets of measurements to check your guess. When you measured Black/Yellow was it actually 1 ohm?

Once you know how your transformer is laid out create a diagram similar to the following:

|--- 6.5---|---7.7---|---?---|

| |---------9-------|


If Black/Green produces 6.5 volts and Black/Yellow produces 7.7 volts then Green/Yellow will produce 6.5 + 7.7 = 14.2 volts.

Hope this helps. Good luck!

iceng2 years ago

In my experience with 220vac the heavy gauge red and blue wires are the secondary winding. And makes sense as the a 600 va /12v = 50 amps going through the secondary.

tajeshwar28 (author) 2 years ago

hey sorry their is little mistake... output is on secondary side... that is the two thich wire....and input to primary is 220V ac

Well, a transformer is basically a lump of iron, called a core, with a bunch of copper wire wrapped around it. Each separate length of copper wire is called a winding. Moreover, each winding has some number of turns, i.e. the number of times that length of wire circles around the core.

The transformer's ability to step-up, or step-down, voltages, depends on the ratio of number of turns in these windings, and this turns ratio is a number you want to discover, if you've got plans to use some found transformer in a new application.

The easiest way to discover the turns ratio, is to apply a small AC voltage to one of the windings, then measure the voltage on the other windings. Then infer the turns ratio from the voltage ratio.

I asked Google(r), "how to find turns ratio of a transformer", and one of the pages it returned is this one,


which gives an OK explanation of the test with AC-voltage setup.

The reason for using a small test voltage, is so the current that flows, through the winding you apply the voltage to, will be a small current. By the way, the other winding(s) have no load(s) connected, so the current through those windings is zero.

Also this page,


gives a good overview of the simple models for how transformers work.

I forgot to mention, you can get some qualitative information about the windings using just from a measurement of the DC resistance of each winding, found using a multimeter.

The low voltage windings tend to have thick wire, and smaller number of turns. Thus low voltage windings have low DC resistance.

In contrast high voltage windings tend to have thinner wire, and larger number of turns. Thus high voltage windings have high resistance.

For example, if your transformer has three windings, and the resistance measurements for these are 5 ohms, 5 ohms, and 30 ohms, then it is likely the two 5 ohm windings are the low-turns, low-voltage windings, and the winding measuring 30 ohm winding is a high-turn, high-voltage winding.

Also in the picture you attached to this topic, the winding on the left side of the picture is attached to much thicker external wires (the red and blue wires in the picture) suggesting the previous designer was expecting large current in this winding. So this winding is probably a low voltage winding.

Anyway, the reason these sort of qualitative measurements are useful, is because they can help inform you how to set up your AC-voltage test.

For example, it would probably be easiest, least damaging, to the transformer to apply your test voltage to the winding with the largest number of turns. Also when you do this, you expect the voltages output on the other windings to be less than the input voltage, because they have less turns than that of the winding you're applying voltage to.