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How to wire this transformer? Answered

ok, anyone know how to connect this transformer to mains power ..

i get this from my UPS backup ..


Just by looking at it, it is going to be hard to tell what wire is what.

By the way, it would be easier to tell what wire was what if you had not removed it from its natural context. That is to say if it were still connected to that backup power inverter thingy, then you follow the wires, and see: This wire goes here, so it must do this. That wire goes there, so it must be part of that thingy. It's a little pointless for me tell you this now, unless you, like, remember, where every wire was connected.

Another way, in the state this transformer is in now, for to find what winding is what, is to sort of discover its windings using an ohmmeter, or a multimeter set to its resistance measuring mode.

For example, discover two wires connected to each other, but not to any of the other wires, and this is a winding.

Discover three wires connected to each other, but not to any of the others, and this is probably a center-tapped winding. Also if the resistance measured between these three wires measures R, R, and 2R, then that's definitely a center-tapped winding.

Also regarding resistance, the windings intended for the high voltage (low current) side, have a large number of turns, and are made of thinner wire. In contrast, the windings for the lower voltage (higher current), have a much smaller number of turns, and are made of thicker wire. As a result, the high voltage windings tend to have a much larger DC resistance than the low voltage windings, and DC resistance is what you're measuring with your ohmmeter.

I am ?guessing? typical values of winding resistance for a transformer like the one you've got there will be in the range of maybe 2 ohms to 200 ohms. But the more important fact is the difference in your resistance measurements, since I am expecting the higher resistance windings to be the ones made for higher voltage (and lower current), and vice-versa. The windings with low resistance are intended for low voltage (and higher current).

Next, supposing you have found a winding that you are confident can handle some AC mains voltage, then you can try connecting it to AC mains through an incandescent light bulb. This is the old style light bulb, the kind with just a filament in it, like maybe one rated for 60 watts or so.

The reason I am suggesting connecting a light bulb in series with your winding, is to protect the winding from over-current, in the case you somehow picked a winding which offers too low an impedance to the AC mains, so you wont burn out the winding, or trip a breaker.

Anyway, supposing that trick works, then the winding will have some measurable AC voltage across it, and you could measure this, with your AC voltmeter, or multimeter set to measure AC voltage. Also, important for this trick: I am assuming all the other windings on the transformer are open circuit, nothing is connected to them, and nothing will be connected to them during this test, except for an AC voltmeter.

Hopefully you sort of see the purpose of this second test. The transformer is energized, but not really moving any power from one side to the other, since all its secondary windings are open, with zero current flowing in them.

So there should be a measurable AC voltage on the primary winding, the one you are powering, and also voltage on the secondary windings. Moreover, the ratio of these measured voltages should correspond to the ratio of the turns of the various windings of the transformer.

And this test should tell you what you want to know about the turns ratios.

The question of how much current each winding can handle is more tricky, but it is probably a safe bet that none of these windings will withstand more current than they were designed to take, nor will the transformer move more power, than it was designed for in its former life as a battery back-up.

By the way, I am sort of assuming you know how to work with mains power without electrocuting yourself. In my home country the mains voltage is around 110 VAC, but in other parts of the world its 220 VAC. You know, just try to avoid electrocuting yourself, because your friends would miss you if you were dead.


looooooong answer ha.. i understand how it works.. thank you very much...

I am glad this makes sense to you.

I forgot to mention one other possibility when probing with the ohmmeter to measure the resistance of the windings.

That is: it might be the case that some of those wires are just two wires connected together, but not through a winding; i.e. they just tied two wires to one terminal, for some reason. In that case you would measure a really low resistance, like as close to zero as your meter will measure. Also the resistance of an actual winding, one of the low voltage, low resistance ones, might be just a few ohms greater than a short, a short length of wire.

Although with the lightbulb trick, you should be able to put a dead short in series with it, and all that will happen is the lightbulb turns on, at full brightness, as expected.

yep. anyway i'm not gonna touch this without some one help ,thanks for the advices..

What do you expect to get out of the transformer?

Do you know it used to be a mains transformer?

You need to identify the primary and secondary coils.

In general the primary coil of a step down transformer will have a larger resistance than the secondary assuming the wire cross section is the same.

output 24v with A

yeah it can use with 230v mains, i saw some video on youtube

Seeing things on You tube isn't the same as knowing what you have in your hand. The transformer should either be marked with it's rating or you must KNOW where it came from and what sort of voltages it used and produced.

I can't help but think that your not yet ready to work with mains voltages. I know that sounds boring but electricity can and does kill, either you or your friends and family. An astonishingly low voltage and current is considered a danger to life.

You need a much better understanding at lower voltages then you can apply that knowledge to using and working with mains voltages. Low voltages are also much easier on components.

yep that's true but i want to make spot welder using this transformer. thank you by the way..