Transformer newbie, can I use this thing? - Page 1
Forum section: electronics / beginners

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: January 08, 2013, 06:08:59 pm
content: So I've been thinking about building my own bench supply instead of buying one, and after looking at prices for power bricks, I thought I'd possibly take a whack at building my own power circuit. Anywho, I got these old UPSes that I don't really want to fix, so I ripped out one of the transformers, but I can't seem to find any info on it.Excuse the bad mspaint...I'm assuming I can rip out the wires I don't need, but since I can't find any info on it, and the UPS died, I can't just turn it on and measure each set of wires (not to mention, working on live mains is scary)...Is there another way I can find out what voltages this transformer outputs?Thanks

author: alanb
author_rank: Frequent Contributor
timestamp: January 08, 2013, 06:42:09 pm
content: Provided that you have correctly identified the main input side you could connect this to a low voltage ac source. The output voltages would then be reduced in proportion to the the reduction in the input voltage. For example if you feed in 24 volts instead of 240 all of the measured outputs would be a tenth of the value that you will get when running it off the mains. The danger would be if you have not identified the the input side correctly as applying a voltage to the output side would step up the voltage on the input.What ever you do I would work on this as if high voltages are present.Work with one hand only, keep the other in your pocketNo metal jewelry (rings etc) on your handsUse insulated toolsKeep your multimeter on the table don't hold it in your hand.Good luck

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: January 09, 2013, 03:21:06 am
content: Can't seem to find anything laying around to power it with... I think I'll just buy some coil wire and re-wrap it when I'm ready to use it.Thanks

author: IanB
author_rank: Super Contributor
timestamp: January 09, 2013, 03:28:55 am
content: Quote from: justanothercanuck on January 09, 2013, 03:21:06 amIf you mean to take it apart and rewind it--don't do that, you'll ruin it.Much better to leave it intact and figure out its specifications.

author: planet12
author_rank: Regular Contributor
timestamp: January 10, 2013, 04:31:26 am
content: Depending on what kind of UPS you pulled this out of, and where in the circuit it was, there's a high likelihood that it's a high frequency transformer for switch-mode operation.What is the core material made of? Is it ferrite (a solid dark gray/black material) or sandwiched steel plates? If the former, it's a high-frequency transformer, and plugging it directly into 50/60Hz AC mains is going to do Bad Things(tm).Do a Google image search for "SMPS transformer" and see if it looks like those.

author: StuUK
author_rank: Frequent Contributor
timestamp: January 10, 2013, 06:34:04 am
content: ATX power supplies pulled from old desktop computers make great (and safer) 'roll your own' bench supplies. Just visit your local dump, you're sure to find one.The transformer in an old UPS is highly likely to be of the 'wrong type' for your purposes.Just google 'ATX bench supply' and you'll find loads of examples.

author: dr_p
author_rank: Frequent Contributor
timestamp: January 10, 2013, 09:22:15 am
content: Be very careful with the mains connection! Really!The transformer is most likely iron cored, heavy (2-3kg) and fit for 50-60Hz. In your UPS, the inverter is always working, either from this transformer, or from the 12V battery.Continuity means a low resistance (typically <50 ohms). It's not zero, so it's not the same wire. It's a winding (coil).You will have to deduct what goes where, since it's unlikely to find any info on your custom transformer.Let's take an example transformer:Note that V1 / V2 =almost= N1 / N2. This means that a transformer with 100 primary turns and 10 secondary has a 10:1 ratio that also applies on voltages. You give it 240V on the primary - it will output 24V. Everything is AC, of course.So more turns means more voltage. But that wire has a resistance, sothe higher the resistance of the winding, the higher the voltage(assuming same gauge wire). And resistance you can measure without disassembling the transformer. Now we're getting somewhere - we can find out the ratio of every winding and have an idea of the ratio between the voltages.You know that it's from a 12V powered UPS and that means 220V primary and 12-14V secondary. So you're expecting more or less a 15:1 ratio. On a simple transformer, that's all we need, but on yours there are be other windings.An ideal transformer has no losses, so a 10:1 ratio means that to supply 24V at 10A you need to power the transformer from 240V, and it will only use 1A. Input power = output power, since there are no losses. Now, a real transformer has an efficacy of let's say 70% so values are lower, but the principle is the same.Higher current needs thicker wires, so what we get from this is thatlower voltage windings tend to have higher gauge wires(relative to primary wires). This is a clear indication of which side is the secondary (thicker wires), sincetransformers generally have all the primary wires on one side and all the secondary on the other. Even schematic diagrams are drawn this way.OK, now we know which is the primary side and which is the secondary one. You have to measure the resistance of every winding and write it down on a diagram similar to this:From your schematic, the left side seems to be the primary, but you have 2 windings here. If they are of equal resistance, then they are for 110-220V compatibility. They are wired in series for 220V, or in parallel for 110V.However, I suspect that one winding is high R, meaning mains input, and one is low R, that the UPS uses to tweak the input, according to your mains voltage. Meaning if your mais voltage is too low, it "adds" some more turns to the primary to compensate for that. Even if it will probably provide some low voltage, I suggest you don't use it, as it's not very well isolated from the main 220V winding.On the secondary side, you probably have the Red-Blue-White that is a high current (thick wires) center tap double 15V winding. Meaning 15V - 0 - 15V used for the powering the power inverter. Measure resistance from Red-Blue that should be equal to that from Blue-White and half of that from red to white.You also have another secondary winding (Blue-Yellow), of thinner wires, isolated from the first one, probably for some other low-power circutry. It's resistance should be comparable to that of the 15-015 winding, since it is also low voltage.I've drawn a schematic of what I thing the connection diagram is

author: dr_p
author_rank: Frequent Contributor
timestamp: January 10, 2013, 09:27:56 am
content: I have a similar transformer

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: January 10, 2013, 09:01:14 pm
content: I tried taking it apart, but the E/I plates are all stuck together, so I'm not going to bother with it any more. Even if I could find out what it's designed for, I want something like 36/18/9 for the secondaries... so I'm trying to find a DIY kit, or at least the plates to make my own.Thanks

author: M. András
author_rank: Super Contributor
timestamp: January 10, 2013, 09:30:45 pm
content: get a toroid transformer you can wind your own secondary, as you need. few turn of wire a layer of isolation paper/tape (nomex or anything similar) and you can wind the next secondary.

author: IanB
author_rank: Super Contributor
timestamp: January 10, 2013, 09:31:57 pm
content: Quote from: justanothercanuck on January 10, 2013, 09:01:14 pmDon't think you can just take transformers apart or rewind them ad-hoc. It's much more complicated than that. If you do it without a full understanding of all the details of winding, insulation, wire sizes, taps, impregnation and a host of other details, you will get a transformer that is not efficient, that does not do what you expect, or is even dangerous.