Transformer Identification - Page 1
Forum section: electronics / beginners

author: hgg
author_rank: Frequent Contributor
timestamp: November 16, 2014, 10:42:19 am
content: Hi,I found a transformer lying around and I was wondering if I can use it for a small power supply.Can you help me identify if it is a mains 220V transformer?Red/Black pair resistance is 106.4 Ohm and yellow pair 0.9 Ohm.Red/Black looks like its the primary side but 106 Ohm seems a bit low for 220V.What do you think?Thank you.George.

author: Zero999
author_rank: Super Contributor
timestamp: November 16, 2014, 02:03:27 pm
content: That sounds right to me. What resistances were you expecting to measure?

author: hgg
author_rank: Frequent Contributor
timestamp: November 16, 2014, 02:08:02 pm
content: I don't really know.I am also measuring 0.9MOhm between the metal casing and the black wire.Is this normal?

author: planet12
author_rank: Regular Contributor
timestamp: November 16, 2014, 08:00:46 pm
content: 0.9Meg / 900k is very very low between a winding and the metal shroud. If your measurement is correct, the insulation has broken down and the transformer should be thrown away (or rewound, if you're into that kind if thing).Make sure you've got good contacts between your meter probes and the winding and shroud, with your fingers not touching either (or any other stray paths between the two points), and check it again.If it checks out (your meter should read it as an open circuit), the next step I'd do would be to connect the primary in series with an incandescent light bulb, then to the mains (careful! Use isolation transformer if you have one, RCD/GFI as an absolute minimum, keeping in mind mistakes = electrocution). The bulb should not come on unless you short the secondary wires together - and you'll also be able to measure the secondary AC voltage while you're at it.If the bulb lights with the secondary open, either it's not a 220/240V rated transformer, or it has shorted windings somewhere.

author: hgg
author_rank: Frequent Contributor
timestamp: November 16, 2014, 08:14:37 pm
content: QuoteThat's what I thought...The measurement was correct.I tried to open it to see if I can find the short but I destroyed it... I damaged some of the windings.It was packaged like a tank. Inside all around it had a very crusty yellow compound, (maybe somekind of glue?).Probably it was faulty. I wish I had waited a bit longer so that I could have tried your advise tocheck it on the mains.Anyway, thank you!Regards,George.

author: miguelvp
author_rank: Super Contributor
timestamp: November 16, 2014, 08:17:00 pm
content: Closest I could get is this:4-251V-34800And that is for a betamax vcr rated for 33 watts and multiple outputs, but the poster mentioned 120V input, that doesn't mean it wasn't capable of dual voltage.http://www.antiqueradios.com/forums/viewtopic.php?f=2&t=220755Nope, no dual input, picture of schematic is too big to attach.http://s17.photobucket.com/user/steviefan1/media/sanyoVCR4900powersup_zpsfee695f1.jpg.htmlBut since it's destroyed it doesn't matter much

author: planet12
author_rank: Regular Contributor
timestamp: November 17, 2014, 04:49:22 am
content: The crusty yellow compound would be varnish. Transformers are normally vacuum-impregnated with it both for extra insulation and also to stop vibrations due to magnetic effects (an iron core transformer can have magnetic flux densities in the 1-2 tesla range inside it).

author: hgg
author_rank: Frequent Contributor
timestamp: November 17, 2014, 06:43:37 am
content: Now its too late... I destroyed the poor thing.Anyway, thanks guys for your suggestions!George.