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Old 22nd January 2002, 10:02 PM   #1
JoeBob is offline JoeBob  Canada
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Default Probing transformers.

I've found this transformer lying around, it's an alright sized E-I (about 10lbs), so I thought I could find something to use it for. The only thing is it's got 3 wires ont he primary that are marked live neutral and ground, but on the secondary there are 10 wires... And I can tell that some wires are smaller/larger then others. Three small ones, then one slightly bigger one, followed by 5 larger ones then one that's two insulated wires together. It's a "BANDO BEM1-RDW".

I just want to know how to probe it for it's voltages. I'm gathering there's two (or more?) secondaries with different voltages, so if I probe the live and neutral on one secondary then probe the neutral on one and the live on the other, or whatever random wires I probe for AC voltage there will be a problem, right? Shorting things like that with my multimeter will cause problems (and danger to my health), am I right? I'm hoping not, but I'm thinking it wouldn't be good. If I can't do that how should I go about finding it's pinouts for the secondaries and what voltages they are?
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Old 23rd January 2002, 12:05 AM   #2
PassFan is offline PassFan  United States
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As long as your meter is set on a high enough voltage you won't have any problem. You don't want to touch any wires to other wires or yourself. I use little orange wirenuts from home depot to cover the ends of the wires then take them off two at a time. That way you don't have to worry about an accident.
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Old 23rd January 2002, 12:31 AM   #3
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This is where things get dicey. Live and neutral do, indeed, sound like they'll be the primary. Is the insulation black? In general, single winding primary leads are black.
Ground? Hmmm. Could connect to a shield. Could connect to one of the secondaries. Don't assume it's part of the primary just because it comes from the same side of the transformer.
The best thing to do is sit down and test continuity between each and every lead before you hook it up to any power at all. Twist or tape leads that are part of the same winding together. Obviously, you don't want the ends to touch, so fold them outwards at the ends.
If you're feeling really paranoid, use another transformer with 10 or 20V secondaries to power the primaries on this one. That way, you won't have quite the shock if one set of leads should turn out to have 300V on them.
Don't laugh, I got the ever-livin' whoofle knocked out of me once in a computer power supply. 5V...okay...another 5V winding...okay...12V...okay...TINGLE (followed, of course, by lotsa loud cussin').
For who knows what reason, there was a 325VAC secondary on this transformer. They weren't using it for anything. It was just tied off. But, man, what a rude surprise.

Grey
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Old 23rd January 2002, 12:41 AM   #4
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With the transformer unpluged from the power, use your multimeter on the resistance setting to tell which of the secondaries are connected .... just pick 2 secondary wires @ random and measure the resistance between them.... do this for all the wires... those that measure infinite resistance are not connected, if you find more than 2 wires that appear to be connected to the same wire, measure the resistance between them in all combinations ... the highest resistance pair in the start and finish of the winding while as the resistances decrease you move closer to the center of the winding ... once you know what the secondary winding looks like, draw it on a piece of paper with all the resistances you've measured then power it up and with your multimeter on the highest voltage setting .. or auto ranging mode, measure the voltage between each of the wires as per the diagram you've just made.... dont bother measuring voltages between 2 wires that are not part of the same secondaries slowly but surely you'll get a better picture of what the transformer is capable of.
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Old 23rd January 2002, 01:29 AM   #5
JoeBob is offline JoeBob  Canada
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Ah, thanks for all the input, I'll go do that now... I understand, but I hope I don't fry something.
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