Help identifying transformer windings

[ppppenguin]

You're lucky that your cheapo DVM survived over 1000V. I wouldn't trust it again after exposing it to that kind of voltage. Wouldn't even trust that sort of DVM to measure mains.

Many good quality DVMs aren't rated for more than 1000V.

Nick, as you correctly say, when evaluating an unknown transformer just a put a few volts on the mains primary at first. If you inadvertantly put a few volts on a heater winding you will get something approaching mains voltage on the primary. If you're not expecting this it's dangerous.

[Mark Hennessy]

Winding 3 could be the best thing for your £2.99 meter. I wouldn't expect it to last terribly long, and at least then, you'd have to throw it away

Joking aside, you're extremely wise to shroud the terminals

[SurreyNick]

Ah! Hold on. Have I done something daft?
I only put 10v on winding 1 to measure winding 3 and then extrapolated the answer i.e. I had 26v, 26v and 52v and then multipled these by 24. I assumed the voltage gain would be linear.
Nick

[AlanBeckett]

That sounds like a splendid idea.
I'd have used my Variac and an AVO8, but that's just what  I have available.

Alan

[SurreyNick]

Phew! That's a relief.
I must learn to use my AVO7. I bought it over a year ago and it's still shrouded in bubble wrap - tut tut eh?
Nick

[Mark Hennessy]

I agree - that's the right way to approach it

[ppppenguin]

Sorry. I mistakenly thought you'd put mains on it. I also thought that was a very unwise thing to do with an unknown transformer.

[SurreyNick]

Although I didn't put mains onto the transformer to test it, you had every reason to advise caution. I didn't make clear that I had only applied a few volts and someone who doesn't know the dangers involved who came across this thread may have assumed the same and actually done that. I think it was a very good thing for you and others to have highlighted the danger.
Nick

[ppppenguin]

I'm glad you clarified this. Your original post where it appeared that you'd actually measured the high voltages made my blood run cold. And think you were saved by the same providence that often protects children and drunks. In fact, what you did was entirely sensible but the way you reported it made it look otherwise.

We've all done daft things, sometimes downright dangerous and stupid things, and I'm as guilty as anyone else. Those of us who are still here have survived to tell the stories. They may serve as cautionary tales for others.

I've been trying and failing to find a report online where an electrician died from an arc flash incident cause by using a cheap DVM on 208V busbars in the USA. I know I've seen it before. OK, you are most unlikely to get arc flash on a domestic installation however daft youu are but cheap DVMs are still not really safe to use on mains.

[SurreyNick]

You are absolutely right regarding cheap test gear, particularly when it can be used with lethal level currents. It's laziness on my part because it's small and always on-hand so has become my go-to item. However, I don't trust it at all, particularly in terms of my safety so I only ever use it with low voltages and very small currents and never fully trust the readings.

On the theme of safety, I do find people of my generation tend to have a much healthier respect for the dangers of electricity than today's youngsters and young adults do. I suspect few people realise that just 100ma can stop a heart and that RCD adaptors won't necessarily save their life because 30 milliseconds of 30A can still be lethal.