Laycock said:
What colours, how many wires and where are they on the transformer?
Chris
No, that shouldn't be a question mark at the end. Because all
of that does often help to figure out the windings.
The used to be a color code for transformers, though I'm not sure
it was always consistent, and I am sort of doubtful it's being used
nowadays, with transformers coming from all kinds of locations across
the globe.
But yes, the color code used to be fairly constant on the primary,
which to some extent is what you need most.
If the leads come out in more than one place, the one with only two
leads is likely the primary (but I don't think I'd take this
as absolute). This also doesn't help if the secondary has only two
leads (or if the primary has a dual winding).
Sometimes you can get information if you can see the wires on
the actual transformer, something possible with open frame units.
Likely, the primary has smaller wire than the secondary, but again
that's not always the case.
You can always determine sets of wires by using an ohmmeter to
find pairs or sets. Again, with a pair of wires and a set of three
wires, likely the pair is primary.
Once you have the sets or pairs matched up, then maybe the color coding
makes more sense. I have no idea where to find the color code in
present material, but if you find a pair that does match the color code,
that increases the chance that those are the primary.
Old reference books, including the ARRL Handbook, would likely have
the transformer color coding, and one might find such books at the library.
If you have an idea of what the transformer is, ie voltage and even useage,
that might help. A low voltage transformer will have fewer turns on
the secondary than on the primary, so the primary should have a higher
resistance on the ohmmeter than the secondary.
Once the primary is determined, then one can hook it to the AC line
and measure voltages on the other sets of wires. The potential danger
in this is that those voltages may turn out to be quite high, depending
on the transformer, or if you've made a mistake on the primary.
You could lessen the danger by taking a known low voltage transformer,
and power that from the AC line, and use that to feed the alleged primary
of the uknown transformer. Then the other widings will produce accordingly
lower voltates.
Michael