Newbe v. simple Transformer question

[Rarkov]

Slightly off topic but...
I just bought 2 500VA transformers (TOTAL overkill...but useful for future) and a 120VA transformer, 10 Audio Grade 6800uF caps and lots of other PSU goodies...for the bargain price of...

£140!!!!!

Thanks Maplins! They make a killing out of me! If I lived in USA I'm sure I'd pay alot less!

Never mind!
Gaz

[PMA]

Steve,
of course. Just didn't want to confuse :-))
Pavel

[Steve Eddy]

Originally posted by PMA
Steve,
of course. Just didn't want to confuse :-))
Pavel

Oh I know. I wasn't intending to take away anything from your post. I replied because your drawing helped illustrate more clearly something I'd said previously. Thanks!

se

[jnxw2]

Well I must admit I'm lost for words, I only discovered this site this morning, but the amount of replies is incredible

Thanks everyone


And now to build this thing....

[Michael Rothacher]

If you have a (two secondaries) transformer with unidentified leads, is it possible to determine the dotted leads with an AC signal generator and a scope?

[Steve Eddy]

Originally posted by mrothacher
If you have a (two secondaries) transformer with unidentified leads, is it possible to determine the dotted leads with an AC signal generator and a scope?

If by unidentified leads you mean not identified in terms of relative polarity, then yes.

Just feed a sinusoid into the primary and connect the probe of one channel across the primary. It doesn't matter which primary lead you attach the probe to or which you attach the ground to. It's AC so polarity is relative. Whichever lead you attach the probe to, designate that lead as the reference. In other words, that will be the primary lead that will be assigned a "dot."

Then connect the other channel to the seconary (or one of the secondaries if the transformer has multiple secondaries). Again, it doesn't matter which lead you attach the probe to or you attach the ground to.

Using the same timebase for each channel, check the phase of the two signals. If they're in phase, then the secondary lead that the probe is attached to is of the same polarity as the primary lead that the other probe is attached to and this lead will be the "dot" lead for the secondary.

If they're out of phase, then the lead that the ground is attached to will be the "dot" lead for the secondary.

Repeat as necessary for any other secondary windings.

se

[Michael Rothacher]

Terrific explanation! Thank you, Steve.

[paulb]

Originally posted by mrothacher
If you have a (two secondaries) transformer with unidentified leads, is it possible to determine the dotted leads with an AC signal generator and a scope?

An easier way that doesn't require a scope, just a voltmeter:
Apply a signal to the primary; you should be able to read voltage from both secondaries. Then just connect the secondaries in series and measure across them; if you've connected them correctly ('dot' to 'non-dot') you'll get twice the voltage. If not, you'll get close to 0.

[Steve Eddy]

Originally posted by paulb
An easier way that doesn't require a scope, just a voltmeter:
Apply a signal to the primary; you should be able to read voltage from both secondaries. Then just connect the secondaries in series and measure across them; if you've connected them correctly ('dot' to 'non-dot') you'll get twice the voltage. If not, you'll get close to 0.

Yes, that will work as well. I gave the answer I did because the original poster asked specifically how to do it with a generator and a 'scope.

se