xerxes
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Posts: 1,115
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Post by xerxes on Jun 7, 2006 0:58:28 GMT
I wondered whether one of the resident gurus could explain something about transformers.
I've been looking at transformers and see that you can attach the secondary outputs in series or in parallel.
So if I have a transformer, for example this one:
TOROID 80VA 12V+12V 3.33A(RC)
With a 0 - 230v primary and two secondary outputs of 12v. Am I correct in saying that if I wire the outputs in parallel I get 12v, but twice the amps, 6.66A in this case, and if I wire the outputs in series I get 24v, but the amperage remans at 3.33A?
Also, if you have two primaries of 0-115, 0-115, these can be connected in series, to make a single primary of 0-230v, correct?
I had a look around the web for a "how to connect transformers for idiots guide", but didn't turn up anything. Does anyone know of any?
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rickcr42
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Post by rickcr42 on Jun 7, 2006 1:34:01 GMT
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Stormy
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Post by Stormy on Jun 7, 2006 11:46:18 GMT
As far as I can tell, you seem to have nailed it Xerxes.
Just make sure you insulate the junction between the two primaries or you'll have a 120VAC wire just waiting to ground itself on the casing/your fingers, and remember not to create a shorted turn by connecting both ends of the mounting bolt to the casing.
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xerxes
Been here a while!
Posts: 1,115
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Post by xerxes on Jun 7, 2006 12:09:18 GMT
Thanks guys,
I think I stumbled accross the Hammond examples, but one thing it didn't really confirm is the doubling of either the voltage, or the amperage on the secondaries, depending on whether you connect them in series or parallel.
One last question. If I have a transformer with a primary of 0 - 230 and two secondaries, 0-12 and 0-12, and I only want to use one of the secondaries, what do I do with the spare. Can they be left disconnected, what do you do with the spare wires of the unsused secondary?
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Stormy
100+
Advocates putting smokers in a "Sin Bin"
Needs to learn to keep his big mouth shut.
Posts: 153
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Post by Stormy on Jun 7, 2006 14:59:51 GMT
Connecting them in parallel does theoretically double the current/power rating, otherwise the transformer would have to be rated at 40VA for 120VAC operation as you'd get half the power if you could only use the current rating of one of the paralleled primaries. Two 3.33A secondaries in parallel = 6.66A as the current flowing through each coil is still 3.33A.
The "spare" secondary could be left unconnected without harm as far as I am aware (open circuit with voltage but no current at that point), but you should insulate the ends or clamp them into a terminal block to stop them from touching stuff. You may as well parallel them with the other secondary even if you don't intend to make use of the extra current, but make sure you get the phase right to avoid weird magnetic phenomena!
Theoretically your output voltage should move around half as much under varying load when the secondaries are paralleled because you are drawing half as much current as you would be with just one. This means that the percentage current change relative to the maximum available is halved, and that is directly proportional to voltage regualtion. However, most toroids have pretty good regulation, and if you're running something that is drawing only a small portion of the total current available, voltage swing will probably be in the order of millivolts anyway!
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