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Old 5th January 2011, 09:57 PM   #1
HP8903B is offline HP8903B  United States
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Default Wiring Buck Transformer with GE transformer Help!

I got a pretty good idea on how to wire a buck transformer.
However, I am confused about this particular GE transformer that I have. Please see picture.

Please help me how to wire it to work with 120V with minus 24V. My AC line is 124V and I want to bring it down to 100V.
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Old 5th January 2011, 11:31 PM   #2
PWR RYD is offline PWR RYD  United States
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Connect: X2 - X3

Input

Hot connects to: H1 - H3 - X1


Output

Hot connects to: X4


Neutral for both input and output connects to: H2 - H4
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Old 5th January 2011, 11:43 PM   #3
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Connect H1 to H3.
Connect H2 to H4.
Connect H2 & H4 to X1.
Connect X2 to X3.
Connect the line voltage across H1 and X4.

Use your AC voltmeter and verify ~103 VAC from H1 to X1. If you've got it, you're done. Connect your load across H1 and X1.

If instead you've got ~155VC...
Connect H1 to H3.
Connect H2 to H4.
Connect H2 & H4 to X4.
Connect X2 to X3.
Connect the line voltage across H1 and X1. Verify ~103 VAC from H1 to X4.

Last edited by Ty_Bower; 5th January 2011 at 11:50 PM.
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Old 5th January 2011, 11:45 PM   #4
HP8903B is offline HP8903B  United States
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Got it. Thank you very much!
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Old 5th January 2011, 11:47 PM   #5
HP8903B is offline HP8903B  United States
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Since it is 250VA rating, does this mean that I can use it up to 2500VA? Someone said that when you connect a transformer as a buck, the rating is multiply my 10.
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Old 6th January 2011, 01:31 AM   #6
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You are limited by the secondary current, since all of the current is passed through it. So at 12Volts you should be able to connect up to 20.8 amps. You have to use both secondaries in parallel, as well as both primaries in parallel.

The transformer is going to be a 12VAC X 20.8 amps or 250VA. With the secondaries in series you'll get 24VAC at 10.4 amps and still 250VA. The transformer is always going to be a 250VA.
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Old 6th January 2011, 02:01 AM   #7
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I think Zigzagflux is the guy who understands this topic well. He posted on the last buck autoformer question here: How to wire a 'Buck' transformer
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Old 6th January 2011, 02:09 AM   #8
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Another question: Is it okay to have the transformer hooked up all the time (with the equipment off)?
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Old 6th January 2011, 02:18 AM   #9
PWR RYD is offline PWR RYD  United States
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Quote:
Originally Posted by Ty_Bower View Post
I think Zigzagflux is the guy who understands this topic well. He posted on the last buck autoformer question here: How to wire a 'Buck' transformer
I've done a dozen or so buck or boost transformers (single phase and 3 phase) and the drawing in this link is not the proper way to wire it. You want to wire the primary HV winding in parallel with the line in, then wire the secondary LV winding in series with line (either in phase for boost, or out of phase for buck).
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Old 6th January 2011, 03:51 AM   #10
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Transformers are most flexible; you can use them any number of ways, and there is more than one way to skin a cat.

Both methods will work. My preference is with Ty's connections, which are based on my prior recommendations in the linked thread. A number of reasons:

1. Ty's connection applies 124V to a winding set rated nominally for 144V, so you run with lower volts/turn, therefore lower flux, therefore lower radiated magnetic fields. Benefit for audio systems depending on where the xfmr is located. Pwr's connection applies 124V to a winding rated nominally for 120V. Not exactly a huge problem, but it is what it is.

2. Ty's connection results in total I/O capacity of 1292 VA; Pwr gives you 1032 VA. Check my math; I'm good at making mistakes.

3. Ty's connection produces 103V output, which with a little load current and transformer impedance, will give enough voltage drop to get you exactly at 100V. Pwr's connection produces 99V output, with voltage drop you get below the requested 100V.

Pick your poison, but I see little disadvantage to Ty's connection.
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