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Old 3rd April 2004, 01:15 AM   #1
Myren is offline Myren  United States
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Default Two Transfomers => Center Tapped?

I got a whole bunch of big honkin huge (non torodial transformers) from some dumpster diving. But they're not center tapped. Can they still be used? They have a common ground, so i cant just tie ones + to the others - lead, afaik.... Is there any way to circumvent this?

If so, i just need to figure out where i'm going to scrounge some huge honking caps from.

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Old 3rd April 2004, 02:33 PM   #2
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Common ground? ins´nt that just chassis connection. Seems unlikely that one end of secondary winding is "grounded". If so You can still put the secondarys of two transformers in series and use the "common grounds " as center tap, just reverse phase of primary.
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Old 3rd April 2004, 08:25 PM   #3
Myren is offline Myren  United States
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even though there's no physical connection between the secondary and the primary coils, i still thought there'd be a a common reference ground voltage which would prevent such chaining.

just in case, here's one for circuit breakers. :-]

thanks
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Old 3rd April 2004, 08:33 PM   #4
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Hi Myren,

If you goal is to make a + and – supply for an amp then simply use one trannie with a bridge rectifier for the V_plus and use another trannie with a bridge rectifier for the V_minus. It only works well if both trannies are equal.

BTW. What do you mean by “common”?

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Old 11th April 2004, 10:03 PM   #5
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Default side benefit of using two transformers

A potential benifit is to cancel magnetic interference from power transformers through positioning or reversing primary polarity (as previously suggested) of one of the two units.

I've seen use of dual transformers in older dbx gear (160 compressors, I think it was, the ones with a VU meter and wood side panels).
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Old 12th April 2004, 12:53 AM   #6
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Hi,

Maybe the so called "Common Ground" is just an electrostatic screen?

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Old 12th April 2004, 03:22 AM   #7
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Default common ground

Pardon me if I'm repeating the obvious. Get an ohmmeter and check out all the leads.

You can draw a schematic of how you think the transformer is connected, what leads go to what. Perhaps the primary is black and black with a white stripe, etc. Secondary might be red and red with a white stripe, this extra "common ground" wire might be green. So draw that as a transformer, and put the label colors down.

Set your multimeter on the low resistance range (like 100ohms or 10 ohms if you spent).

The primary will read really low resistance, the secondary might be higher or lower depending upon parameters, but between the primary and secondary, there will be a nearly infinite resistance, since they're not connected.

So you could check your "common ground" this way. If its a shield it will have near infinite resistance to all other transformer leads. Measure for conductance between this lead and the transformer case. Sometimes this connection to the transformer case is provided, probably as a safety consideration.

Usually power transformers don't have electrostatic shields, but some do (check-out Plitron transformers).

Good audio transformers always have such shields and then some.
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