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R core primary/secondary
R core primary/secondary
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Old 13th February 2018, 01:01 PM   #1
marconi118 is offline marconi118  Germany
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Default R core primary/secondary

Found a nice 150VA R core transformer.

the primary has 2 windings one on each side of the R core

Secondaries are on top of the primaries.
Are all R core build like that?

I thought that for optimal separation of primary secondary, the primary should be wound on one side of the R core and secondaries on the other side?
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Old 13th February 2018, 04:04 PM   #2
FauxFrench is offline FauxFrench  France
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I had to look on the net for the shape of an "R"-core transformer. It actually looks like a rather squared "O". Why "R"?
Anyway, not all R-core transformers are made as you describe but many are. The advantage of putting the secondary on top of the primary is that you have a much better coupling.
As long as the safety regulations (insulation) are complied with, you can do as you describe. By separating the primary and secondary on each leg you can have an even better insulation, but more than needed serve no purpose. Perhaps for high voltage use.
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Old 13th February 2018, 06:03 PM   #3
marconi118 is offline marconi118  Germany
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i mean capacitive isolation to avoid high frequency noise from the mains enter the PSU and amplifier
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Old 13th February 2018, 07:57 PM   #4
FauxFrench is offline FauxFrench  France
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I get your point. But as it is an iron core, the capacitive noise can pass primary -> iron core -> secondary. Today an EMI filter, eventually part of the power cord receptor, takes care of such grid-noise.

I can only tell you that I have such an R-core transformer with two similar coils on each leg. Each coil has a primary and a double (15V-0-15V) secondary. It is some 40 years old.
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Old 13th February 2018, 08:44 PM   #5
CBS240 is offline CBS240  United States
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The principle of the solid Raceway or R-core operation depend on two equal and opposing fields. This prevents the entire core being magnetized because flux doesn't circulate around the entire core as traditional transformers, only the two sides where the windings are. This means Eddy currents don't circulate entire core so no need for lamination. Efficient and very low leakage flux. Kind of like two equal transformers in series or parallel but both primary and secondary loads must be equal or core misbalance will occur. More can be explained HERE.
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Last edited by CBS240; 13th February 2018 at 08:50 PM.
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Old 13th February 2018, 09:21 PM   #6
FauxFrench is offline FauxFrench  France
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Thanks a lot CBS240. Now the guy (or girl) who knows his (her) transformers entered the discussion.
A balance principle - interesting!
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Old 14th February 2018, 10:24 AM   #7
marconi118 is offline marconi118  Germany
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Thanks a lot for this info!

so my r core has 4 secondary (2 for each side) and 2 primaries put in parallel

strangely the 2 secondary of one side have 15.2V but the 2 secondary on the other side are 15.6v

should I unwound the 15.6V to bring them to 15.2V?

I would like to put all 4 secondary in parallel
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Old 14th February 2018, 12:15 PM   #8
FauxFrench is offline FauxFrench  France
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I would put them in parallel through separate diode(s) for each winding. Then, the windings cannot source one another.
I would be surprised if the number of turns is different, if the transformer is marked with the same output voltage for all four windings. Unloaded, even the same number of turns may leave different voltages.
Try eventually to load the windings at 50% (one at a time) and see if the voltages are more alike when loaded.
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Old 14th February 2018, 12:33 PM   #9
marconi118 is offline marconi118  Germany
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it is marked 30 + 30 v 2.5A because one secondary is in series with a secondary at the opposite side

15.6+15.2
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