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Primay phase / secondary phase with stacked toroids
Primay phase / secondary phase with stacked toroids
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Old 14th November 2019, 07:24 PM   #1
coolnose is online now coolnose  Europe
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Default Primay phase / secondary phase with stacked toroids

Hi all,

I am currently working on the final setup of a (Firstwatt) F5 turbo in dual mono configuration, that is 1 toroid/PSU board per channel in a common enclosure. The 2 toroid primaries are joined at the softstart board.

The toroids are stacked (definitely NOT "shorted") and when working on getting the mechanical and audio hum of the toroids down to an acceptable figure a forum member suggested swapping the primary phase of one of the toroids.

I did so and the result was immediate, the mechanical hum went down close to nothing, the remaining hum is probably due to the "poor" quality of the toroids themselves and also the audible 50Hz/100Hz residue in the audio (yes, I am on the old continent) went down a lot.

I suppose there's some kind of magnetic coupling issue when both in (primary) phase.

I can't get my head around it, so I am taking the risk to ask a dumb question:

Does inverting the primary phase of 1 of toroids imply swapping the seconday phase of that transformer as well ?

Right now it's working fine as is (i.e. secondaries of both transformers wired the same way), it's not like I can't sleep at night because of that, but I suppose someone knows more than me for sure!

Any input appreciated!

Thanks,

Max
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Old 14th November 2019, 07:31 PM   #2
FauxFrench is offline FauxFrench  France
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Hi Max,

Your exact configuration is not clear to me but I can state that changing the phase on the two primary wires leaves the phase changed (180 degrees) on the secondary windings as well.

I guess the member suggested this to change the leakage-coupling between the two toroidal cores.

I hope your sleep is now assured.
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Old 15th November 2019, 06:16 AM   #3
PRR is offline PRR  United States
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> imply swapping the seconday phase of that transformer as well ?

Yes; and if they fed the *same* load it would already be blown-up.

But if you are Dual Mono then they feed two *separate* loads, neither fussy about its power phase, so that is fine.

The cancellation of mechanical (and electrical?) forces is new to me and may be very valuable to others.
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Old 15th November 2019, 09:24 AM   #4
coolnose is online now coolnose  Europe
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The question now is can I further improve the (non)coupling in inverting the 2 secondaires of that "swapped" transformer:

Beginning of 2nd secondary-End of 2nd secondary=OV-GND=Beginning of 1st secondary - End of 1st secondary.

Now thinking of it that might be usefull in a single bridge configuration where the "common" is directly connected to ground which is not my case though...

Thaughts ?
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Old 15th November 2019, 07:05 PM   #5
FauxFrench is offline FauxFrench  France
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If they are stacked in the sense that one is put on top of the other, you may try to put magnetically shielding material in-between the two transformers. One insulating sheet, then an iron plate and finally another insulating sheet.

One member once had mechanical noise problems because his fastening means actually formed a closed conductive circuit acting as a false secondary winding. Try removing the fastening means to see if it helps.

Try, if possible, to separate the two transformers physically to see if it changes the noise.

Could we eventually have a photo of the two transformers and their connection to the rectifier(s)?
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