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Are toroidal transformers best?
Are toroidal transformers best?
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Old 24th February 2020, 01:24 PM   #131
Bonsai is offline Bonsai  Europe
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Growling = almost certainly then DC on the mains or the core is nearing saturation.
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Old 24th February 2020, 01:32 PM   #132
daanve is offline daanve  Netherlands
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Originally Posted by alexberg View Post
Where did I say bout insulation coming off?
Here:

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Originally Posted by alexberg View Post
Moreover varnish dissolves wire insulation and if the x_former of yours was not designed to be impregnated then so be it.
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Old 24th February 2020, 01:38 PM   #133
Jakob2 is offline Jakob2  Germany
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Originally Posted by Bonsai View Post
Growling = almost certainly then DC on the mains or the core is nearing saturation.
Exactly; saturation due to "normal" operation (audio power amplifier) will usually not be noticed because of the high level coming from the loudspeakers.

The advantages of toroidal transformers (very steep magnetizing curve, no air gaps, max flux concentration, low core magnetization losses and low resistance of the windings therefore very high effiency)lead to the two common problems, very high inrush current (when switch on at the "wrong" phase angle) and core noise (the growl that you've mentioned).

The before mentioned vacuum impregnation helps against other noises coming from loose metal sheets and/or windings and betters the insulation, but can't do next to nothing against the growl coming from the magnetostriction of a saturated core.
The common cure is to make the toroidal transformer a bit less optimal, by reducing the flux (winding calculation) and usage of other core materials with less steep magnetization curve and more losses.
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Old 24th February 2020, 02:02 PM   #134
Bonsai is offline Bonsai  Europe
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Agreed Jakob - we in fact mentioned all those things you raised a bit earlier in the thread - but, it certainly does no harm to reiterate them!

My cores are wound at about 30% below the ‘optimum’ for the core size so the tolerance to mains DC is much better.
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Old 24th February 2020, 11:45 PM   #135
TonyTecson is offline TonyTecson  Philippines
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i got a toroid from a well known winder, antek, it was a china job, and the toroid came to me doa, open primary windings....

if you look a the toroid there are no signs of damage the one can see...

so what i did was to dismantle the thing, lo and behold, the primary winding was broken in several strands in one place, so i thought then, someone must have dropped the thing and the toroid landed edge first....

so this is one thing with toroids, do not drop them.....
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Old 24th February 2020, 11:46 PM   #136
TonyTecson is offline TonyTecson  Philippines
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Originally Posted by scottjoplin View Post
Yeah, "growl" is the right word
even EI's do this when saturating...
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Old 25th February 2020, 12:51 AM   #137
TonyTecson is offline TonyTecson  Philippines
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I tried that in my youth. ALmost impossible to wind a decent transformer with used wire - and especially the secondary’s! But ok to reuse for coils etc.

We used to go to a local motor re-winder. He’d weigh the roll(s) of wire we selected and we’d take it away wind our transformer and take the rolls back and it would get re-weighed and we’d pay for what we had used. Later when I earned a bit more money, I’d just get the transformer wound to spec - they were EI cores (late 1970’s/ early eighties).
there is a reason why i never reused copper wires, when i was 14, i attempted to make a traffo using copper wires taken from ballast transformers for fluorescent lighting....

my first attempt went up in smoke and scared the hell out of me....

so from thereon, i never used used copper wires ever again...
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