should I go for broke?

[Tom Phillips]

Thanks Ray,
That makes sense. I wonder if the phase at last turn off thing is really got any basis in fact.
Tom

[Ray Ivers]

Tom,

I wonder if the phase at last turn off thing is really got any basis in fact.

That's the first I'd heard of it. My take was that if the AC was switched at a zero waveform crossing there would be no surge and if it was switched at a waveform peak there'd be max surge, like any other transformer - the difference being the toroids' max-surge characteristics, as mentioned in the Plitron quote.

Ray

[Steve Conner]

I agree with Ray FWIW. Switching on at just the "wrong" instant in the cycle hits the core with twice the flux density it's designed for, so it saturates. The transformer now effectively has no core at all, so it draws huge magnetizing current. The time taken for it to calm back down depends on the L/R time constant. Toroids suffer worse than E-I core trannies because they have a higher inductance, lower resistance, and sharper saturation characteristic (no distributed air gaps)

Smaller toroid PTs can be switched directly onto the line OK, but the larger ones tend to blow fuses at random. My experience with toroid PTs was in solid-state hi-fi where the oversized filter caps just make the switch-on surge even worse, so I always used a soft-start in that case. I think it gives the unit a classier feel too, if it powers up with a gentle hum and clicking of relays rather than a loud Twang! that dims the lights.

[Ray Ivers]

Steve,

a loud Twang! that dims the lights.

... or a small prap! followed by silent darkness (gee, how Poe-ettik ).

I'll report back on how the zero-crossing relay works when (and if) I ever get the thing wired up. I think I've already mentioned the PTC-thermistor surge suppressors too - Plan B in case the fancy SS relay was a waste of time & money.

Ray

[Enzo]

I like the thermistor, when they heat up, they essentially disappear. Simple, elegant, reliable. Other fancier things are just adding uneeded complexity - more things to fail.

I would not have thought there was residual magnetization in the toroidal core, just like the man says above, depending upon where in the cycle the power is turned on, there can be an instantaneous spike in current as the core fills. The surge is from that, not core memory. Or so my thinking goes.

[R.G.]

either way the info I wanted to share is that there is a guy named bill muller (www.mullerpower.com) who is a member of the alternative energy community who has discovered a material that is basically just black sand left over from gold minig that he calls Amorphous Polycrystalline Ferrite that I guess is extremely magnetically efficient, doens't make eddy currents, elminates hysteresis, can de-magnetize almost instantly etc, and is a choice material for cores. it would be interesting to experiment with this material as a core material for a guitar or stereo amp transformer and hopefully when i'm a bit more experienced I'll get my hands on some and try it out.

I checked Bill Muller's site.

It's sad. Mr. Muller was apparently a devotee of the idea that there is power available for free. The appearance of the terms "over unity" "perpetual motion" "zero point energy" in a positive and supportive manner is a reliable guide to the fact that the rest of the content is fictional.

Amorphous polycrystalline ferrite sounds very much like the raw material for what eventually is made into sintered ceramic ferrite corres. The easy way to experiment with this material for guitar or stereo amp transformers is to buy pre-made ferrite cores.

You're going to run into the problem that physics is still physics even when the materials are from an odd source.

Amorphous polycrystalline ferrite (APF) particles would have an overall HUGE distributed air gap if made into a magnetic core. Air gapped cores require many more turns of wire to achieve the same magnetic results. APF materials also have a permeability constant of at best 1/5 that of iron, and a much lower saturation flux density. So you need five times the volume of APF to do the magnetic work, you can only drive it to a fraction of the flux density before saturation - if you could ever get enough turns of copper on it to drive it.

Play with it if you like - but try not to expect that it's going to magically be better than what a lot of smart people worked on for about a century to get right.

[jimi]

I found this in the UK they sell PT kits. Looks interesting

[MitchK]

I found this in the UK they sell PT kits. Looks interesting

wheres the link?