I am trying to use this supply for a tube preamp:
https://www.antekinc.com/content/AS-2T200.pdf
It has a high DC resistance, but they state that the Tx can provide 4A at 6.3V. That would be an impedance of 1.7 Ohm? Should I use that for the Voltage supply series resistance in LTSpice when calculating inrush currents, regulation, etc? Having a zero ohm power supply in simulations causes a lot of problems with current calculations, of course.
https://www.antekinc.com/content/AS-2T200.pdf
It has a high DC resistance, but they state that the Tx can provide 4A at 6.3V. That would be an impedance of 1.7 Ohm? Should I use that for the Voltage supply series resistance in LTSpice when calculating inrush currents, regulation, etc? Having a zero ohm power supply in simulations causes a lot of problems with current calculations, of course.
As a first approximation, just use the 20 ohm secondary resistance for inrush.
There's not enough info for any more.
There's not enough info for any more.
The 20r is for the 200V, not the 6V.
We have 7V drop on 209V winding at 65VA which is like 1/3rd of full rating. A bit of extrapolation suggests 21V sag on 209V at full load, or 10%. A reasonable guess for 200VA toroid. There's no reason the 6V windings are the same, but probably similar. So the 6.3V 4A windings may be 6.93V at zero A, or series resistance 0.63V/4A, or 0.13 Ohms.
I'm away from my good chair and abacus, and may have slipped some cogs. But on a 6V 4A winding, part-Ohm series makes more sense than 20 Ohms. "Matched" is equally unlikely because heat.
Thanks for pointing out something I miscalculated.
The impedance of the toroid would be the voltage drop across the coil / output current, not the output voltage / output current like I was assuming.
Spent all day yesterday flip flopping between "this needs a current regulator" to "this doesn't even put out enough voltage under load!"
You also pointed out another convention of Tx manufacturers: It sounds like theyll add a few turns to account for loss? I was not aware of this, but that would be nice.
You paid for "6.3V @ 4A" or whatever (this lump is more complicated and not clearly specified). You will try to use it that way. If you don't get that 6.3V @ 4A you will complain.
Everything sags. You may get a no-load number but you are much less likely to complain about it (in most rational situations). So yes, they add turns to account for sag.
A cheap and tiny 5VA transformer can have 25% 30% sag. Heat is not the problem, only price. Yes you do pay more for your electricity than a perfect transformer, but 1VA is $0.000,25/hour is often negligible. (Times dozens of trannies in millions of houses it does add-up, so wall-warts are going away. The 25,000VA street transformer for my house has about 2% sag at full load. While I never pull full load, all the tranny loss is on the power company side of the meter (they pay) so it is worth building for low losses.
Normally the spec is given at full rated load, for example: 18VAC at 3A.
The voltage would rise if measured with the secondary open circuit, or if the load is less than 18V / 3A = 6R.
The unloaded voltage rise could be from 5% to 10% compared to the full rated load.
Thanks for the wisdom on convention, its always humbling and incredibly practical to get answers from here.