[ms660]

Originally Posted by kalee20

Agree! Actually, I was trying to make the point that ten minutes work with a soldering iron, some wire, diodes, lots of microfarads and a load is probably quicker than 15 minutes with Otto Schade's techniques.

But your own simplified analysis has indicated even faster there's likely to be a problem... transformers are loaded together at 73VA, and the OP's first post informs us there's only 40VA rating to play with.

It does, of course, depend on why the manufacturer has rated the transformers at 10VA per secondary. If it's because of temperature rise, the OP is in trouble. If it's because that's the loading at which the voltage has dropped more than 5%, but temperatures are still entirely comfortable, then happy days! (Though I doubt whether the second scenario is the case!)

I chose 15 Volts to allow for a regulator, using Schades curves only takes a few minutes:

Make an assumption that Rs/Rload is 6% and choose the ripple percentage of choice, with those two figures 2pi*f*C*Rload can be got from the ripple % curves (for full wave) Using that figure, determine the ratio for the DC output to the peak AC output from the transformer using the appropriate set of Schade's curves, use those two figures to determine the VAC output needed from the transformer.

For the RMS current through the diodes, half the Rs/Rload percentage and double the 2pi*f*C*Rload figure to obtain the diode RMS current to it's average current (DC) ratio from the appropriate set of Schade's curves, multiply the diode DC current by that figure then multiply the result by the square root of 2 (1.414) to determine IAC.

It's taken me at least 15 minutes to write this but 5 minutes for the calcs....

Lawrence.