Dave M wrote:
Yes, variacs are a bit pricey when compared to non-variable transformers,
but certainly not a bank breaker. In this case, a variac would certainly be
the best solution, since the OP wanted a simple circuit for reforming
unknown capacitors. His capacitors might be rated at 450VDC or 50VDC. It
wouldn't be such a great idea to connect a 50volt capacitor to a 400VDC
source, even with a honkin' big resistor between them.
The only other solution would be to build several DC supplies for different
voltage capacitors. He needs a variable voltage source that can be adjusted
for the appropriate reforming voltage.
Another way, if he doesn't have a variac, is voltage dividing the
output to get reduction he needs to the max voltage of the cap.
Something like 10 5W resistors in series from V+ to gnd, 10K each.
Then he can pick the "max tap" that gives him the closest voltage
under the cap's v rating as the max, and reform in steps using the
lowest voltage tap first and progressing up to the "max tap". With
his 350V transformer, that would be good for 50V up to 500V caps.
Ed
