Dave.H said:
I would like to know a general value & wattage rating for bleeder
resistors. I do occasionally recapping of vintage radios and would
like to build a unit with a resistor and alligator clips to attach to
the electrolytic leads to discharge them. The electrolytics I come
across mostly are rated for 200 to 600 volts.
A bleeder is generally always in place, low wattage, high resistance,
may take quite a while to bleed down (RC of a minute or more), so that
it won't load the circuit too much when running.
A shorting stick (applied to caps without a bleeder) is generally not
"alligator clipped on both ends" since it is generally a poor idea to be
quite that close, and is usually a lower value, high-wattage resistor.
Exact figures depend on the caps in question - figure a reasonable time
constant (ie, you'll hold the shorting stick on the capacitor for 5 or
10 seconds, and want it to be down to, say, 6 V - about 5 RC time
constants, so a time constant of 1-2 seconds) for 600V on the largest
typical capacitor you work with. One side has a clip and lead, the other
side has some sort of stiff electrode, and an insulating stick handle
leads back to the operator.
Remember that an easy method to up the power is to use multiple
lower-resistance resistors in series - it may be much simpler to find 10
2 watt resistors than 1 20 watt resistor. You can also use a light bulb,
(nice low resistance 100W [or whatever you buy] resistor, easily found)
but in that case you need to check that it has not broken, and/or use a
resistor in parallel with it so that you have some discharge even if the
filament does break.
Once the cap is shorted, if there's some chance of stray charge pickup,
a two-alligator clip lead (no need for a resistor, but there can be one
if it makes you happy) can be installed.