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> Ok, I was thinking of adding resistance to lower current draw.Im
fully aware > of the dangers.I dont fool around like you may think.One thing is I need to > know the type of resistor to use as a bleeder.I know I need like a 10K 50 > watt or so but what TYPE is good?Im thinking metal oxide? > > Matt Hi Matt,
Use metal oxide. They have the highest voltage to length ratio,
before they burn.
450 volts, though is more than most any resistor
is specified for, unless you're using something really big. Even large wirewound
resistors are seldom rated for more than 300 volts across them (unless you get a
significantly higher voltage value from the square root of their power and
resistance values; about 500V or greater)
Something like (4), 5-watt, 10-K resistors,in
series, is better as a bleeder. There is less chance of breakdown, when
things get old, damp, or heat fatigued.
Here's one other thing I STRONGLY reccommend - put
a neon lamp directly on the capacitor.
Use a regular neon bulb (like NE-2H) with aseries
resistor of 470K-ohm (for 450 volts). Use this in conjunction (in parallel)with
the bleeders across the cap. Now you will know if the capacitor contains
anything more than about 75 volts - in other words, the neon bulb will light
when there is *LETHAL* danger in the cap (but of course you still can get a
good, but probably survivable jolt with it out.)
(I was never trained by a professional. I am self
taught, and I helped instruct the advanced electronics course at my high school,
'93-'94. I got my first 600 volt electrolytic when I was 7 and learned
everything the hard way. There was electrolytic juice sprayed all over my
bedroom, more than once!)
I've been jolted so many times that now I
always use the neon bulb indicator. It's a life saver, and I can't overstate
that. I even had an "out of body" experience after taking 1uF @ 20 kV across the
chest in '98, I saw myself twitching on the floor!! (This is actually one jolt I
do not regret. It's how I came to have faith in
God :-)
Just recently I found an oil capacitorthat I
don't think I charged since I was a 15 - I assumed it was discharged, since
it was at least 10 years since I last charged it. It shocked me so bad thatI
threw it across the room, and shouted.
Each of these (and more) have happened because I
wasn't using a neon indicator; I "remembered" discharging the capacitor butwas
obviously wrong.
Use crimp style loop terminals, like the kind used
on terminal blocks; you can solder everything in to these (I don't recommend
crimping, though since it can come loose), and screw the loops
in so the external resistors and lamp are always on the capacitor.
Then you can see the danger.
Graham
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