Re: draining filter caps
- From: Jim <askme@xxxxxxxxxxxxxxxxx>
- Date: Sat, 31 Mar 2007 14:38:30 -0700
Stephen Cowell wrote:
"Jim" <askme@xxxxxxxxxxxxxxxxx> wrote in message news:130r785dotalt78@xxxxxxxxxxxxxxxxxxxxx
Jim wrote:
...
Simple applicaction of that equation says that with a 1M resistor on a 100 uF charged to 500V, the time factor is 100 seconds. Each time factor is the time it takes to lose 63.2% of the supply voltage. In five minutes, voltage falls below 25V.
HARDLY a week.
But Willie already knows all of that, because he's an EXPERT!
I don't think your Java calculator is taking the
electrolytic memory effect into consideration...
those things are like batterys, in that an electro-
chemical reaction takes place and they create
voltage. You model it with a resistor in series
with a battery, across the cap. If your series
resistor is not much smaller than the one in
the model, you will have greatly extended bleed
times.
__
Steve
.
You raise an interesting point. I know that the older caps get, the more they get that "memory effect." Therefore, a 1M resistor may take longer. However, I'm not sure how significantly longer it'll take. Although the caps build voltage, they don't get anywhere near a full charge back. Not as much potential. So we might be talking a few extra seconds. Doubtful that it's more than a minute. I do have some very old caps around, but they haven't been used in a while so a real life test may not tell me anything.
Keep in mind I never suggested 1M, I was just countering Willie's "take a week" comment. I like to do the lead from the preamp plate, and leave it there while working.
.
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