Re: [CAD_CAM_EDM_DRO] Re: Capacitor safety questions

The safety rule for things like lethal capacitors is that the charge has to
be bled down to a non-lethal level by the the time you get the cover off.
i.e. From the time you turn it off until you can get your fingers on it.
All bets are off if you work on it powered up. 10000 MFD charged to 100 V is
very lethal. Use a bleeder resistor. The resistor below will have about a 10
second time constant, so the cap should be bled down in 30 seconds or so
(not counting motor loads.)

D.

----- Original Message -----
From: "bull2003winkle" <bull2003winkle@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, December 26, 2003 6:44 PM
Subject: [CAD_CAM_EDM_DRO] Re: Capacitor safety questions


> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "volitan712003" <volitan@o...>
> wrote:
>
> Divid:
>
> Look for my comments below.
>
> > Hello,
> >
> > I just ordered a 12,000uF x 100V capacitor for my power supply. I know
> > capacitors can be deadly but I have no concept of what a micro farad
> > is. If this cap is fully charged, is this thing big enough to kill?
>
> Yes, it is if the voltage it's charged to is high enough.
>
> > Another question is how can I check it so I know it's discharged. I'm
> > guessing it would have too much power to hook my volt meter up
> > directly.
>
> No, voltmeters just measure voltage, they don't know anything about
> power. Your voltmeter will read the voltage across the capacitor just
> fine. Just STAY on VOLTAGE. The best way to discharge a capacior is
> with a resistor. For that size cap I would suggest a 100 ohm 10 watt
> wirewound resistor. When first connected it will draw 1 amp. The
> current will drop as the voltage decreases so the resistor won't hive
> time to get hot.
>
> Good power supply design has a bleeder resistor connected across all
> large capacitors to discharge them when power is removed. For this,
> the resistor is always drawing current so you will want a larger
> value. A 1000 ohm 20 watt resistor would be a good choice. It will
> draw 100ma. from the power supply but that should not be noticable.
>
> Regards;
>
> Ken
>
> > Thanks!
> > David
>
> David:
>
>
>
>
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