Date:         Sat, 2 Jul 2005 22:15:44 -0700
Reply-To:     Jack <john.cook58@VERIZON.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jack <john.cook58@VERIZON.NET>
Subject:      Re: Electrical discharging a capacitor
In-Reply-To:  <008601c57f3f$894ae020$884a9f04@mountlbcfw9s79>
Content-type: text/plain; charset=US-ASCII

Screwdrivers work ok for the smaller caps, BUT some specific
capacitor types and large HV caps can not only spread molten metal
around the atmosphere (what used to be a screwdriver tip) but the
contents of the capacitor itself as it explodes.  Discharging through
a resistance is much, much safer.

Don't underestimate the damage an exploding HV cap can do.  BTDT.  I
remember a 2-star general ducking for cover when some caps started
exploding in a system being demonstrated.  That was worth the mess!

Also, beware of charge recovery.  I think someone referred to the
fact that some capacitors can recover a dangerous level of charge
even after having been shorted and discharged, due to dialectric
effects.  Typically, this means leaving the discharge circuit in
place for a long enough period of time.  CRTs are infamous for this
phenomena.  I can show you a scar ...

//Jack

On 2 Jul 2005 at 12:52, Tom Miller wrote:

> I was taught in school to use a screwdriver.  Touch the tip to one terminal,
> and lay the shaft down across the others.  It arcs but not enough to burn
> the screwdriver.  We used to charge them up and then toss them to some
> unsuspecting nerd in class.  Not enough juice to be lethal.
>
> Nerd
>
> ----- Original Message -----
> From: "Doug in Calif" <vanagon@ASTOUND.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Friday, July 01, 2005 8:38 PM
> Subject: Electrical discharging a capacitor
>
>
> Anybody know how to safely discharge a capacitor?
>
> Playing with another small ac unit and they have a capacitor  (110v) about
> the size of a tennis ball.
>
> I would like to be able to continue doing my vanagon tinkering without
> losing my eyebrows.
>
> I believe there are 3 spades on it and its my understanding you can connect
> a standard light bulb say 60 watt to it and it will
> discharge and then its safe?  no?
>
> If you dont hear from me again, that was incorrect. (grin)
>
> Doug
>
>
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