I don't know if anyone has mentioned it but you also need to be careful
when shorting the cap to ground, that the ground circuit for the cap
hasn't opened up. For instance the meter resistor that bill mentions
from B- to chassis ground. If that is open you will not discharge the
cap with your shorting stick by hanging it on the B+ side of the cap.
You could even burn that resistor open in the process of shorting the
cap! You could get a bang and only partially discharge the cap thinking
you were successful in the discharge.
You need to also short from the - side of the cap to the + side of the cap.
Incidentally you guys are not calling that shorting stick by it's right
name. It is better known as a "Jesus" stick, as that is usually what is
said when the device is used successfully on a hot circuit.
Many years ago at an Air force radar transmitter every once in a while a
new guy would touch the "stick" to the HV supply of the 10 mega watt
transmitter and forget to shut the HV off first! They would always call
the stick by it's proper name and usually turn a little white and get
weak in the knees! The over current relays would immediately shut things
down so no damage was done other than a large pit in the end of the "stick".
73
Gary K4FMX
Bill Coleman N2BC wrote:
> I'm not sure what resistor you are referring to Rich.
>
> In the power supply that bit me there were two 100K 225W resistors in series
> across 4KV and one was open - no arcing. Examination of the open resistor
> showed only a hairline crack a couple inches from one end.
>
> If you mean the current limiter you propose in a shorting stick, would you
> trust it to arc so you knew it was open?
>
> I'll go for the big bang of a heavy hunk of wire right to ground. Safety
> glasses on, one hand in my pocket.
>
>
> Someone mentioned watching the HV meter. In the case I had, the HV meter
> indicated zero - that's the bug I thought I had. The metering was done
> across a small (10K ?) 25W resistor which was at the bottom of the open
> bleeder. Never trust the meter!
>
> 73, Bill N2BC
>
> ----- Original Message -----
> From: "R. Measures" <r@somis.org>
> To: "Bill Coleman N2BC" <n2bc@stny.rr.com>
> Cc: "AMPS" <amps@contesting.com>
> Sent: Sunday, April 24, 2005 8:40 PM
> Subject: Re: [Amps] Shorting Sticks
>
>
>
> On Apr 24, 2005, at 2:26 PM, Bill Coleman N2BC wrote:
>
>
>>It won't get warm at all if it's open...
>
>
> What will prevent the open from arcing?
>
>>
>>----- Original Message ----- From: "R; Measures" <r@somis.org>
>>To: "Bill Coleman N2BC" <n2bc@stny.rr.com>
>>Sent: Sunday, April 24, 2005 5:18 PM
>>Subject: Re: [Amps] Shorting Sticks
>>
>>
>>A typical value for a current limiter resistor in a shorting stick is
>>400 - 1000-ohms, 100w. Discharging even 200J barely gets a 100w
>>resistor warm.
>>
>>On Apr 24, 2005, at 1:52 PM, Bill Coleman N2BC wrote:
>>
>>
>>>As one that has literally come across an open 225W bleeder.... I would
>>>never
>>>trust a resistor in series with the shorting stick. If the caps are
>>>charged, something has already failed. If the caps get damaged, too
>>>bad. I
>>>would rather kill a few bucks worth of parts than me.
>>>
>>>73, Bill N2BC
>>>
>>>PS: It's a good idea to routinely test the shorting stick too.
>>
>>Agreed, but if the I-limiter resistor is open, there would be a
>>considerable fireworks show.
>>
> snip
>
>
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>
>
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