Re: Capacitor Safety Discharge Method (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 08 Aug 2007 18:04:04 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Capacitor Safety Discharge Method (fwd)

Hi Chris,

I think you'll be fine to use a wirewound resistor in that application 
(if you desire). Or if you like, just use a carbon resistor. Calc the 
discharge time, current, and power dissipation of the resistor to arrive 
at a value that won't easily fail and something that won't take forever 
to drain (often a trade of time and current). I typically throw a 
resistor right across the filter cap terminals and a fast high current 
diode on the output of the filter to prevent reversals from reaching the 
supply circuit. A 15 to 30 second bleed time is not necessarily a bad 
thing and sometimes necessary depending on voltage and current levels 
along with what is practical in size to use. Whatever you do, don't 
design the filter bleeder at the ragged edge (this is what kills 
bleeders). Derate the power dissipation by at least 2 and it should 
survive the life of the equipment.

Take care,
Bart


Tesla list wrote:

>---------- Forwarded message ----------
>Date: Wed, 08 Aug 2007 01:43:57 -0400
>From: Crispy <crispy@xxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: Capacitor Safety Discharge Method (fwd)
>
>On a DC coil, is it safe to use a wirewound resistor in this way to
>discharge an electrolytic smoothing capacitor?  Would the inductance in
>the resistor set up a high-frequency oscillation which could harm the
>caps due to voltage reversals?
>
>Chris
>
>On Tue, 2007-08-07 at 06:45 -0600, Tesla list wrote:
>  
>
>>---------- Forwarded message ----------
>>Date: Mon, 6 Aug 2007 23:34:56 -0500
>>From: resonance <resonance@xxxxxxxxxxxx>
>>To: Tesla list <tesla@xxxxxxxxxx>
>>Subject: Re: Capacitor Safety Discharge Method (fwd)
>>
>>
>>One can make up an inexpensive HV relay using a standard 120 vac  1" 
>>solenoid.  Just mount a pair of tungsten contacts.  Use a small "leverage 
>>arm" so that the solenoid moves the contacts approx 3 inches and discharge 
>>thru a high power 5 Ohm wirewound resistor.  Works great and fab cost is 
>>around $25.
>>
>>As someone else commented, always check with a hotstick in case the resistor 
>>ever blows out.  NE-2 neon bulb connected thru a 1 meg resistor in series 
>>(to ground)  attached to a plastic rod works good to detect any remaining HV 
>>charge.
>>
>>
>>Dr. Resonance
>>
>>Resonance Research Corp.
>>www.resonanceresearch.com
>>
>>
>>----- Original Message ----- 
>>From: "Tesla list" <tesla@xxxxxxxxxx>
>>To: <tesla@xxxxxxxxxx>
>>Sent: Monday, August 06, 2007 9:54 PM
>>Subject: Re: Capacitor Safety Discharge Method (fwd)
>>
>>
>>    
>>
>>>---------- Forwarded message ----------
>>>Date: Mon, 06 Aug 2007 20:38:11 +0000
>>>From: nancylavoie@xxxxxxxxxxx
>>>To: Tesla list <tesla@xxxxxxxxxx>
>>>Subject: Re: Capacitor Safety Discharge Method (fwd)
>>>
>>>Hi, Chris. Thats exactly what I was trying to get an answer to in the
>>>previous posts and I think that if you kind of read between the lines in
>>>Bart's reply, you can see that its probably okay to do if you use bleeder
>>>resistors and discharge the cap after the charge has bled off. What I
>>>wanted to use was a Ross Engineering relay rated at 40 kv (normally open
>>>contacts) and wire it across the terminals of the capacitor and
>>>resistors.It would then just be a simple matter of flipping a switch and
>>>doing the work of the screwdriver in a much safer fashion.Anyone see a
>>>problem? Wyatt
>>>
>>>-------------- Original message -------------- 
>>>From: "Tesla list" <tesla@xxxxxxxxxx>
>>>
>>>      
>>>
>>>>---------- Forwarded message ---------- 
>>>>Date: Mon, 06 Aug 2007 01:53:57 -0400
>>>>From: Crispy
>>>>To: tesla@xxxxxxxxxx
>>>>Subject: Capacitor Safety Discharge Method
>>>>
>>>>Hello,
>>>>
>>>>In light of the recent discussion about the necessity of a manual
>>>>discharge for the tank capacitor in addition to bleeder resistors, I've
>>>>been considering an easier method of manual discharge than the
>>>>stick-a-screwdriver-in-the-spark-gap method for my coil. I was thinking
>>>>about an electronic method, and here's the idea. Would it be possible
>>>>to have a linear pull-style solenoid with an electrode that, when
>>>>powered, would retract its electrode from another static electrode, to
>>>>act as the safety discharge? The normal state (no electricity applied)
>>>>would be to have the contacts together, and the capacitor shorted. Of
>>>>course, the electrodes would have to be insulated from the solenoid.
>>>>Also, would it be possible to immerse this under oil, if the gap
>>>>provided by the solenoid was insufficient to prevent sparking over in
>>>>normal operation, or would the oil coat the electrodes and somehow
>>>>prevent safety discharge?
>>>>
>>>>Thanks,
>>>>Chris
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>
>>>      
>>>
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>>    
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