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Re: [Amps] Current thinking on HV supply bleeder current?

Subject: Re: [Amps] Current thinking on HV supply bleeder current?
Date: Tue, 28 Feb 2012 17:04:16 -0500 (EST)
List-post: <">>
Jim, T=RC is the equation to discharge 65% of the energy. T is seconds, R  
is ohms and C is farads.
Those big wirewound resistors have a voltage rating that should be  
followed. An over voltage will lead to premature death by way of an open turn.  
takes time but will happen eventually when you least expect it. Since they  
are in series, only one resistor has to go open to create a death dealing  
Over the years, I have seen this happen enough that I will not use wire  
wound resistors for bleeders. Now 10 to 15 series connected 3 to 5 watt  
resistors are used as needed to limit the voltage to 300v or less. This also  
serves well as a hv meter multiplier.
Yes, it takes a while to bleed the voltage. If in a hurry, the tube idling  
current will bring the voltage down to a few hundred volts in a few 
seconds.  Then the shorting stick only causes a modest pop instead a giant 
Do be careful: there's danger lurking out there!
Gerald K5GW
In a message dated 2/28/2012 3:49:50 P.M. Central Standard Time, writes:

[forgot  to CC this back to the list]

Thanks, Jim.

I believe your  comments about heavier bleeder current being a carry-over 
are probably  true.

I'm going to pencil in four 100k, 20-watt resistors with a  working 
voltage of something greater than 1KV. I don't know if that would  bleed 
4KV in 32uF off in 2 seconds or less, but it would get there. If I  trip 
over any energy storage equations in the next few days I may try to  work 
it out just for fun.

Thanks and 73,
Jim, N7CXI

On  2/28/2012 1:34 PM, Jim Hargrave wrote:
> Jim,
> The ARRL  handbook has two recommendations.
> Bleeder resistance that will  bleed the HV to 30 volts in 2 seconds after
> shutdown.
>  Another place it recommends a bleeder resistance that will equate to  
> 30% of the anticipated max load.
> The later seems to be  a carry over from Tube rectifiers, where the 
> assisted in  parallel current regulation.
> My Clipperton-L has 800k which is  distributed across the series filter
> capacitors. (HV is around  2800)
> That will give you a range that should fit most  "Treasure Box" of parts.
>      73s de  Jim
>          W5IFP
>    >  -----Original  Message-----
>    >  From:  
>    >  Behalf  Of Jim Barber
>    >  Sent: Tuesday, February 28, 2012  2:43 PM
>    >  To:
>   >  Subject: [Amps] Current thinking on HV supply bleeder  current?
>    >
>    >
>   >
>    >  I have a 3KV, 2A CCS transformer,  and 32uf of filter. What's
>    >  the  current
>    >  state of argument for appropriate  bleeder current? The last time 
>    >  came up I  seem to remember seeing everything from "HV safety bleed 
>   >  only" up to a rather high number.
>     >
>    >  So... 100 ohms per DC volt? That would  work out to a convenient 
>    >  which could be  four 100K in series, each with 1KV or so across 
>     >
>    >  Comments?
>     >
>    >  Thanks,
>    >   Jim N7CXI
>    >   _______________________________________________
>     >  Amps mailing list
>    >
>    >

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