[Amps] Bleeder Resistor Inquiry

[Joe Subich, K4IK]

Mike, 

Your bleeder resistor is too small.  

4000 volt transformer with fullwave bridge should 
produce at least 5600 volts no load. 

5600 volts across 100K -> 56 ma 

56 ma * 56 ma * 100K = 313.6 watts 
313.6 watts >> 225 watts 

At a minimum, you need either: (1) a pair of those resistors 
in series, (2) a 200 K 225 watt bleeder or (3) a 100K 500 watt 
bleeder.  Even then, you will be not have a lot of safety 
factor and probably need to provide cooling for the bleeder. 
Safer yet would be a (series) string of four 50 K 225 watt 
bleeders.  

Finally, is the resistor rated for > 5 KV?  Most are not.  

73, 

   ... Joe, K4IK 
 



> -----Original Message-----
> From: amps-bounces at contesting.com 
> [mailto:amps-bounces at contesting.com] On Behalf Of aborg
> Sent: Sunday, April 24, 2005 9:44 AM
> To: Amps Amps
> Subject: [Amps] Bleeder Resistor Inquiry
> 
> 
> I am currenty building a HV Power Supply using a
> 4800vac pole pig, 40uF 5kv oil filled cap , 10kv PIV
> rectifier board, 20 amp variac and a 100k 225watt
> bleeder.
> 
> The initial power up started well without the bleeder
> connected to the circuit after 30 min burn-in no
> problems. Discharged the circuit and added the 100k
> bleeder and 5 mins the bleeder starts to smell and the
> exterior paint starts to bubble. Shut it down and
> examined the circuit, all seem accurate. 
> 
> Question : Is my bleeder to small ?
> 
> P.S. : The variac was set at 4KV at all times.
> 
> Mike-KK4MS
> a_borg at yahoo.com
>