Dual-500 king of the Castle

Fully powered both channels. All good but!
I have stopped to figure best solution for a problem I created. Having added separate power supply for constant voltage to the control board I have eliminated any built in power drain from the main caps. In other words they do not discharg. I need to add a resistor that will drain the Cap’s say over a couple of minutes but not effect overall performance of the power supply. We have 35,000 uf at 240 volt.

Anyone got a calculation for what may be best would be a help
 
So set up test on low rail voltage of 160 volts.
used a 10k 2 watt resistor. About 6 minutes down to 15 volts. The resistor got up to 1’80* F under power

then two in series 104* F with 160v rail. About 10-12 minutes to discharge

retested using two 220 k 2 watt in parallel
Only 80* F but may take 1 hour to discharge
 
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The Powerful Difference said:
Actually, this sounds like a reasonable solution -- especially if you have a sign (on the inside of the top cover / or even on top of the top cover, 'Fear This' style ) to tell anyone going in something to the effect that "Please wait 6+ minutes for lethal voltages to dissipate BEFORE proceeding."

(Preferably in stencil font -- always catches my eye/makes me stop & read for comprehension...must be my military background. :0)

This way you've more than covered the bases, safety-wise. Anyone who puts themselves within touching distance of coke can-sized caps should know that they are at risk, and should be discharging B4 proceeding...
Click to expand...
Yes it matches the service manual. I may look for a relay to fast discharge on powerr off.
 
grapplesaw said:
Fully powered both channels. All good but!
I have stopped to figure best solution for a problem I created. Having added separate power supply for constant voltage to the control board I have eliminated any built in power drain from the main caps. In other words they do not discharg. I need to add a resistor that will drain the Cap’s say over a couple of minutes but not effect overall performance of the power supply. We have 35,000 uf at 240 volt.

Anyone got a calculation for what may be best would be a help
Click to expand...
Put a 1N4004 diode to your main caps
 
Gepetto said:
Put a 1N4004 diode to your main caps
Click to expand...
Ok. I have them on the rails as fly back diodes
I best see if I have thoughts in backwards as well

here is one on neg rail
 

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Gepetto said:
Put a 1N4004 diode to your main caps
Click to expand...
Ok added one across + & - cap
No real discharge happing

fly back diodes are 1n4004. Also correctly oriented
 

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Anyway testing continues. Both channels work with low input. Time to button it up for heavy duty loads and fuses.
 
grapplesaw said:
Ok added one across + & - cap
No real discharge happing

fly back diodes are 1n4004. Also correctly oriented
Click to expand...

Hi Glen, you will have to describe your dilemma a bit more fully for me to understand and recommend. Perhaps a quick hand sketch, snap a photo of it and post it.
 
Joe the issue is the main power caps do not discharge over a few minutes. Actually hold charge for hours. Not to safe I’d say.

As a new feature I no longer take power from the main caps to the control board as it has its own power supply ( pictured sorta) tied to the the ac output of the main transformer. The reason is to have 80-0-80 constant supply voltage to the control board.
When you run off the rail for supply to the control board this voltage changes from 80-0-80 to 120-0-120. This change in voltage really only effects the Bias voltage as it gets fed from the rails. Therefore it’s not optimized for best bias voltage in one or the other rail voltage as you set it be best with high rail not low.

I have fly back diodes on both positive and negative rail of each channel. These are not discharging residual stored voltage in power caps. I added one 1n4004 across the positive and negative main cap and this did Not help to discharge them. Of coarse I can manual do it and I can also do it with pair of resistors giving a constant drain, not my desired choice.

what part of the pl700 circuit accomplish this job to discharge the caps over time. I always thought it was leakage in the control board.
I do not recall this problem on any other build only this with the second power supply which , by the way drains very quickly?
 

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So removed the second power supply. Caps now discharging as I suspected when bias supplied by rails through control board. Will have leave idea for later thought
 
grapplesaw said:
So removed the second power supply. Caps now discharging as I suspected when bias supplied by rails through control board. Will have leave idea for later thought
Click to expand...

I am not really following what you are attempting to do Glen...
 
My change to a separate board power supply has now been sorted out. I changed to high voltage supply windings after confirming with Joe on doing this. Thanks again Joe for being there for us.

I still get a small change in Bias but only .02v swing and this is because of residual heat difference from the rails static voltage change. Now I have .372v on high and .354v on low. I am very pleased with the out come

I have added a 15k wire wound resistor across the main caps for slow discharge when turning off. This may be replaced with a fast dump resistor and relay combo. We’ll see if that’s needed or not
 
Why are you concerned about cap voltage drain if your On delay/off relay is working?? What are you thinking here Glen?
 
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