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Author Topic: HV Power Supply capacitor question  (Read 1301 times)
W4FBI
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Posts: 244




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« on: September 11, 2017, 03:13:40 PM »

Revealing my HV power supply ignorance here.

My internal supply has four 150uF/ 450v electrolytic capacitors (in series) for the 1400v DC. (Gee, that nets only about 40uF if my old electronic theory is correct)

I will be replacing the caps. I have several 330uF/  450v caps.

Wouldn't they work just fine?

thx

Alan
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AC5UP
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Posts: 4413




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« Reply #1 on: September 11, 2017, 03:59:56 PM »

They would, providing nothing gets pinched or crunched physically and the airflow within the chassis remains good...

My only concern would be the potential for a cold start current inrush increased enough to damage the HV rectifier(s).  This is easily addressed with beefier diodes.  Newer HV parts are more robust than their predecessors of 20-ish years ago and not expensive to upgrade.
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W6EM
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« Reply #2 on: September 11, 2017, 04:00:26 PM »

Alan:  Not knowing what the peak DC voltage of your supply is, I can't answer exactly.  But, if there are 4 each, 450VDC rated capacitors in series, their composite DC rating would be the sum of their individual voltage ratings, or 1800VDC.  Also, a good idea to have some high value resistors across each capacitor to help ensure equal voltage drops across them.
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N4NYY
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« Reply #3 on: September 11, 2017, 04:15:26 PM »

They would, providing nothing gets pinched or crunched physically and the airflow within the chassis remains good...

My only concern would be the potential for a cold start current inrush increased enough to damage the HV rectifier(s).  This is easily addressed with beefier diodes.  Newer HV parts are more robust than their predecessors of 20-ish years ago and not expensive to upgrade.

I think you need to take up fishing!
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AC5UP
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« Reply #4 on: September 11, 2017, 04:19:57 PM »


I think that's one halibut of an idea!
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W4FBI
Member

Posts: 244




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« Reply #5 on: September 11, 2017, 04:30:42 PM »

Alan:  Not knowing what the peak DC voltage of your supply is, I can't answer exactly.  But, if there are 4 each, 450VDC rated capacitors in series, their composite DC rating would be the sum of their individual voltage ratings, or 1800VDC.  Also, a good idea to have some high value resistors across each capacitor to help ensure equal voltage drops across them.

Yes, there are 120K (2 watt) resistors across each cap. I'll keep those (after checking their value)..
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KH6AQ
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« Reply #6 on: September 11, 2017, 05:03:27 PM »

The higher capacitance capacitors have at least two downsides:

1. If the PS is a capacitor input type the charging current pulses will be narrower resulting in higher RMS current; the transformer will run hotter.
2. The PS will have twice the stored energy (80 vs 40 Joules) and this will make any arc event more destructive.
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N4NYY
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« Reply #7 on: September 11, 2017, 05:56:52 PM »


I think that's one halibut of an idea!


You on the air yet? I traded my FT-950 + $50,  for a TS—590SG. Been waiting like 5 years to talk to you!
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