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capacitor bank

C

Crusher

Well-Known Member
May 12, 2007
841
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Louisville, KY
Looking to build a cap bank. But not sure what caps to you. How do I figure out ESR? Also ho do I figure out how much current the capacitors can safely handle? Looking to build a cap bank that is rated for about 7kv. To be used for a single 3cx3000a7 or a 3cx6000a7. Any help or direction would be greatly appreciated.
 

You know way more than I, but building a cap bank that size seems like a balance between performance and pocketbook.

400v seems to be as high as you can go before choices rapidly fall off, and at 400v you need at least 25 caps and then capacitance starts to fall off.
 
Agreed, but was trying to see if anyone could point me in right direction. I was looking at some of the russian caps, the 5kv ones. But after reading QRO parts post on cap, they say they are good for 2 amps. They are only rated at 40uf each. 2 in series gives me 20uf. So I would have to run 2 parallel banks of 2 series capacitors to get 40uf @ 10kv. Love the voltage rating and 40uf aint bad. But shipping and all included looking at $900+ for capacitors.
 
I think you'll have well over $900 in electrolytics to get over 40uf @10kv, but do you really think you'll need 4 of those for a 3cx3?
 
vo1ks said:
What overall capacitance and voltage rating is required?
We tossed a bunch of very large high voltage stuff at work a short time ago but there might be some more left...
Click to expand...


:eek: Damn! Wish I had known that.:cry: I'm looking at a pair of 3-500Z's for HF down the road, maybe as a winter project next winter. I am a bit stuck on the filter caps. I have a single 100 uF can but only 2500 volts or four cans of 5000 volts caps but only 4 uF. I really don't want to go the electrolytic route and prefer the large oil filled cans.
 
We turfed several 15uF @15kV capacitors.

I snagged a bunch of smaller ones and gave to someone in Fall River. He may be willing to share, can't imagine him ever using two boxes of caps.




Captain Kilowatt said:
:eek: Damn! Wish I had known that.:cry: I'm looking at a pair of 3-500Z's for HF down the road, maybe as a winter project next winter. I am a bit stuck on the filter caps. I have a single 100 uF can but only 2500 volts or four cans of 5000 volts caps but only 4 uF. I really don't want to go the electrolytic route and prefer the large oil filled cans.
Click to expand...
 
Maybe I'll see him at the Downeast Amateur flea market in the spring. (y) I always keep my eyes open there for such things HV or RF related. I haven't heard the date for it yet this year. I hope I'm off. If not I may have to burn up one of my banked days and take it off.
 
Oh man, those 15uF @ 15kv would have been nice. Just parallel 2 or 3 and I'd be happy. ( 359, I just picked up a big tube the other night. A 3cx15000a7). Plenty of dissipation.
 
You would need approx. 40-50uF total for a 3CX3000A7 @ 2 amps plate current to stay at 3% ripple. Go here for a calculator on power supplies: Martin E. Meserve - K7MEM - Un-Regulated Power Supply Design
It is best to run electrolytics at 70-80% of their maximum voltage rating of 450 volts per cap.
So you would need 21, 1500uF @ 450 volts caps for that supply ($22.95 a piece @ RFParts). That would give you a total capacitance of 72uF @ 9450 volts.
The equalizing resistors I use are 100K 5 Watt Metal Oxide resistors across each cap.($.65 a piece RFParts).
Also parallel each cap with a 6A10 diode ( banded end on positive side of cap).
The diodes are for if one or more of each string of diodes in the full wave bridge ever shorts, the diode with start to conduct and shunt the AC voltage to ground blowing the HV fuse.

Hope that helps.
 
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