Filter Cap

[W8UJX]

Would this capacitor be ok for use as a filter cap in  a 2 KV, 500 mA DC power supply I am building?

Tks,
Jerry, W8UJX

http://www.ebay.com/itm/High-Voltage-Capacitor-200uF-2100VDC-5-/271221115114?pt=LH_DefaultDomain_0&hash=item3f2609c8ea#ht_140wt_919

[W7TFO]

I'd give it a go, but with a stout bleeder and soft-start.

2KuF is going to look like a dead short to your rectifiers for a bit.

73DG

[KA2DZT]

Jerry,

Are you planing on using a input choke in your supply?  An input choke will reduce the inrush current.  Little easier on the capacitor as far as constant ripple.  Not all caps are OK to use right off the rectifiers without an input choke.

Hard to tell what service those ebay caps were designed for.

Fred

[K5UJ]

What's the power supply for?  I'll assume it's for an AM rig in commenting.

I'd look for something else.  reasons:

1.  Those look like energy discharge caps to me.  Maybe they are designed for filter duty but I've never seen anything like that for 2 KV filtering.

2.  for 2 KV you'll have to series a pair.  2.1 KV rating isn't enough and even if it were, you'd have 200 uF 

3.  Even with two, you'll have 100 uF.  That's way way too much with a filter choke and it is too much for a cap input filter and no choke.  The reasons are that the stored energy is too much.  If the cap suddenly did a fill discharge for some reason, it might do some expensive damage.  More important, assuming you key the rig by switching the AC service to the h.v. supply primary, the cap charges every time you key into transmit.  A soft start with a time delay relay is okay for a leenyar where the B+ stays on, but speaking for myself, I wouldn't want to recharge that much capacitance on every single transmission, even with a high resistance bleeder.

[W8UJX]

Thanks Rob,

All your comments make sense.  The rig I would probably use this cap in would be an AM rig.  Power supply for either the plate modulated RF final or the modulator.

Choke input wiht 866A tubes.  Even then it would probably require a soft-start circuit which I don't want to deal with.

The reason I asked the question in the first place is I thought it might be some kind of energy storage cap.

I think I will go with my gut and pass it up.  My gut has saved me money in the past.  Hi...

Tks,
Jerry, W8UJX

[w7fox]

If this is an "energy storage" capacitor, it may have short life if run at the maximum voltage.  I had a conversation with an engineer at another cap factory, and she told me this type of capacitor is not meant to be charged up and sit there for long periods of time.  She suggested running it at about half rated voltage.  Good luck.

[KE6DF]

I have a couple similar caps.

Mine have higher voltages (3.5K in one, and 4.8K in the other).

And they are about 35 and 40 uF.

I figure they would work OK at about 1/2 the rated voltage.

They are defibrillator caps. So they are designed to charge up and then discharge thru paddles.

But I suspect as medical devices, they are very high quality so I won't hesitate to use them in a PS.

But, I agree with the suggestion to get two of these and use them in series in a choke input circuit.

You also might want to put a series wire-wound resistor in the B+ output lead -- say 20 ohms -- so if somehow the PS gets shorted, the current at the caps would be limited.

Dave

[K1JJ]

Are these the same type of caps as the so called "photo-flash" caps?

The P-F caps are also very compact.  I have a few that are rated at 51 uF at 5KV and are the size of a small loaf of bread.  I've run them at 3500 - 4KV in cap input service for many years with no problems.

T

[WQ9E]

The rule of thumb seems to be these energy storage caps will live a reasonable life in filter service at 75% or less rated voltage but it would be good to measure the heat rise in service.  This measurement should be with the power supply loaded because that is when the heating will occur.

Rob makes an excellent point about the need to manage energy storage/availability with large value capacitors.  They will sink an incredible amount of current during initial charge and you don't want your plate iron to be the only control of peak current.  During a fault the current discharge of a high value cap is even more spectacular and can be very deadly and destructive.