Capacitor Questions

[jmaf]

Earlier this month I had the chance to buy a few of these from a junkyard sale here in town: imgur: the simple image sharer

So here are a few questions for you guys, pardon in advance if they're too basic or obvious.

1) What would you do with these? Of course I'm thinking tube amps But shrinking coins, cutting cans or popping hard disk plates to the sky are no bad idea either

2) They're rated at 415 VAC, but on the EPCOS datasheet it says they were tested at up to 3000 VAC for 10 seconds. Question is: what would be a safe DC rating for these? Can I hook them up to 500 VDC? I have a circuit here with 900VDC +B - can I even dream of hooking one up there?

3) After I brought them to my shop, one of them leaked some oil in my hand. It didn't smell, no itching, no irritation...I ran to the tank and washed my hands thoroughly, knowing the hazards of old transformer oil, but I must have been in direct contact with it for 2 to 3 minutes till I got to soap and water. You guys think this oil was toxic?

4) What does the kvar unit mean in practice, as explained to a 5 year old? Does it mean I can safely discharge the C * V^2 energy stored in it at a rate of 3.3 KV power?

Thanks very much in advance!

[tedmich]

transferring capacitor AC voltage ratings to DC is design specific but a 1.5-2X higher DC rating is common.

they are PP film caps with non PCB oil, so not as toxic and very old ones (PCB are an incredibly environmentally durable, medium strength toxin), but I wouldn't rub in eyes, feed to cat etc.

Leaking caps don't perform well as the oil is needed for rated performance

here is a decent description of kvar
http://standby.iea-4e.org/files/othe...ctorBasics.pdf

[Austin]

Did you try asking in the forums at 4hv.org: News? They probably could answer your questions and they are quite knowledgable in the art of blowing stuff up! I have learned alot from them...

[jmaf]

Thanks, tedmich. If the 2x ratio can be applied here, my 900 VDC supply almost makes it. Will give it a try, most can happen is blow something up....my trusty lamp current limiter oughta help. Thanks for the pdf as well, will give it a read.

Austin, thanks for the link. Had not been to that site before, lots of interesting stuff there on their forum as well, will have a look after work.

[tedmich]

Thanks, tedmich. If the 2x ratio can be applied here, my 900 VDC supply almost makes it. Will give it a try, most can happen is blow something up....my trusty lamp current limiter oughta help. Thanks for the pdf as well, will give it a read.

Austin, thanks for the link. Had not been to that site before, lots of interesting stuff there on their forum as well, will have a look after work.

I disavow all such action ! please consider using series caps with equalizing resistors before pushing 900vdc in these caps, something like this

550uF @ 1800VDC $35 at Apex Jr

[Gingertube]

Thes caps are used a lot by the HiFi crowd.
DC rating is root 2 x the AC rating (that is 1.4 times) so they are good for around 580 Volts DC. If you need more voltage rating then you will have to buy something else or series connect 2 or more of them WITH voltage share resistors added.
When considering voltage rating you must take into account that at switch on your power supply rail will go high (to the peak value of the unrectified AC) until the tubes heat up and start conducting at which time the power supply rail will drop back (assuming the caps haven't gone bang in the mean time).

Taking that into consideration I would not want to have more than the quoted 415V of DC across them during normal operation.

Cheers,
Ian

[jmaf]

Gingertube, that's an interesting reply. It makes logical sense to me, at least on first sight, that it should be twice the AC rating RMS.

A 220V AC RMS voltage is actually a 440 V swing, also RMS, which is what root 2 x VAC would give us, twice peak to peak, then RMS'd. So the AC capacitor should be able to handle a maximum rating for isolation during the full AC swing which we can approximate to twice the rating.

Thanks again.