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Re: Another 942C failure mode?

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Mike,

At 09:11 PM 6/11/2005, you wrote: 
Hi Terry,
               What value total cap value are you running on that DRSSTC?


37.5nF 8000V rated.  It is just four Geek style caps in series.

Also the voltage and the current? 

13.5 amps RMS  432 amps peak.

I'm thinking of leaning toward the 200 amp oil caps we use in the induction heater tank circuit, or the smaller ceramic water cooled (draloric) mushroom caps, 20 kV, .0076 and 250 running amps CCS, it sort of depends on what you are using to for an opinion.
Regarding these thermal failures, it might be cool to place IR phototransistors so they only look at critical items and not room light as an early warning system.
Mike

Generally, the caps are so cheap a failure is not a big deal. For the cost of an IR system, you could over design the caps many times.

Cheers,

        Terry

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Saturday, June 11, 2005 9:41 PM
Subject: Re: Another 942C failure mode?


Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Jimmy,

At 01:22 PM 6/11/2005, you wrote:


Last time I ran my DRSSTC, I hurt my MMC. I Had assumed it to be overcurrent, because I was running additional cycles (up to 20 or so), wasn't giving it rest between runs, and the current (and therefore voltage) didn't build up past the 14th cycle or so anyway. They were getting very hot, and the sparks gradually shortened, until I noticed something wasn't right, and shut it off. The capacitance was higher than normal, and the next morning, it was closer to what it should be, but still over. I was pretty confused, but i guess it could be due to a shorted cap. I guess I should look for one. What are your thoughts?

If the cap over heats, the poly will start to melt together and it will not unwrap easily. Heat weakens the poly. At about 100C, things really go bad fast. Even though the outside is just hot, the inside may be super hot. If it is heat damage, all the caps may be hurt. Steve's overvoltage things seems like just a bad cap went but sustained high current and the heat from it can mess up the whole thing.

It is interesting that you and Steve have damaged MMCs. Perhaps the DRSSTC needs to have the MMCs looked into more. The MMCs may need to be made a bit stronger than normal for DRSSTC use. Of course, like me, the MMC was probably the last thing one was worrying about. You can always just whip together another one. I note, that my protectors with their single big caps get a little warm too. My MMC is enclosed so I will not know if it gets hot until it is too late. I never considered how it might like running at 6000 BPS :o)) I guess it has not blown up yet...

Cheers,

        Terry