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Plastic Polystyrene Plate High Voltage Capacitors

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LAN_403

HM_Murdock

Wed Sept 08 2010, 11:10PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

(no caliper here, so had to test it out the old-fashioned way...on a cutting board with a fire extinguisher handy!)

Ok...more results...

On my spark gap, I had to shorten my gap to 3mm with the plates. By comparison, my saltwater cap (which shows just over 10nF), sparks fine at 4.5mm. No real measurement, but the spark is noticeably louder (and produces more of an ozone smell) on the saltwater cap vs. the plates.

Ran the spark gap for about 20 seconds with the plates, with no melted plastic on the plates.

There was, however, a buzzing sound from the plates when the gap was set too wide to fire (4.5mm). Will fire it up again after dark to see how bad the corona is from the plates...

Anyone able to make sense of these results?

Adam Munich

Wed Sept 08 2010, 11:24PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Well If it fires at 3mm, the caps are likely charging to about 3-4000V. Corona could very well be the problem. Putting the caps under oil should give you much better results. Peanut/canola/vegetable oil will work fine.

As for the buzzing, what did it sound like? 60hz hum or something different?

Proud Mary

Thu Sept 09 2010, 12:23AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Grenadier wrote ...

Well If it fires at 3mm, the caps are likely charging to about 3-4000V. Corona could very well be the problem. Putting the caps under oil should give you much better results. Peanut/canola/vegetable oil will work fine.

As for the buzzing, what did it sound like? 60hz hum or something different?

Didn't that German chappie Kronjaeger used to make Marxes and such out of polystyrene burger cartons, rather than take them as evidence to the nearest digestive diseases clinic?

Adam Munich

Thu Sept 09 2010, 12:30AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

It would appear so.
Marx

HM_Murdock

Thu Sept 09 2010, 12:31AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Buzzing sounds like hair clippers, only not nearly as loud...

In the dark, there is no visible light coming from the plate stack.

Not enough oil on hand to submerge stack...

Adam Munich

Thu Sept 09 2010, 12:35AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Sounds like the plates are vibrating because of electrostatic force. I assume you're charging them with a neon sign transformer?

Maybe the caps aren't preforming too well because they are too big. Not enough current is supplied to charge them every half cycle. (though I highly doubt this)

HM_Murdock

Thu Sept 09 2010, 01:18AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

(Yes, 9kV/30mA NST - added it to detail list above...thanks)

You may be on to something...

I removed 5 layers and cranked the clamp down hard and was able to get up to 5.5mm spark gap. Safety gap was firing off about once every 4 or 5 seconds (ran it for about 20 again), then there was a little hisssing noise...

Postmortem revealed the bottom 4 layers had been punched through (see pic below).

Took about 20 seconds to replaced the 4 layers, now running at 16 plates, 14.7nF and a 5mm spark gap. Loud as hell and stinking of ozone :)

Also, now the safety gap fires if the spark gap does not (so I can't tell if the plates are still buzzing). Made no adjustment to the safety gap, it wasn't firing off before and now it does. I assume this means my voltage increased?

Pic shows hole in foil and plates, as well as the cardboard template I made for cutting out my foil (used razor knife on the foil)

Hernan

Sun Sept 12 2010, 05:15AM

Registered Member #1614 Joined: Wed Jul 30 2008, 03:08PM
Location: Argentina
Posts: 52

Hi to all, nice cap Mike.
I'm starting to make a similar DIY parallel plate capacitor with square heavy duty alu foil plates and polypropilene bags for induction heating so I would like to know if anyone has tried to build a capacitor for this application.

I`m thinking to use 140 with 3 inch per side plates to obtain about 0.17uF. the plates would be atached to a bronze bolt with a passing hole for watercooling them..
comments would be preciated

thanks

radiotech

Sun Sept 12 2010, 11:33PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

The clamp capacitor looks great. Is there some way of measuring if it pushes or yields against or to the clamp pressure when DC is applied. Does it hum when 50 Hz is applied?

HM_Murdock

Mon Sept 13 2010, 02:22AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

I do not know about 50htz, but it did hum at 60...

I also have a plan in mind for encasing the plates in oil (without having to submerge the clamp), which I hope will stop the blowouts I am seeing while allowing me to get more volts out of it. So far the open air version is good for short runs on my SGTC (less than 15 seconds).

So far, that simple stack is getting me the following results (more info and video on my SGTC thread in the TC forum)

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