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Adam Munich

Fri Sept 17 2010, 02:05AM

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

I'm going to use this thread to document my adventures with homemade capacitors, and the strive to possibly build a 1MegaVolt marx with them.

I went to office max, and they wanted $40 (forty!) for a pack of 100 OHP sheets. So that wasn't going to happen. I ended up getting a pile of them from a teacher, and they are assorted. There are HP ones, Avery ones, and staples ones.

The HP and Avery are cellulose acetate, while the staples ones are made out of the same stuff as sandwich bags. Unfortunately the HP ones are covered in the same kind of glue that is used on envelopes, so that will be a pain to get off. I'm speeding up the process by soaking them in my hot tub with the jets on.

I'm going to make 15kV caps for many reasons.
1. I don't want to deal with side flashover.
2. I don't want corona on my spark gaps
3. I want this to be LOUD. Lower voltage = Higher capacitance
4. I don't have a lot of sheets
5. My highest voltage DC source ATM is (2x) full wave rectified 15kV 25mA NST.

I plan on using 6 sheets per cap. I'm going to test both the acetate ones and the lunchbag ones, and see what's better.

Here's a picture of the sheets. This thread will be pic heavy.

Avi

Fri Sept 17 2010, 03:02PM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

is this going to be in or out of oil?
those hole punched things so seem to work quite good (in air) because they are sealed at the sides but have their limitations eventually

803

Fri Sept 17 2010, 07:56PM

Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191

Good luck!

may I sugest you cut them into 4ths and use them, that would save space.

Patrick

Fri Sept 17 2010, 08:07PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

some advice Grenadier, build a kind of cubic rectangle shaped cap that will fit inside the largest pipe diameter, you can get. this will give you the ability to vacuum pull oil, after all an 8.5 " dia pipe 11" long might be hard/expensive to find. but a steel water pipe 4 " x 10" is easier/cheaper, and your capacitence is assumed to be the same in each case, as an exapmle.

Adam Munich

Fri Sept 17 2010, 10:41PM

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

3 hours and one box of M. Clean magic erasers and all the HP ones are all clean.

I measured the thickness of both the HP and (Avery was the other brand name) sheets and they are both 3 mil. I bought a box of Reynold's wrap and I'm going to put some together now and I'm going to use 8 sheets per cap. I'm not doing any vacuum or oil, as that will be a big pain in the *ss to do for every cap; these will be used in a marx generator after all. Flash over won't be a problem since these will be run at 15kV.

Muttyfutty!

Sat Sept 18 2010, 01:40AM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

Ahhhhh.... Oh dear, the same caps I made last week failed
on my single un-rectified 15 KV NST. 1 neat, burning hole through
7 layers of OHP Transparency. Ouch!
Be VERY careful with 6 layers, Dont Operate them for too long. Good luck!
regards,
mike

Adam Munich

Sat Sept 18 2010, 02:37AM

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

Well mine (2 sets of 4 layers) seem to be holding up just fine!

I made 5, then ran out of OHP sheet. Need to find a place to get more. I think I may have bitten off more than I can chew with a 1 MV marx, because I'll need 70 capacitors. That's 560 OHP sheets! I intend to try my best though, but I'll still need to find a lot more sheets. No more HP ones though, I'm done scrubbing glue.

So I measured them, and I must say they are all pretty close. 3 were exactly the same! However I killed my multimeter on the last one. Apparently it built up enough charge by simply putting it together to kill my DMM.

Now I need to go meter shopping tomorrow and burn a hole in my wallet.

Values are as follows.
3x 2.80nF
1x 2.86nF
1x 2.97nF

These are very stable caps, and pressing them or changing the temperature doesn't seem to affect the value at all. Definitely suitable for TC use.

I hooked them all in // to my 15/25 NST (half wave rectified by 32 1n4005's) and they make one hell of a crack. It left my eyes burning and my ears ringing after 5 seconds of that racket. There is no problem with flashover and they don't seem to mind not having a spark gap either. They don't hold a 15kV charge for very long due to corona loss, but hold 5kV quite well. So If I build a 70 stage(15kV) marx I'll need relatively low value resistors (~250K). They also make an interesting sound when the power is cut, kind of like TSSSSSHHHHHHEEEWW

I'll record it sometime.

I also hooked them up to my supposedly GFCI NST's. Guess what didn't happen? :p

Sadly no video, my video camera's dead and the charger is nowhere to be found. Got pics though.

I had to put the NST on a box in the last one because electricity found it's way through the floor adn gave me a tingle.

Adam Munich

Wed Sept 22 2010, 11:41PM

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

More plastic! Here's what I got.

+ About 25 more acetate sheets, (HP

). More scrubbing tonight.
+ 2x 75 foot rolls of acetate. One is covered in drawings and words, but vis-a-vis markers are easy to clean. The other one is old (yellowed), but nothing else seems to be wrong with it.
+ 1x 75 foot roll of sandwich bag stuff. About 1/3 used, 2/3 unused and clean.

So what should I do with the rolls? A giant 5kV cap, or cut them up to use in multiple small 15kV caps?

Adam Munich

Fri Sept 24 2010, 12:36AM

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

2 hours of scrubbing that dang glue and all I got was 2 made. I ran out of sheets before I could finish another. It's anyone guess as to what their capacitance is, but it's likely to be around the 2.85nf mark.

I tried making a cap with the rolls of plastic and it was fail to say the least. Off the roll the plastic was curved, so it didn't want to stay flat. The plastic sure wasn't acetate, it looked more like a PVC type material. It was also 1mil thinner. I attempted to make the thing with the rolled stuff by adding 2 more sheets to compensate for the thinner-ness. I couldn't get anything to stay flat and when it was rolled uo a whole bunch of air got inside. I thew the thing out before even hooking it up to an X-former. I still haven't tried the sandwich bag stuff.

I was searching online and I found 100pks of sheet for $15 shipped. I don't think it's worth it to buy the stuff. $60 will get me about 40 caps, and even though they will be cheaper than ready made 2.85nF 15kV caps, I'm not sure it's worth it. I'll still attempt to get some more free sheets though.

edit: Dang I just realized I triple posted. Not a real big deal though I suppose. It's not like they're one line posts.

Muttyfutty!

Fri Sept 24 2010, 01:05AM

Registered Member #2915 Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101

WOW, That is certainly impressive!
The largest Value caps I got was about 2 nF. What thickness are your transparencies?
mine are .1mm. (I think)
Have you tried them unrectified?
Nice Diode chain by the Way!
For some strange reasons, My caps are failing on both the Voltage side and the Capacity.
Mains kinda fluctuates over here, We can get up to 270V, Is it a possibility that Iâ€™m
getting considerably more than 21KV peak, 15KV RMS? That would explain why My 7 layered caps keep failing....

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