We need better DIY capacitors / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

We need better DIY capacitors

1 2 next

Move Thread

LAN_403

Forty

Tue May 24 2011, 11:45PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

it can't be that hard can it?

i've had a longstanding idea to take two rolls of aluminum duct work tape and several rolls of industrial packaging tape (wider than the Al tape) on separate spools, layer the ends onto a dowel in a tape-Al-tape-Al-tape fashion, and set the dowel a-spinning.

the same could be done with paper instead of the packaging tape, and then the final roll submerged into oil or some electrolyte to saturate the paper.

I also just found that those foil emergency blankets have a conductive film on one side, and an insulating layer on the other. haven't tested the breakdown of the insulator yet, but this material could be useful as it doesn't tear easily like Al foil.

does anyone know the internal layout/chemistry of those massive pulse discharge capacitors that we all covet?

Inducktion

Wed May 25 2011, 12:59AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

I know you can use anti-static bags, since they have metalization like you say about the emergency blankets. The only issue is they aren't very big and don't come in rolls long enough to make a big enough cap.

Arcstarter

Wed May 25 2011, 01:51AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well a typical discharge cap is PPE and aluminum. You can get a large amount of PPE from a hardware store :http://www.lowes.com/pd_228558-18632-DCFF-2_4294806301_4294937087_?productId=3273611&Ns=p_product_prd_lis_ord_nbr|0||p_product_quantity_sold|1&pl=1&currentURL=%2Fpl_Drop% 2BCloths_4294806301_4294937087_%3FNs% 3Dp_product_prd_lis_ord_nbr|0||p_product_quantity_sold|1&facetInfo=

Also, plastic plate capacitors work well.

And as it was said on that thread,, it would have low ESL like most stacked plate caps do.

ScotchTapeLord

Wed May 25 2011, 02:01AM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

I did some testing with the mylar emergency blankets and they aren't reliable, at least the ones I had. The aluminization layer is very thin.

Jrz126

Wed May 25 2011, 02:07AM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

the aluminum tape sounds like it might work, assuming the glue isn't conductive. By the time you're done playing around though, you could have bought one off eBay.

2Spoons

Wed May 25 2011, 06:36AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Forty wrote ...

the same could be done with paper instead of the packaging tape, and then the final roll submerged into oil or some electrolyte to saturate the paper.

I have a large roll of kraft paper under my desk waiting to be turned into HV caps. Still undecided on wax vs castor oil for impregnating the paper.

cedric

Wed May 25 2011, 09:02AM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

why not trying to make a diy electrochemical cap :two layer of aluminum foil separated by glass fabric immerse in some? chemical...,for coil gun or other high power experience it could be easy to get capacitance in the farad range for few 100's volts,the only think needed is a big bucket...

ConKbot of Doom

Wed May 25 2011, 12:50PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Obviously a spriral wound cap would be quite inductive, if you wound it with a 4-conductor stackup (anode, paper, cathode, paper, anode, paper, cathode ) connected the anodes together and cathodes together at the center of the coil, so its a bi-filar winding, it would obviously reduce inductance, but would it reduce a lot? Or would the fact that the current is distributed make so the currents dont cancel?

Dr. ISOTOP

Wed May 25 2011, 01:35PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Back in the day, before MMC's, coilers would often roll their own capacitors using poly sheeting and foil.
The conclusion was it is very difficult to roll a reliable pulse capacitor - lots of little things (weak spots in dielectric, air bubbles, corona, etc) would eventually eat the dielectric and cause a failure.
The big, low rep rate metal pulse caps use multiple smaller oil-paper-foil units internally series-paralleled; the high rep rate ones use PP-foil units.

Ash Small

Wed May 25 2011, 02:40PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

ConKbot of Doom wrote ...

Obviously a spriral wound cap would be quite inductive, if you wound it with a 4-conductor stackup (anode, paper, cathode, paper, anode, paper, cathode ) connected the anodes together and cathodes together at the center of the coil, so its a bi-filar winding, it would obviously reduce inductance, but would it reduce a lot? Or would the fact that the current is distributed make so the currents dont cancel?

You can avoid the inductance problems by leaving the aluminium foil protruding from the dielectric, one polarity one side, and the other polarity the other side. Binding the protruding aluminium foil with wire then means the current doesn't have to flow round in a spiral, but simply flows in and out sideways (hope that makes sense, I'll roll some later this week and post some photos. I'm trying to locate some suitably thick clear polythene sheet at the moment, rather than using the black stuff I've used in the past)

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob