100kv 10ma / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

100kv 10ma

previous 1 2 3 4

Move Thread

LAN_403

Microwatt

Mon Jan 24 2011, 01:15AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

I want to charge capacitors in a fast way. I need 10ma under load.

Dr. ISOTOP

Mon Jan 24 2011, 01:36AM

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

You're charging 100KV caps?
Use an XRT...that's what I'll use for my Marx.

Microwatt

Mon Jan 24 2011, 03:26AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

self built caps. we are taking 6 5 mil mylar sheets in rolls and wrapping them into a capacitor. I am building a rolling machine that will help keep the thousands of feet of aluminum foil and plastic in center. easily in the tens of microfarad range for less than 1000 dollars of materials. maybe I could fill my 5 acre yard full of capacitors and let them go off?

Adam Munich

Mon Jan 24 2011, 03:34AM

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

Take a look at this, 5 mils of Mylar isn't going to hold back 100kV.

Dr. ISOTOP

Mon Jan 24 2011, 05:35AM

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

You do realize there are commercial pulse capacitors that can store 10's of KJ for < $1000 on Ebay, right?
Building HV capacitors out of foil and mylar and expecting them to last any reasonable amount of time is not going to happen; there's a reason why commercial capacitors are hundreds of dollars each and are so bulky.
FYI my 110 nF of 100KV capacitors weigh about 200 pounds...10's of uF will be considerably larger, especially when you don't have professional machinery to build the capacitors.
Also, a giant rolled spiral will have *very* high self-inductance, limiting the rate at which your caps will discharge.
In short, you're probably not going to be able to do it. I'm not trying to discourage you; I'm just warning you before you go spend thousands on raw materials.

Microwatt

Mon Jan 24 2011, 06:45AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

did you read the post there will be 3 layers of 5 mil plastic. Three layers on top three at the bottom. The inductance will be considered minuscule since the method of rolling will leave the capacitor plates hanging off the edges. what this does in cylindrical coordinates is change the direction of the current flow. so instead of having the electrons move around in phi direction which is basically a coil we move the electrons in the Lengthwise direction. perhaps zero inductance? discharging 100kJ in 50ns!

Ash Small

Mon Jan 24 2011, 06:59AM

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

That's how I roll mine, the overhang at the ends is the trick here, you bind it with copper wire. BTW, I use polythene (polyethylene), not sure how thick, I've never measured it, but it's the type that builders use under concrete. I've not had any problems with them.

EDIT: just googled it, looks like it is 250-300 microns.

EDIT 2: Don't use the re-cycled ones, though.

Dr. ISOTOP

Mon Jan 24 2011, 08:42AM

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

Microwatt wrote ...

did you read the post there will be 3 layers of 5 mil plastic. Three layers on top three at the bottom. The inductance will be considered minuscule since the method of rolling will leave the capacitor plates hanging off the edges. what this does in cylindrical coordinates is change the direction of the current flow. so instead of having the electrons move around in phi direction which is basically a coil we move the electrons in the Lengthwise direction. perhaps zero inductance? discharging 100kJ in 50ns!

OK, your good to go on the low-inductance part.
But that still doesn't change the fact that you're not going to get any decent life out of a giant bank of home-rolled capacitors. The corona will eat away at the dielectric, causing it to fail. The whole assembly will have to be oil filled...I doubt the instructions on the HVWiki scale well to larger capacitances.
As I said, there's a reason why commercial pulse capacitors are HUGE and EXPENSIVE.
If you want a mighty bang, there are some 10KJ caps on Ebay right now with very cheap starting bids and VERY EXPENSIVE shipping.

Microwatt

Mon Jan 24 2011, 10:04AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

How about put that monster cap inside a 10" pvc pipe. Seal off the ends and put a few gallons of mineral oil in there. proceed to suck out the airbubbles with your choice of straw or vacuum pump.

previous 1 2 3 4

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