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Just finished my 3.5kj cap bank & RL test results

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LAN_403

FastMHz

Wed Mar 29 2006, 02:08AM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Mine are the 57/20 SKKH in the attached datasheet

1143598129 179 FT5246 J Electronics Semipack Skkh5720e

I am using 3 in parallel...I have 3 more and will add them for 6 total in parallel for safety since I'm barely making it with 3.

Quantum Singularity

Wed Mar 29 2006, 03:54AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Congrats... 357ft/sec wow! I got to get me a chrono.

A few things a was thinking about... its definately about quick pulses as my 120uF cap charged at a few kJ is probably very similar to yours at the same power level (although I am sure different size coils and different triggering will definately make them not perfectly equal for a given power level). And I beleive my 1 cap has about .1 ohm ESR wich is probably higher than your cap bank. Its true the esr will half when paralleling two caps, but that doesnt mean the current will double. Current is V/R. There is other R in the circuit than just the ESR so the circuit resistence will not quite half, and the current will then not quite double. I want to try different series/parallel configs to figure out wich is better. Remeber, the induction disk launcher wants maximum di/dt. So the common railgun consesus that a longer less current pulse is better than a shorter high current pulse doesnt hold true here. Heck even my 4uF caps would launch a light weight copper ring pretty high with the first coil I ever made (totaly non-optomized). So I am a bit hesitent on how my new 9100uF caps will work but it seems FastMHz has proved that multi-thousand uF caps will do quiet well with this design. Keep up the good work!

FastMHz

Wed Mar 29 2006, 07:14PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

It would be neat to find out the ESR of my bank...how would I measure that? Mine is actually wired 4S4P so individual cap loads shouldn't be too bad.

Your 120uf charged to about 7650 volts will be about 3.5kj.

Your caps will work well...from my experimentation and testing, I would recommend wiring your caps 6S2P so you get 1500v @ 3033uf...having that extra cap is hard to fit in...or even 4S3P for 1000v @ 6825uf since you're using thicker wire.

Quantum Singularity

Thu Mar 30 2006, 01:24AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Did you get a good deal on those scr's? The few similar models I found for sale are $50+ per each. I dont think I could afford 6 of them! I got another scr question I'll post on the general electronics forum.

I only charged my big cap above 5kV once. That is the really mangled disk thats on my EMP Ringlauncher webpage. It also kinda messed up the weak launching coil I was using at the time. The disk in my vatar the ended up in the roof might have been that high or even higher though, I didnt have a meter at the time so there wasnt any way to tell. But judging by how dish-shaped it warped and comparing to my other disks it was definately around the 7kV mark or more.

I am not sure about the ESR of lytics... I am guessing that would have to be on a spec sheet somewhere from manufacturer, if it was ever listed. I was told by a few people mine was .1 ohm on my Maxwell, and that would be correct with the facotry specified 100kA max discharge (10kV/.1ohm=100kA).

FastMHz

Thu Mar 30 2006, 02:25AM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

I bought them off a fellow forum member a while back...your best bet is surplus, which is what I think mine were anyway.

FastMHz

Sun Apr 02 2006, 05:32PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Interesting question: why doesn't steel launch? I placed a steel disc on my coil and fired it and it didn't budge! Would this happen with any ferrous material?

Electroholic

Sun Apr 02 2006, 06:17PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

You use Alu disk because you want low resistance, light weight, so the repelling force generated from eddy current can accelerate it.
Now, if the disk is ferromagnetic, the coil will suck it down when fired.
Notice we put the slug behind the coil when firing reluctance type coil guns?

FastMHz

Sun Apr 02 2006, 07:26PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Makes perfect sense...that's so obvious now I feel stupid

FastMHz

Fri Apr 07 2006, 07:07PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Got my new diodes from Mouser, rated for 25a @ 1600v, far higher than I'll need while charging my bank. So I did a test to see how it was all working and put, for the first time, the 1/4" thick aluminum disc on my latest and greatest dual layer coil, put a soda can on that, and then a brick on the soda can. I fired it at only 1000v since I was indoors, which in my bank is 1.8kj. The brick flew 6 feet into the air, and the can was 1/4 it's original height. It was so loud it scared me - I thought something blew up...I'll get my brother to take some footage soon so everyone here can see what computer grade electrolytics can really do

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