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Just finished my 3.5kj cap bank & RL test results

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LAN_403

FastMHz

Thu Mar 23 2006, 01:57AM

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

OK guys and gals; I just got another cap bank identical to my existing one as used in my experiments already posted and wired them all up so I have one large bank. I tested it indoors on a "rocket" and charged to 100v and hit the ceiling...this sucker can charge to 1400v and shall be tested outdoors only

I have some math/electronics law questions though.

First, some facts:

The original 1.7kj system was wired for 7200uf @ 700v.
The new bank is wired for 3600uf @ 1400v (basically two of the 1.7kj banks in series)
I made a new coil with twice the length of wire...basically, two spirals on top of each other. I did this to keep the amps the same as they were on the 1.7kj system but double the magnetism.

So the new setup has twice the coil, half the microfarads, twice the voltage. My question is how does this all inter-relate and, in a perfect world, would I get twice the launching power?

GimpyJoe

Thu Mar 23 2006, 02:39AM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

I'm not sure about the answers to the other questions, but make sure you insulate the coils really really well from each other. I have had coils arc through the layers and it's not fun to rebuild a coil from scratch when you've just finished one

Sebastian

Thu Mar 23 2006, 11:20AM

Registered Member #233 Joined: Wed Feb 22 2006, 09:06AM
Location: Dortmund, Germany
Posts: 7

made a new coil with twice the length of wire...basically, two spirals on top of each other.

Do I understand you correctly that you want to use the 2 Cap banks for a single coil each an the coils are wound ontop of each other?

If that is the case I see a big problem with the magnetic fields canceling each other...

GimpyJoe

Thu Mar 23 2006, 01:50PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

only if they're wound in the wrong direction. Considering he already tested it I don't think there will be a problem

Sebastian

Thu Mar 23 2006, 04:39PM

Registered Member #233 Joined: Wed Feb 22 2006, 09:06AM
Location: Dortmund, Germany
Posts: 7

Funky wrote ...

only if they're wound in the wrong direction. Considering he already tested it I don't think there will be a problem

True

FastMHz

Thu Mar 23 2006, 06:58PM

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

Both spirals are in series...I'm feeding one pulse of 1400v into them.

I did find that they need to be wound in the correct direction. When I first wired it, I did a really low voltage test and the layers pushed apart...I put on a ton more epoxy and re-wired it so the fields all go in the same direction. My dual layer coil is made by wrapping a spiral on a round block of wood, covering it with epoxy, then putting on thin magazine paper and clamping another wood block on top. Then I repeated this process. The coil is a solid shunk of epoxy, but the projectiles are only a paper width away from the actual wire, so magnetic coupling is great.

I know my Qs were a bit confused...because I'm confused! I guess what I'm trying to figure out is how can math be used to explain that it will be twice as powerful now as it was on one bank, given that the capacity is half and the current is the same. To me, this means the pulse will be half as long as it was, so how many times more powerful will the magnetic field be given the dual layer coil vs single layer, twice the voltage and half the capacitance?

Marko

Thu Mar 23 2006, 07:35PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

For electrolytic caps maybe better is to wire in paralell because ESR/ESL usually limits current more than load impedance.

In paralell you will get double max current and again 2x faster discharge time, but you have higher capacitance.

As your coil behaves as load too maybe best is to test both circuits yourself.

Advantage of 1400V is that you can use triggered gap for very high speed switch (there are some small losses but fast switching may actually improve overall efficiency).

Yohan

Thu Mar 23 2006, 08:33PM

Registered Member #194 Joined: Fri Feb 17 2006, 07:52PM
Location:
Posts: 19

Will he have problems with a 3.5kj cap bank.?

<shakes magic 8-ball>

"Yes."

Too much power. You're going to heat the coils to the point of barrel contortion if you charge that much beyond 2~2.5kj. Problems is, you can't get the heat away fast enough without some sort of active cooling. I'm not sure how this would react for your induction setup though.

in a perfect world, would I get twice the launching power?

No. Many, many reasons why. Law of diminishing returns for one.

But, if you've got a camera capturing everything, go ahead and give her a run. I'd be interested to see the end result.

GimpyJoe

Thu Mar 23 2006, 09:35PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Yohan wrote ...

Will he have problems with a 3.5kj cap bank.?

<shakes magic 8-ball>

"Yes."

Too much power. You're going to heat the coils to the point of barrel contortion if you charge that much beyond 2~2.5kj. Problems is, you can't get the heat away fast enough without some sort of active cooling. I'm not sure how this would react for your induction setup though.

in a perfect world, would I get twice the launching power?

No. Many, many reasons why. Law of diminishing returns for one.

But, if you've got a camera capturing everything, go ahead and give her a run. I'd be interested to see the end result.

It's a ring launcher, so no problem with the barrel. The problem I forsee is that with the softening of the epoxy from coil heating, the coils may touch and short.

...

Fri Mar 24 2006, 01:26AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I would say that in a perfect world you wouldn't get exactly 2x the power. So far the only thing I can think of is the lowered coupling because of the double thickness coil and the increased esr of the circuit (paralleled caps/coils doubled it). If you had ideal caps, ideal inductor, etc you would (conservation of energy)

I see no reason why it would not work, with 3.5jk you have about 0.88calories, or the ability to raise the temp of a 100gram coil by about 15F (assuming 5% efficiency). Or it it is really small at 10g it is stil only 150F, which is still within the ratings of most wire/epoxy. I wouldn't worry about it. If you don't want for it to cool down you could epoxy it to a heatsink which should cool it very quickly. I don't see how a barrel is involved with a pancake coil.

As to arking over, I really doubt that you can get 1.5kv to ark though a piece of magnet wire regardless of the pulse shape. I have used magnet wire at 10kv/20khz and got a ton of corona but no arking over.

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