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Re: SISG New Cap Construction

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Scott,

For a "single" MOT (I might save my three Mark Dunn boards for the "dual MOT" system now >>:)))... with the new charging circuit, I can fire at 5400V fairly easily at a low input voltage keeping the MOT far out of the saturation voltage. With 6 x 900V SISG PIRANHA sections with the new charging circuit (known as PIRANHA). At that voltage, I needed to reduce the peak current since it was getting near 1000 amps!!! Dan sent me many GE 42L3332 caps when I bought his stuff to get me started in DRSSTCs long ago (like a year :o))). When I went to two 330nF (165nF primary cap - two in series) The primary peak current drops to 666 amps so back in range for the IGBTs. So the nice new value is two 330nF caps in series for 165nF effective Cp. The cap voltage per leg is 4kV, so two 2x2 arrays in series. Irms is about 20 amps. Probably easy to hit with standard 150nF 2kV geek caps too... The metalized GE caps are in spec there too... Ok, just a "tad" out >:-))

But this is "ONLY" for "120BPS operation"!!!!!!! The charge resistors go to 1.5K now at 100W and are fairly critical. I just order them off DigiKey... If you push it to higher BPS, "FIRE" is expected!!! The DOW foam uses "propane" as a pressurization gas =:O

I think "you" like wide BPS range. In that case, stay with the 470nF caps as before. I am just playing with this new "4 hour old" stuff... Even though I am limited to 120BPS in the "new" configuration, energy goes from 1.52J/bang to 2.4J/bang. Almost 60% more power (120BPS) ;-)) More BPS helps streamer length "some", but more voltage seems to be almost primary firing voltage "linear" >:D I "think" it will do 40 inch arcs... I am holding off on making the secondary stuff incase my present design is too small to support them bigger arcs.

It is all in "flux", but so is the bleeding edge of our sport ;-)) But you can't go too wrong in any case... The"safe" option is as before with the two 470nF caps. The "bleeding edge" is with higher firing voltage pushing two 330nF caps in center grounded series hard...



At 10:42 PM 8/9/2006, you wrote:
Terry -

As I'm just at the point of soldering up my SISG MMC, what's the new target capacitance value?

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, August 09, 2006 9:07 PM
Subject: SISG New Cap Construction

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Bart,

At 08:06 PM 8/8/2006, you wrote:
....Low and behold, you now throw this new cap containment system in front of me!!!! I'm back to being "p***** off" at myself - again!!!

Just to tease you more :o)))

With my SISG computer model finally working, I was able to run a bunch of numbers today and decided my present cap value was too high and should be reduced just a little for optimal performance from one MOT (but the present one has a much wider BPS range!!). So I found I had the parts on hand to make the new MMC!!! This time, I took pictures...

First I wired up the caps with solder, bleed resistors, Kapton tape, G-11 insulator sheet wire terminals...


It does not matter how it "looks" as long as it is sound electrically. You are never going to see it again ;-)) All connections are heavily soldered and the ring lugs are soldered to the brass bolts. Then, I took the plastic gutter pipe and cut it to 8 inches and made holes for the bolt terminals. You then install the guts...



The bolts are held with loctite 271 and are D*** Tight!! They should never come loose, but if they do, the foam holds the other side so they can be re-tightened anyway.

Then I masked off the pretty parts and covered the bench with plastic and tape getting ready for the foam fill.


Then you just blast the inside with foam from the inside out trying to avoid big air spaces:


After a few hours it expands and does its thing as it pleases:


The Dow foam really does not expand super much which is good.

Later tomorrow, I will cut off all the dried excess gushing from the ends. Then let it dry for about a week to be sure all the foam inside is totally dry (but it can be used right away) If there are any big gaps, I can always re-foam them again...

After about a week, I will cut out shallows in the foam ends and fill them with two layers of epoxy. Then just mask off and paint the ends with white paint. It should then look just as good as any commercial cap. I may add mounting tabs too with the epoxy step above.

This cap will be used right at all its ratings. But if it blows up, all the caps will be dead anyway so no need to worry about "fixing it". But it should do find and having the cap part rock solid is simple and cheap with this method!!

The gutter pipe was $9 for like teen feet. The can of foam was $6. You can pick out the dry foam from the can tip, applicator, and ream the tube very easily to use it again. It does seem to expand a little less with many uses. Maybe I did not shake it enough though... Be sure to read all the instructions for the foam since it can be nasty if misused...