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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Homemade rolled cap is still ging to be HUGE, for 6nF you need a pretty big tube to fit it in. Look at TDU's site.
You need some nice LDPE sheets and mineral oil to make it work reliably. But you won't get that cap easily to be in size parameters of the small secondary.
For that bottles, I have two big ones here that measure 0,7nf each, so let's say your smaller ones are 0,5 and bigger are like mine. (I guess glass thickness doesn't diffeer much). That would be 3*0,5 + 2*0.7 = 2,9nF.
Probably the MMC would be a neat thing to do but you'l be quite limited in voltage.
You can try to find some small, highest-possible voltage caps, I think you need some pretty high voltage (30kV+) for that ZVS.
Again this is pain if biggest you have are let's say 1-2kV and you need to series a huge bunch of them.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
30kv I always thought that if my gap fired at, say 5kv, I wouldn't need to make a cap with a voltage rating the same as the flyback... I'll have to take that into account.
I'll probably buy a bunch of those yellow poly caps soon, I can get 10nF or 22nF caps rated 1500v each.
I've blown up a number of caps already trying to make an MMC
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
You should make MMC quite a bit higher than input voltage for long and prosper life. Theoreticaly you can use it at somewhat-higher-than sparkgap voltage, but it is enough that gap misses one firing and it will die.
You can maybe fight this with safety gap, that must be well adjusted. And equalising resistors are apsolutely necessary.
I once easily blew my big 20kV MMC with rotary gap and 15kV transformer that way!
Coil looks good, and you could even put much bigger secondary on it
Wtth some 200W of power you could perfectly use that 40mm PVC pipe, maybe 20cm long or so.
You have much more power there that this small secondary can give off.
It seems that you have plenty of space left in that case, so you can try to make a stacked capacitor or a nice big MMC. I tought that you were about to make the box much smaller...
Registered Member #206
Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72
I've put my 3. nanoSGTC(ugly setup) in a plastic tube and filled it with wax after racing sparks and top-to-bottom streamers killed version 1 and 2. The coil is 2x4 ( ) cm, the tubing 2.5x5cm big and there are still some top-to-bottom streamers if I open the gap >0.5mm (the MMC is rated for 16kV DC... kind of wasteful...). At least the streamers dont set the coil on fire anymore.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
Thanks for the comments
I've decided I'm definitely going for an MMC now, and this coil has turned into quite a large unplanned project!
As for the case, I already had the wooden supports so it was just to save time. It turned out neater than I had planned, and I even sanded down and stained the wood to try and get it all looking similar (it is built with oak, beech, and plywood). Anyway the flyback can stand upright in the case as it is, and I have room for the MMC.
I will probably leave the secondary for now, but depending on performance with the new MMC I will either wind a new secondary, or start a new coil altogether
New sparkgap is a 4-spark multigap made from brass nuts, spaced .5mm apart.
Registered Member #229
Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
Turn to MMC Avalanche, you waste a lot of power with those loosy homemade caps. Experiment with the gap and the input voltage for the driver. For a specific voltage input the gap will work just fine. Apply full voltage and then crank down the variac until the BPS go low and the streamers are eratic then turn up a bit. You will see that the spark gap noise has some good tone when everything is right.
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Mini SGTC
I always thought that if my gap fired at, say 5kv, I wouldn't need to make a cap with a voltage rating the same as the flyback... I'll have to take that into account.
) cm, the tubing 2.5x5cm big and there are still some top-to-bottom streamers if I open the gap >0.5mm (the MMC is rated for 16kV DC... kind of wasteful...). At least the streamers dont set the coil on fire anymore. 
