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On my 16kV MOT 8 stack coil I wanted to increase efficiency by moving the primary as close to the secondary as possible. The primary is helical and about an inch and a half from the secondary all around, and it's wound on a 10.5 inch diameter bucket (wheras the secondary is on 8&3/4 inch PVC)
The secondary seems to be arcing to the inside of the bucket... though I've enameled it and varnished it as if there were no tomorrow, it still seems to want to arc to... nothing!
The primary is coax cable. Cheap and long. Another reason- copper is pricey and the coax was actually free from some place... I think I found it, but it's brand new. I have a lot of turns on there right now, and it seems to be coupling hard... it looks like the output of the coil is about 50kV at 60 hertz! That was a hell of a painful shock- good think i was holding the glass part of a flourescent.
But I fear if it keeps arcing it will be to the detriment of the secondary winding. Should I find a way to fill the space with oil? Any tips?
One idea I had was to move the primary to the inside of the secondary. At leastit would be stopping the corona dead against the PVC. But my concern, if I ever get this thing tuned good- is that the toroid might want to arc down through the body of the coil to the primary. Which would be no bueno and would kill the power supply... They're MOTs and under oil, but hell, they're not indestructable.
Registered Member #530
Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178
This is due to poor coupling. I'd stick will Greg Hunter's primary design and go with a flat coil - 3/8" copper tubing. A child can build one its that easy. Tuning is VERY easy! vetical primaries are always difficult to get "just right". Next I'd put the primary below the last turn of the secondary coil with the flat primary design... and presto - no more inter-secondary arcing!
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
On my 16kV MOT 8 stack coil I wanted to increase efficiency by moving the primary as close to the secondary as possible. The primary is helical and about an inch and a half from the secondary all around, and it's wound on a 10.5 inch diameter bucket (wheras the secondary is on 8&3/4 inch PVC)
Thinking that higher coupling will always give higher efficiency is flawed understanding even if flashovers weren't a problem.
Use conical primary, nothing else. Don't get the angle too high, under 30 degrees is usually enough.
Such a huge most stack is absolutely haphazard and power hungry, and unless you are generating 10-15 foot arcs with it you are obviously being silly and haven't done closely enough googling.
Start off with a small neon sign or oil igniter transformer, prices of other parts also go down.
You absolutely need to buy some copper pipe, or flashing, for smaller coils you can probably use 3mm solid copper wire.
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
I would suggest not putting the primary inside the secondary, you will probably find that it will arc straight through the PVC! Definately go with the pancake spiral and raise the secondary about an inch above it. Get some copper pipe too, cause with that size secondary and power supply, you will need a decent surface area primary (because of skin effect) to get the power into the secondary. Oh...and don't touch the spark!
Registered Member #530
Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178
Marko wrote ...
Thinking that higher coupling will always give higher efficiency is flawed understanding even if flashovers weren't a problem.
Use conical primary, nothing else. Don't get the angle too high, under 30 degrees is usually enough.
Such a huge most stack is absolutely haphazard and power hungry, and unless you are generating 10-15 foot arcs with it you are obviously being silly and haven't done closely enough googling.
Start off with a small neon sign or oil igniter transformer, prices of other parts also go down.
You absolutely need to buy some copper pipe, or flashing, for smaller coils you can probably use 3mm solid copper wire.
I hope you weren't aiming that comment at me marko...ahhem! I was saying a flat primary design might be easier to build and coupling would be easier to play with for sure. That idea of a conical primary is also a great idea too.
I'd never want to fool with an 8 pack MOt supply simply because they are very unstable and flashover
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Secondary arcing to... primary?
