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wiring 4 mots for 240

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Marko

Wed Feb 21 2007, 01:30PM

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

So here's the 'Smart' way to do it. Both core ground returns are connected to neutral so each core never has more then the appropriate level of potential on them. Then each primary winding still gets 120, and both are out of phase by 180, giving you 4KV midpoint grounded and the MOT's are happy.
If you want more current then just add your two more MOT's in with paralleled HV lines.

People don't don't stress the MOT's just because they like so; one has actually little choice if he wants to get decent tank voltage for his TC. Most people would consider 8kV as lower end, and at 4kV it would be big trouble getting such a coil to run. It would require rotary gap and very large MMC (bottle caps are totally impractical for such low voltages), wich would also imply a huge coil with very low resonant frequency.

At 4kV, described 50nF capacitor would yeld 0,8J of energy, not much for 4 MOT coil.

Also, paralelled MOT's will 'short' their differences in secondary voltages, so they need to be exactly equal.

So in some cases it's simply much more desirable to overrate the MOT's, put them in oil or maybe leave cores floating (dangerous).

Most popular voltages for SGTCs seem to be between 10 and 20kV. With MOT's, some people use voltage doublers and DC resonat charging just to get as high as posible voltage.

There are many people here who have lots of experience with big coils, MOT's and DC resonant charging.

Generally, in AC system, seriesing all MOT's for 8..10kV actually seems to be only choice despite insulation and other problems associated with it.

Hazmatt_(The Underdog)

Wed Feb 21 2007, 08:48PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I just want to point out that if you leave a core floating with 2KV input, you really need to realize that the 120V primary could get shorted at some time to the core which has 2kv on it!
So for anyone new to this, remember that floating a core makes it a pretty big insulation hazard.

Marko

Thu Feb 22 2007, 09:47AM

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

So for anyone new to this, remember that floating a core makes it a pretty big insulation hazard.

Sure it is a hazard, but you can either cope with that hazard (oil, safety insulation) or just make the MOT take 4kV from it's output to core if you ground it.
AFAIK, most MOT's actually don't seem to have trouble with this, especially if they are under oil.

If core is floating, there is insulation both between primary and core and between secondary and core, minimizing the chance of breakdown... but in my opinion I would also ground the core!

It's much better for the MOT to burn out, rather than you, in the end.

jameselectric

Thu Feb 22 2007, 08:08PM

Registered Member #535 Joined: Sun Feb 18 2007, 06:03AM
Location:
Posts: 65

excellant site tells alot about mot's

jameselectric

Fri Feb 23 2007, 08:26AM

Registered Member #535 Joined: Sun Feb 18 2007, 06:03AM
Location:
Posts: 65

what would be a reasonable tank cap value. how would you go about figuring this?

sparky

Fri Feb 23 2007, 08:51AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I have a dual MOT and a quad MOT supply running a 4" Tesla Coil. I get 5' 6" with my dual and 9' 2" with my quad... output sparks. Who said 2 MOTs can't run a coil!?

Marko

Fri Feb 23 2007, 01:21PM

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

Who said 2 MOTs can't run a coil!?

Sure they can, but if you have 8 mots and want to use them all it's most logical to wire them for highest possible voltage. Also, if you are 4kV, you can use AC resonant charging wich would also stress your MOT's insulation.

Paralelling MOT's also has it's poblems due to difference of secondary voltages.

Dr. Drone

Fri Feb 23 2007, 04:18PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
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sparky

Sat Feb 24 2007, 10:46PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

Firkragg wrote ...

Who said 2 MOTs can't run a coil!?

Not a chance! I've been using MOTs for years now and never have I had a MOT fry due to lower voltage higher current operation. Paralleling MOTs is an easy thing to do.

Stressing insulation to 6kV can be an issue if the transformer is run in open air - this should be done in dielectric oil ONLY!!

jameselectric

Sat Feb 24 2007, 11:55PM

Registered Member #535 Joined: Sun Feb 18 2007, 06:03AM
Location:
Posts: 65

what kind of caps are you guys using with the mots (cap value). I have a static spark gap. 8 turn primary and my secondary measures 17 by 4.250. giving me 1000 turns at a ratio of 4:1 with 26 AWG

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