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wiring 4 mots for 240

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jameselectric

Thu Mar 08 2007, 02:00AM

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

its happy at about 3 or 4 turns out. going out lessens the sparks as does going in makes no difference.

jameselectric

Thu Mar 08 2007, 03:08AM

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

just some pics of my setup. there is 2 toroids the smaller one shows a little corona

CT2

Thu Mar 08 2007, 05:54AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Do you have a big fan blowing on that gap? Because mots run alot of current, and they need good quenching. Also you may want to look at setting up a multiple spark gap. Doing that would probably help alot, it made a huge difference when I used a 15/60 and then switched from a single to a multiple gap.

jameselectric

Fri Mar 09 2007, 03:29AM

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

well i hooked up my shop vac and holy s*&^ i'm getting like 10 in sparks. inadequate quenching was my problem. The sparks surge and get bigger each time they surge. before they get to big thought it blows my variac breaker. caps too big?. Thanks everyone for the help i will post pics of my sparks. tap is still on the 3rd turn out.

J. Aaron Holmes

Fri Mar 09 2007, 04:46AM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

jameselectric wrote ...

well i hooked up my shop vac and holy s*&^ i'm getting like 10 in sparks. inadequate quenching was my problem. The sparks surge and get bigger each time they surge. before they get to big thought it blows my variac breaker. caps too big?. Thanks everyone for the help i will post pics of my sparks. tap is still on the 3rd turn out.

Only the third turn, eh? I'm actually quite surprised those MO caps don't just pop. They must be seeing peak currents of 500-800 amps or so, which is probably like 500-800x what they're rated for

Some pulse-rated caps are probably a good idea...

The trick with lower-voltage coils like this is finding the best balance of physical coil size and power. You certainly want as much topload as possible without making the coil look silly. A fatter coil form may be the next step to increase inductance. The idea is to get the resonant frequency down to the point where you can put a lot more turns on the primary, thereby reducing peak primary currents, gap losses, and correspondingly increasing performance for the power. Three turns on the primary coil is nearing OLTC territory, and with so little inductance in your primary coil, a good percentage of your total primary inductance may be coming from other things, like the wiring between your caps, gap, and primary coil. Meaning you won't get full poop. You want the vast, vast majority of your primary inductance to actually be in your primary coil. Very short, fat wiring will help there.

All this really gets at why using higher voltages on SGTCs makes life WAY easier, and why MOT-based SGTCs are actually a hard challenge! As voltage goes up, bang energy exponentiates, allowing the same coil power (and streamer output) to be realized with a MUCH smaller cap, meaning that you can dump 100's of uH into your primary coil, making your primary current fall like crazy. Your gap losses then decrease exponentially, your gap quenches ~1,000,000x better, and your caps are way happier.

Regards,
Aaron, N7OE

jameselectric

Fri Mar 09 2007, 06:02AM

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

I know the mot is a hard way to go lol that is why i am planning on working on a solid state coil the next go around. my nst coil and especially this mot coil have taught me alot about theory and what changing each component in the tesla coil getup does. . which is what we are all after knowledge and bigger sparks. i think this coil is done for now. mots seem like a lot of work for what they do.
Thanks everyone

sparky

Sat Mar 10 2007, 02:48AM

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

first off MO caps are very lossy - they are NOT ideal caps for pulse discharge operation as they are mylar/paper/oil dielectric - they will heat up - and some have been known to burst explosively running off tesla service...

MMC type Pulse discharge capacitors from CDE are ideal. You know you could send an email to the company and ask if you might be able to "sample" some of their mighty fine 0.68 uF 1600V rated caps.... these are what I use on my MOT and big NST coil.

jameselectric

Fri Mar 16 2007, 05:28AM

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

just a light with my huge toroid

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