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Pros and cons of tesla coil primary supplies.

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dmg

Thu Jul 01 2010, 04:28PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627

or you can do this with 2 MOTs.. and if you are not satisfied with the voltage, you can run it through a multiplier to achive your voltage (doubler/quad is usual)

This method however will work when you use DC resonant charging, or if you run if off the raw 2 MOTs, you can still make a decent AC powered coil.

quicksilver

Thu Jul 01 2010, 05:53PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

The more I learn about this hobby the more I liken it to things like car & bikes.
You can put bigger and bigger engines in something and still get marginal performance. But if other areas of the thing are paid attention to, you can get seriously great performance from an existing supply.

I once made a small coil and it was slightly out of tune and I didn't know it. I eventually found what the issue was and the thing really preformed so much better I was surprised. I did the same thing recently and made every volt & ma count from a coil that was just balanced right. I really thought it was a different supply.
Because that's what I was doing a great deal of the time. I would just put more horse power into an unbalanced unit, thinking that would yield better performance (which is actually logical).

I've tried a bunch of different things but the overall unit coming together made much more of a difference than a pair of transformers with a multiplier, etc, etc. Of course I'm not trying to talk you out of it. I'm just saying that I was not milking the most from what I had, even though it functioned OK: I didn't look at the little things.

A long time back Kawasaki made these bikes that were two strokes that had 3 cylinders. They screamed faster than most of today's bikes. Because they had a great balance of a serious motor and a light frame. The analogy holds for me in most stuff. Often it's the small change that yields the big dividends.

Adam Munich

Thu Jul 01 2010, 06:42PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Hmm, i wonder if 4 MOT's in series could work, if i float the cores of the outer two and insulate them in oil.

Something like this

Now 60A is a lot to draw on a 120v line, so i'll ballast these to limit the output current at around 100-200ma. (higher if i could find a suitable power source) When i use an NST, i don't build a ballast per-se, but plug it into my 100' extension cord. It does a very good job of limiting current.

I could also use the dryer line i have downstairs, or the 120v hot tub line. Sadly i don't have a 3 phase to play with. Otherwise id go out and buy a laserscope and have a blast.

If i use a rotary spark gap, i could maybe pull this off with 3transformers.

My goal will be 6 foot discharges.

dmg

Thu Jul 01 2010, 07:52PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627

That setup will work with mots, NSTs on the otherhand are a bit sensetive to overvoltage, seriesing 4 of em will be very harsh for the transformer and will probably lead to failiure, MOTs on the other hand can handle this abuse and much more if they are under oil.

also, as quicksilver has said.. I belive that what matters most is a well designed and tuned system, rather then cramming as much power as possible.

Adam Munich

Thu Jul 01 2010, 07:59PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I never intended to series NST's I was planning on series-ing MOTs to allow enough voltage for a decent spark gap. There is no need to series an NST, but MOT's are free, and can supply some decent current. I've decided on those for my coil. (I wont start this project for about three months though)

dmg

Thu Jul 01 2010, 08:02PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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Posts: 627

In any case, doing that with NSTs will kill them
but people have seriesed more then 6 MOTs and had not had any failiures (I personally only had 1 MOT die on me.. and I play alot with them) so they will make a very nice supply, just keep them under oil and do not run them for too long, and they should last for a long time.

another thing I found really helps with MOTs and their current draw is power factor correction on thier primaries.

edit: I deleted quote

Adam Munich

Thu Jul 01 2010, 08:36PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Woops, That was a typo. Sorry bout that

dmg

Thu Jul 01 2010, 09:01PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
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Its all good,
another neat feature ive found with mots.. seeing how they can tolerate higher voltages then what they where ment for, they can be run without a filter (sometimes a pair of chokes and a safty gap is really all thats needed, however if you use DC resonant charging instead of AC, then you eliminate the filter all together, since DC resonant involves a charging reactor for the tank.. only downside is the expence of more parts, bieng the beefy reactor (usually several henries.) and the HV diodes nessasary for rectification and as blocking doides for the reactor.

but with this system, seems you can get very large arcs from small coils... let alone a medium one.

here is an example of one of these coils if you are unfamiliar with this concept.. Steve mconner has done a good job on it too:

and if you wish to stick strictly to AC, then you can still get very nice results with only a few MOTs.
hope this helps.

Adam Munich

Thu Jul 01 2010, 09:38PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

That's a nice circuit. I wonder if i use 4 MOT's in series, i could drop the voltage doubler and simply use a full wave bridge rectifier with some smoothing caps. Long strings of 1n4007's in oil filled pvc would not only look "fancy", but they could be made cheaply. More power could be supplied to the coil that way, and if the DC circuit is as nice as you say it is, then a 4.5' tall secondary could put out quite a long arc if tuned right. I may have to make it thinner and taller though, because i wouldn't want everything to go to the strike rail.

Got any pics of DC coils?

dmg

Thu Jul 01 2010, 10:13PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

Unforchantly, until I have joined this forum, I have not bothered to document any of my previous projects, and at the moment I have no funcioning DC system (pretty much all my coils where fast lashups, and now thier parts are bieng consumed by my permanent coil project that I am building right now, as for the rectifier, it would most certanly work, but one thing that should be done is soft starting for the MOT stack, since such a filter capacitor for the DC will probably have a lot of inrush current upon start up.
also, do not expect a miraculous effect from using DC, it is merely a different charging system, and is usually used for high powered coils, but if tuned right, large tank capacitor, then you will get pretty decent arcs.. about the 6 feet arc lenth, I am personally unsure, it is probably doable, but I cannot offer you any garantee, most coils Ive ever seen that made 6 feet with spark gapped systems where 6 inches to 8 inches and above.
I mostly like MOTs since they are take up less space then a bank of NSTs, can be abused, not to mention thier good current outputs.

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