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3 MOTs in series

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Kyle

Sun Aug 30 2009, 02:52AM

Registered Member #2325 Joined: Sat Aug 29 2009, 10:08PM
Location: Southern California
Posts: 11

Hello, (First post here :P)
I have a quick question, if anyone can point me in the general direction of how to do this (Or give me a schematic). How do I wire three MOTs together in series? I've never messed with more than two MOTs and a few capacitors, but I really don't want to risk smoking anything. Do I need to have the HV out wire off of one transformer hook to the core of the other?
Thanks,
Kyle

3l3ctrici7y

Sun Aug 30 2009, 04:14AM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

OK.. you are wanting to connect the outputs in series, and the inputs in parallel? Then....

Physically this is how you do that; connect the primaries in parallel (careful of the phasing or you will not get the results you want). Disconnect the three secondary wires from the iron cores and connect that wire to the normal output wire of the next mot. On one end of the string of mots, you will have the normal HV output wire, and at the other you will have the wire you disconnected from the core of that mot.

Beware that in connecting the primaries in parallel, you are holding the whole works close to line potential; stood off by the electrical insulation. Now with that in mind; at one end you have one end of the HV secondary and at the other you have the other end of the HV secondary. You are fundamentally tripling the stress on the electrical insulation. It could arc over and cause all kinds of problems including death and/or lifelessness. Do not leave any of the secondary/HV wires connected to any of the cores.

If you are really wanting to be safe, you can put the whole works in oil. That will significantly increase the dielectric strength.

Is this your first HV project?
This is a kind of a risky thing you're wanting to do.
Please wait for others to chime in before continuing :)

J. Aaron Holmes

Sun Aug 30 2009, 04:25AM

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

Welcome aboard, Kyle!

A bit of Googling for "MOT stack" (the HV nerd's jargon for MOTs in series) ought to serve you well. The Web is positively overflowing with examples of how to series MOTs. It's an end unto itself for some, in fact! What's more, the Site Rules (see Part II) request that you do your own research and forbid asking for schematics.

Cheers,
Aaron, N7OE

teravolt

Sun Aug 30 2009, 05:41AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

3l3ctrici7y is correct one problem though how do you plan to keep the mots from arcing to the metal core as you go from mot to mot. what is the end purpace for mots

Frosty90

Sun Aug 30 2009, 10:30AM

Registered Member #1617 Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139

I have run 3 MOTS in series in open air before. However it wasn't for long, and with the output open circuit, the transformers were hissing/crackeling with corona, although I couldnt see it, due to the daylight, but I think any prolonged use like this is really pushing the insulation. I wouldn't reccomend it!

Cheers,
Jesse

Kyle

Sun Aug 30 2009, 05:26PM

Registered Member #2325 Joined: Sat Aug 29 2009, 10:08PM
Location: Southern California
Posts: 11

This has not been my first HV project; just want to have a bit of arcing fun with three MOTs instead of two - possibly with some resonance going. ;P I have looked up information on how to wire up MOT stacks, but always saw 2, 4, 6, 8.. etc, never three. I wanted to reconfirm that the HV out wire off one tranny is connected to the secondary of the other. I plan to use oil - as I have already had arc-overs with two MOTs deshunted. D: I couldnâ€™t pinpoint the location, but it seemed near the primary on one transformer. It was quite weird, though â€“ as I had hot glue all over the primary + secondary coils and the arc ate right through it. It worked fine afterwards, though. =] And yes, I do take PLENTY of precautions playing with HV. I have been using a 4.5 foot piece of PVC pipe with a rubber handle on it + rubber gloves. The MOTs are in an ammo case under oil on top of some ceramic tiles, and everything is wired with 12 gauge AWG. I had one more question â€“ is vegetable oil fine to use as a dielectric/coolant? I have been using it with my two MOT stack, but just wanted to reconfirm it is fine to use. I cannot get ahold on any mineral oil out here that isnâ€™t quite costly. Thanks for the help!

Frosty90

Mon Aug 31 2009, 05:40AM

Registered Member #1617 Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139

Plain vegetable oil would probably have alot of moisture in it, so it would be unsuitable to use unless you de-gas/dry it under vacuum.

Cheers,
Jesse

J. Aaron Holmes

Mon Aug 31 2009, 02:03PM

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

Kyle wrote ...

<snip> I cannot get ahold on any mineral oil out here that isnâ€™t quite costly.

Where approximately is "out here?" You might be surprised.

Cheers,
Aaron, N7OE

Kyle

Mon Aug 31 2009, 04:01PM

Registered Member #2325 Joined: Sat Aug 29 2009, 10:08PM
Location: Southern California
Posts: 11

Mainly just little 16oz bottles the sell at pharmacies for around $4.99 each. That begins to add up quite quickly. D:

MinorityCarrier

Mon Aug 31 2009, 06:24PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

I believe you can dehydrate veggie oil by adding calcium chloride (de-icer) or some other highly hygroscopic salt to it, shake well, allow the salt to settle, then decant the oil (through filter paper as a precaution).

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