Re: MOTs...exploring the low end of TC voltage

To: tesla-at-pupman-dot-com
Subject: Re: MOTs...exploring the low end of TC voltage
From: "Luc" <ludev-at-videotron.ca> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sun, 27 Feb 2000 13:04:50 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Tesla List wrote:

> Original Poster: "Gregory R. Hunter" <ghunter-at-accucomm-dot-net>
>
> Fellow Coilers,
>
> The subject of microwave oven transformers (MOTs) in Tesla coil service
> comes up often on this list.  In response to the many queries about MOT
> power supplies, I conducted a simple experiment.  I hooked up two 900 Watt,
> 2400VAC MOTs in series for 4800vac at around 385ma.  I used no ballasting,
> no RF filtering, no nothing.  Mains current was from a standard 115v 20A
> household outlet.  I connected the twin MOTs to my 4" x 24" coil which
> normally runs on 2 x 9kv/60ma NSTs with .023uF MMC & single static vacuum
> gap.  I closed the spark gap a bit for reliable firing and let her rip.  No
> output.  I put a breakout point on my toroid and tried again.  This time I
> got a frantic, brush-like blast of discharge about 12" long!  It looked
> like a flame!  I can't even hazard a guess about how many bangs per second
> this thing was going.  However, I could only run a few seconds at a time or
> the mains circuit breaker would trip.  Still, it does demonstrate that a TC
> can operate on a low voltage, high current MOT power supply.  If my setup
> was optimized for such a supply, perhaps by using a bigger tank cap, and if
> I ballasted the MOTs or wired them for 230v, I could get useful performance
> from what was for me a FREE power supply (my MOTs came from  discarded
> ovens).  In the next few weeks I will wire up the twin MOTs with two
> half-wave voltage doublers, proper protective filtering, safety gaps, etc.,
> and have a nice 1800 Watt, 12kvdc MOT supply.  But now I know the doublers
> aren't strictly neccessary.  Starving students and other low budget coilers
> take heart.  Your Tesla coil power supply is only as far away as the
> nearest junk yard!
>
> Best Regards,
>
> Greg Hunter
> Cochran, Georgia

I plan to experiment a power supply with MOTs.You can cut the welding of the
core on the primary side (I try and it's easy) put out the primary and the low
voltage winding. On the MOT i have the primary have 130 turns ,i plan to wind
1/6 of the turn (22 turns) with heavy thermalyse 10 or 12 gauge wire and quip
that primary well isolate from the core reweld the core put 6 modify MOTs in
serie and running them under oil .If i calculate well the i will not have
arcing between the primary and the secondary if i have 1/8" of transformer
paper (under oil) between the primary and the core .With proper ballasting you
probably run this assembly near 5KVA (like a small Pig) cheaper and multiple
tap :4KV, 8KV, 12 Kv.

My only problem :i don't have a lot of time to find 6 MOTs of the same spec
and do the modification (I work to much)  it's gone a take long time for me to
do it. If any one find it's a good design please try it and post.

Luc Benard (Montreal)