Re: MOT power supply

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Henry and all,

You are far from crazy, Henry - it turns out that this circuit
effectively is self-ballasting because the 1.1 uF caps that form the
voltage doubler circuit are in series with each HV leg of the MOT's. So,
even when you short circuit the HV to the tank circuit with a spark gap,
the MOT's never see anything worse than the capacitive reactance of the
capacitors at mains frequency. This circuit was discussed a little bit
last month on the T-2 list. To my knowledge, Marco Denicolai was the
first coiler to use a similar circuit in his earlier MOT-powered coil.
However, its self-ballasting properties were apparently only recently
appreciated.

In principle, this approach could be used with other unballasted
transformers. Short-circuit current could be controlled by changing the
capacitance values... but I'd sure want to put a fast fuse on the LV
side just in case I lost a series cap... :^)

Nice circuit to remember for future MOT designs.

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Hhchicken1-at-aol-dot-com>
> 
> Hi Chris!
> The others on the list probably think i'm completely nuts but...
> I use two MOTs in series (ripped from identical ovens tho it probably doesn't
> matter), with the cores connected and primaries in parallel running straight
> from 240v mains with no ballast.  Each HV output goes to one terminal of a
> capacitor taken from the same microwave (thats 2 caps in total), each is
> 1.1uF 2000VAC.  The other side of the caps are connected via a string of two
> HV diodes from the microwaves, and the tank circuit input is taked from
> either side of the diode string to form a voltage doubler:
> 
> -----------------------------| |------+--------------
> |MOT             MOT    1.1uF 2000Vac |             |
> +{#               #}--|               _             |
> {#}---|---------{#}  |               ^ microwave   ---
> {#}  (~)240Vac  {#}  |               | diodes     HV to tank
> {#}---|---------{#}  |               _             ---
> {#               #}  |               ^             |
> |+---------------+|  |------| |------+--------------
> 
> Apparently this gives 12kv pulsed, which is plenty to run my Tesla coil,
> which despite being amazingly inefficent gives me  12 inch sparks.  On a
> better designed coil this could give up to 90 inch sparks according to
> WinTesla!
> 
> Hope I've been of some help,
> Henry Hallam