Re: MOT trouble

["Kevin Ottalini" <ottalini-at-xxxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Finn:
	Convert to DC ... you won't need the safety gaps or such
a tricky setup procedure.  You also no longer need to deal with
all the sync problems and you can use several MOTs at a time in
parallel (each with their own rectifier) or make a full-wave MOT
setup with two transformers.

You also won't need any AC-side ballasting ... just a reasonable
DC-side limiter resistor and a single AC variac (perhaps a small
second one for the ASRG).

Best,
	Kevin

----------
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: MOT trouble
> Date: Sunday, November 26, 2000 3:52 PM
> 
> Original poster: "Finn Hammer" <f-hammer-at-post5.tele.dk> 
> 
> Gang!
> 
> I have just discovered a problem with using MOT`s as transformers for
> Tesla Coils.
> This would not be so big a problem with static gap operation, but it is
> a problem with rotary driven coils.
> 
> MOT`s are cheaply made transformers, engineered at the limit to meet a
> prize point, where a minimum of insulation, copper and iron is used.
> However I wanted to give them a try, now that they are cheap.
> 
> The lack of copper in the primary winding reveals itself as a high idle
> current, there are just not enough turns to create the inductance needed
> for a low idle current draw. This is perhaps not a problem when the coil
> starts to draw current, but when trying to set the safety gaps, it
> becomes a nuisance.
> 
> The way I set the coil up for work is this:
> I short the power controller, and turn the current limiting variac up,
> untill the current that I want to run is reached. Then I connect the
> MOT`s. However, with the heavy current draw at idle, a very large
> voltage is present across the current limiting variac, so I am unable to
> set the safety gaps. If, on the other hand, I remove the current
> limiting inductance, by turning the variac towards full stop, I have
> another problem: Although this produces the full voltage at the output
> terminals of the MOT`s, when the safety gaps fire, I also see an intense
> current flowing, causing the fuses to blow. Putting damage, although not
> irrepairaple, to a single winding of the current limiting variac.
> 
> I guess the only way to get around this problem is to either knock the
> shunts out of the MOT`s and use the liberated space for additional
> primary windings, or set the gaps with the assistance of another, more
> well behaved transformer.
> 
> Any ideas?
> 
> Cheers, Finn Hammer
> 
> (Guessing it is time to wind another porkchop)
> 
>