Re: [TCML] mots in series

[Scott Bogard <teslas-intern@xxxxxxxxxxx>]

Neal,
     If you are asking if wiring one leg of your MOT stack primaries in 
series on a 240V line, and the other leg on another 240V line out of 
phase, will give you the same voltage but less current, the answer is 
no, the only way to reduce current is to ballast, generally using 240V 
is so you can pump more current in without flipping breakers!  I hope 
this answered your question.

Scott Bogard.

Neal Namowicz wrote:
> Thanks David and Scott,
> I'm glad I asked. Now, just out of curiousity, if one were to use two 
> pairs, one pair on each leg of a 220v line, would that give 8kv at 
> half the current of putting them all on one 110v line?
>
> Neal.
>
> ----- Original Message ----- From: "David Speck" 
> To: "Tesla Coil Mailing List" 
> Sent: Saturday, June 21, 2008 9:40 AM
> Subject: Re: [TCML] mots in series
>
>
>> Neal:
>>
>> 1)  Definitely not!  You would connect the two cores together for the 
>> two center transformers, and then you would have to properly phase 
>> the 120 VAC Primary inputs so that you see ~4 kV across the two HV 
>> terminals.  This minimizes the voltage stress between the bottom end 
>> of the HV windings, and the core, which is at ground potential.  In 
>> effect, you create a midpoint (center tap) grounded transformer, just 
>> like a standard NST.  If phased incorrectly, then the HV outputs will 
>> be in parallel, doubling the current available at 2 kV, but not what 
>> you want.
>> If you are seriesing 4 or 6 transformers, then you have to disconnect 
>> the bottom of the HV windings from the cores, and float the cores of 
>> the outside transformers.  The outermost two transformers of a 6 MOT 
>> stack almost always have to be immersed in oil to prevent secondary 
>> winding - to - core breakdown, even if the cores are floated.
>> If you try to go to an 8 MOT stack, then you have to provide 
>> isolation transformers for the outermost MOT primaries, as secondary 
>> to primary breakdown then becomes a problem.  At that point, it's 
>> easier to buy a 5 or 10 KVA pole Pig from Dr. Resonance and have 
>> everything wrapped up in a nice neat package.
>> You should try to reasonably match the transformer pairs 
>> symmetrically for voltage output on either side of ground.  If you 
>> have pairs of transformers with higher voltages than other pairs, 
>> then use the lowest voltage transformer pairs in the center of the 
>> stack, and the highest ones on the outside.
>> HTH,
>>
>> Dave
>>
>> Neal Namowicz wrote:
>>> Hi,
>>>
>>> Virtually all the mots I have, and have seen, only have the one hv 
>>> output (ok, a couple have a hi and low output), since the other end 
>>> is attached to the core. So to series two (or more) together, would 
>>> I have to
>>>
>>> 1. attach the output of the first to the core of the second?
>>> 2. I'm "assuming" that phasing is not an issue like it is with nst's 
>>> in parallel, but could someone confirm or correct me on this?
>>> 3. Since the core is "hot", do I just let the cores float, as in not 
>>> grounding them to house or rf ground?
>>>
>>> I've looked thru various sites at schematics, but I'm still not 
>>> clear on this.
>>>
>>> Thanks for your help,
>>>
>>> Neal.
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