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Re: [TCML] NST polarity
Thanks for all the info. I was not really interested in wiring NSTs
parallel, I just wondering if the finters and capacitors in the HV circuit
needed to be wired in a certain way. I know know that it does'nt matter.
Thanks,
John
On Sat, Mar 26, 2011 at 7:44 AM, David Speck <Dave@xxxxxxxxxxxxxxxx> wrote:
> Ahhh, yes.
>
> If John wants to parallel one or more NSTs for increased current, he could
> use the technique I used. There are several ways to go about it.
>
> If you have identical NSTs, there's a pretty good chance that they have the
> same relative polarities. Regardless or whether they are identical or not,
> I started by arbitrarily marking one of the 120 VAC input terminals as "+"
> on both NSTs, and one of the HV terminals on ONE of the NSTs also as "+".
> To determine which HV terminal on the second NST saw also "+", connect 120
> VAC to both NST primaries, with the hot (black) lead to BOTH "+" input
> terminals, and the neutral (white) wire to the other terminals. Ground both
> cases together to the green wire.
>
> I then connected a length of neon sign tube (a 4 foot conventional
> fluorescent tube would also work) between the arbitrary "+" HV terminal on
> the first NST, and one of the HV terminals on the unknown NST. It is
> critical that both cases are grounded, as they will complete the circuit.
> (NSTs usually have the center tap of their secondaries connected to the
> case).
>
> Apply power to the pair of NSTs, by slowly the applied voltage through a
> Variac. If the tube lights at a low applied primary voltage, you have the
> "Wrong" polarity, and the opposite terminal on the unknown transformer is
> the "+" terminal.
>
> If you get to full, or nearly full primary voltage without the tube
> lighting, then you have identified the connected terminal on the unknown NST
> as also being a "+".
>
> (Fine print: if the NSTs have slightly different output voltages, the tube
> may light when nearly full voltage is applied even if the polarities match.
> You can verify the correct arrangement by reversing the HV terminal
> selection on the unknown transformer. The tube will light at a much lower
> applied voltage if you have connected a "+" to a "-" terminal.)
>
> Select one transformer as a reference unit, and you can proceed to phase
> all the rest of your NSTs if you want to have a bank of three or more in
> parallel.
>
> You can now safely parallel the two NSTs by parallel connecting all the "+"
> power input terminals, and the corresponding "+" HV terminals together.
>
> I've also heard of a similar process that involves drawing arcs between
> terminals but I think my way may be a bit safer and more controlled.
>
> Dave
>
>
> On 3/26/2011 10:59 AM, dave pierson wrote:
>
>> I was wondering if the output on NSTs have specific polarities.
>>>> (positive/negative) If so, how can you tell which on is positive
>>>> and negative?
>>>>
>>> Conventional iron core NSTs produce alternating current output. Each
>>> terminal is positive on one half of the AC line cycle, and negative on
>>> the other half.
>>>
>>
>> When one HV terminal is positive, the opposite terminal is negative,
>>> and vice versa.
>>>
>>
>> Concur. However, IF the question relates to paralleling,
>> the instantaneous polarity is critical. The archives
>> will have much, keyword:
>>
>> phasing
>>
>> .
>>
>> best
>> dwp
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