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[TCML] Pigs on Long Island
Hi everyone,
We are planning to move so I've decided to downsize my coiling a bit and get rid of a pair of pole transformers I bought from T&R back in '96 or so. My question to the list is how do you get rid of this type of transformer? A friend of mine who is a lawyer thought selling them wasn't worth the possible liability, but aside from that I am not sure what to do with them (they have their original pcb certifications). We are on shelter island near the end of Long Island and there are no scrap places nearby, though if scrapyards do take these things maybe one would pick up. One is 14.4kV 10kVA and the other is 19.9kV 15kVA. Any thoughts?
I have a pair of potential transformers I plan to use going forward since they are more compact and easier to move.
Zap!
Charles Brush
Sent from my iPhone
On Aug 16, 2013, at 1:32 PM, Dan Kline <misterpaslow@xxxxxxxxx> wrote:
> Hi Jason,
> This is excellent information. Do you have any kind of a schematic you could send a link to?
> Thanks,
> Dan
>
>
>
>> ________________________________
>> From: Jason Johnson <jasonmsusolar@xxxxxxxxx>
>> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
>> Sent: Friday, August 16, 2013 12:23 PM
>> Subject: Re: [TCML] Single MOT Coil?
>>
>>
>> I too have had good luck with a single MOT. Utilizing a level shifter
>> circuit (as the thing was designed for after all) is a great way to both
>> increase voltage and limit current. To lower current, you just lower the
>> capacitance in the level shifter. I have used three microwave caps in
>> series on a small coil to provide low, medium and high with no variac or
>> heavy ballast (capacitors are way lighter than iron cores and copper
>> windings). That particular coil uses a hyperbaric style single static gap
>> that is made from 3/4" copper pipe fittings, a length of 4" PVC pipe and a
>> vacuum cleaner blower (the blower motor is on a dimmer set to about 50%). I
>> have also built rotary gaps that work well at these voltages (~5 kV firing
>> voltage). Total gap spacing is around 1/16".
>>
>> In the microwave, there is very little current limiting from the magnetron.
>> Most of the impedance that is seen by the plug-in side of the world is
>> because of the level shifter capacitor on the high voltage side. The
>> magnetron is approximately 50% efficient - meaning that a 750 watt oven
>> (typical) will have a 1500 watt transformer/level shifter. To get 1500
>> watts at 2000 volts (again typical values) you need about 2667 ohms of
>> impedance. At 60 Hz, a 1 uF capacitor is 2653 ohms. With transformer
>> saturation and component value tolerances thrown in, I think it is a wash
>> and is safe to say that microwave oven transformers are designed to be
>> capacitively ballasted on the high side!
>>
>> To get half the wattage, you can use two caps in series for half the total
>> capacitance. You could also use those two caps in parallel to double the
>> wattage. Simple jumper arrangements on the cap terminals allow you to
>> change the power settings easily, just be sure to do it when the coil is
>> off and the caps have had a minute to discharge. All modern microwave
>> capacitors seem to have an internal bleeder, but I like to add an extra one
>> anyways.
>>
>> Biggest piece of advice by far that I have learned about level shifters
>> driving Tesla coils is this - *use lots and lots of voltage headroom on
>> your level shifter diode*! Filtering helps too, but for example I use 30
>> 1N4007 diodes in series for my single stage level shifter (i.e. 30 kV at 1
>> amp rating for a 5600 volt nominal level shifter peak voltage). That
>> finally seemed to be enough to handle the RF nastiness - faster diodes may
>> require less safety factor but I haven't tried.
>>
>> Also, it seems to me that the tiniest MOTs are still capable of delivering
>> LOTS of current, so use the smallest one in your collection. With one or
>> two microwave caps strapped to the top or side of the little beasty you are
>> very hard pressed to find a more compact, lighter 1kW supply (at least one
>> based on an iron core). The duty cycle is limited, of course - but you
>> would also be hard pressed to run your coil for long enough to bother the
>> MOT and even then you can add oil cooling with not much extra mass or
>> volume.
>>
>> Good luck!
>>
>> - Jason
>>
>>
>> On Thu, Aug 15, 2013 at 7:48 PM, Dan Kline <misterpaslow@xxxxxxxxx> wrote:
>>
>>> Thanks, Ted.
>>> Very interesting information! I have considered building a DC coil in the
>>> past so that I could tune in a perfect break rate and get max sparkage that
>>> way.
>>> I may go this route since I can build upward but not outward :) But about
>>> the space issues, I think I may just move to larger apartment sometime in
>>> the near future.
>>> Dan
>>>
>>>
>>>
>>>> ________________________________
>>>> From: Tesla <tesla@xxxxxxxxxxxxxxx>
>>>> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
>>>> Sent: Thursday, August 15, 2013 3:46 PM
>>>> Subject: Re: [TCML] Single MOT Coil?
>>>>
>>>>
>>>> Team
>>>>
>>>> I'd qualify some of the points Mark makes.
>>>>
>>>> MOT's are magnetically shunted and do have some degree of current
>>> limiting. The current limiting characteristics and low voltage are very
>>> impacting for classic AC designs but as the DC dual level shifter with
>>> resonant charging designs illustrate it is possible to get 20 kV from a
>>> single MOT which is entirely adequate. Current input can be controlled by
>>> the size of the primary capacitor and break rate avoiding the current
>>> limiting issues. See theory at
>>> http://www.richieburnett.co.uk/dcreschg.html (Richie has a wonderful site
>>> with the best material on DC designs I’ve found)
>>>>
>>>> I advocate the use of some power factor correction in these designs to
>>> lower the input current drawn.
>>>>
>>>> http://scopeboy.com/tesla/tc2schem.html
>>>> http://www.capturedlightning.org/hot-streamer/drilling/dccoil.html
>>>>
>>>>
>>>> Rgds
>>>> Ted in NZ
>>>
>>>> --------------------------------------------------------------------------------
>>>>
>>>> -----Original Message-----
>>>> From: Mark X2
>>>> Sent: Thursday, August 15, 2013 10:19 PM
>>>> To: Tesla Coil Mailing List
>>>> Subject: Re: [TCML] Single MOT Coil?
>>>>
>>>> Gary's right, go for a small NST. A MOT isn't current limited and the
>>>> voltage is just too low to get a decent working spark gap.
>>>>
>>>> <SNIP>
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