Re: [TCML] MOT ballasting options

[Atomic <atomicrox@xxxxxxxxx>]

Do you know if these new inverters are of any use for coiling?

On Fri, Jan 4, 2013 at 10:40 AM, drieben <drieben@xxxxxxx> wrote:

> Brian,
>
> You shouldn't have issues with the HV diode that is already
> inside the microwave oven, so long as you use it according
> to its designed purpose (which is to act, along with the ac-
> companying filter capacitor, to pretty much double the
> output 1 x AC voltage from HV to transformer to 2 x DC
> voltage output.
>
> As far as your ballasting issue, another idea would be to
> connect both the 120 volt inputs of two MOTs and their
> HV outputs in series with each other. This would in effect
> be doubling the core cross section of the transformer(s)
> so that they would be nowhere near core saturation
> during operation, as they typically are during normal ope-
> ration. Manufacturers typically make the transformers as
> absolutely bare-bones small as they can get away with to cut
> on production cost and consequently, they run on the verge
> of core saturation. Doubling up two in series would definitely
> alleviate this issue, as each transformer would only be see-
> ing half of its normal operational voltage on both the primary
> and secondary coil. And since you mention that you have ac-
> cess to several good microwave oven "guts", this could prove
> a viable option for you.
>
> BTW, just in case anyone wasn't aware, the iron core
> HV transformers of microwaves are starting to become a
> thing of the past, just like the iron core NSTs, as solid
> state inverter technology is now the rule for the HV source.
> That's why the newer microwave ovens now feel lighter
> than their equal sized and wattage rated older counterparts.
>
> David
>
>
>
> ----- Original Message ----- From: "Brian Hall" <brianh4242@xxxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Thursday, January 03, 2013 8:22 PM
> Subject: RE: [TCML] MOT ballasting options
>
>
>
>
> Thanks all for the advice and experience stories, even the CW rectified
> schematic to get DC HV from the output of a MOT.
> Are there any circuit diagrams or basic description for how I would use
> microwave oven caps (and possibly diodes) to have a capacitive ballast,
> since it sounds like it may have the least amount of power loss?  While
> still keeping the current draw to 10 amps or so?  It also sounds easier and
> less expensive than making an inductive ballast since I have most of the
> good innards of four or five microwaves.   I want to probably start simple,
> maybe a 12 to 18 inch high secondary with a 1:4 ratio on its cylindrical
> dimensions, driven from a single MOT.   Could I get by with a single static
> spark gap where its only 1 to 2 kv? Or would it even help to get a higher
> HV out using the MOT, MOC and diode straight from the microwave to get a
> higher voltage, if the diode can handle the power from the bigger HV out
> and not just from the little cloth covered wire for the magnetron?  Has
> anyone popped a microwave diode before from putting it straight on the 1 to
> 2 kv output of the MOT?
>
>
>
> ------------------------------**----
>
> Brian Hall
>
>
>
>
>  From: cn@xxxxx
>> To: tesla@xxxxxxxxxx
>> Subject: Re: [TCML] MOT ballasting options
>> Date: Thu, 3 Jan 2013 13:20:38 -0700
>>
>> Hi, David,
>>
>> Your incandescent resistor warming your garage proves that every cloud
>> has a
>> silver lining.  Kind of like the old vacuum tube oscilloscopes.  A couple
>> of
>> Tek 517s would keep a garage pretty warm, too.  What do you use for an
>> inductive ballast?
>>
>> Cheers---
>> Carl
>>
>>
>>
>>
>>
>> -----Original Message----- From: drieben
>> Sent: Thursday, January 03, 2013 5:51 AM
>> To: Tesla Coil Mailing List
>> Subject: Re: [TCML] MOT ballasting options
>>
>> Hi Carl,
>>
>> Yes, you do bring up a good point as to the power waste of
>> resistance ballasting in large coils. I have a large power resistor in the
>> control panel of my Green Monster coil that I can add in series to my
>> everpresent inductive ballast, if I so choose to help in smoothing
>> the output or just for additional attentuation. I believe the mea-
>> sured resistance of my power resistor is only 0.5 ohms, so you'd
>> think thaere wouldn't really be that much in the way of voltage
>> drop here. However, when you're typically running ~60 amps
>> that translates to 1/8 of the total circuit impedance at 240 volts
>> input (240/60 = 4 ohms), so that's 30 volts dropped out. I have
>> the option of  switching the resistive ballast on or off while the
>> coil is in operation and the difference in the output sparks is
>> definitely noticable! The sparks become noticable dimmer and
>> weaker looking when I add the resistance. Also, the resistor
>> will gradually warm to incandesence if ran in this manor, as
>> 30 volts x 60 amps = 1800 watts of wasted power! On the
>> bright side, the resistive heating does contribute to warming
>> my garage on these cold winter days ;^)
>>
>> David
>>
>> ----- Original Message ----- From: "Carl Noggle" <cn@xxxxx>
>> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
>> Sent: Wednesday, January 02, 2013 10:19 PM
>> Subject: Re: [TCML] MOT ballasting options
>>
>>
>> > It would be good to stick to capacitors or inductors for ballasting, >
>> since
>> > they don't dissipate any power (ideally).  A resistor such as light >
>> bulbs
>> > or salt water will reduce the power available from the source.  It would
>> > only be practical for small coils.  The most efficient resistive ballast
>> > would dissipate half the power in the resistor and half in the TC. >
>> Using
>> > a DC supply and controlling the firing rate is probably the best ide,
>> > needing no ballast.  Have to watch out for the large energy storage in
>> > the
>> > C-W capacitors, though.
>> >
>> > BTW, the rectifier circuit in the drawing is a center-fed >
>> Cockroft-Walton.
>> >
>> > ---Carl
>> >
>> >
>> >
>> >
>> >
>> >
>> > -----Original Message----- > From: Jim Lux
>> > Sent: Wednesday, January 02, 2013 8:53 PM
>> > To: tesla@xxxxxxxxxx
>> > Subject: Re: [TCML] MOT ballasting options
>> >
>> > On 1/2/13 6:58 PM, Andy Cobaugh wrote:
>> >> On 2013-01-02 at 17:17, Jim Lux ( jimlux@xxxxxxxxxxxxx ) said:
>> >>>
>> >>> the "500 ft spool of wire" as an inductor has some simplicity and
>> >>> appeal.. I can't recall what it's inductance is, but it's on the list.
>> >>> (copper being expensive these days, it's not as cheap as other means)
>> >>
>> >> I think the 500ft spools of #12 THHN stranded copper measure around >>
>> 9mH.
>> >> The mostly complete spool that I use with my potential transformers
>> >> measures 8.5mH.
>> >>
>> >
>> > 9mH = 3.4 ohms at 60 Hz, 2.8 @ 50
>> >
>> > 1 spool = 35 Amps at 120 V, 60 Hz
>> >
>> >
>> >
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