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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