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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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