Re: Ballast

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

But watch out with that 100A across 1 ohm, because it will dissipate 10 kW!!
The best overall solution is to use a current transformer.  The usual
current transformers are rated for a 5A secondary current and 50,100,200,
etc. amps through the hole in the middle. That is, their turns ratio is
10:1, 20:1, 40:1, etc. They run about $20-25 BRAND NEW, and around $5 used
surplus.

You can get standardized shunts (50 mV = rated full scale) fairly easily,
or a short piece of copper wire can serve as an admirable shunt.  AWG10 is
0.001 ohms per foot.  Make your shunt, then calibrate it with a known
voltage and load (I wouldn't use a 100W light bulb, by the way, because
their resistance isn't all that constant).

Say you coil up 10 feet of AWG10 (for 0.01 ohms).  You get a good quality 1
ohm resistor, hook it in series, hook up a car battery (so about 12 Amps
will be flowing, dissipating 150W in the resistor!), measure the voltage
across the whole thing, measure the voltage across the 1 ohm (it will be
around 12V), measure the voltage across your shunt (should be 120 mV, or
so), and now you have a calibration.

You can use finer wire, or NiChrome, also.



Tesla list wrote:
> 
> Original poster: "R Heidlebaugh by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
> 
> on 11/05/01 4:29 PM, Tesla list at tesla-at-pupman-dot-com wrote:
> 
> > Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<A123X-at-aol-dot-com>
> >
> > I'm planning to make a gapped core ballast with an MOT core. I'm looking to
> > get
> > around 16amps, or 8amps if I use my variac to take the voltage to 240v.
> > Anyway,
> > can I just use the original primary as the winding for the ballast? Also I
> > don't have anything to measure the current with. Will radioshack have good
> > enough meters?
> >
> > Mark
> >
> >
> If you measure the voltage across a known resistor you have the current
> equiv. I like to use a 1 ohm or a o.1 ohm resistor so I dont nead to think
> about conversion. If you use less than 0.1 ohm you nead good meters and
> calibrated standards. 100v across one ohm is 100 amp
>     Robert H