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RE: [TCML] Jacob's Ladder
--- On Mon, 2/2/09, Thomas Ryckmans <thomas.ryckmans@xxxxxxxxxx> wrote:
> What happens if you don't have current limiting on a
> MOT-powered Jacob's
> ladder? The current flowing through the spark keeps going
> up until the MOT
The JL presents a short-circuit to the MOT, and current instantly climbs beyond the capacity of any normal residential circuit breaker. Run times will be measured in seconds. Even with the fast-tripping breaker, the MOT or MOTs will become smoking hot. The power cord to the MOT will become quite toasty too.
You can extend run times a little by immersing the MOT(s) in mineral oil and using sturdy power cables (forget those cheap orange extension cords from Wal-Mart, I'm talking 30A RV cable!). You can also use a heavy-duty appliance outlet to provide more current. I have tried all these measures in the past but I now consider them silly. It's much safer and more sensible to simply use a ballast.
Look for "ballast" in the TCML archives and you'll get plenty of hits. A bundle of iron wire or rebar wound with a few hundred turns of #12AWG should work. A large MOT core gapped and wound with all the THHN wire it can hold will probably do too. I once used a pair of MOTs with their primaries in series and their secondaries shorted out. This limited the current to about 20A. An AC arc welder also makes an excellent and pretty much "bulletproof" ballast.
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