RE: DC powered Coil single phase 14.4KV 5KVA pig DCPTC ?-)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>

>It is a bit of heresy to incorporate a DC coil given the Tesla/Edison
debate
>:-)

Well the business end of the thing is still as AC as can be. Anyway Tesla
himself designed DC coils, I suppose to sell to people who had a DC mains
supply. I've seen circuits in the CSN for coils running off 220 or 600v DC
with resonant charging and a mechanical contactor or mercury break as the
"spark gap". Kind of like a 19th century OLTC.

I also built a DC mini coil which was great fun. It used a 10kV DC supply
that resonant charged a 12.5nF 22kV MMC bank (to around 20kV) and a rotary
gap spun by a vacuum cleaner motor. I was able to adjust the break rate from
about 100 to 500 bps, below 100 the gap would fire twice per presentation,
and above 500 the power supply voltage sagged so the sparks actually got
shorter. It seemed to work best around 400 bps where it produced 40" arcs
using 1000w of power.

The secondary was 3.5" by 18" so it was kind of the big end of mini coils.
If you tried running it on a tabletop I suppose it would fry the ceiling.
But anyway I think DC coils are great if you can stand the extra hassle of
rectifying and filtering a high voltage supply. 3-phase is a lot easier
because the output of a 3 phase bridge rectifier is already smooth enough
without filtering.

Draining the energy out of the filter cap need not be a problem. You just
use the smallest possible filter cap, put hefty bleed resistors across it,
and live with the power loss due to these resistors.


Steve Conner