Re: Water rheostat?
From: David E. Sharpe[SMTP:sccr4us-at-erols-dot-com]
Reply To: sccr4us-at-erols-dot-com
Sent: Saturday, September 06, 1997 11:17 PM
To: Tesla List
Subject: Re: Water rheostat?
Tesla List wrote:
> From: Felix[SMTP:73374.1547-at-compuserve-dot-com]
> Sent: Friday, September 05, 1997 7:31 PM
> To: BlindCopyReceiver:;;;-at-compuserve-dot-com;
> Subject: Re: Water rheostat?
> Would you mind telling me some typical numbers that you found reasonable
> for electrode areas, spacing, and water volume? My starting point right
> now is simply the tables of alleged resistivity, from which I can cal-
> culate what kind of dimensions look theoretically reasonable---along
> with theoretical calculations of how slow a startup one could achieve
> without boiling. But along with the theory I'd like to benefit from
> someone else's practical experience if I may.
> Regarding electrical (as opposed to boiling) hazards, my relevant
> credential is that I built our house from scratch including all wiring.
> Having advanced to the handling of 12,000 v from neons, maybe one gets
> too blase about a mere 110. I sure treat my neons with plenty of
I too built this rheostat not having funds to support nichrome heaters
or the like. I like having some resistance in the power path, if for no
other reason than to limit available short circuit in case something
decides to go "high order"!
Also a warning, be very careful about potential electrolyte's. Baking
soda is relatively benign, only CO2 is produced. When I built my first
rheostat I decided to use regular table salt...WRONGO!!!
When operating, the unit it produced trace amounts of CHLORINE GAS!!!
The unit electrically performed OK, but the end result was NOT
ACCEPTIBLE FOR OBVIOUS REASONS.
I added enough electrolyte to allow about 20V drop at full engagement
and full current. The unit would successfully handle several kW
for 2-3 minutes before electrode heating, steam generation, etc.
became a concern. If higher power is a requirement, using a car
radiator, electric fan, and natural convection cooling with a more
substantial container would allow building a liquid rheostat capable of
perhaps 10-20kW for high power machines, without huge expeditures of
DAVE SHARPE, TCBOR