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Re: Water rheostat?
From: David E. Sharpe[SMTP:sccr4us-at-erols-dot-com]
Reply To: sccr4us-at-erols-dot-com
Sent: Friday, September 05, 1997 8:45 PM
To: Tesla List
Subject: Re: Water rheostat?
Tesla List wrote:
>
> From: Felix[SMTP:73374.1547-at-compuserve-dot-com]
> Sent: Thursday, September 04, 1997 7:49 PM
> To: BlindCopyReceiver:;;;-at-compuserve-dot-com;
> Subject: Water rheostat?
>
> I'm advised to buy a variac to smooth out my switch-on transients. But
> why not an electrolyte rheostat which is $100 or so cheaper? I
> visualize a PVC pot of salt water containing basically two wires, one
> with a well-insulated handle. Such rheostats were used for various
> purposes in Tesla's day. Even a small volume of water could absorb
> the waste heat of a brief startup.
> Can anyone tell my why this wouldn't be a good alternative?
> /
Felix
I am presently using a baking soda (sodium bicarbonate) electrolytic
rheostat in a 5kVA magnifier system. It consists of 2 fixed SS plates
1/8" x 10 x 14 in a 2x6 wood frame with an additional 1/8 x 10 x 14
SS moveable plate adjusted up and down by a windshield wiper
motor running a 1/2-13 fiberglass lead screw. About 1 tablespoon of
baking soda in 3.5 gal of tap water will easily support up to 45A
-at- 240 VAC at full engagement. FWIW, the whole assembly sets in a
standard Rubbermaid special PVC trashcan. Total cost including
3 SS plates, < $20.00.
Just check water level and replenish as necessary. Liquid rheostats
were SOP in Railroad Electric Traction for at least 30 years.
Regards,
DAVE SHARPE, TCBOR