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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