12 VOLT controller [RE-wrenches]

[Pat Redgate]

In a message dated 10/12/2003 , solarman4 at yahoo.com writes:

> It needs to be a 12VDC power supply.  We are currently using an inverter 
> and
> 110Vac differential.  It's off-grid and we don't have the extra .5A to 
> waste.
> 
> 
  I have gotten around using a differential controller for PV powered hot 
water systems by running the DC power through a collector mounted snap switch and 
then through another snap switch on the tank.  In fact you can run your 12v 
line through the lower (or upper) thermostat (also a snap switch) on a standard 
electric water heater.  The adjustable tank snap opens on rise (usually 
adjustable between 110 to 150 F) and shuts off the pump when the temp you set is 
attained.  The snap switch on the absorber closes on rise (can also be 
adjustable) which would prevent the pump from running until a preset temp is achieved.  
Not as efficient as a differential controller, but works very nicely on a 
standard TWO tank system.  On a ONE tank system you would want to make sure that 
the collector snap is set at >tank temp.  

Snap switches are $5 to $10 and you can get them anywhere from Grainger's, 
Johnstone or your local HVAC supply.

But, I'd much rather use an off the shelf DC Diff Controller.
 
Patrick A. Redgate
AMECO
Long Beach, CA
(562) 595-9570
www.amecosolar.com

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