12 VOLT controller [RE-wrenches]

[Allan Sindelar]

Patrick,
The problem I see with the approach you have described is that it allows the
PV pump to shut off at high storage tank temperature. This would allow the
collectors to stagnate on summer days, shortening fluid life and possibly
blowing off the PRV. I would rather see no high-limit shutoff, and rather a
thermostatic mixing valve to prevent overheating. How do you handle this?
Allan @+NRG

----- Original Message ----- 
From: "Pat Redgate" <solarpro at aol.com>
> >
>   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
>
> --
> [Non-text portions of this message have been removed]
>
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