Solar well control [RE-wrenches]

[Windy Dankoff]

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William,

Hear Ye All Wrenches -- Matt Tritt is STILL selling solar water pumps  
after all these years, so DO WHAT HE SAYS. HE'S CRAZY!

I agree with using a "toggle"-action (positive shutoff) float valve  
and a small pressure tank to eliminate on/off chatter. As long as the  
pump has the reserve lift capacity to hand the brief increase in  
pressure to shut off. I've recommended this many times. There's an  
inexpensive valve called Hudson Valve that is commonly used for animal  
watering -- $25. I tested one once, and then recommended it to  
numerous people and never got back any bad reports. Search it and  
you'll find what you need to know. Matt or Jeff? Ever try one?

With all respect to Matt, If diaphragm pumps are the bottom of the  
line, then SunPumps is the TOP of the bottom. Their Quad has been  
especially good for many years, in part cuz it's limited to about 100  
feet and all the diaphragm pumps have done MUCH better in that lower  
lift range, including Shurflo. Certainly, for low water needs they may  
be worth considering.

So yes William, your logic is perfect. I've used standard Square-D  
pressure switches and been able to adjust them down to about 15 PSI  
shutoff, or maybe lower, I don't remember. Below that, they get  
sloppy. Set the pre-charge in the pressure tank to roughly half of the  
cut-out pressure. It doesn't seem to matter much what it is, but if  
you get an on/off chatter (water hammer) at the P switch, re-adjust  
the pre-charge pressure.

Normally, you would run the P switch to a low-level control circuit on  
the SunPumps controller, so arcing won't happen.

But just cuz I have nothing better to do, I'll advise on switching DC  
directly:

Regarding mechanical contacts on switches, relays, etc. if they have  
both DC and AC ratings, you will always (far as I've known) see that  
the amp rating at 32VDC is equal to the amp rating at 125VAC. The only  
exception I've seen to that is directly in the PV array circuit, where  
the voltage, when it breaks, rises far higher and may sustain an arc.  
On the Square-D P switches, I remember not seeing a DC rating on the  
switch cover, but seeing it in the catalog listing.

Be sure to use both sets of contacts. That will suppress any arcing.  
If the system is negative grounded (not necessary or advisable on a  
stand-along solar pump),  you should break only the positive side, per  
code. In that case, run it through BOTH sets of contacts IN SERIES.  
Whether you do this or break both + and -, it's the same effect. Any  
arc would have two jump through two gaps in series.

My two dull pennies.
Windy


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