Hydro and PV diversion, part II [RE-wrenches]

Bob-O Schultze, Electron Connection econnect at snowcrest.net
Thu Apr 22 12:50:21 PDT 2004


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Hiya Gary and Gang,
In the first place, if you are going to set up a diversion type 
charge controller system which incorporates the PVs and the hydro, 
you need two. See 690.72 (B)(1). I generally do this anyway in a 
hydro system because I hate service calls. A C40 into a 1500W-120V 
water heating element (or two) would be my first choice. If I've done 
my math right, one element should dump about 315W when fed 55.2VDC. 
Morningstar's new TriStar should work OK too, but until they pony up 
the UL listing vigorish like everyone else has to do, I'm not going 
there.
I set the bulk voltage to 55.2 or so. Lower than I would with a 
series CC in a PV system. Your batteries will likely spend a good 
deal of time at that voltage. Anything much higher will cause them to 
gas lots. For a secondary, I generally use the FX or MX 12V relay to 
turn on a 25A Continental Industries solid state relay which will 
turn on a cheap 120vac air heater. You can find them with 500W, 750W, 
1500W settings to match your inputs. Set the on voltage a few tenths 
higher than the bulk on the C40 and the off voltage about 4-5V lower. 
If you use this set-up, make DAMN sure your T&P valve works well and 
is vented to the outside, cause it may get a workout. Steam bath 
anyone?
In your particular scenario, where the PV wattage is SO much higher 
than the hydro AND you've got a MX60 anyway, I'd use the MX to ride 
herd on the PVs in series mode and a C40 to dump to a DC water 
heating element. 500W is FAR less likely to cause a steam bath than 
2900W, yet should still heat a fair amount of water. The ac air dump 
would still be nice. If you use it, set the turn on voltage higher 
than the other controllers. Since you want the system to heat water 
on a regular basis, I'd set the C40 as above, the MX to whatever you 
would usually set for a PV system, and the air dump a bit higher.
Good Luck, bob-O
-- 
Bob-O Schultze, Electron Connection
PO Box 203, Hornbrook, CA 96044
800.945.7587 or 530.475.3402
fax 530-475-3401
www.electronconnection.com

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