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As planned I have installed the Xantrex C-35 charge controller in the offgrid house. This was a bit of an adventure..
First I had to wait around in town all day for the UPS man to deliver the thing. Of course he didn't until 4, so by the time I got over to the house it was almost dusk. Further delayed by necessary visiting with the nearest neighbor (a country thing), who claims there are "panthers" up this holler.. So by the time I was ready to work, it was nearly too dark.
First I checked the battery bank which I had left charging for a week without a controller or backflow diode. It had gained only half a volt (to 10.5v), so now I knew I really did need the controller in order for the sun to work for me while I am away.
Then, barely able to see, I swapped that bank to provide house power. By 10 pm, using just my laptop, I'd drained 1.5 volts from it and it was as low as it should go. I had 4 hours of laptop battery. This was a bit of a problem since I tend to stay up until 3 am on it.
Instead, I spent 2 hours, by kerosine lantern light, exposing, tracing, and testing wiring. I was able to find 2 wires that were clearly going to the battery bank and had current, and 2 others that were labeled as going to the panels, and, in the dead of night, had no current. Great, I thought, that's the wires I need, let's hook up the controller..
And I did, although only to the battery, since after all I couldn't be certain the other two wires were for the panels, without seeing voltage on them in the daytime. (This turned out to be probably wise, because in the morning, when I tried it, the controller reported no PV voltage. They turned out to be mislabled, and actually connected the battery to the breaker box.)
The problem with doing all that stuff at midnight is it took me quite a long time to wind down. I normally start winding down at 10 am and get to sleep at 3. Last night I got to sleep at 5.
My four hours of battery for my laptop were nursed all hours through the night. Mostly thanks to powertop and the improved power saving of the kernel these days. And to not having wifi or anything enabled. I do wonder if my recent use of redshift to redden the screen causes the it to use less power at night, as I have never gotten five hours out of this laptop before.
Anyway, to get the controller hooked up to the PV array and actually charging the batteries, I ended up having to rip lots of wiring out of the wall, until I simplified the mess to something I could understand. And at the moment I've bypassed the PV array's breaker, which is certainly a safety hazard. So more wiring to do, but I did get it working.
Finally, I hooked the house wiring up to the same battery bank that is being charged from the panel. This house had been using a 2 battery bank setup, because without a charge controller to moderate the PV voltage (17-25 volts), you can't also connect a load that expects 12 volts. The charge controller fixes that problem.
The other battery bank is sitting unused for now. Later, I will equalize and connect the two, in order to get one large(ish) battery bank.
Now, during the sunny fall daytime, I can use all the power I want; it's free from the sun. Battery bank shouldn't drain at all when I use power during the day, and the controller should charge them up and keep them topped off, so they'll be there for me at night.
Now to verify that it's working like it's supposed to!
(I posted some documents and more thoughts from this here).