Diary from the cabin, page 7

6-9-06

Mystery solved, or plot to drive me crazy(er)? The voltage leak is gone as in not there. If you recall my last thrilling diary entry, I discovered a slight voltage leak here at the cabin. Well, I tried to track it down then decided to take another crack at it this weekend. Now it's not there. It's the chipmunks. They're trying to drive me crazy because I won't let them stay in the cabin. 

I've got a new meter, ditching the cheapo which has been retired to monitor the bank. I now use a Sperry meter that seems to work pretty good.

I discovered that I had made a serious miscalculation in my bank setup. In order to be able to swap out batteries in the bank when needed, I thought a centralized connection point for all the wiring would be cool. Too bad I neglected to think about what I was doing. Instead of having a big bank, I had a small bank. Let me explain. When you're using 12 volt batteries to set up a bank, normally you tie them together, positive to positive and negative to negative. This creates what can be thought of as a bigger battery. For instance, say you have 2 100 amp hour batteries. If you connect the positives and negatives, you will have a single 200 amp hour battery bank. Conversely, if you gang connect all the cables, you still have a 100 amp hour battery.  Well, that's what I had done, ganged all the connections together and then like a nitwit scratched my head wondering why in the hell I had no reserves.

So, I reconnected the bank like I should have left it in the first place and we're good to go again. I also added another battery to the bank (I'm still finding deep cycle marines from the same manufacture date). This brings me up to 454 amp hours. The 90 watts of panels brings up the bank pretty good from about 12.5 volts.  

Normally, if I see anything approaching 12.5 volts (90% charge or 10% of the available power used), I put a charge on the bank. Well, with my half assed connections, guess what? The bank went down FAST. I thought I had a bad cell somewhere. But, it was because I had tried to make the bank all nice and pretty instead of thinking. So, everything is better once more and I have plenty of reserves. For instance, when I first started doing this off the grid thing, I had 130 amp hours. That's twice a day charging just running a couple of compact fluorescent lamps and the laptop that I'm writing on. With the 454 amp hour bank, my reserves are much higher and as you get bigger on the bank side of your power system, you discover that when you disconnect your loads for the night, there's more of a recovery in the batteries which means less charging. Here's an example: the smaller bank I used to have would be at, say, 12.5 volts when I went to bed. When I got up in the morning, it might be 12.57 volts. Well, this weekend, the bank was at 12.5 volts when I shut everything off for the night. In the morning it's 12.64. You're stressing what you've got less and getting more out of the system. Like having a big engine in your car, you stress it less than you do a tiny engine.

I also switched back to my Xantrex inverter; the Vector just isn't as efficient when it's running. I think I'll mount it in my truck as a backup power source. That way I can leave the generator at the cabin so I don't have to haul it around with me.

Here's a little voltage chart that shows your state of charge using a digital multi meter.