My house entered full power saving mode with fall. Lantern light and all devices shutdown at bedtime.
But, it felt early to need to do this. Comparing with my logbook for last year, the batteries were indeed doing much worse.
I had added a couple of new batteries to the bank last winter, and they seemed to have helped at the time, although it's difficult to tell when you have a couple of good batteries amoung a dozen failing ones.
The bank was set up like this:
+---- house ----
| |
+( 6v )-+( 6v )-
| |
+( 6v )-+( 6v )-
| |
+( 6v )-+( 6v )-
| |
+( 6v )-+( 6v )-
| |
+( 6v )-+( 6v )-
| |
+( new 12v )-
| |
+( new 12v )-
Tried as an experiement disconnecting all the bridges between the old 6v battery pairs. I expected this would mean only the new 12v ones would be in the circuit, and so I could see how well they powered the house. Instead, making this change left the house without any power at all!
On a hunch, I then reconnected one bridge, like this -- and power was restored.
+---- house ----
| |
+( 6v )-+( 6v )-
| |
+( 6v ) ( 6v )-
| |
+( 6v ) ( 6v )-
| |
+( 6v ) ( 6v )-
| |
+( 6v ) ( 6v )-
| |
+( new 12v )-
| |
+( new 12v )-
My best guess of what's going on is that the wires forming the positive and negative rails are not making good connections (due to corrosion, rust, broken wires etc), and so batteries further down are providing less and less power. The new 12v ones may not have been able to push power up to the house at all.
(Or, perhaps having partially dead batteries hanging half-connected off the circuit has some effect that my meager electronics knowledge can't account for.)
So got longer cables to connect the new batteries directly to the house, bypassing all the old stuff. That's working great -- house power never dropped below 11.9v last night, vs 11.1v the night before.
The old battery bank might still be able to provide another day or so of power in a pinch, so I am going to keep them in there for now, but if I don't use them at all this winter I'll be recycling them. Astounding that those batteries were in use for 20 years.
A few recommendations from what I see there, the simplest change I would do to improve the (dis)charging of the batteries would be move one cable to the other side of the bank, like this:
That way the batteries "further away" will also get a decent charge. A good exercise is to calculate the wire length from plus to minus for all batteries. The topology above is not ideal, but usually quite enough. You should take care mixing old and new batteries, if you have a current clamp you can try monitoring the charging and see that all batteries are being utilized and no battery is being over charged.
Check with a voltmeter that the 6V packs are balanced by measuring the midpoints. A temporary solution that can help if they are not is connecting all the midpoints with a thin (like 2 mm2 or so) cable and letting them settle. If this doesn't help you may need to swap the pairs around to get them better matched
Just a few suggestions to get started, hope it helps!
i am not an expert in the field, but it seems to me damaged / discharged batteries may actually be a liability. If you discharge a lead-acid battery too much, it gets damaged and charging it can't quite bring it back to its original capacity, as the terminals get full of crap. "Too much" varies from one battery to the other, but 11.1V is definitely too low, especially for a battery bank, where that voltage is more an average than the lowest charge point (which means some batteries are lower than 11V!).
The worst about damaged batteries in a battery bank is that they bring down other batteries too: the stronger batteries will try to charge the weaker batteries and discharge faster.
Another way to think about this is that every battery is also a resistance as well, even more so when it is damaged.
I can't explain, however, why the two new 12V batteries wouldn't be enough to power the house, unless you have too much of a power drain - I don't know the exact setup here (how much wattage is hooked to the circuit and the exact capacity of the individual batteries) so I can't guess much...
I hope that helps!