My Screwy 31

NinerBikes wrote:

landyacht318 wrote:
Another Sunday Hydrometer dipping.
I used 43 a/h last night, and averaged 38 this week. ~97% solar recharge each day. With one or two alternator blasts in the evening for a few miles.


I was a little later checking today than previous Sundays. It had been sitting at 15.3v for about 3 hours and taking 1.2 amps, after ~2 hours at 14.7v All loads still on the 31 battery, not switched to the other.

I dip the Hydrometer, 1.285, all three. Temp compensated, as all readings have been.

This is 0.005 higher than I've ever been able to get this battery upto. I assume it is due to water loss. Which is noticeable, but nowhere near the danger zone.

I wonder if this is the zone I should never fill it above? The SG level sweet spot perhaps.

And this 1.280+ reading came without me having to run the voltage upto 15.9v for up to 2.5 hours as every other Sunday has.

Not what I expected today.
Considering backing off the voltages a smidge for this week.

If you live near/around the OC, and had four consec near 100F days... well, that could be a little hot, Voltage wise, for those temps.

In another thread, for the first time ever, I got 1.280 on my T-1275. A full 10 points higher than I've ever seen. And a low cell that was 15 or so points lower was only 10 points lower this time. I triple checked that one low SG cell, in disbelief.

Maybe next Sunday, try 30 mins at 15.9V and see where you are at? Sooner or later you'll find the minimum minutes at 15.9 to get the jb done 1x a week.

Your seeing good numbers on the SG now, and not much voltage sag either? Sounds like you are fine tuning the sweet spot, bit by bit.

Perhaps the big 31 and the big T-1275s have enough plate area that you get more variation in SG after a while? IMO based on my T-1275s you can just ignore differences between cells' SGs.

My three year old, four 6s are all pretty close in all cells when at baseline full at 1.300 across the board. But

My two "previously enjoyed" T-1275s that load test out to 270AH of rated 300 on the ten hour test I do (so are 90%) have always had SGs all over the place.

When I first got them last August they were lower in SG than after I had nursed them back to good health, but the same cells have been lower or higher than the others every time. It is just that now all the cells are higher than before as their baselines.

The highest I ever got them was last November after a nursing session and the batteries have been used while camping off and on last winter and lately here every day since mid-April at the seasonal spot with solar.

So for the last month they never got quite full until two days ago I took them aside and did a solar overcharge on them (all day at 15.5 volts.)

Today after resting a day, they are at
Battery A- 1.280, 75, 70, 90, 85, 90
Battery B- 1.275, 75, 95, 75, 75, 75

That is as good as I can get them (same as last November), so that is the baseline for them. It all shows that after a month of camping and not getting to full in that time, they can still be made to get to full with a special effort. It also shows that SGs can be all over the place among cells and it doesn't seem to matter with these batteries.

BTW, I have decided to leave them at that on a float charge for the rest of the summer and just go with the four 6s, since as Niner said, the T-1275s need a lot of attention, can't be banked with the 6s very long (more than a week, say) because the T-1275s need a different level of solar charging from what the 6s need, and it is too complicated keeping adjusting the settings on the controllers and splitting the banks, etc. Getting to be a PITA actually.

I could go all summer with just the two T-1275s or with just the four 6s, but the simple thing to do is go with the four 6s. That puts all the solar (360w) on the 458AH bank which is way over-doing it, but that is another story :)