My Screwy 31

NinerBikes wrote:
I believe it was a post I read by BFL the other day in one of MexicoWanderers thread about charge controllers MPPT break even or something. about how his T-1275 needs about 15.5V daily to keep the SG up, whereas his 6 volt GC2's were pretty much good at 14.8V to keep the SG up, daily.

Would not at all be surprised if these bigger 12V jars need more oomph to get the SG up there and topped off, due to greater internal resistance to charging. Evidently charge controller voltage is not a one Voltage fits all batteries.

Will be very interested in seeing your results on the 14.8V charging for a week.

Me too. I am still learning how to manage my collection of batteries and solar stuff so it all comes out even every so often.

The T-1275s do need extra attention compared with the 6s, but I am not sure that they need so much 15.5 as all that, so long as they get plenty of 14.4 or so. The trouble is they get used a lot for inverter draw at 100a at a time, while the 6s only get hit with a lot of furnace etc at 20a typical draw. Say television plus furnace or whatever.

Got back to trailer today after the solar had been on all batts for two days no draw since early first day. 6s are all at 1.300 after being on the "float" of 14.4v during most of that time after getting to 14.8 first.

Not sure what that does to my usual story they need over 15v to reach baseline SG.

Meanwhile the used T-1275s have been at 14.8 all day and are not up to their highest achieved (so now baseline) SGs I got them to after all that nursing last winter. They are about 0.005 below the baseline in all cells.

I ASSume if I give them enough time at 15.5 they will get back to baseline SG, but that would mean not using them for inverter work meantime.

Perhaps I am screwing this whole thing up by having the big inverter draw on the T-1275s and the furnace etc on the four 6s. That worked out right in the colder temps but now it is getting warmer and less furnace, so the T-1275s are working harder than the 6s. Maybe I should switch jobs for them and put the 230w panel on the two T-1275s and just have the 130w on the 6s.

Or I could just gang the whole bunch and let the electrons sort it out among themselves. I did that in the winter, but the way I had the six batteries wired up the two 12s got short-changed for charging.

I am reaching the point where once again in nice weather, I have too much solar and too many batteries :) Maybe time to sell the 130w, its controller, and the two T-1275s to some unsuspecting newbie, and just go with four 6s and the 230w panel like a normal person. We'll see.