Max Charging Current of typical GC2 battery

OldSmokey wrote:
I'll give you a pro tip here and it's for Trojan T105's
but is applicable to other GC2's if used with care..

it's all about max heat capacity, for a T105 the best figure I would use is 0.05 watts per Ah. a T105 has an internal resistance of 0.003 Ohms . so that's 0.001 Ohms per 2 volt cell.

The max thermal charge limit is square root of (.05 x 225Ah) / .001 = 106 amps. yes.. you can charge a T105 at this rate..
this is approx c/2

I wouldn't advise you do this often, but it can be done.

Somebody a few years back posted that he was talking to a Trojan tech support guy about all this, and he said the Trojans could accept any amount of amps at first.

The whole thing is based on the simple fact that the acceptance rate at any SOC depends on the voltage. If you are at a lower SOC then at any same voltage the batt will accept more amps than at a higher SOC. (which is why amps taper in the Absorption Stage). For the same SOC, jack up the voltage, and it will accept more amps.

If you hit the batt with a huge amps rate, the voltage will spike and amps will immediately taper to what the battery will accept.

You can see in my ugly graph above how that works where there is a diminishing returns in going to higher amps for how long it takes to do a 50-90. Even if the battery will accept way more amps, you might only save 10 minutes of generator time going to a 70 vs a 55, so why pay way more for a way higher amp charger and then need a way higher wattage generator to run that higher amp charger, just to save 10 minutes of gen time? OTOH there is a big diff in time between 55 and 35 amps on 220AH.

(You double the times for doubling the AH at the same amps, BUT you do not halve the charging time on the same AH by doubling the charging amps.)

You have to do a proper analysis of the whole picture to decide on your best bet for a set up for how you (not some other guy) camps.

Meanwhile--yes, on solar it is not always possible to get to full each day. You can go days and days with an incomplete recharge, and get sulfated. Later on, when the sun shines and you can get to full, it does not mean you are out of the woods.

You still need to desulfate from all that time earlier on. You can avoid a lot of that if the weather forecast is any good, by doing a bit of gen charging in the morning so there is time for the solar to catch up that same day and get it done.

Above, I described winter camping, but here in August on solar it is way different. Gottaluvit! Who cares about batteries? It is all about corn on the cob, BBQ steaks, and picking blackberries for dessert (after a swim up at the lake of course) :)