Why do battery needs a float current?

Almot wrote:

So my question is why I see daily 2AH in data log instead of expected 0.3AH?
Or, if you prefer, - why do I see 0.3A current instead of expected 0.3AH/7=~0.04A?

float voltage too high

It could be the accuracy of the Rogue amp meter. It's resolution is only +/- 0.1A.

Add another amp meter (multimeter) in the charging circuit. Do they match?

Sal

Please guys, don't get confused. Have a rest from crazy holiday shopping and think. Mena - yes, 0.3AH SHOULD go into the battery to compensate for self-discharge, but I observed 2AH going in, daily.

Observed instantaneous current is 0.3A.
With such a current the battery should get 0.3*7hours =~2AH a day, and it does get 2 AH a day according to controller data log.

Projected daily self-discharge of 300AH AGM bank = 0.3AH.

So my question is why I see daily 2AH in data log instead of expected 0.3AH?
Or, if you prefer, - why do I see 0.3A current instead of expected 0.3AH/7=~0.04A?

My only guess is that battery becomes a space heater while on the float, and therefore is taking more charge than if it were self-discharging quietly on its own, without a power source.

It is probably how it should be, but I hoped to get some scientif-ish reasoning from the audience. In the Rogue manual - written like a brief 101 on charging issues, btw - it recommends Float setpoint 1% of the bank, i.e. 3A for my 300Ah bank. So my 0.3A - after a week of floating - is within the norm.

Almot wrote:
5% controller loss is nothing compared to 7-fold "overhead" that Im seeing (2AH/0.3AH=7).

I think you are confusing two different things. It looks like the .3A is the Amps (instantaneous) into the batteries. 2Ah is the total for the day. (.3*6.7 hrs = 2Ah).

Any current in excess of what is needed to charge or make up for self discharge of the battery has to be dissipated in some way. Since you are running current through a resistor (battery), some is lost to heat and some also to electrolysis. 2 Ah a day isn’t that much. Looking back at my data log, mine averages 4 to 5 Ah per day. That is with all parasitic loads disconnected (4 GC2s).

I'm confused, is that .3Ah going IN to the battery?

BFL13 wrote:
The monitor needs power, so that is a parasite

Rogue MPPT 3048 manual

From memory, the whole Rogue controller loss is ~5% of input power, this includes the display. I don't have fancy-shmancy Trimetric monitors ;)

5% controller loss is nothing compared to 7-fold "overhead" that Im seeing (2AH/0.3AH=7). Besides, I think the controller 5% loss is not recorded on the display. When the log on display says "2 AH out", then it means "out", i.e. from controller to battery. Unless I'm missing something.

The monitor needs power, so that is a parasite

I'm going to assume the loss is due to the inefficiencies of batteries and chargers. As for the math or the chemical explanation, I don't know.

I have maintenance battery chargers on four different battery systems and they all work fine. (Two in my coach, one for my motorcycle and one for my CPAP backup.) They replace the electrical energy lost due to inefficiencies of battery design.

This almost sounds like a problem that doesn't need solving. Sorry, but I had to say that.