Is Your Battery Really Charged?

[currinh]

Originally Posted by fudge_brownie

Hugh
I see you have an 2011 Escape 19, assuming you have the dual 6 volt batteries you may have the prior model of batteries from Interstate, the U series. I believe the voltages are even higher for these batteries as recommended by Interstate. Charging would be at 15.5 volts and the P1 setting would be 15.4.

Paul:

I should have included that. Our 19' has a single 12v battery, an Interstate SRM-27. It's 95-100 Ah, wet cell. It was in the trailer when we got it so I don't know if it was original or not. I had it checked and it's in good shape. When it goes we'll replace with two 6v of some kind.

Our stock converter, WFCO, charges at 14.4v bulk, 13.6v absorption, and 13.2v float. The GoPower solar charger uses 14.4v bulk/absorption and 13.7v float. I don't see any times associated with these.

Trimetric suggests setting the voltage set point just below the changing voltage. For these chargers that would be some 14.3v. They suggest setting the current set point at Ah capacity divided by 50. For my 100 Ah battery that would be 2A.

Trimetric also suggests an alternative method. This is to set the voltage set point just below the float voltage, for these chargers 13.1v AND set the current set point to Ah capacity divided by 90, for my battery 1.1A. For this scheme the battery is declared fully charged when it's been in float mode long enough that the charging current has dropped below 1A.

These stock chargers aren't adjustable, so I suspect the 14.4v will leave the battery under charged. I'm wondering if Trimetric's float method would give a better indication of when to declare the battery charged. Any thoughts?

This doesn't affect the changing of the battery, just Trimetrics starting point for counting down Ah to 50% discharge. But I'll use this "gage" for battery maintenance and protection so the more accurate the starting point the better.

Thanks.

[currinh]

It may be miss leading to talk about voltage for bulk changing. My understanding is that initial, or bulk, changing should use constant current. The voltage should rise until a set amount of current goes to the battery. I've read this current should not exceed C/5 (Ah rating for battery divided by 5). For a 100 Ah battery that would be 20A. As the battery is charged the voltage will rise until it reaches some set point. I've read this point should be 14.4v, but I'm sure this varies. This leaves the battery about 80% changed.

Once this voltage is reached the charger goes into absorption mode. Here the voltage is held constant, again I've read about 14.4v (or so). As the battery charges the current will slowly decrease. This likely varies, but I've heard this should continue until the current falls to about C/100 (Ah rating of battery divided by 100). For a 100 Ah battery this would be 1A. This brings the battery up to about 95% charged.

After the absorption phase the charger goes to float mode, a lower constant voltage. Here I've seen 12.8v to 13.2v. This phase tops off the last 5% and then maintains the battery fully changed.

My stock WFCO and GoPower changers both mention a fixed voltage for bulk changing. I don't think this is optimum. I looked at the specs for the Blue Sky 30 and it seems to follow the above charging scheme. The Blue Sky should be quite a bit quicker to charge a somewhat discharged battery. But once up to about 80% they'll be about the same, and be pretty slow. Unless the absorption voltage on the Blue Sky (or similar) is increased. Likewise, I don't think additional solar panels are likely to speed changing above 80%.

But I also read that wet cell lead acid batteries can be charged at 15.5v in the absorption phase. I'd be worried this may start to boil off water though. It points to the possibility of raising the absorption voltage set point in the Blue Sky which could reduce changing times. Might be worthwhile. Any thoughts?

I'll have to get one of them "hydrometers" and go camping. Or maybe just get a couple of junk novels and go camping. Better yet, take the wife and the dogs and go camping.

Go camping.

[Donna D.]

Originally Posted by currinh

....
I'll have to get one of them "hydrometers" and go camping. Or maybe just get a couple of junk novels and go camping. Better yet, take the wife and the dogs and go camping.

Go camping.

I'm with you! I'm thinking most of us are former tent campers and can "deal" with zero electricity (except maybe CPAP users). If I step inside my trailer and don't have lights? So WHAT! I've got a propane stove, hotwater heater and frig. I'm already AHEAD of being in a tent!