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AGM battery equalisation


ya_fohi
 

Hi all,

I have what seems to be a charging issue with my West Marine AGM92 batteries. They do not seem to be accepting a charge past about 75% capacity. They are 4.5 years old. Am I correct in that these batteries can be equalised? Would this solve the problem? If so would anyone know for how long equalisation should be carried out for and at wht voltage?

Cheers,
Paul
Ya Fohi - Amel 54 #98



greatketch@...
 

Paul,

I won't comment on the West Marine brand specifically, but MOST AGM batteries can not be safely equalized.

But... you are likely being mislead by your instruments.  Your battery meter measures the [Amps into the battery] and [Amps out] multiplies by an [efficiency factor] and subtracts to calculate [Amps used], and then divides by the size of the battery bank that was entered when it was setup.  Very small errors in this calculation can add up over time to cause the meter to miss report the state of charge. There is no way this kind of meter will actually measure a decline in capacity of the batteries, in its calculation it ALWAYS uses the battery capacity that was initially entered into its memory.

Best thing to do is to fully charge the batteries. Plug in to shore power and run the battery charger overnight at least, if that is possible. Then reset the meter to read 100% charge.  Your only real way to measure the capacity of the batteries is to draw them down, and watch the voltage drop.  If the voltage is lower than it used to be when the meter reports a "50%" state of charge, then that reflects a decline in capacity.

Bill Kinney
SM160, Harmonie
Georgetown, Great Exuma Is., Bahamas


---In amelyachtowners@..., <sharongbrown@...> wrote :

Hi all,

I have what seems to be a charging issue with my West Marine AGM92 batteries. They do not seem to be accepting a charge past about 75% capacity. They are 4.5 years old. Am I correct in that these batteries can be equalised? Would this solve the problem? If so would anyone know for how long equalisation should be carried out for and at wht voltage?

Cheers,
Paul
Ya Fohi - Amel 54 #98



ya_fohi
 

Bill,

Thanks for your feedback. I have charged the batteries for three days then disconnected. I then measured the initial voltage after disconnection then again after at least 12 hours. They all show a drop of 0.1 - 0.2 V over that period, and their final voltages range between 12.3 and 12.7V which according to my lookup table is between 69% and 88% capacity. I guess that after fouir years I expect some loss of capacity, but should I be comcerned? Is ther a chance that the low ones may be drawing down the good ones and so should I replace/remove them?

Cheers,
Paul


Alan Leslie
 

Paul,
My advice and that of others is that if you are going to replace the batteries, you should replace all of them at the same time.
The low voltage batteries will certainly drain power from the higher voltage ones and in the process they will all fail at some point.
Any series/parallel battery arrangement at least needs to have e.g. in a 24v system of paralled banks of 2 x 12v batteries in series all the mid points of those series units connected together to try to balance the voltages across each battery and best to also install a battery balancer that will ensure that mid point stays at half whatever the charging voltage is.
We have this arrangement but with 4 x 6v batteries in series and 3 banks of those paralleled. The batteries are AGM and they have been in the boat for 5 years this April with no noticeable loss of capacity - yet.
Cheers
Alan
Elyse SM437


greatketch@...
 

I agree with Alan, a difference in voltage of 0.4 indicates a serious imbalance on the batteries pairs.  Normal AGM batteries are especially sensitive to chronic undercharging, and the batteries that are at 12.3 volts likely haven't been brought up to full charge for a while.

Bill Kinney