What is "Absorption Time" with AGM battery charging?

[Free Agent]

I have the Pro Mariner charger set to AGM (glass mat) batteries, and it wants to know what absorption time I desire from 1 to 4 hours option.

The ProMariner owners manual just says contact the battery MFG for absorption time.
I get no response from Optima either writing or on their website. "Optima Jim" seems to have vanished as well.

This particular battery bank is four 12V, 31M lite gray Bluetops.

Anyone have a clue of what I should set absorption time at?
And what the hell is Absorption Time?

[noelex 77]

Absorption time is the time the charger will hold the batteries at the bulk voltage.

If we start with a flat battery the battery charger will put all the current into the battery it can and the battery voltage slowly rises. When the voltage hits the bulk voltage charge point say 14.7v the charger will hold the voltage at this level for a certain time , the absorption time. After the absorption time has past with the battery kept at 14.7v the charger will drop back to the float voltage.

If you cannot get the information from the battery manufacturer,2 hours is a typical absorption time. Start with this and see what current is going into the battery ( not the total current becase some will be suppling loads) at the end of this time, just before it drops back to float.
It should be about 2% of the battery capacity in amp hours. If the current is more increase the absorption time and vice versa.
The absorption time is not as critical as the bulk and float voltages. So generally 2 hours will be near enough

[Free Agent]

Thank you.
Really appreciate the response.

[GordMay]

You’ll have to determine your absorption cycle time by trial & error. Start with less (1 hr) and increase as necessary.

Generally, the absorption charge cycle should continue until current to the battery declines to about 2% of battery capacity in Amp-hours.

Optima specifies charging until current drops to 1 Amp.
➥ Optima Battery Charging - AGM Battery Charging

[sailinglegend]

Originally Posted by GordMay

.....Generally, the absorption charge cycle should continue until current to the battery declines to about 2% of battery capacity in Amp-hours.

Lifeline say 0.5% of battery capacity for a 100% charge.

[Journeyman]

For other AGM batteries such as Odyssey AGM TPPL batteries it is 0.001C10 or 8 hours. According to their manual if I am reading it right.


This would mean 0.80A for an 800Ah bank.



However the implication is that if the 0.001C10 is not met after 8 hours you are not fully charged.


I presume that would occur much later during the Float mode's trickle charge?



Note that when programming a battery charger typically you set a minimum Bulk time and and a maximum Absorption time.


This creates a dilemma since once charged to Float (or at any time in the process) if you disconnect the charger and reconnect it, the charging process starts over from the beginning.


And if you have a charger that does not sense charging current, and can only rely on a Absorption timer, the fully charged battery will hold at Absorption voltage for the full timer value. In the Oyssey case, that is 8 hours.


Picture a glitching shore power supply while you are away for a month that has your battery bank continually at the high Absorption voltage.


Is this detrimentally overcharging the battery? Ask your manufacturer I guess.

[noelex 77]

Originally Posted by Journeyman

For other AGM batteries such as Odyssey AGM TPPL batteries it is 0.001C10 or 8 hours. According to their manual if I am reading it right.


T.

This is the requirements for a fully charged battery. Battery manufufacures like to specify this very high because it means they can claim maximum capacity. It is not the recommended point to terminate the absorption phase, the charging will continue slowly in the float phase. I don't even know of a charger that could be set with an 8 hour absorption time.

I do agree however that enering the bulk phase even for only 2 hours is not good if the battery is fully charged. Some of the better battery chargers will check battery voltage on start up. If the voltage is high they will enter float mode rather than bulk mode. Using return amps is even better, but few chargers do this.

[goboatingnow]

A charger cannot "enter bulk phase" if the battery is charged no matter what it does. bulk phase is a battery SOC state not anything the charger does. ( even if it's twinkles all the LEDs on the front to say differently )

Dave

[noelex 77]

Originally Posted by goboatingnow

A charger cannot "enter bulk phase" if the battery is charged no matter what it does. bulk phase is a battery SOC state not anything the charger does. ( even if it's twinkles all the LEDs on the front to say differently )

Dave

So when a charger or solar regulator is in the phase formally known as the ""bulk phase". What do we call it?

I thought something along the lines of:

"the phase when the charger is rasing the battery voltage towards it's highest voltage, excluding the even higher voltage that we used to call the equalisation voltage"

I think it might be a bit wordy and confusing, but I am open to suggestions