Absorbtion Time for AGMs

[belizesailor]

I recently retired my venerable old house bank gel cells (12 years old!) and replaced with AGMs (LifeLine GPL-8DA x 2).

Now Im reconfiguring my charge controllers (alternators: NS2, Solar: BlueSky 3000i, shore power: Freedom 20...even more ancient than the gel batteries).

LifeLine recommends 14.3 absorption voltage, 13.3 float, but no specific suggestions on ABT.

Pretty straight forward otherwise, but looking for input on setting Absorption Time (ABT).

Recommended ABT for AGMs?

Vary ABT by charge source (alt, solar, shore)?

[belizesailor]

A few more specifics:

Alternators 65A x 2 on twin engines each controlled by its own NS2 regulator.

Solar 3 x 125W panels. Max charge output of 3000i controller is 30A, but normally dont hit that max except in near perfect mid day conditions. Usually more like 15-20A.

Shore power charger, max of 100A.

[Adelie]

My understanding is that absorption ends and float begins at a specific current rather than after a specific time. The battery manufacturer usually specifies the current.

The GPL manual from Lifeline is here: http://lifelinebatteries.com/wp-cont...cal-Manual.pdf.
Table of Contents say pg 19 for charging.

Need more help, get back to us with a quote from the manual.

[a64pilot]

Absorption time will be based on depth of discharge so no way to give you a direct answer
I have mine set at 4 hours. I came to that number by watching charge amps though, your time may be shorter or longer. I think an extra hour won't hurt but an hour short over time will.
Just my opinion

[a64pilot]

Just Solar unlikely you will ever get to float .
I just watch my charge current once my charge rate gets to .5% bank capacity plus house load the time for float.

[belizesailor]

Originally Posted by Adelie

My understanding is that absorption ends and float begins at a specific current rather than after a specific time. The battery manufacturer usually specifies the current.

The GPL manual from Lifeline is here: http://lifelinebatteries.com/wp-cont...cal-Manual.pdf.
Table of Contents say pg 19 for charging.

Need more help, get back to us with a quote from the manual.

Actually....all my regulators have both an ABT and an ABV (Absotption Voltage) parameter setting. Absorption ends on all of the regulators when EITHER parameter (time or voltage) is met.

As you so helpfully point out, the LifeLine manual (which Ive already read of course) does not specify an ABT limit only ABV. To paraphrase from the LifeLine manual, and quote from my original post:

"LifeLine recommends 14.3 absorption voltage, 13.3 float, but no specific suggestions on ABT."

Thus my question.

[ranger58sb]

Ask Lifeline? They've kindly answered my questions in the past...

-Chris

[Adelie]

Originally Posted by belizesailor

Actually....all my regulators have both an ABT and an ABV (Absotption Voltage) parameter setting. Absorption ends on all of the regulators when EITHER parameter (time or voltage) is met.

As you so helpfully point out, the LifeLine manual (which Ive already read of course) does not specify an ABT limit only ABV. To paraphrase from the LifeLine manual, and quote from my original post:

"LifeLine recommends 14.3 absorption voltage, 13.3 float, but no specific suggestions on ABT."

Thus my question.

The info is there, read the WHOLE section on charging starting at pg 19.

[Sea Lyon]

I have a 800 amp/hr bank of Lifeline batteries. Lifeline says the batteries are fully charged when batteries except .5 percent amp of total bank capacity at asportion voltage. That is 4 amp for us. It takes several hours to get here, we sometimes run the generator early morning then charge with 410 watts of solar. Late in the spring with longer days we sometimes get down to 4 amps but not consistently. I find in easy to get down to 6 to 8 amps. That last bit is tough!We have absorption set for 4 hours.

[a64pilot]

Ideally the charge for Lifeline batteries should end at .5% of the banks rated capacity, my 660 AH bank should go into float when charge rate is 3.3 amps for example. Of course you have to add your house draw to that, so if You draw 10 amps then absorption should end at 13.3 in that case.
However not all controllers can be set to end at a charge rate, some may can only go by time.
The wild cards on using time are of course charger size and depth of discharge of the bank.
Your just going I think have to watch your charge rate to determine an average time for your bank, too many variables for one answer to be correct, and indeed it may vary from one day to the next depending on depth of discharge, available Solar and house loads too.
However being an AGM bank which isn't real tolerant of PSOC cycling, if you err, I'd err a little towards extra time at absorption as opposed to regularly ending charge early.

Unlikely for you to regularly reach a fully charged status on Solar alone, likely you will never get to float

[belizesailor]

Originally Posted by Adelie

The info is there, read the WHOLE section on charging starting at pg 19.

As stated, I have, and my reading comprehension is quite good. The LifeLine manual does indeed give a formula for "time to reach full charge", but this formula is for total time, not just ABT.

Per the manual:

"The time to reach full charge at temperatures in the range of 68 to 86°F (20-30°C) can be estimated from the following equation:
Time to Reach Full Charge = [(DOD/100) x Rated Capacity (Ah) ÷ Rated Output of Charger (Amp)] + 2 hours."

In the case of my installation, if we assume DOD is normally never below 50% and use the combined 20h rating of both batteries (255 + 255) then we can just use a constant of 255 for the first part of the equation.

My alternators are derated slightly to keep from baking them and Ive never seen more than about 120A total output so Im using that for combined alternator charge capacity.

Calculated time to full charge:

Alternators: 255÷120+2 = 4.125
Solar: 255÷30+2 = 10.5
Shore: 255÷100+2 = 4.55

Since this formula includes bulk charge time, Im going to assume it gives in effect a worse case scenario for ABT and set ABT to the above values (as close as I can anyway)...I may later adjust based on observations.

[a64pilot]

Also take a look at Maine Sails site, in it he does a comparison of time to full charge for a Lifeline battery with a couple of different sized chargers.
It may help to know that there is really no such thing as bulk, bulk is nothing more than absorption, but due to limited Charger size, absorption voltage is unachievable. Also "full" is of course the end of absorption, so it could be said that there really is only one stage of charging, absorption.
4.5 hours or so for a bank in very good condition from 50% is darned close, however most of us won't go all the way to 50% so maybe 4 hours?
As a bank ages the time to charge increases of course.

[belizesailor]

Originally Posted by a64pilot

...
The wild cards on using time are of course charger size and depth of discharge of the bank.
...

Yes, purely for charging purposes a single value ABT is an over simplification. I think ABT as used by most chargers/regulators is really more of a safety mechanism so that you just dont indefinately pump juice into a battery that is never going to reach ABV...and thus potentially damage the battery (further).

A question I will follow up with the regulator makers about.

[a64pilot]

I'm confused by your use of ABV?
I understand absorption voltage of course, for us it's 14.3 but don't understand how voltage is used to terminate charging?

[belizesailor]

Originally Posted by belizesailor

Yes, purely for charging purposes a single value ABT is an over simplification. I think ABT as used by most chargers/regulators is really more of a safety mechanism so that you just dont indefinately pump juice into a battery [snip] ...and thus potentially damage the battery (further).

A question I will follow up with the regulator makers about.

I stated that incorrectly....just scratch the "...never reach ABV..." part of the original post.

Both my NS2 and 3000i will step down current as needed to maintain ABV at set point (14.3 in this case) until ABT expires.

I think ABT limit is there so the regulator does not just keep pushing current (though be it small) at the battery...potentially overcharging.

At ABT expiry the regulators switch to float.

With an optional battery monitor component, the 3000i will switch from absorption to float when a preset current level is reached (factory default = 1.5 amps). This is a much better way to handle it I think and should be easy to implement...be interesting to know why more regulator/charge manufacturers dont do this.