Absorbtion Time for AGMs

[Maine Sail]

Originally Posted by a64pilot

You were the one I believe that pointed out that bulk was just a charger trying to get to absorption voltage but could not due to it was current limited, and in fact nothing happens, no difference In programming etc occurs when the charger hits voltage set point and current begins to drop, just it hit its voltage set point was all.
That in fact a three stage charger was actually two stage?
Float is a maintainer voltage, very little charging occurs in float, that the bank should be ideally 100% charged prior to float?
Did I not understand?

On edit, I guess a time will start once absorption voltage is reached if termination is to be done by time

No what I said was that a "bulk charging voltage" meaning "constant voltage" or voltage held steady is NOT bulk or constant current charging it is CV.

You can have bulk charging = CC or constant current or max current source potential

You can have a bulk transition voltage = where the charger moves from constant current to constant voltage.

You can have absorption charging = CV or constant voltage charging

You can have float charging = CV or constant voltage charging

You can have equalization charging = CV or constant voltage charging

What you can't have is "bulk charging" where voltage is held steady because this is constant voltage charging and bulk is constant current or the max current potential of the charge source.. In bulk charging the battery voltage is always rising.

[belizesailor]

This discussion has left me with the following impression: using ABT to end absorption phase is rubbish. Absorption phase should be ended based on a low end threshold of current acceptance. ABT is really only useful as a safety mechanism to prevent indefinately pushing juice into a battery that will never reach end of absorbtion phase state and then possibly be damaged (further...because it likely already is degraded/damaged and thus wont fully charge).

None of my current regulators/chargers do this (and all are all highly regarded brands). Any out there that do?

[conachair]

Originally Posted by belizesailor

This discussion has left me with the following impression: using ABT to end absorption phase is rubbish. Absorption phase should be ended based on a low end threshold of current acceptance. ABT is really only useful as a safety mechanism to prevent indefinately pushing juice into a battery that will never reach end of absorbtion phase state and then possibly be damaged (further...because it likely already is degraded/damaged and thus wont fully charge).

None of my current regulators/chargers do this (and all are all highly regarded brands). Any out there that do?

Never seen one, amps going out of the charging source isn't really any good as the charger has no idea where the current is going, batteries could be fully charged but still with some current from the charger running the laptop/fridge etc so charger thinks it still needs to charge more.

[belizesailor]

Originally Posted by conachair

Never seen one, amps going out of the charging source isn't really any good as the charger has no idea where the current is going, batteries could be fully charged but still with some current from the charger running the laptop/fridge etc so charger thinks it still needs to charge more.

Charging a loaded battery complicates matters so maybe why most dont do this. BlueSky offers the option (absorption end on low acceptance) if used with their BMS. Presumably there are more sensors/smarts in the BMS so it has a handle on current in and out.

Both my Next Step and BlueSky will switch from absorption back to bulk if acceptance increases (like when a load is applied) so they have some sort of current acceptance based threshold behavior built in.

[belizesailor]

Originally Posted by Adelie

I was starting to wonder if you were looking at a different document.

The one I linked to is the general one on the Lifeline website.

I downloaded my copy (version D) just a few months ago when considering battery choices. Version E, the one you posted, was released 2/17.

The table they added is at least an official recommendation, but like any guesstimate of ABT it falls short...really they give an arbitrary number of hours with no specifics regarding charger capacity etc. So in the end its ptetty bogus too.

Im guessing a discussion much like this one ensued at LifeLine and someone finally decided: " screw it, put x hours in there".

[boatbod]

Originally Posted by ranger42c

The Lifeline manual recommends 14.3V plus/minus .1V at 77°F (25°C).

Maybe your normal temperature conditions are different from that?

-Chris

I know what the published paperwork says, but I urge you to call Lifeline, describe how you plan on using the boat and then see what they say. Some years ago I followed those written instructions and it nearly cost me 4 batteries in 5 months. Spoke to tech support and they said charge them harder!

[john61ct]

Originally Posted by belizesailor

using ABT to end absorption phase is rubbish

I've seen a more sophisticated setting, where ABT is varied as a factor of the time it took Bulk to get up to CV, so a more depleted battery or poor insolation conditions means longer time held at Absorb.

But yes, based on declining current to the bank is much better.

Originally Posted by belizesailor

Any out there that do?

I've got a Bogart Trimetric shunt-based coulomb-counting battery monitor coming that can act as the charging brains for a solar controller SC-2030

I reckon the likes of Victron, MasterVolt, Xantrex, Redarc must do something similar with their "integrated solutions" at the​ high end.

Also check out ​MidNite Solar KID or Classic unit with their Whizbang Jr

[belizesailor]

Originally Posted by john61ct

...

I've got a Bogart Trimetric shunt-based coulomb-counting battery monitor ...

Wow, that sounds impressive...like the Time Domain Reflectometer I used to try to slip in the budget that always got vetoed. [emoji30]

Im not going to replace my controllers over this...they kept the last bank alive for 12 years...with factory default ABT...so pragmatically its not proven to be a big consideration for me.

Most others here have basically said..."set it to x hours"...totally arbitrary, but its also worked for them.

But it will be on my list should I need to replace a controller in the future.

[a64pilot]

Originally Posted by belizesailor

None of my current regulators/chargers do this (and all are all highly regarded brands). Any out there that do?

]
My Outback 80 will end absorption based on charge acceptance rate or I believe time as well. I think. Truth is I program both float and absorption voltage at 14.4 and leave them there when I am not plugged into shorepower, I have never been able to quite yet get to 100% SOC on Solar alone, but I am a heavy electrical user. When plugged into shorepower I program both absorption and float to 13.3V. I see no need in starting out at absorption every morning when the bank is already at 100% SOC

I think my Balmar 614 does, although it is real new to me so not sure. I have yet to program it, I have it at its own AGM program now.

My Sterling Pro Charge Ultra I think does, although I'll admit what it uses I'm not sure, it does seem to prematurely kick into float though, turning it off and back on resets the cycle and it will stay in absorption then until 100% SOC. You can't change its programming as far as ending absorption, so whatever it uses, your stuck with

My Magnum 2812 inverter charger is programmable to end absorption at either time or charge rate.


However due to the ever changing house loads, even ending at acceptance rate is not always perfect. I generally have about a 10 amp house draw, but that varies of course based on fridge cycling on and off and other things, the only way to be perfect with ending charge cycle at acceptance rate is to have no house load.
I just watch it, if I see house load at 10 amps, and battery charge acceptance rate is 13 or so, time to drop into float.

[a64pilot]

I am curious though, since got 12 years out of a Gel bank with your set up, why did you change to AGM?

[belizesailor]

Originally Posted by a64pilot

I am curious though, since got 12 years out of a Gel bank with your set up, why did you change to AGM?

Local availability.

[john61ct]

Originally Posted by belizesailor

Wow, that sounds impressive...like the Time Domain Reflectometer I used to try to slip in the budget that always got vetoed. [emoji30]

Im not going to replace my controllers over this...

Not saying you should, but open forum discussion are for everyone to learn from, and I'm hoping some other options for current-based charge termination will come out of this one.

I just clarified the type of BM to distinguish from ones like SmartGauge which don't count amps in/out.

BTW I used TDRs every day as a campus data network geek, you can get rough but good-enough ones for just a couple hundred these days. Don't see the need on a boat though 8-)

[john61ct]

Originally Posted by a64pilot

the only way to be perfect with ending charge cycle at acceptance rate is to have no house load.

As discussed a bit above, a monitor with its shunt mounted on a separate charge buss at the battery should​ avoid that problem.

[a64pilot]

Originally Posted by john61ct

As discussed a bit above, a monitor with its shunt mounted on a separate charge buss at the battery should​ avoid that problem.

I don't understand how, any current removed from a battery will actually come from the charging source when its being charged, the charger will see both the charging load and whatever else is being drawn from the bank.
I guess you could connect the house load to the other bank and charge one bank at a time if you were really anal about it.

[john61ct]

No, two separate lead House banks is in general really not a good idea. My understanding is that the charging source at higher voltage is carrying the loads, nothing is actually coming from the battery while the loads' needs are lower than the source's output current.

The charge controller's shunt is placed so only the "remainder current" going into the bank is measured, and thus charging can be terminated when that drops to endCurrent, .005C or .002C, whatever mfg specs.