AGM Charging Questions

[crayiii]

Originally Posted by a64pilot

So, did you ever get to float yesterday and what was the acceptance rate when you did?

One controller went into float when the house load dipped at times. The other controller spent most of the day in bulk. We ran the ice maker and watermaker a bunch.

The lowest voltage we recorded overnight was 12.53 and that was while we were pulling 20 amps out of the bank.

I used the microwave this morning and pulled 80 amps with 10 going in from solar and the voltage dropped to 12.38 after one minute.

[smac999]

Originally Posted by crayiii

I'm at absorption voltage 14.25 today at 11:30. There is currently 36 amps being accepted by the batteries.

Why is your absorb voltage so low? That is gel values. Agm should take more then that. Some will take 14.7. Increase the voltage and the amps will go up. Right now that is the max the batteries will take at that voltage level and that soc level. You’re probably at 95% or so. And it will take a long time to reach 100. No mater how big the solar or charger. This is where lithium shines.

If you were down at 50-80 % you should be taking the full current of the solar. Once you get above that the batteries will start to take less and less

[crayiii]

Originally Posted by smac999

Why is your absorb voltage so low? That is gel values. Agm should take more then that. Some will take 14.7. Increase the voltage and the amps will go up.

That's what Mastervolt specifies. https://www.mastervolt.com/charging-batteries/

[a64pilot]

Originally Posted by crayiii

One controller went into float when the house load dipped at times. The other controller spent most of the day in bulk. We ran the ice maker and watermaker a bunch.

The lowest voltage we recorded overnight was 12.53 and that was while we were pulling 20 amps out of the bank.

I used the microwave this morning and pulled 80 amps with 10 going in from solar and the voltage dropped to 12.38 after one minute.

What was the batteries acceptance in amps by the end of the day while in absorption?
Meaning output of panels, minus consumption.

So if panels are outputting 30 amps and the boat is using 10, then acceptance is of course 20 amps, I don’t believe your charged until it’s less than 5.

I don’t believe your getting fully charged. Forget all the volts and amps your watching, those don’t really tell much, however the acceptance rate at the time you drop to float does, and is the only indicator for charge you can get on an AGM as you can’t check specific gravity.

So what does the manufacturer of your batteries say your absorption voltage is? My Lifelines for example it’s 14.3. Some may be higher.

Also the controller that’s dropping float early isn’t helping you.


Try this, lock them into absorption voltage by whatever means, one way is to set float to absorption voltage, then see how low your acceptance amps get at the end of the day.
Even if you stay in absorption for an extra hour or two it’s not going to hurt anything, especially if just once.

[Sternwake]

When batteries age it takes less amperage, for a lesser duration before they hit absorption voltage. They hit absorption at a lower state of charge, BUT the absorption stage also takes longer for amps to taper to the prescribed 'full' level at absorption voltage, even though their total capacity is lower and one 'might' think lesser total capacity means less time to reach full charge.

Fact is, as AGM batteries age, the amps taper slower and slower towards the magic threshold of 0.5A per 100Ah of capacity, when held a absorption voltage, and near end of life batteries might never have amperage at absorption voltage taper that low, but bottom out somewhere above that, and start rising while the battery heats.
Got to find the amperage floor at absorption voltage, and switch to temp compensated float then before they start rising again along with battery temperature.

If the solar controller's absorption stage is set for X amount of time, instead of float being triggered by an amperage threshold, and this time is NOT extended as the batteries age, then they start aging faster, losing capacity faster, faster than they need to.

So the batteries in question, are likely sulfated.

I am of the opinion Sulfated AGMs stand the best chance of potentially recovering capacity, not by bringing them to equalization voltages from already 'high' states of charge, but by discharging them way low relatively rapidly, and then instantly hitting them with as much amperage as one can muster, and hopefully this is at least 30 amps per 100AH of capacity, and preferably more, much more..

The high amps held for longer heats the battery helping to dissolve the sulfation.

In my Experience with Northstar TPPL AGMS, this is a restorative slap in the face, and when I notice lower voltage than expected for Ah removed under X amount of load, I often increase the DC loads and intentionally bring the battery to 11 volts or less, an then instantly hammer them with high amps to 14.7v and keep its temperature under 105f, which is no issue as long as I start out under 85f, but nearer end of life can become one.

After such treatment not only is my expected performance returned, but the amps taper to 0.5% of capacity faster than the day before too, meaning instead of say 4 hours absorption it is back down to 3.25.

I believe Firefly mentions the high amp restorative recharge regimen too, as it heats the plates.

I've not tried Lifelines EQ procedure, 15.5v for 8 hours after regular 'full charge' as the high amps from low states of charge was always effective in my use. However I avoid chronic undercharging as much as is possible and have not personally cycled a Lifeline to this point.

The TPPL AGMS seem to not appreciate low and slow solar only recharge regimens, even if amps taper to 0.5% of capacity at absorption voltage day after day. No close experience with regularly deep cycling other large AGMS so no comment, but I have my suspicions.

My opinion is AGMs make for poor solar only recharge batteries, unless they can somewhat regularly be hit with high amps from their most depleted state. Solar does not qualify, as it slowly ramps up to solar noon. I equate this to being forced to breathe through a cocktail straw after running a sprint while holding one's breathe. Battery cruelty/ torture.

Prevention of sulfation by insuring full charges when the sun is still shining, is easier than trying to restore capacity after the fact. 15 minutes of a capable alternator early morning when batteries are most depleted, can shave 2 or more hours off the time it takes the solar to reach absorption and give the batteries not only the time they need in absorption but then several more hours in float wile amperage tapers towards zero.

One has to insure ones charging source holds AGMS at absorption voltage for the proper duration, A duration which changes as the batteries age/ accumulate cycles, and it's likely AGMS are more susceptible to capacity loss when 'good enough' = 98% charged, compared to flooded deep cycles all other factors being equal.

If 30+ amps per 100Ah of 'when new' capacity, applied from a well depleted state, cannot be accomplished with one's charging sources, lower the capacity one is trying to high amp recharge at once.

Monitor battery for excessive heating, as once it starts it accelerates and stop if it gets to 120F, I try to stop at 105f, but have seen 111.5f. It shot there quickly from 102f.

Obviously such a regimen is not to be done each and every recharge.

The batteries in question are showing they are not happy. One might no be able to restore lost capacity, or much of it, but one can slow further decline, instead of having the capacity decline accelerate.

Seems when most lead acid deep cyclers notice capacity decline, it is too late to really slow it down appreciably though, much less restore any.
Depends on the skills and measuring tools of the observer as well as the tools required to perform any capacity restorative procedures, which might or might not be effective.

One figure that I find enlightening with smaller batteries and big charging sources is what I call 'quench charging' ..... How many amps does it take to reach absorption voltage instantly, from low states of charge.

My group 31 103AH Northstar AGM is somewhere well over 138 amps with about 130 deep cycles on it, many of those to well below 50% SOC. I can't muster more than 138amps to find out what the quench amperage is, and I'm hoping it is many hundreds more deep cycles before 138 amps is enough, but figure that's unlikely. Time will tell.


One other observation when quench charging, is 138 amps brings battery voltage quickly to 14.4, but then as amps remain at 138, voltage at battery terminals falls back to 13.9v and then from there climbs again towards 14.7v, over about a period of 6 to 7 minutes of 138 amps.
If I were only shooting for 14.4v when attempting 'quench charging', it would appear to happen nearly instantly. That voltage decline was certainly a surprise, and I've seen it occur on both flooded marine batteries and AGM when doing this with large charging sources an not a huge amount of still healthy battery capacity.


I've some small Asian AGMS, one 18AH the other (newer) is 22AH. Their 'quench' amperage when well depleted, is currently 42 and 57 amps. Their cases say 5.4 and 6.6 amps maximum. I usually aim to only double this 'maximum' charge rate, as 42 amps quickly tapers to ~25 and then slowly tapers. 57 tapers to ~35 quickly and then slowly tapers from there. and I do get a bit nervous hitting them with ~5 to 6 times the recommended maximum amperage rate when there is no reason to do so.

On the opposite end of the spectrum My previous Northstar-27( 6.5 years old and 1400+ deep cycles at this point, is now a workshop floor battery/buffer/filter/paperweight and somewhere under 10AH of remaining capacity. When depleted to 10.5v and quench charging it, hooked to 100 amps of power supply set to 14.7v, it rises there instantly with just 9 amps and quickly tapers. It heats up rapidly too.

I rarely turn the power supply up much more than 13.6v now on this battery. I closely watched 'quench' amperage taper on this battery for most of its final 4.5 years of life. Its removal from service was not a shocking event when it occurred, other than it took longer than expected.


One thing about draining a sulfated battery low quickly quickly with high amps, performing a high amp recharge, is one can test the efficacy of the high amp full charge by duplicating the initial discharge rate and comparing performance post high amp recharge to full, measure the time it takes to hit say 11.0v, or 10.0v like Odyssey AGMs reconditioning procedure states

https://www.odysseybattery.com/wp-co..._Procedure.pdf

I've not sucked my Northstars quite that low.

[crayiii]

I think I may be putting too much trust into the battery monitor. I've done my best to set it up but I may have been too conservative on the charge efficiency and reset parameters resulting in a SOC % being too low.

Yesterday was cloudy and I purposely ran the batteries down more than normal in the evening and overnight. Then this morning it was foggy until about an hour ago so I know they got used more than normal. Even so, 12.39 (while there was a 18amp draw) was the lowest the voltage got to.

Now, at 11am and still foggy, solar is putting in 48 amps. I'm guessing that when the monitor has been reading 65%, it must actually be a bit higher.

[smac999]

battery monitors need to be plugged into a dock often for full recharging and resetting to be accurate they will drift more and more off if they never get to full. solar will reset them to 100% sometimes too early.

[crayiii]

Originally Posted by smac999

battery monitors need to be plugged into a dock often for full recharging and resetting to be accurate they will drift more and more off if they never get to full. solar will reset them to 100% sometimes too early.

I set very conservative values in the monitor so it never resets when in solar alone.

I have 675 ah of capacity and the batteries are 6 months old. My settings in the monitor are as follows.

Capacity - 650ah
Charged voltage - 14.2
Tail current - 0.50%
Charged detection time - 3m
Peukert exponent - 1.25
Charge efficiency factor - 90%

I think this is resulting in the SOC displayed on the monitor to be lower than actual.

This morning it showed 57% and 12.44v. There was no charge sources active and 15 amps was being drawn. When I shut the loads off, voltage went up to 12.67.

[Sternwake]

That tail current setting of 0.5%, are amps actually tapering to 3.25 @ 14.25v before it reverts to float voltage?



When I first got solar and was new to it all, I thought my 'float current' was not a threshold at which it switched from absorption to float, but that i could control how much to feed the batteries in float.

Of course it does not work this way and that first set of batteries died a very premature death, because as soon as my solar got these batteries to absorption voltage, it switched to float.

Make sure this is not occurring.

[crayiii]

Started the generator this morning and the batteries took 80 amps (max for the charger) so, I'm thinking everything is working the way it should.

[Tikitour]

I recently bought 3X Lifeline 210amp AGM batteries for my sailboat. I am a full time liveaboard so I am constantly using the batteries. I use a wind generator and 315 watts of solar to charge them and I want to make sure that I am charging them properly. I use roughly 50-60amps during the night and I find most days I am able to top them back up to %100 according to the master volt charge controller. However I am finding that the charge controller never goes into float. Is this a problem even though I have replaced all the owing amps? The charge controller during the day will go between acceptance and bulk charging depending on the charging volts. If a cloud shades out the solar panels it will drop back into bulk and I assume to reach a float status I have to be in acceptance for a measured period of time, which I am not able to reach due to the charge going between bulk and acceptance. My other question is at times I won’t replace all the owing amps because the charge controller will go into acceptance to early and at a decreased rate of charge I cannot replace the owing amps. Is this normal? Also is there anything I need to be doing to maintain my AGMs. Thanks in advance