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AGM Mystery Capacity Crash Below 75% SOC UPDATE

BFL13
Explorer II
Explorer II
Update 28 Sep.

I had an issue with one of my AGMs last Spring where it seemed to act well until all of a sudden it crashed under load when below 75% approx. Now they are all doing it.

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29883938.cfm

I decided to wait till Fall to do anything about it all. Well, the other day while camping with the whole bank of 450AH worth (as rated--not actual amount now) everything went well at first--high amp draws on MW, kettle, and toaster, no problem-- until:

Morning voltage 12.7, indicating approx 75% with these batts according to spec sheet, and ran the kettle (90 amps) three times within an hour or so (coffee), no problem with voltage drop or anything, and then toaster 70 amps, and poof! Voltage drop crashed to big amount, inverter quit. Yipes. BUT-- voltage then bounced back to 12.7 and we still had "12v" for all the usual stuff in the RV no problem.

That day, got the batts nearly full via generator and solar and then all the high draw things worked again no problem. Until next morning, same thing again.

A few kettle runs (voltage drop 0.7v each time to 12.2--as low a drop as it ever was when all new, so perfect as the baseline) and then poof! Voltage drop crashed next time, and that was that. Except bounce right back to 12.7 (supposedly about 75% SOC with these batts--and AH count confirmed by -90AH from whatever the capacity really is of the 450 rated.)

And again after that we still had 12v ok at normal low RV voltages for all other things rest of the day--just no high draws allowed.

Ran some tests at home today, and all three AGMs are doing this. Act perfectly with low voltage drops until down to about 75% and then they can't handle high amp draws, but still can do low amp draws.

The change-over is not gradual, but is a drop off a cliff kind of thing for the high amp draws. Ok at low amp draws.

Back when I had old and tired Wet batts, at some point they got so low in capacity (SOC), they could not do the high amps at lower SOC (say 65% instead of down to 50% as before they got tired) without hitting the inverter low voltage. BUT this is way different. There is this sudden crash.

What does it all mean? What has happened inside these AGM batts that makes them do that? (I am not asking what to do, but just want to know what the heck is going on)

Thanks.

PS--I will not attempt the Lifeline recovery thing Mex mentioned in the linked earlier thread. Too scary! And these are not Lifelines that are stronger built than most other AGMs either. So I will toss them if I need to before trying that, even if it would work maybe.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.
68 REPLIES 68

MEXICOWANDERER
Explorer
Explorer
๐Ÿ™‚ LY!
Excellent find. Kudos to the vendor for accurate description and honest caveats.

BFL13
Explorer II
Explorer II
Here is something on full_mosey's AGM:

https://www.osibatteries.com/p-28573-eaton-powerware-pwhr12500w4fr-battery-12v-vrla.aspx

----------

Thanks LY, I will check that out. When I split the bank I can only have the Trimetric on one of the sets at a time, so having the ammeter on the second charger (converter rigged as a portable charger) would be handy for sure if doing two sets at once to speed things up.

I have never understood why they don't put an ammeter on converters same as they have on any portable charger. How hard can it be?

I will be able to use the Trimetric when finishing up the second 27 today, now the Tri is freed up from doing for the other batts. That will show the amps when using the converter at 16 volts after the VEC is done at its 15.8. (the VEC has its own ammeter)

The VEC is down to less than 4 amps when it gets to 15.8, so it won't likely be many amps getting to 16. Find out later today.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

landyacht318
Explorer
Explorer
BFL13, put an ammeter on the output of your adjustable voltage powermax. Best 20$ you will spend this month.

I just bought this one in the 50 amp version for my 40 amp meanwell, ships from Canada, should a got the 100amp:

https://www.ebay.com/itm/50A-100A-Voltage-DC-Voltmeter-Current-Power-Meter-Energy-tester-Charger-Amm...https://www.ebay.com/itm/50A-100A-Voltage-DC-Voltmeter-Current-Power-Meter-Energy-tester-Charger-Ammeter/264288477006?hash=item3d88d21f4e:m:mZfKuBsQ86hjmFx0ncyeQTA

I like the external shunt and the very small clear OLED display.

The amperage is quite accurate, and has a tiny trim pot to dial it in closer.
Voltage on mine reads 0.1v low, which irritates me greatly, but I'll get over it.

Its unidirectional. Just counts juice flowing in one direction. Volts ,amps, watts, amp hours, watt hours, and has an ambient temp sensor on the backside of the display too. I put 45 amp anderson powerpoles on mine input and output, can discharge the battery with a load for x amount of time, note the Ah and WH Flip input and output around, reset it, then charge it, see how much WH and AH it takes before amps taper to 0.5% at Vabs.

Plenty of space in the casing of the Powermax to install the display in a rectangular hole you cut with a dremel and cut off wheel, with lid removed, and while you are in there get rid of the 270 degree potentiometer and install a Bourn's 10 turn potentiometer of the correct value. Makes fine tuning voltage to the 0.01v so much easier than the provided potentiometer.

BFL13
Explorer II
Explorer II
To clarify if needed, my AGMs are not "telecoms" so I don't know how much of this might apply to telecoms. Several members here do have AGM telecoms in their RVs.

On the 20% rule, don't forget that is only for the Bulk stage when under about 75% SOC at the start of the recharge. At about 75%, the acceptance rate at 14.4 volts falls below 20%, so it is impossible to meet that rule after that point. You will go straight into the Absorption Stage and amps will taper.

That is not a bad thing as long as you do go to the final 0.5/100 thing often enough (somehow) when shallow cycling on solar.

I got one 27 back up in SG using Mex's advice. Low and slow all the way to 16v. Took about 18 hours. Started with the VEC1093DBD at 4 amps with Equalize blinking, so it would continue to 15.8. SG was just into the White when that stopped and it said FUL. Then I put on my PowerMax set to 16 volts and ran that for a few hours. Don't know what amps that was. SG came up nicely into the Green, and it is now on Float. Doing second 27 now.

Mex did say that 15.8 is NOT the same as 16!

What a difference from ten years ago fighting with those horrible 27s to get their SGs up into the Green! Sure helps when you know how and have the right equipment. Takes a lot of your time though. Wouldn't be good for a working stiff getting back from camping Sunday night and heading off to work Monday morning!
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

pianotuna
Nomad II
Nomad II
Hi BFL13,

Mine weigh in at 115 lbs. Telecom jars are a surplus acid design. Capacity is 139 amp-hours each.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

full_mosey
Explorer
Explorer
BFL13 wrote:
100lb AGMs sound like 4Ds Some of those can be 200AH, while my 8D at 150 lbs is rated 250AH. AGMs except Lifeline seem to have spec max charging at about 30% charging rate. So 50 amps on 150AH works.

I had the 100AH AGMS for a year before they got in this MH and for the two years since they have been recharged per Mex's rules (20% bulk, 0.5/100) The 8D was second hand so I don't have its history. It has worked ok for a year until this started.

It seems to arise from repeated high amp draws where heat must build up inside and warps or cracks the plates somewhat. One high amp run I can get away with, maybe--we'll learn more about that when next out camping.

The mix of 27s with these AGMs is a quick-fix attempt to get more time with these AGMs before I have to get a new battery set. One of these days I will have four new batteries all the same, and have no more trouble ๐Ÿ™‚


I use them like they are 150Ah. There is a 100lb Lifeline that is 150Ah. They are 13+in long and 11+in tall. I do have a G31 Johnson Controls and these are basically just taller.

I lifted the dinette seat and the label reads 'pwhr12500w4fr'. I have read that as 12V, 500W. I used the 2 with the 1000W inverter and the 4 are used with the 2200W inverter. The spec sheet includes a constant Watt chart.

I cannot meet the 20% rule with the 4. The charger is 75A and the 600Ah total for the 4 would call for 120A to get 20%. Adding 20A solar which usually is not usually coincident is only 95A. However, I am a stickler for getting to .5%.

I will be running capacity tests in Oct. I expect to draw 150A for 2 hours to prove the bank is ready for next year. I too like a silent breakfast. That is extreme though. When I first started using a converter, I was happy to get 80A for 30 minutes from a 79Ah Deka.

The Spartan charger calculates ABS time during Bulk. The time can be from 1 to 12 hours. I can manually restart the Spartan and get an extra 1hr ABS as often as I want.

HTH;
John

BFL13
Explorer II
Explorer II
100lb AGMs sound like 4Ds Some of those can be 200AH, while my 8D at 150 lbs is rated 250AH. AGMs except Lifeline seem to have spec max charging at about 30% charging rate. So 50 amps on 150AH works.

I had the 100AH AGMS for a year before they got in this MH and for the two years since they have been recharged per Mex's rules (20% bulk, 0.5/100) The 8D was second hand so I don't have its history. It has worked ok for a year until this started.

It seems to arise from repeated high amp draws where heat must build up inside and warps or cracks the plates somewhat. One high amp run I can get away with, maybe--we'll learn more about that when next out camping.

The mix of 27s with these AGMs is a quick-fix attempt to get more time with these AGMs before I have to get a new battery set. One of these days I will have four new batteries all the same, and have no more trouble ๐Ÿ™‚
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

full_mosey
Explorer
Explorer
BFL13 wrote:
I do in fact adjust the charging voltage for temperature, so that when camping in February and ambient is 35F, I will set 15.2 instead of 14.7 as in July. The adjustable voltage PowerMax "LK" line of converters lets you do that manually.

My old VEC1093DBD portable charger has built in temperature comp and you can see it working when it operates at higher or lower voltages.
Neither compensates for battery internal temperature though, just ambient.

The AGM guides insist upon temp comp. If you set the spec 14.4 (for 77F) in February at 35F, you will be undercharging the AGM, with no way to see the SG failing to rise to the right amount.


With temp-comp charging, you do not manually set the charge Voltage.

There is no point in discussing SG with AGMs.

If you will read through my linked topic you will see that I use the .5% rule when charging. Float is optional and NOT a valid charging Voltage. You must eventually apply charging Voltage until the .5% rule is achieved.

My solar chargers will repeat and lengthen ABS daily as necessary until the .5% rule is done. I have graphs that show when the solar is falling behind and that is when the genny is used. Charging can be spread out over days within limits.

HTH;
John

full_mosey
Explorer
Explorer
BFL13 wrote:

...

--When doing my capacity testing with Wets at the 20 hr rate,

..


Here's a bit of heresy. I don't know my SOC and my battery specs do not include any AH rating. I do not use an AH meter(fuel guage).

Ok, they are Eaton Powerware label AGMs and weigh 100.2lbs. 100lb AGMs have around 150AH ratings. I work with that. I have a PDF spec sheet but the link to the Eaton website is now broken. The spec sheet lists; 260 full discharges, 800A for 5 sec, 50A charging max, etc.

Apparently they are tel-com pulls. I have two sets; a set of 2 that I have used since 2015, and a set of 4 that I have used since 2018. The batteries are 5+ years old when I get them. The set of two are dated Oct 2009 and the set of 4 are dated Mar 2013. I believe they are UPS type.

When I bought the newer set last year, I also bought a inverter/charger. This his has a conditioning setting similar to the Lifeline 5.5 Conditioning procedure. I used this procedure on each battery before installation in my van.

The older set of two are going into my new TT along with a 1000W/50A Magnum.

I have had 2 AGMs fail since 2009 when I switched. One was a Bass-Pro(Deka 8A24M) and the other a Optima Blue 55AH. Both would only show 10+ Volts at rest after charging. Both failed suddenly and not over a period of time like yours.

I don't mix battery types.

Did you charge yours separately or all together as one big bank?

HTH;
John

BFL13
Explorer II
Explorer II
I do in fact adjust the charging voltage for temperature, so that when camping in February and ambient is 35F, I will set 15.2 instead of 14.7 as in July. The adjustable voltage PowerMax "LK" line of converters lets you do that manually.

My old VEC1093DBD portable charger has built in temperature comp and you can see it working when it operates at higher or lower voltages.
Neither compensates for battery internal temperature though, just ambient.

The AGM guides insist upon temp comp. If you set the spec 14.4 (for 77F) in February at 35F, you will be undercharging the AGM, with no way to see the SG failing to rise to the right amount.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

full_mosey
Explorer
Explorer
BFL13 wrote:
I have always used the same voltage vs SOC at all ambient temperatures. Is that proper?

The AGM loses 15% capacity at freezing vs at rating temp of 77F, so is it still 13.0v when full? BUT at freezing temp, your charging rate of 14.8 is now supposed to be adjusted upwards to 15.2 volts to compensate for the cold. Voltage going opposite directions there maybe.
...


Hi BFL13;

In support of temp-comp charging, I offer link.

I also believe the electrolysis(bubbling/gassing) that is sought after by FLA users, is a waste of charging energy for AGMs, as there is no requirement to stir the electrolyte .I know AGMs are recombinant, but IMHO, that is a recovery process in the event of gassing.

A temp-comp charger should automatically charge faster/cheaper while avoiding electrolosis.

I have looked at the annual temp variance for BC. Your temps are influenced by the Pacific Ocean and do not vary widely like they do in Oklahoma, USA. I need temp-comp. My battery temps can vary 10C inside of 24hrs. I have graphs that show daily charge Volts decreasing automatically while charging is in progress. No set and forget knob twisting will do that.

HTH;
John

BFL13
Explorer II
Explorer II
Interesting results from a mix of 27s with AGMs!

Tried out the mixed bank in a backyard test to see if it was ok to go camping with and not have to come home early.

I have no idea what the bank is in AH with the strange way the AGMs act now, but I chose to run the bank down at 25.5 amps because that is the max using all the lights. 30 amps would be for 600AH, eg. I have 650 as rated total, but can't get that with the "broken" AGMs.

Loaded voltage started at about 12.7 and after five hours it was 12.1, with 127AH drawn. If this were a normal 20 hr rate draw down, the 12.1 loaded would be about right for being at 75% SOC (as seen on previous tests) and the five hours is right. SG of the 27s was 1.265 (was 1.275 at start)

Turned off all lights , no load, immediate bounce back 12.45 so ran a kettle test. 90 amps starting at 12.4-drop to 11.7, was 11.5 when kettle clicked off, bounce back 12.3.

Back to the 25 amps of lights test 12.1 loaded another two hours and voltage 11.9, SG of 27s is 1.200ish (which is 50% SOC)

Wanted to see if it could still do the kettle, and it did, holding at 11.3 before click off-- no crash.

Looking dubious at only 7 hours (instead of 10) to get to 50%, and AH 216, so is "full" only 432? Seems very low.

Disconnected all batteries to take individual bounce back voltages, where 12.4 would be 50% of AGMs and 12.2 for the 27s.

After one hour, the two 27s were at 12.17 and 12.21 so really at 50% confirmed by matching SG numbers.

The two 100AH AGMs (tested in April at 90) were 12.78 for one and 12.69 the other. The 250 was 12.59.

So the AGMs were letting the 27s do the work! But without the 27s added in, no kettle.

So the AGMs were about 75% (by voltage--could be anything actually) while the 27s were at 50% at the end of the test run. Still plenty of camping AH left to go in the AGMs, but the 27s are at 50. If I went further I would still be fine for running things, but the 27s would be taken down below 50 to unknown level.

Puzzle. I need a way to disconnect the 27s and continue (but without high amp draws) just on the AGMs. But how to tell when the 27s are at 50 using the whole bank, unless I take SGs? (No thanks).

I still have the switches where the two AGM 100s can be separated from the 250 so I can recharge them separately, and now that means I can have the 27s and the shaky 250 in one set and the two not as shaky 100s in the other.

One approach might be to start camping with only the 27s and 250 and wait till voltage indicates the 27s are at 50%, then switch so all draws are from the two full 100s, but no high draws allowed. That would give longer till a generator recharge is needed, and keep the 27s above 50%. Total time would be less than using the whole bank at once (Peukert), but gets more out of whatever the AGMs have in them for low amp draws like the furnace and usual RV loads.

Not ideal, but we could probably get by like that until I get new batteries eventually. Have to go camping and find out, now it looks like it ought to work.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

BFL13
Explorer II
Explorer II
Here is some detail of the test I did at home to see if the two 100s did it too or was it just the 250. I see I ran the two 100s as a bank, so not individually as I reported earlier. Batteries were full at beginning according to 0.5/100 method the day before.

Method was use the full kettle with cold water till the kettle clicked off, boiling. Then dump the hot water, rinse with cold, and refill with cold for next run. Numbers from the Trimetric. I took turns so each had a little rest before its next run.

Runs in sequence for the 200 and 250 showing: before start voltage, initial voltage after start (the drop), and voltage when kettle clicked off, immediate bounce back voltage, and time of run. (Time variations probably due to different water temps at start)

Kettle 90 amps was 45% for the 200 as rated, and 36% of the 250. EDIT- when it happened earlier when camping, it was with the whole bank so 90 amps was then 20%.

Run 1.
200- 13.4, 12.4, 12.1, 12.9, 9 minutes
250- 13.0, 11.9, 11.9, 12.9, 8 minutes

Run 2
200- 13.0, 12.1, 12.0, 12.8, 9 minutes
250- 12.9, 11.9, 11.8, 12.8, 10 minutes\

Run 3
200- 12.9, 12.0, 11.8, 12.7, 8 minutes
250- 12.8, 11.8, 11.6, 12.5, 10 minutes

Run 4
200- 12.8, 11.7, rapid drop to 11.1, 3 minutes inverter quit 10.3v
250- 12.7, 11.6, rapid drop to 11.1, 4 minutes inverter quit 10.3v

Separated the two 100s and resting no loads --45 minutes later-- voltages : 250- 12.77, 100(1)- 12.76, 100(2)- 12.82

( 13.0 is full, 12.4 is 50%, 12.7 is about 75% resting.

Notes:
Run 4 initial voltage drop seemed ok, but then the running voltage drop fell right off

Run 3 showed first sign of trouble with the 250

Similar results for the 200 and 250 but with 45% vs 36% draws indicate the 250 is in worse shape than the two 100s? But they all did it whatever shape they are in.

One of the 100s might be in better shape than the other based on the 45 minute bounce back voltages.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

landyacht318
Explorer
Explorer
Was it this thread that the topic of constant current loading was discussed?

This item claims to be a constant current device no matter the battery voltage.



If it works as described, one just needs the 77 degree water bath to achieve accurate capacity results.

https://www.ebay.com/itm/150W-200V-20A-Constant-Current-Electronic-Load-Battery-Discharge-Capacity-T...