AGM Battery charging woes please help

Submitted: Thursday, Oct 02, 2008 at 18:26

ThreadID: 62218 Views:5047 Replies:6 FollowUps:22

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TentEnKaMan

Hi all. :)
I have 3x100Ah AGM batteries hooked up in parallel & a 50Amp Durst charger which charges both flooded and gel batteries. However after the car failed to start one day we used it to charge the car battery and I failed to switch the charger back from flooded to gel when i hooked it back up to the caravan and our AGM batteries. I ended up noticing when the batteries switched from "Bulk" to "Absorption" (3 stage charger) and then switched the charger from Flooded back to Gel battery. However we have found that ever since then that we only seem to get light use out of the batteries (Est. about 65Ah) and then the inverter lets out a low battery warning. The batteries then charge for approx 90mins on absorption not bulk and then sit on a float charge again. so with a 50amp charger the most possible i could be putting back in would be 75Ah, out of 300Ah.

Does anyone know any tricks to get the full use back out of them? We tried actually leaving them running with the inverter screaming coz of the low voltage for about another 4 hours and I reckon used another approx. 50Ah they were happy to deliver about 130 watts during this but didnt have enough to start our fridge, which admittedly is just a small normal AC fridge and probably quite thirsty on the power at startup but we never used to have any hassles. Is my best bet to use up 250Ah with inverter howling a few times to try and get them to charge properly again? All advice greatly appreciated, lost my job recently so hoping not to have to replace them..... lol

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Reply By: Member - Phil G (SA) - Thursday, Oct 02, 2008 at 18:44

Reply By: Member - 1/2A - Thursday, Oct 02, 2008 at 20:26

Thursday, Oct 02, 2008 at 20:26

I have 2 AGM Fullriver 110 amp/hrs batteries in my system and have a Power Saver 40A Smart Charger and have the charger selected to flooded, this gives a charge of 14.2v - 14.6v during the bulk charge and 14.6v for absorption charge. If I selected to Gel type the Absorption charge would be too low at 14.2v the specification for my AGM's is 14.4V~14.9V/77?(25?) and as you can see 14.2v volts is to low. You might have to select your charger to Flooded.
Make sure you have the batteries paralleled so that only first battery in the parallel network supplies the positive load and the last battery in the parallel network supplies the negative load to your system. If you don't connected the batteries as I've explained, the battery with the least internal resistance will be doing most of the work and will fail to hold its charge before the other batteries.

AnswerID: 328186

Follow Up By: Member - Phil G (SA) - Thursday, Oct 02, 2008 at 20:44

Thursday, Oct 02, 2008 at 20:44

AGMs will charge fine at 14.2V, but not as quick as at 14.4-14.7.
My 100Ah Remco AGM (very similar to the FullRiver) will fully charge on a 13.8V regulated power supply, if left on overnight. If I hit it with a CTEK at 14.7V then it will only take an additional 0.4Ah.

FollowupID: 595485

Follow Up By: Member - 1/2A - Thursday, Oct 02, 2008 at 20:54

Thursday, Oct 02, 2008 at 20:54

According to the Fullriver specifications if you want your battery to last then the bulk charge should be between 14.4-14.9 and if you charge at 14.2 you may not get a full charge. My Nissan only puts out 14.2 but when I set up camp my solar set up will top up the batteries to the correct level.

FollowupID: 595486

Follow Up By: Member - Phil G (SA) - Thursday, Oct 02, 2008 at 21:33

Thursday, Oct 02, 2008 at 21:33

1/2A,
I don't believe that charging at 14.2V will cause the major undercharge problem described in the original post.
AGMs have float charge voltage of 13.6-13.8V, and according to what I've measured, will fully charge if left on for long enough.

Cheers
Phil

FollowupID: 595490

Follow Up By: Member - 1/2A - Thursday, Oct 02, 2008 at 21:52

Thursday, Oct 02, 2008 at 21:52

Phil
It is possible that the fault is caused by the way the batteries are paralleled, but by not charing a battery to its full capacity reduces its life and it my be as simple as selecting a switch from Gel to Flooded.
Also before you go into a float charge the battery must be fully charged the voltage should be between14.4 and 14.9. This means that through your cars alternator you can't get a full charge.

FollowupID: 595497

Follow Up By: Mike Harding - Thursday, Oct 02, 2008 at 21:59

Thursday, Oct 02, 2008 at 21:59

>Also before you go into a float charge the battery must be fully
>charged the voltage should be between14.4 and 14.9. This means
>that through your cars alternator you can't get a full charge.

Rubbish.

Mike Harding

FollowupID: 595499

Follow Up By: Member - Mike DID - Friday, Oct 03, 2008 at 05:48

Friday, Oct 03, 2008 at 05:48

AGM battery manufacturers data sheets (and my testing) make it quite clear that they will charge fully at 13.8 volts - it just takes longer.

Specific wiring arrangements of paralleled batteries will have no effect on charging them fully - when the last 20% of charge goes in to top up the battery, it happens at low current.

It's more likely that the connections to one of your batteries is faulty or a battery is faulty. Measure the voltage at the actual battery post - NOT the clamp that connects to the post.

Separate the batteries and charge and load-test them separately.

FollowupID: 595522

Follow Up By: Member - Mike DID - Friday, Oct 03, 2008 at 05:51

Friday, Oct 03, 2008 at 05:51

"Also before you go into a float charge the battery must be fully charged the voltage should be between14.4 and 14.9. This means that through your cars alternator you can't get a full charge. "

NO !

The only problem you will have with an AGM in an engine compartment from a properly working Alternator is over-charging from the high temperatures.

FollowupID: 595523

Reply By: TentEnKaMan - Thursday, Oct 02, 2008 at 22:33

Thursday, Oct 02, 2008 at 22:33

wow, thanks guys this gives me a bit to think over. My durst charger has a 3 way float voltage charge selector 13.8/13.5/13.2 volts we use it on 3.8 volts. The batteries are wired with two external ones connected into the middle one and both the negative and positve terminal from this battery runs to the inverter. Charging was done in a similar fashion. Although I did check them all independently recently in case there was a connection fault, but they all showed up as float charge only (after being charged whilst wired up)

Seems that a flooded charge could be worth a go, especially if there a write off otherwise, but do people think I should run them down calculating 250Ah-ish despite low voltage warning before i charge them? When I tried using the extra 50Ah they did charge for 150 mins rather than 90 mins. Could it be a battery charge memory problem coz i switched them part way thru?

Thanks everyone who has taken the time to help me, its greatly appreciated :)

AnswerID: 328210

Follow Up By: TentEnKaMan - Thursday, Oct 02, 2008 at 22:35

Thursday, Oct 02, 2008 at 22:35

I will grab a multimeter and test them seperately too, I guess the 75Ah im getting would be equivalent to two dead batts. and one good one at least.... maybe... lol

FollowupID: 595501

Follow Up By: TentEnKaMan - Thursday, Oct 02, 2008 at 22:43

Thursday, Oct 02, 2008 at 22:43

I will also definitely try reconnecting them as mentioned above too

FollowupID: 595502

Follow Up By: Member - JohnR (Vic) - Thursday, Oct 02, 2008 at 23:28

Thursday, Oct 02, 2008 at 23:28

No chance you have had them lower than 55% charge is there - 11.5v? I have 10x35amp batteries in parallel to give me, yes 350 amps. There is a battery management system and cut-out to ensure I can't go below that level as the battery life would be shortened.

I also would think if your charger is sophisticated it may have a desuphation process. My Xantrex 20 amp does, where you press a recessed butting to begin a process of trying to desulphate the batteries. With my system, I am told I should run the process every few months. The desulphation mode runs the charging at 14.4v for some of the time and you can hear the batteries bubbling. You must ensure stable power when you do it though so the manual says!

I usually leave my batteries on charge nearly all the time to ensure they top up as I have a 12v fridge on much of the time too, though I also may have a solar array charging part of the time too. It tends to mean the 240v charger is on a couple of days a week.

Don't forget though a 50 amp charger will only run at 50 amps for a short time, just as my 20 amp one does too for 20 amps. It floats up and down a lot so a full charge takes a while.

FollowupID: 595509

Follow Up By: TentEnKaMan - Friday, Oct 03, 2008 at 00:44

Friday, Oct 03, 2008 at 00:44

Thanks JohnR. Unfortunately I havent had a multimeter to check as of yet. As they are AGM battereies not SLAB's i believe that you can use 90% of them rather than the 50-55% of SLAB's. I guess we could have broken the 50% barrier but our inverter screams very loudly (and annoyingly unstoppably lol) as soon as the batts are low and we have always been very diligent to immediately either turn off the inverter or charge the batteries immediately at the first sign of a low voltage squeal, it will wake us up in the middle of the night if it does go off always has.
The time i ran then for an extra 4hrs drawing roughly an extra 50Ah with the inverter screaming low batt, id had them charge for only 90 mins for quite some time so figured it had the extra charge buried in there. On this basis i estimated my usage at 120-140Ah. I may of course have been completely incorrect on that assumption.This is the only time that I have done this, and the batteries behaviour has improved but only slightly since i did this.
I am unsure of whether this desuphation applies to AGM batteries but will definitely look into it. I was thinking i may just leave them on float for a couple of days now that im back on household power so its good to hear that might be useful. thank you again for your advice. :)

FollowupID: 595513

Follow Up By: Member - Mike DID - Friday, Oct 03, 2008 at 06:00

Friday, Oct 03, 2008 at 06:00

Kimberly Kampers recommend drawing up to 80% charge from their AGMs.

What will kill ANY Lead-Acid battery (Wet, Gel, AGM) is not storing them fully charged.

You MUST have an accurate digital voltmeter - don't trust the charger - you can't see if wiring has gone high resistance.

Don't leave your battery in storage until you've checked that it has at least 13.6 volts measured on the POSTS - NOT the clamps.

FollowupID: 595524

Follow Up By: Member - JohnR (Vic) - Friday, Oct 03, 2008 at 08:25

Friday, Oct 03, 2008 at 08:25

TentEnKaMan I think you need to monitor your batteries pretty well and more so when you have more of them, being a greater investment. I have a sophisticated gauge built into the battery monitoring that tells me the state of charge in amps stored/or in percentage, amps + or -, positive of course coming from a charger and voltage in the batteries. I have seen on another guy's camper the result from inadequatly secured leads between batteries, just like an inadequate earth lead.

Mike your comment "Kimberly Kampers recommend drawing up to 80% charge from their AGMs." is very much at odds with what their manual states and with the setup. There is a Redarc that stops you drawing anywhere near that. I know a fellow whose frozen fish ran out the door to meet him when he thought the fridge would have gone longer. :-(((

FollowupID: 595529

Follow Up By: Member - JohnR (Vic) - Friday, Oct 03, 2008 at 08:42

Friday, Oct 03, 2008 at 08:42

The desulphation - TentEnKaMan sorry, yes it isn't generally mentioned with AGMs but some do it religiously and it seems to work well for them too. Mike there are new sheets on desulphatioon circulated to KK dealers on desulphation, we have quite a few owners doing it.

FollowupID: 595532

Follow Up By: Member - Mike DID - Friday, Oct 03, 2008 at 09:16

Friday, Oct 03, 2008 at 09:16

Yes, it looks like KK have changed their statement on discharging AGMs - "NOTE: Discharging AGM Batteries below 50% will shorten cycle life "

Although they still say " batteries can sustain deep discharges without damage".

The problem is determining when a battery is discharged to 50% - volatge measurements while drawing current are very misleading. The ony reliable way is to measure cumulative charge/discharge current with correction for Peukerts Law and self-discharge.

FollowupID: 595534

Follow Up By: Member - Mike DID - Friday, Oct 03, 2008 at 09:23

Friday, Oct 03, 2008 at 09:23

Interestingly this KK page only refers to recharge time from 20% capacity - i.e. 80% discharge.

KK

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Follow Up By: Member - JohnR (Vic) - Friday, Oct 03, 2008 at 13:36

Friday, Oct 03, 2008 at 13:36

Mike, a lot of "contrasting" information around about the battery systems. One fellow who professed to know a lot told me on EO last year that 10 batteries in a Karavan would fight one another for charge! Pretty laughable really that they had some form of intelligence to do that. I grimace a bit abut 10 batteries just the same, I would rather have two of four.

FollowupID: 595555

Reply By: TentEnKaMan - Friday, Oct 03, 2008 at 10:33

Reply By: Maîneÿ (wa) - Friday, Oct 03, 2008 at 19:05

Friday, Oct 03, 2008 at 19:05

Take the 3 x batteries and remove them from the van, totally separate each battery from the next and charge each individually for 48 hours @ the recommended voltage.

Put a multimeter on each battery 24 hours *after* it has been disconnected from the charger.

Note the voltage for each battery and then re-post with the three relevant Voltages please.

Mainey . . .

AnswerID: 328313

Follow Up By: TentEnKaMan - Friday, Oct 03, 2008 at 20:49

Friday, Oct 03, 2008 at 20:49

will do mainey thanks for the help
i got multimeter this afternoon these are the results ive got before i read this.

435pm After 24hr float charge on gel setting 12.9volts at inverter (all 3)
440pm 300watt radiator switched on
447pm 11.99 volts at inverter
501pm 11.93 volts at inverter
515pm 11.81 volts at inverter
530pm inverter squeals low battery- voltage measures 11.99 volts at inverter after the 300watt load is removed but inverter running.
Switched charger to flooded battery setting
536pm bulk charging stops and goes to absorption
645pm charging goes to float
750pm charge at inverter 12.9 volts (12.8 volts with inverter on)
300watt radiator switched back on

Please note that I tried all this before reading your post, my next plan of attack was to rewire it as suggested above so i will try the two together thank you :)

FollowupID: 595586

Follow Up By: TentEnKaMan - Friday, Oct 03, 2008 at 23:03

Friday, Oct 03, 2008 at 23:03

CONTINUED
820pm 11.97volts at inverter
835pm 11.63 volts at inverter
840pm inverter low battery warning. 12.11volts at inverter after load removed. Tested resistance on all joined terminals after removing inverter. all within 0.1-0.4 Ohms. Seperated batteries for testing, also labelled them to ensure consistent reporting. voltages recorded Batt1 12.28v Batt2 12.44v Batt3 12.25v. Failed to test inverter input resistance, wondering now if perhaps this was loose, I have the fattest power leads i could fit in the 1000watt inverter and they are only 25cm long. Seems I have a disparity of almost one volt between inverter and battery. Is this normal?

928pm Batt1 put on charge on its own direct from charger on flooded setting
1002pm reaches float charge
1006pm remove charger and retest voltages Batt1 dropped from 12.94 to 12.84v within about 2 mins. Batt2 and Batt3 test exactly same voltages as reported above (havent been charged yet)
1010pm Batt1 returned to float charge

FollowupID: 595607

Follow Up By: oz doc - Saturday, Oct 04, 2008 at 08:30

Saturday, Oct 04, 2008 at 08:30

Hi TEKM, I think it might be more accurate if you let the batteries rest for a couple of hours after charging, before you test them. doc.

FollowupID: 595628

Follow Up By: Maîneÿ (wa) - Saturday, Oct 04, 2008 at 09:09

Saturday, Oct 04, 2008 at 09:09

"Failed to test inverter input resistance, wondering now if perhaps this was loose, I have the *fattest power leads* i could fit in the 1000 watt inverter and they are only *25cm* long.
Seems I have a disparity of almost *one volt* between inverter and battery.
Is this normal?"

TEKM, If you are suggesting you are loosing 1 Volt, in just a 25cm length of cable, yes it's wrong, but it can't be that - can it?

The test reports of Batt1 @ 12.28v, Batt2 @ 12.44v and Batt3 @ 12.25v are all low (but you know that) so as I said earlier, allow each battery to be fully charged and then test them individually.

Mainey . . .

FollowupID: 595630

Follow Up By: TentEnKaMan - Saturday, Oct 04, 2008 at 09:59

Saturday, Oct 04, 2008 at 09:59

thanks ozdoc and mainey i did put batt1 back on charge atfer checking its voltage and will leave for 48hrs as suggested then recheck voltage. thank you

FollowupID: 595635