| Author |
Message |
candyman
Samba Trout Slayer
Joined: December 20, 2003
Posts: 2694
Location: Missoula MT
|
 Posted: Wed Feb 19, 2020 5:32 pm Post subject: Am I slowly murdering my AGM house battery? |
 |
|
So my last 100ah agm battery lasted only 3 years. Pretty disappointed in that and am wondering what I did wrong. I just purchased a new one and want it to last longer. I was thinking about how I treat it and here are my scenarios. At camp I use 1-2 100 watt solar panels with an mppt 40amp controller to charge. Ideal conditions will fully charge the batter in several hours. My use is furnace, truckfridge, leds, phone charging etc... when at home I have an iota converter/charger that I keep it plugged into for storage and also use to charge when needed. When driving I have a unidirectional surepower 1314a relay that will allow the battery to charge off alternator at around 14.6-14.8v (subie 2.5 alternator). This last part is what has me concerned. I drive a lot with the battery fully charged and t is still seeing 14.8v from alternator. Is this technically over charging the battery thus slowly killing it? I have read that AGMs are sensitive to overcharging. When the house battery is fully charged, either from solar or from iota smart charger, should I keep it from getting a charge from the alternator when driving to prevent it from overcharging, or am I looking at this wrong? There are times on road trips that it will see this consistent voltage for hours at a time.
Thanks for any input! |
|
| Back to top |
|
 |
DanHoug
Samba Member
Joined: December 05, 2016
Posts: 4790
Location: Bemidji, MN
|
| Posted: Wed Feb 19, 2020 6:39 pm Post subject: Re: Am I slowly murdering my AGM house battery |
|
|
couple of questions/points.... what brand was the battery? where was it made? good AGMs are expensive.
do you really need to charge from the alternator with 200 watts solar? does it current limit the charge rate to 20% of the battery capacity? answer is no.
does the Iota charger have a specific AGM setting? i don't know.
how low have you run the battery down? while AGM is somewhat tolerant to discharge, the Depth of Discharge has a profound effect on battery life. did the batt come with a spec sheet on DoD vs charge cycles?
_________________
-dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
|
| Back to top |
|
|
Howesight
Samba Member
Joined: July 02, 2008
Posts: 3274
Location: Vancouver, B.C.
|
| Posted: Wed Feb 19, 2020 7:19 pm Post subject: Re: Am I slowly murdering my AGM house battery |
|
|
AGM batteries are generally damaged more easily than lead-acid units from charging at higher-than-specified voltages. In the OP's case, there is no mention of the charging profile settings used in the MPPT solar charge controller. The charging voltage needs to be no higher than 14.4 volts and the float voltage needs to be no higher than 13.8 volts at 70 degrees Fahrenheit, and even lower in hot ambient temperatures.
The OP does not indicate what the Iota charger is set at for charging and for float, but again, float at 70F and under needs to be 13.8 volts or less and even lower at higher ambients.
As for 14.8 volts from the alternator, it would be a useful exercise to see what the actual voltage at the AGM battery under driving conditions is. My Subaru SVX alternator often has voltage at the house battery pulled down significantly by the normal summer weather electrical draws including the AC draws on the rad fan, compressor clutch, evaporator fans, Truckfridge, etc. (I accept that relying on these draws to save your battery is not a sound approach).
It may be necessary to simply disconnect the house battery from the alternator charging system when the AGM battery is already fully charged. The Surepower isolators (I have the 1315) do allow you to wire in SPST switches to override the isolator and keep the house battery disconnected or keep it connected to the starting battery.
In my case, I use a Trojan lead-acid battery which is far more tolerant of high charging voltages. I have the opposite problem in that my alternator draws in summer can pull the system voltage at the Surepower 1315 low enough to disconnect it and leave me without alternator charging for the house battery. I have gotten around this by switching manually to "always connected" and then have to remember to undo this. (Maybe my rad fan needs replacement?)
At the end of the day, the charging directions from the specific battery manufacturer must govern since even the same design and "group" of battery from different manufacturers can have different charging profiles. Some manufacturers have recently (in the last couple years or so) changed their charging guidance for lead-acid designs to slightly lower voltages for lead-acid designs, presumably due to unacceptable numbers of over-charging damage claims. In the lead-acid battery segment, the main cause of premature failures/deaths in the past was thought to be chronic undercharging and over-discharge which may explain why battery manufacturers stressed charging and especially float charging. The pendulum now seems to be swinging over to protecting against overcharging.
_________________
'86 Syncro Westy SVX |
|
| Back to top |
|
|
candyman
Samba Trout Slayer
Joined: December 20, 2003
Posts: 2694
Location: Missoula MT
|
| Posted: Wed Feb 19, 2020 7:19 pm Post subject: Re: Am I slowly murdering my AGM house battery |
|
|
| DanHoug wrote: |
couple of questions/points.... what brand was the battery? where was it made? good AGMs are expensive.
do you really need to charge from the alternator with 200 watts solar? does it current limit the charge rate to 20% of the battery capacity? answer is no.
does the Iota charger have a specific AGM setting? i don't know.
how low have you run the battery down? while AGM is somewhat tolerant to discharge, the Depth of Discharge has a profound effect on battery life. did the batt come with a spec sheet on DoD vs charge cycles? |
All good questions,
The AGM is a generic wheel chair battery that you can buy off ebay for about $169 or so. So its a cheapy for sure which may play into the short life.
Sometimes I do need to charge from alternator If camping with no sun and then moving from place to place. I dont always deploy The panels if we are just overnighting somewhere and driving out the next day, then the alternator does all the heavy lifting.
The panels will do the proper current limit charge etc as the mppt controller is smart unit. Its a renogy rover mppt 40
The Iota , as far as I know, charges it the way AGMS like to be charge with bulk boost float etc, hitting 14.8 then 14.1 then float at 13.5. According to everything I have read this is sufficient
As far as battery drain, i dont think I have ever drained it lower than 12.2. But I have only gotten partial day charges with solar and still had loads on the battery through the night. Thus never allowing the battery to get to full charge while still using it |
|
| Back to top |
|
|
candyman
Samba Trout Slayer
Joined: December 20, 2003
Posts: 2694
Location: Missoula MT
|
| Posted: Wed Feb 19, 2020 7:27 pm Post subject: Re: Am I slowly murdering my AGM house battery |
|
|
| Howesight wrote: |
AGM batteries are generally damaged more easily than lead-acid units from charging at higher-than-specified voltages. In the OP's case, there is no mention of the charging profile settings used in the MPPT solar charge controller. The charging voltage needs to be no higher than 14.4 volts and the float voltage needs to be no higher than 13.8 volts at 70 degrees Fahrenheit, and even lower in hot ambient temperatures.
The OP does not indicate what the Iota charger is set at for charging and for float, but again, float at 70F and under needs to be 13.8 volts or less and even lower at higher ambients.
As for 14.8 volts from the alternator, it would be a useful exercise to see what the actual voltage at the AGM battery under driving conditions is. My Subaru SVX alternator often has voltage at the house battery pulled down significantly by the normal summer weather electrical draws including the AC draws on the rad fan, compressor clutch, evaporator fans, Truckfridge, etc. (I accept that relying on these draws to save your battery is not a sound approach).
It may be necessary to simply disconnect the house battery from the alternator charging system when the AGM battery is already fully charged. The Surepower isolators (I have the 1315) do allow you to wire in SPST switches to override the isolator and keep the house battery disconnected or keep it connected to the starting battery.
In my case, I use a Trojan lead-acid battery which is far more tolerant of high charging voltages. I have the opposite problem in that my alternator draws in summer can pull the system voltage at the Surepower 1315 low enough to disconnect it and leave me without alternator charging for the house battery. I have gotten around this by switching manually to "always connected" and then have to remember to undo this. (Maybe my rad fan needs replacement?)
At the end of the day, the charging directions from the specific battery manufacturer must govern since even the same design and "group" of battery from different manufacturers can have different charging profiles. Some manufacturers have recently (in the last couple years or so) changed their charging guidance for lead-acid designs to slightly lower voltages for lead-acid designs, presumably due to unacceptable numbers of over-charging damage claims. In the lead-acid battery segment, the main cause of premature failures/deaths in the past was thought to be chronic undercharging and over-discharge which may explain why battery manufacturers stressed charging and especially float charging. The pendulum now seems to be swinging over to protecting against overcharging. |
Thanks Howesight
The battery cycle use says on the battery 14.5-14.9. The mppt controller, while I can manually control, is auto set for agm at 14.8 as is the iota. They both slow down at 14.1 and float at 13.2-13.5.
As far as alternator while driving voltage, i have a volt gauge on my scan tool and it fluctuates between 14.4-14.8 depending on loads like lights, fans etc... i also have a volt gauge for the house battery and it reads the same as the scan tool read out
Maybe manually disconnecting from house battery when fully charged would be worth while if it indeed does harm the battery. Thats what I want to find out though. |
|
| Back to top |
|
|
Abscate
Samba Member
Joined: October 05, 2014
Posts: 22668
Location: NYC/Upstate/ROW
|
| Posted: Thu Feb 20, 2020 4:45 am Post subject: Re: Am I slowly murdering my AGM house battery? |
|
|
Most casual and weekenders are better served by lead acid batteries.
_________________
.ssS! |
|
| Back to top |
|
|
candyman
Samba Trout Slayer
Joined: December 20, 2003
Posts: 2694
Location: Missoula MT
|
| Posted: Thu Feb 20, 2020 7:20 am Post subject: Re: Am I slowly murdering my AGM house battery? |
|
|
| Abscate wrote: |
| Most casual and weekenders are better served by lead acid batteries. |
I wanted to go that route but everyone loves to poo poo that idea because of the off gassing. Im thinking i may go that route next if this one fails prematurely |
|
| Back to top |
|
|
djkeev
Samba Moderator
Joined: September 30, 2007
Posts: 32625
Location: Reading Pennsylvania
|
|
| Back to top |
|
|
joetiger 
Samba Member
Joined: January 27, 2005
Posts: 5078
Location: denver
|
| Posted: Thu Feb 20, 2020 11:43 am Post subject: Re: Am I slowly murdering my AGM house battery? |
|
|
I had a lead acid Group 27DC in my 2wd and it worked very well. When it died (on the road in Oregon) I was able to pick up a replacement at a little parts store for $100. Gotta love the simplicity and availability.
_________________
Joe T.
'86 NAHT Vanagon GL Syncro/ supercharged ABA 2.0 "Pigpen"
'04 GTI 1.8T
'04 Golf R32
"get metaphysical with it. if it's simply a means to get to and from places, it will let you down. if it becomes your zen, it can't fail you." -dabaron
"Still, it's good to be afield."--VWagabond
Available Now! Vanagon to Louisiana--A Two-Lane Reckoning Through Past and Present
www.josephtrussell.com |
|
| Back to top |
|
|
|
