oh sheet agm levels at 12 v

blueskies

my backup system is 12v.  the batteries are agm type 12v 100 amp hour / non-spillable lead acid.  i haven't messed with them for a year and the voltage reads 12 volts exactly. have I ruined them?  never used ... 

InCogKneeToe

I am not sure what your system is or how it is maintained, but I have successfully charged many AGM Car Batteries that have been Stone Dead like 3v.  

It does require a AGM capable Charger I have used 2 different Schumacher's with great luck. The $500 Merctronic Diagnostic Charger at work won't do them and Fails them.

blueskies

Thanks InCogKnee Toe.  It's just a small bank so I can't be out too much even at worst.  I just remember reading 12v is actually dead but I don't know how that applies to agm.  

BB.

12 volts is not "dead", but down a lot... Normally suggest 75% state of charge, then recharge (around 12.5 volts or so--Check AGM manual).

AGMs are not supposed to sulfate as easy--So why not charge them and use them. If they take and hold a charge, and have enough AH to support your loads--Go ahead and use them.

Most AGMs seem to need recharging every 6 months (maximum between charges) at ~75F/25C. If they have been stored at 18F or 10C colder (like a basement), they should last almost 2x longer between charges. If they have been kept in a hot building/garage/etc. at +18F/10C over room temperature, they should be recharged every ~3 months or sooner.

I have had pretty good luck with "real" float chargers (like BatteryMinder and BatteryTender brands). And Costco had a Duracell brand Lead Acid/Li Ion charger that seems to work well too:

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=battery+minder

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=battery+tender

https://www.amazon.com/Duracell-DRMC4A-Lithium-Battery-Maintainer/dp/B07MW39STH

I tried the cheap float chargers--And they overcharged the batteries instead of properly floating them.

-Bill

blueskies

Thank  you BB and incogneto.  When the sun comes up, I plan to connect fuses and breakers to my Midnite Solar Kid for this small backup battery bank and see how it goes.  If someone thinks a charger is neccessary before this, let me know., please.  Thanks both.

blueskies

ring, ring, BB and Photo - in case you get the message before I get up again and start again.

blueskies

ps - you are both under-appreciated.  Not by me.

blueskies

future entheusiasts:  I try to use specified wire but if your availability is limited, this can help you use multiple wires to achieve the needed awg:  Don't do this in your house - maybe a cabin

https://www.wirebarn.com/Combined-Wire-Gauge-Calculator_ep_42.html

Wheelman55

I’ve abused a couple of AGM batts and have gotten them back to 95% or so using a smart charger.  Here’s a SOC chart: 

Best of luck with your bank. 

InCogKneeToe

blueskies said:

future entheusiasts:  I try to use specified wire but if your availability is limited, this can help you use multiple wires to achieve the needed awg:  Don't do this in your house - maybe a cabin

https://www.wirebarn.com/Combined-Wire-Gauge-Calculator_ep_42.html

Yes, Multiple Wires can be used and Multiplied. Generally 3 numbers lower. 2, 12awg=9awg. 2 14awg=11awg.

https://www.wirebarn.com/Combined-Wire-Gauge-Calculator_ep_42.html

BB.

Leaving the Midnite Kid plugged in a running should be a good start. Double check the charging and float voltages are correct for your brand/model of batteries. The Kids are a very good controller and can be left connected 365 days a year and should keep the battery bank properly charged (the only time an MPPT controller should be disconnected is if the array, for example, covered with snow for a few months a year--The MPPT controllers, when in the "dark", do consume some energy and slowly will discharge the battery bank. PWM controllers generally draw less power for the micro controller, and discharge the bank much slower in the dark).

Some of the chargers (like some BatteryMinder models) include a desulfator mode... I have no idea if the desulf mode does anything good (or bad).

And that generic warning about connecting solar charge controllers... Always connect the battery first to the controller (and disconnect last). They need the battery connection to boot properly and figure out 12/24/48 volt battery bank base voltage. If you connect the solar power first, the controllers can get confused on boot, or in rare conditions, can even be damaged if the solar panels are connected (with sun) before the battery bank.

-Bill

softdown

Wheelman55 said:

I’ve abused a couple of AGM batts and have gotten them back to 95% or so using a smart charger.  Here’s a SOC chart: 

Best of luck with your bank. 

I find those voltage levels optimistic. 12.8 volts is a fully charged battery if measured 24 hours after charging. Anything over 12.8 volts is a meaningless surface charge with almost no ooomph. Assuming ~ 75F temps of course. 

BB.

Some 100% state of charge AGM batteries seem to "rest" at/around 13.0 +/- VDC.

-Bill

softdown

BB. said:

Some 100% state of charge AGM batteries seem to "rest" at/around 13.0 +/- VDC.

-Bill

The goal posts keep moving. 12.8V was long the gold standard for 100% SOC. Mine never went up to 13V. Of course different manufacturers etc. 

Marc Kurth

The actual numbers can be manufacturer specific. A brand new fully charged Concorde AGM will read 13.0v with negligible variation between 32F and 110F. You will get the same number 4 hours after charging and two weeks after charging.

After the battery ages a few years, it will gradually settle to 12.8v to 12.9v until the end of its life. Because of this, some manufacturers will specify "12.8v or higher."

Again, with Concorde: A dead battery is 10.5v under load, but it will gradually rebound to 11.6v after removing any loads. So 11.6v is the standing voltage reading of a Concorde battery at 0% SOC.