AGM Batteries seem to have stopped holding charge

Julian · December 2012

The system is this:

2 210 24 volt panels
Morningstar prostar 30 charge controller
2 banks of 2 12 volt Optimia Blue Top Marine AGM batteries (in series and parallel)
Simalex 600 watt pure sine wave inverter

This is used to run 2 laptop computers and 1 lcd monitor 24 x 7

There is a redundant ac switch which will switch to ac whenever necessary

It has worked perfectly for 2 1/2 years with the batteries easily providing all night power to the machines. The ac would only kick in when there was a lack of sun to charge the batteries (rainy days for example)

Suddenly the system does not hold any charge. This did not happen gradually, as I would expect from battery failure. Instead it was sudden right after
a few days of no sun. When the sun returned the system would switch to solar from sun up to sun down but second the sun goes down, the solar fails with no charge in the batteries.

I have checked the charge controller and it is working properly (even switched it out with a backup we have with the same result).

The inverter appears to be working properly.

The batteries after sundown show 21 volts.

Is it really possible that over $600 worth of what were sold to us as the "top of the line batteries for this purpose" last less then 3 years???? I sure hope not!

Is there any other possibility that I can check to resolve this.

Any advice would be welcome

Thank you

westbranch · December 2012

Re: AGM Batteries seem to have stopped holding charge

Welcome, if you post more info about the watts used by your 24/7 use we may be able to assist. also what is are the stting on the CC for charging?

BB. · December 2012

Re: AGM Batteries seem to have stopped holding charge

Yes--Very possible. Marine batteries are not (usually) deep cycle batteries. And even AGMs seem not to last quite as long as (good quality) flooded cell batteries (on average).

My guess, anytime the batteries are below ~23.0 volts (11.5 volts for a 12 volt bank) under moderate loads--They should be recharged--They are getting into the 50% or less state of charge zone--which can limit battery life to the 500-1,000 cycle range or so (3 years * 365 days = 1,095 cycles)...

So, more or less, I would have expected you to replace the batteries every 2-3 years in this application (my non-expert opinion).

Do you have a Kill-a-Watt type Watt*Hour (or kWH) meter so you can measure your nightly loads?

Generally, I suggest measuring your loads, then sizing the battery bank to support those loads, then lastly defining the size of the solar array/backup battery charging setup.

It is very difficult to use battery based solar power for saving money if you have grid power available... The $ per kWH cost for off grid solar power can easily be in the $1-$2+ per kWH when you take battery life (3-8 years in general) and equipment life (10+ years for electronics) into account.

Even smaller commercial UPS systems probably replace their batteries every 2 years (or at least they should), and if the batteries have been severily deep cycled (say the genset did not start right away), may need replacing immediately.

For starter systems and systems that are cost sensitive--It is sometimes hard to beat a set of good quality "golf cart" batteries--Especially as a training set. It is not unusual for the first set or two of batteries to be "killed" by the "oh heck" type mistakes that happen along the learning curve. It also allows you to better understand your load/needs with a less expensive set of batteries.

Also, since AGM batteries are "sealed"--You cannot use a hydrometer to measure the specific gravity of the cells (the "gold standard" for state of charge estimation). Battery Monitors are very useful for sealed batteries to help understand what is going one with charging/discharging.

Since you have series/parallel connected batteries, a DC Current Clamp type DMM would be helpful too (monitor current in each battery string, and check battery voltages--Looking for differences such as: open/shorted cells, bad/dirty/loose electrical connections, etc.).

A couple of good Battery FAQs:

Battery FAQ
www.batteryfaq.org

-Bill

inetdog · December 2012

Re: AGM Batteries seem to have stopped holding charge

Julian wrote: »

There is a redundant ac switch which will switch to ac whenever necessary

I don't think that anybody else has commented on this part of your setup yet.

If you have grid power available all of the time (except for outages), then running your devices off "free" solar power is actually costing you far more than the power company would charge for the same amount of electricity. And the reason for that is primarily that you will have to pay to replace expensive battery banks every 2 to 5 years.
Solar power for off-grid locations makes a lot of sense, since there are few alternatives. It can also make sense when the POCO power is either very erratic or very expensive (>$.50 per Kwh).

For locations with grid access, going with a battery system rather that a grid tied system (in which you are using the grid as a giant battery by selling any excess during good sun to the utility and buying it back when you need it.)

waynefromnscanada · December 2012

Re: AGM Batteries seem to have stopped holding charge

Julian wrote: »

There is a redundant ac switch which will switch to ac whenever necessary
The ac would only kick in when there was a lack of sun to charge the batteries (rainy days for example)

Sounds like some sort of automatic switchover to AC when the batteries are run way down, cycled way down below where they should have been allowed to go.
It's normal to not allow the batteries to discharge below the 80% full point, and NEVER below the 50% state of charge if it is desired to have the batteries last a reasonable time. To me, it sounds like your batteries have more or less regularly been allowed to discharge deeply, thus, if this is correct, I'm surprised the batteries have lasted as long as they have.

niel · December 2012

Re: AGM Batteries seem to have stopped holding charge

i can kind of guess what happened here. between the 2 laptops and the monitor you are probably drawing about 1200+wh from the batteries for your loads and at 50ah and 12v each in a 2 x 2 arrangement this is essentially a 24v battery bank at 50ah useable. 50ah x 24v = 1200wh. this is a close workable margin only if you are getting enough sun every day. when it dips into the other 50ah reserve capacity of the batteries and there's insufficient sun to bring them back up you start to deficit charge in that it never catches up before sulfating the batteries some. it was gradual, but you just didn't notice it until another round of little to no sun did it in while you were still putting your loads to it. it obviously was still above the automated utility switchover point, but sulfated batteries can appear good by voltage until they need to carry some current. it was the straw that broke the camel's back so to speak.

as to the pv with 420w total at 59% efficiency overall would yield 247.8wh for every hour of full sun received or about 10.325ah. now i can't comment on the batteries being top of the line or not, but in my opinion you left little room for error. up the pv wattage by at least 50% and the battery capacity by at least 50% as well for better autonomy with more emphasis on the pv capacity. check at what point the utility ac switches in and does that charger supply enough to the batteries?

of course all of this could be horse manure and the batteries just failed. hard to truly say.

PNjunction · January 2013

Re: AGM Batteries seem to have stopped holding charge

I'd be interested to know if the Blue Tops were the dual-purpose "blue/white" casing, or the SLI-designed "blue/black" casing versions - I'd be surprised if the latter actually lasted this long in this application.

Fullpower · January 2013

Re: AGM Batteries seem to have stopped holding charge

If you got TWO full years of service from a pair of Optima batteries, they dont owe ya anything.

AGM Batteries seem to have stopped holding charge

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