agm battery voltage drop

mahendra · December 2013

hi i have some deka solar agm batteries to be exact 4 deka 245ah (20hr ratings).They are under a year old after purchase an have been in light use that is i only use my system when i have sun and with light or moderate loads and occasional heavy loads.my problem is that at rest during the night with no load on the battery till in the morning previously the battery would read 12.7volts.But lately after no load in the night batteries would read 12.6 v in the morning. Is this early battery failure?Is there any measures that can be taken to buffer the impact of this situation ?please help.

Blackcherry04 · December 2013

Re: agm battery volatge drop

You will see some changes as they age. The problem here is that your meter measures to ( .0 ) and you don't know if the were 12.71 and if they are 12.69 now, measured to ( .00 ). Generally you will see a drop in capacity as the age and voltage is not the best indicator to use. As you have mentioned before that your climate is hot and you'd expect a shorter life. When you see posts that my batteries lasted 10 years, they always leave out the the last 5 years were at 50 % capacity or less. You can load test them, but it's not going to tell you that much. Since they are sealed there not a whole lot you can do. If your transitioning to float very quickly you might try to up your absorb ( Time or Voltage ) a little and see if notice a difference.

Have you checked with Deka and see if they have any special instructions for your batteries ?? Concorde Sun-saver's have a special conditioning ( EQ ) for their batteries that lasts 8 hours.

mahendra · December 2013

Re: agm battery volatge drop

mine were never really cycled to 50% dod since i have them i try to keep it at 80% soc at all times and yes it is not exactly 12.6 but 12.64 to 12.67 on the numerous voltage test i took with my multimeter

mahendra · December 2013

Re: agm battery volatge drop

deka has been very miserable with customer support.

Blackcherry04 · December 2013

Re: agm battery volatge drop

mahendra wrote: »

mine were never really cycled to 50% dod since i have them i try to keep it at 80% soc at all times and yes it is not exactly 12.6 but 12.64 to 12.67 on the numerous voltage test i took with my multimeter

I don't know what to tell you brother. Maybe cycle them deeper and see if the longer absorb's help. At 80 % they may not be getting enough charge. I have a car that I drive once a year or so that I keep a Optima battery in, one lasted 9 years and the next 2 years. I'd say that Deka true deep cycle batteries ought to be able to handle 15 V for a couple hours and see if it cleans them up.

vtmaps · December 2013

Re: agm battery volatge drop

mahendra wrote: »

to be exact 4 deka 245ah (20hr ratings)

Are these 12 volt batteries? If so, you have 4 in parallel. If they are 6 volt then you have 2 parallel batteries. In either case, you need to separate the batteries and charge and discharge them one at a time in order to figure out if there is a problem. Your other option is to use a DC clamp ammeter to see if the strings are receiving equal charge... you must be charging at as high an amperage as possible when you make the measurements.

AGM batteries, because of their low internal resistance, are particularly prone to charging imbalances due to the wiring and connections. 12 volt systems are also more prone to the same problem than higher voltage systems.

If there is a charge imbalance, then at least one of the batteries is being chronically undercharged, and it will set the performance limits of the entire battery bank.

--vtMaps

niel · December 2013

Re: agm battery volatge drop

pretty much what has been said is good, but i would like you to clarify for us your statement here,
"mine were never really cycled to 50% dod since i have them i try to keep it at 80% soc at all times...."

i do trust that you are giving your batteries full charges that they reach their absorb voltage for a specified time before being brought back down to float? if only getting to say 13.6v (approx float voltage area) then the batteries are not receiving their proper charge and will not reach 100% soc. that 80% could be a goal of the lowest soc to discharge to, but it is not meant to have the batteries stay at 80% soc.

mahendra · December 2013

Re: agm battery volatge drop

OK i understand what you mean by that Neil thanks for mentioning ,but i meant the are not discharged beyond (judging from voltages) the 80% soc or 20% dod.I am fully aware that batteries can age while it was sitting in the warehouse(before it was bought) as well but i am just trying to clarify if there is any measures that cant be taken to prolong the present life.The reason i am asking is because i read an article which mentioned that batteries need to be discharged to their 50% dod a few times with in their lifetime to replace what they called /referred to as stale power in the batteries,don't really comprehend it but that's what it mentioned .However, articles was general and i am trying to dig a little more to see if this is actually true and if it applies to all types of batteries.So i was simply trying to understand where this failure of the battery is coming from ,since i try to observe all use, maintenance and care precautions with respect to agms.i should also admit that i was experimenting with absorption termination by ending amps for the past few weeks but realized that the 1%-4% of battery ah does not really apply to my type of battery,as a result my battery was not receiving a full charge because absorption was terminated quickly.i have subsequently revert to my old setting and gave my battery bank several full charges.But still the battery did not returned to their normal voltage readings at full charge.

mahendra · December 2013

Re: agm battery volatge drop

guess i will have to check each individual battery.

PNjunction · December 2013

Re: agm battery volatge drop

With the Deka agm's, are you meeting the 14.4v absorption voltage cycle not to exceed 12 hours? Not that you'll be able to do that with limited solar insolation anyway...

Also note that Deka considers an "EQ" for their agm's to be a slightly elevated absorb voltage of about 14.7v. So normally, one would want to meet the 14.4v absorption threshold on a somewhat regular basis. Periodically, it might be good to treat them to a 14.7v absorb once in awhile. Nowhere in their documentation do they suggest what we normally consider a higher voltage EQ of 15v or more.

What is your charge rate? Deka usually recommends getting close the maximum of about 0.2C for longest life.

You also mentioned checking each individual battery - if that is a typical series / parallel arrangement, did each battery get a full charge cycle prior to being placed into the final wiring configuration to help assure that they started out as balanced as they could be?

mahendra · December 2013

Re: agm battery volatge drop

my charge rate is around 0.06 presently but will be upgraded to 0.17.yes i do get to the 14.4 but i wasn't aware of the 14.7 equalize voltage.It says don not exceed 14.6 volts

PNjunction · December 2013

Re: agm battery voltage drop

That's correct about not exceeding 14.6v under normal circumstances. I'll have to double-check the thread, but I sure hope your controller is temperature-compensated!

However, if you actually determine that a "light" EQ would actually be beneficial, in Deka's case then this would be at 14.7v for *that session only* and definitely not to exceed 12 hours. Normally don't even go here.

mahendra · December 2013

Re: agm battery voltage drop

yes my controller is temperature compensated its a midnite classic

niel · December 2013

Re: agm battery volatge drop

you can try to start off with an extended absorb charge and then cycle down to maybe 55%-65% soc or so and then bring it back up with an extended absorb charge again to see if there's any improvement which i think there will be. i'm talking an extra hour or 2 on the absorb charge. i would not eq them with higher voltage.

i do recommend that one should take the batteries through their paces down below 70% soc, but stay above 50% soc, just to exercise the batteries roughly every month or so. if you keep having variances in battery voltage then suspect your wiring or other factors that may be present causing the variations. you can physically switch the low batteries to the high battery positions and see if the voltages stay the same as before or did it improve. of course the voltage readings and positions for each battery must be marked down before and afterward to follow if changes occur. name your batteries for reference, like battery a or 1 or combine the 2. even call them by actual names if you like and put this on a piece of paper to be taped to the battery. the combined method could indicate the string number and battery position within the string.

agm battery voltage drop

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