Battery Failure Mode

Thread Starter

GKP

Joined Aug 15, 2014
12
Marine environment; house bank of batteries four 12volt AGM wired for 24volt output ; Charger 3 stage 100 amp with no thermal sensor; batteries all 6ms old
Battery bank heat readings (on top of battery case with infrared heat gun) one battery reading 128F with localized reading at 141F over one cell; battery charger on; ambient temp. 80F
Is this enough information to indicate a very low internal resistance in one cell as I have assumed?
 

#12

Joined Nov 30, 2010
18,224
One cell heating up 1.43 times as much as its neighbors is a good indicator that you have already found the problem. 141F is in the, "burn your fingers" range, and that's only the case outside where the heat is.:eek:

So, one bit of missing information is: How big are these batteries that you think you can push kilowatts through them?
 

Kermit2

Joined Feb 5, 2010
4,162
rated capacity = 25 amps for 257 min. @ 11.8/11.7 volts per cell.
This is a very deep discharge.
For my system I aimed for a 12.0/11.9 volt per cell final discharge point, which would be a liitle more than 50% discharge. I have 8D size batteries, weighing about 1 20 lbs. each, wired in series to make 48 volts. Since I only want a 50% discharge, I divide capacity by 2. work out new capacity 25 amps for 128.5 min.= 3212.5 divided by new discharge time; 12 hrs.(720 min.) equals new current limit; 4.5 amps. This is what i do to make my batteries last until next sunrise. charge rate is figured for a 5 hour span. they got me through a hurricane once with Air conditioning in one room, coffee, and TV and internet. The system you have described will have about 1/2 of the capacity, or just little less than 1/2.
if you increase the amount of discharge you get more capacity but shorten bsttery life severely.
 

Thread Starter

GKP

Joined Aug 15, 2014
12
One cell heating up 1.43 times as much as its neighbors is a good indicator that you have already found the problem. 141F is in the, "burn your fingers" range, and that's only the case outside where the heat is.:eek:

So, one bit of missing information is: How big are these batteries that you think you can push kilowatts through them?
These are 8D AGM 256 AH
 

Thread Starter

GKP

Joined Aug 15, 2014
12
If it was the case, it would be high internal resistance, not low.
If it was the case, it would be high internal resistance, not low.
In order to get the house bank operational I took an identical battery from my start bank (we were in a remote location) and replaced the bad battery. House bank operated normally. Charger made it down to float voltage. But ....I then put the bad battery into the start bank thinking that it might still be good enough to start the engine and if it was not I would be able to use my parallel switch to start in any case. Wrong; could not even get the solenoid to click with the parallel switch engaged. This led me to believe that the bad cell must have really low resistance. Does this make sense?
 

Thread Starter

GKP

Joined Aug 15, 2014
12

Thread Starter

GKP

Joined Aug 15, 2014
12
High resistance would make more sense, as Kubeek said in post #3.
I
High resistance would make more sense, as Kubeek said in post #3.
Please explain. If high internal resistance my paralleling the second starting batteries should have worked. If the cell had high resistance the whole bank (2 batterers in series for 48 v) just acts like a reduced output bank (normally dead battery)

I am trying to get a handle on the failure mode so I can ascertain if I have a problem with my parallel switch system.
 
Last edited:

Lestraveled

Joined May 19, 2014
1,946
High resistance would make more sense, as Kubeek said in post #3.
Two reasons:

- When you used the battery to start your engine and it failed to do so, this indicates a cell with high resistance.

- The higher the resistance of a cell the more heat it will dissipate. Wattage (heat) = Amps squared, times resistance. The cell with the highest resistance produces most of the heat.
 

kubeek

Joined Sep 20, 2005
5,793
....I then put the bad battery into the start bank thinking that it might still be good enough to start the engine and if it was not I would be able to use my parallel switch to start in any case. Wrong; could not even get the solenoid to click with the parallel switch engaged. This led me to believe that the bad cell must have really low resistance. Does this make sense?
What do you mean by parallel switch? Please show a diagram of how the batteries are acutally connected together. I think everyone was imagining a simple series connected bank of batteries up to this point.
 

Dr.killjoy

Joined Apr 28, 2013
1,196
What do you mean by parallel switch? Please show a diagram of how the batteries are acutally connected together. I think everyone was imagining a simple series connected bank of batteries up to this point.
How did you figure you got 24v from 4 12v batteries in a serial configuration ???
 

Kermit2

Joined Feb 5, 2010
4,162
if the charger stayed in full charge mode snd could not reach float voltage levels, i would suspect a SHORTED cell in the battery. the high temp in in one cell further confirms the shorted out condition. being AGM type it is not possible to wash out the cell and remove the short.
 
Top