Author Topic: What causes lead acid battery cells to short out?  (Read 376 times)

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Offline Red Squirrel

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What causes lead acid battery cells to short out?
« on: May 14, 2019, 01:34:06 pm »
Not exactly renewable energy (UPS) but figured it might fit here.

I noticed one of my 12v batteries was getting warm in my UPS.  I've had this happen before, twice actually, and it's usually a shorted cell.  What ends up happening is because 1 cell is shorted out it essentially turns into a 10 volt battery as it's 5 active cells instead of 6.   Downside is the battery is basically a write off at this point.  I could try to carefully open it and try to see if I can find and clear the short, but it would be a messy job. 

So my question is, what causes that in first place and anything I can do to prevent it?  I figure it's material shedding and then bridging between two plates.  Is this just because they are cheap batteries, would I be better off going with more expensive ones like 6v golf cart batteries?   The ones I'm using now are RV/marine so think because they are also meant for starting the plates are not as robust as a full deep cycle, is that right?

Still not sure if that is what is happening with this particular battery, I'm letting it sit unconnected to see how low the voltage gets but when I first disconnected it, it was 13.2v when the other one also connected in paralell was 13.3.  So not a good sign that it dropped that fast.   I don't have control over the float voltage as the UPS does that, but they usually float at 13.5 which is reasonable.

Just wondering what is best course of action here, should I just look at getting better batteries, or is there anything I can do to prevent this?  I do add water every now and then to top them up.   I'm almost wondering if I'm somehow triggering the short when I do that, could that be?

Edit: tested the cells with the hydrometer, and yep one of them is completely dead.   Another one bites the dust... really need to figure out what's causing this, this is the 3rd one I lose now.  Will I have better luck going with golf cart batteries instead of the RV/Marine ones I'm using now?
« Last Edit: May 14, 2019, 04:07:39 pm by Red Squirrel »
 

Offline bsdphk

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Re: What causes lead acid battery cells to short out?
« Reply #1 on: May 14, 2019, 04:17:01 pm »
Lead-Acid batteries are quite picky when it comes to charging conditions and raised temperatures.

Both too high and too low float-charge voltage will shorten the lifetime, through different chemical mechanisms, and the ideal charging voltage depends on the temperature (3mv/cell/°C) and the exact alloy of lead used in the electrodes.

In general UPS's use the batteries in a very aggressive way, getting better as the UPS gets (much) more expensive.

The best and simplest way to get longer lifetime out of your batteries is to not mount them inside the UPS where the temperature is usually 30-40°C, but freestanding and preferable no warmer than 25°C.  The cabling and fusing is important, and as a rule you will need more copper in the cabling than were used inside the UPS, because the cable is longer.

There is a conference called "BattCon" every year, there are a lot of good papers presented there about just how troublesome lead-acid batteries are and what to do about it.
 

Offline Red Squirrel

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Re: What causes lead acid battery cells to short out?
« Reply #2 on: May 15, 2019, 07:36:30 am »
In my case I don't think temp is the issue, as they tend to run fairly cool.  They are also in a battery cabinet with room to breathe.  Though I had to disable the fans since they were cheap fans and the ballbearings started to go.



Also any way to recover from a shorted cell or is it pretty much over? Even if I was to remove the short the cell would be at 0% discharge, so is that even recoverable? 

I always just get a new battery and recycle the bad one but it feels so wasteful.

For the time being I won't replace this one though, I'll keep the 3 I got going and wait till I upgrade my system.  Want to build a separate battery box as this cabinet makes them harder to maintain.  I may also upgrade to a 48 volt system at some point.  Harder to find the equipment for that though. The big name brands like Cordex or Eltek don't really sell to individuals.

I kinda want to incorporate solar into the system too but we get so much snow it's a lot of maintenance to keep the panels clear every day.
 

Online NorthGuy

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Re: What causes lead acid battery cells to short out?
« Reply #3 on: May 15, 2019, 02:22:42 pm »
A short cell will have less water, and very low specific gravity, and zero voltage. Is this what you're observing?
 

Offline Red Squirrel

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Re: What causes lead acid battery cells to short out?
« Reply #4 on: May 15, 2019, 02:51:03 pm »
I don't have a way to test voltage as it's too awkward getting a multi meter in there, but what basically happens is the specific gravity of all the cells is super high (overcharged) but the one cell is super low (basically pegged as low as it can).  The voltage also reads 10.6ish volts if I recall when it's sat for a bit. If I charge it, it will actually go high enough but quickly drop back to 10.

So it may not be shorted, but it's clearly bad in a way or the other, but also not open, otherwise I would just get no voltage.

As a side note, I was just looking at battery prices on a solar site and noticed that the bigger you go, the more expensive they are per amp hour, does that seem right?  Is there still an advantage of going with bigger batteries vs just having more small ones?  I'm thinking more small ones means it's not as expensive if one does die, but I'm hoping that by going with higher end solar rated batteries they will simply last. It's one thing to lose charge over time as they age, but these are dying completely on me.
« Last Edit: May 15, 2019, 02:52:40 pm by Red Squirrel »
 

Offline mvas

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Re: What causes lead acid battery cells to short out?
« Reply #5 on: May 16, 2019, 04:46:11 am »
RV / Marine Batteries are not true Deep Cycle Batteries.
It is a hybrid "Engine Starting & Trolling Motor" type battery.

Who is the Mfr and what is the Model # of the battery?
What are the voltage & amperage details of your 3-Stage Charger?
When was the last time that you Equalized this battery?

What is the WARRANTY period?
That will tell you how long the mfr expects the battery to last.
Is the battery, now older than the warranty period?

Golf Cart batteries are typically good / inexpensive Deep Cycle batteries.

Typically, a shorted cell is death ...
 

Offline Red Squirrel

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Re: What causes lead acid battery cells to short out?
« Reply #6 on: May 16, 2019, 05:30:09 am »
Yeah I kinda figured too, when I originally picked this battery I had not noticed they were a hybrid and not full deep cycle but they are indeed not true deep cycle.   Then I just kept buying them so I can match them up. But after 3 deaths I think it's time to stop replacing them and move on to another model.   These cheaper retail store batteries don't really tend to have any specific specs or a data sheet but this is the one:  https://www.canadiantire.ca/en/pdp/motomaster-nautilus-group-27-starting-deep-cycle-battery-0102799p.html#srp

The warranty is like a year if I recall, it's not much.  Used to be more but they actually dropped it a few years ago.  This particular one is from 2013.  I would expect to lose some charge but not just outright die this early. 

They also have a full deep cycle version of that battery, which would probably be better, but think I will look into the golf cart ones instead.  Am I right to think that by going 6v because the cells are bigger there's also less chance of failure?  Ex: thicker plates, or do they just use more thin plates?

The inverter-charger floats at 13.5 pretty much constantly, which is good but it does have a bulk/equalize phase as well after a power outage.  It will go up to 14-15 volts for a bit.  Don't think I've ever seen it go past that.   Every now and then I'll turn the breaker off to the UPS as a routine capacity test, which also forces the inverter charger to charge at a higher voltage to somewhat give it an equalize once power is returned. (it's bulk/absorption charge really but guess it still kinda equalizes it).   This is it here: https://www.tripplite.com/750w-powerverter-aps-12vdc-120v-inverter-charger-auto-transfer-switching-2-outlets~APS750

Though you got me thinking... could lack of proper equalize be an issue causing sulfation of plates and more material to eventually shed?  I don't have any real control over telling it to do an equalize, but I could maybe just make sure to cut power to it more often to force it into it's bulk/absorb modes at least.

I do eventually want to look at a dual conversion setup with rectifiers/inverters and I'll probably end up making my own rectifiers as they are actually very hard to find.  They are used in telecom but not something that's really sold to individuals.   If done properly they can have different options such as weekly equalize.   A crude way would also be to use a solar charge controller, I think you can just feed a DC source straight to the input of one right?  As long as it can support that voltage. 
« Last Edit: May 16, 2019, 05:31:54 am by Red Squirrel »
 


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