SLA Battery Explosion and Prevention 4

[Dyno22]

I work in a lab doing start/stops on an engine using an automotive sealed lead acid battery that runs 24/7. Recently the battery exploded. It was determined that the battery had over 700,000 start cycles, so I was wondering if the high cycle counts could have contributed to a failure and can you use the number of cycles as a predictor to future failures where I could swap it out for a new battery?
My guess is that it’s not that easy due to many factors such as environment, battery variability, engine ratings, etc. Another issue I see is that we’re also using a 12V, 2/10 A charger during test to keep the battery charged which may have masked any battery problems and possibly caused an increase in hydrogen buildup in the battery.
If cycle counting is not practical, what other methods could I use to indicate a battery is potentially going bad? I was also thinking I could use a thermocouple attached to the battery to indicate a problem but what would be the location or would I need many locations. Also, what would be the temperature limit I would use to shut the system down? What about load or impedance checks to the battery once a week or after so many cycles? Could this be a good predictor of a battery failure?
Thanks for any comments or suggestions!

 

[MiketheEngineer]

Good ventilation??

 

[MikeHalloran]

I'd look for evidence of electrolyte loss, in the wreckage, or in any units that haven't exploded yet.



Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

That seems like an extraordinary number of cycles to me, perhaps you ran into a casing fatigue problem.

Cheers

Greg Locock


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[GregLocock]

Perhaps you should run a Weibull analysis using the termnated test methodology to see if you can usefully predict a life.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[zzzjim]

Any upward trends in extra charging may provide clues as to battery health .

Other end of life clues , Losing charge when not in use .

 

[DanEE]

I don't know much about the differences in the automotive SLAs i.e. what they do to handle the much more extreme temperature environments and yet still get effective gas recombination..

But the industrial e.g. GNB Absolyte SLA-AGMs must be floated to a quite specific and precise voltage that must track a voltage/temperature profile stated by the manufacturer..

If the voltage is off to one side, the battery tends to have excessive internal positive electrode corrosion (which will bulge the positive terminal upward at the case penetration point), and if off to the other side, hydrogen/oxygen recombination will not be fast enough and the battery will eventually start lifting the 2psi (setting on Absolytes) relief valves, venting gases, effectively drying out the battery due to the loss of un-recombined hydrogen and oxygen.

At any temperature beyond 95 deg F for sustained periods while on float, there is high probability the battery will enter thermal runaway.. I don't know how the automotive SLAs avoid this, since underhood temps can be well beyond 95 deg.

This is one of the best publicly available papers on SLA/AGM gas recombination..

http://www.tms.org/pubs/journals/JOM/0101/Nelson-0101.html

A bit dated, but good info.. There may be some clues with regard to your app and what this paper calls for, at least on the industrial version SLA-AGMs.

I would wonder about your excessive cycle count and how well you were within the float/bulk charge voltage/temperature parameters for this battery.

Another area I've always been concerned about internal cell strap welds breaking (fairly common) inside multi-cell batteries and possibility of subsequent internal arcing in the presence of hydrogen and oxygen. A typical symptom is sudden battery failure (cracked weld) sometimes followed by battery explosion.

 

[KiwiMace]

Sounds like a venting problem on battery that was far past it's life expectancy. Was the vent valve able to be inspected?

Why not use regular (open, vented) wet cells?
SLA or VRLA batteries are known for shorter cycle life. Wet cells emit more H2 but one wet cell battery will not cause major ventilation issues. Use a battery with a transparent casing so the liquid level is easy to maintain.

 

[waross]

I have seen that quite a few times. I don't know the cause but I have a loose theory.
First this is generally a hydrogen explosion. A hydrogen explosion takes the top of the battery off level with the top of the plates. An overload explosion is generally caused by excess heat and possibly steam pressure from boiling electrolyte. Often the end is blown out of the battery.
In mostly unattended standby generators, the battery eventually fails and eventually the set fails to start when the grid power fails.
However, if the set is equipped with a trickle charger the battery lasts a few months longer and when the battery does fail it explodes. I would get a call that the set had failed to start for a grid failure and find an exploded battery. My theory is that the charge current starts producing brown gas. (A mixture of hydrogen and oxygen.)
The electrolyte level has probably dropped below the top of the plates. The starting current, either by local heat or by a spark between the dry plates ignites the gas and away it goes. A periodic load test may be used to indicate end of life loss of capacity of the battery so that it may be changed before it fails. I would suggest test about every 3 to six months but at the same interval. Track the test results and when the battery capacity starts to drop off more quickly, change out the battery.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zzzjim]

the charge current starts producing brown gas. (A mixture of hydrogen and oxygen.)

This is your enemy ,it is just so Explosive . A consequence of over-charging .

Waross Has a good answer , but you may need extra batteries and a safe way to swap them about . Any vented gas will be unkind if you make sparks near it !

 

[Dyno22]

Thank you everyone for your input. It's great to see so many ideas and suggestions being put forth.

A couple of things came to light after further investigation that I wanted to share. First, at the time of the event, there was a problem with starting the engine which consequently had depleted the battery. A short amount of time was given to the battery to recover before another attempt to start the engine was initiated. This is when the battery blew. As Waross theorized, using a battery that was close to end of life, possibly low in electrolytic and with hydrogen gas building up, was a recipe for an event during the cranking event.

Secondly, it appears that a 1200W power supply was used in conjunction with the trickle chargers which have since been removed due to redundancy of the power supply. The PS was set to 14.5 volts and isolated from the cranking event but would be across the battery in all other cases. By observation, it seems that with a fully charged battery and a setting of 14.5v, the battery would accept a charge. As I lower the setting to 13.5v, around 13.8 the battery stops drawing current. I realize that if the electrolytic is low, the chances of an explosive event increases regardless but does a lower setting of the PS have any benefits like reducing overcharging and minimizing electrolytic loss and gas buildup? Does a lower setting cause other issues that may not be apparent now?