We have a backup generator at a remote communiction tower site that uses a regular lead acid 12V battery for starting. It has a keep alive system that keeps the battery charged @ 14V and 55mA up to .2A depending on its charge state. Just recently we found its battery failed and the side of the battery had a huge crack in it from the top of the battery to about midway down the case. We can't figure out why it exploded as the entire system (and charging system) checks out fine according to its technical and troubleshooting manual. Anyone know why a battery can fail like that. I will try to get pics of it later.

 

Was it freezing cold? I've had batteries freeze in the car while I was driving through a blizzard.

Other than that it's possible the water got low which caused the plates to corrode and eventually if you get a short or spark in there it will ignite the hydrogen/oxygen and BAM!

I also had a battery break once when I hit a big dip at high speed and the battery wasn't tied down.

Edwin

 

I've seen one charged @100 amps all night(14+ hours) explode. Rusted the every piece of steel int he ceiling of the shop.

 

As part of a lead-acid batteries normal operation, hydrogen gas is evolved from the electrolyte (as is oxygen I think). That's the bubbles one typically can see inside each cell.

An internal fault that might create a spark is all it takes to set it off.


This is why it's safe practice to connect the grounds of our truck jumper cables to a metallic object >away< from the battery as the final connection. That way we don't ignite the gas.

 

Not cold at all. Quite the opposite. I'm stationed in Guam which has a tropical climate, where its either hot and dry or hot and rainy. Temps range from 75°-95º year round.

 

I would say the gas caused the explosion, although I have only had one blow up from freezing

 

A buddy once went to start his car, and the battery promptly exploded. Blew the top corner off.

Our best guess was that age/vibration cracked some conductor in there, that caused an arc when a load was applied...

Weather was warm, and the car had been running a few minutes ago (so the battery had hydrogen gas from charging).

Anyhow, it isn't unheard of for a lead/acid battery to explode for no apparent reason.

In addition to making the last jumper connection away from the battery, I also make sure I have glasses on.

 

As I said earlier, here are the pictures of it. The terminal that is nearest the crack is the positive (+) terminal.

 

Looks like it sparked right at the positive post, could have been a loose connection.

 

Connection at the terminals was nice and tight. I did peek inside with a flashlight and saw that 2 of the plates were not straight, rather they were warped. I suspect it was internal failure. Makes sense to me as it blew out the sides.

 

JR, 14vdc is too much float voltage for a typical standby L-A starting battery. That is enough voltage to thoroughly charge a battery that has been in cycle service, not standby service. The little charger probably ought to be set to somewhere around 13.25 to 13.6 depending on type of battery(wet cell or Gel-cell, etc).
At that voltage(14v), you are constantly overcharging the battery, oxidizing the positive plates and causing the positive plates to swell from the corrosion to the metallic lead in the cast grid of the +plate. That expansion causes warping of the plates as they grow in width too. As they warp, they also shed those little globs of active lead they are SUPPOSED to retain reducing the capacity of that cell even further.
The electrolyte level goes way down below the plate level as it slowly disassociates the H2O, into H2 and O2 gas from the "gentle"(?) overcharge. Very low electrolyte level means LOTS more volume of explosive H2 and O2 gases in each cell. All it takes is ONE cell to get really low and a little TEENY TINY spark happen between damp plates under load(like during starting)....BANG! The emptier the cell, the bigger the bang!!!
If the plates grow so much that they are greatly warped, they can cause a direct short to the negative side causing a BIG spark that lights off that explosive gas mixture even without putting a load on the battery...


I still take care of lots of good sized UPS and generator equipment (and their batts) at the salt mine and have had some "interesting" times with all those batteries over the years ...
Just this year, they've contracted all the batt maintenance out to a worthless contract company. They don't do a thing to keep them up but they take our Co's money all the same...After all, their ulterior motive is to $ell our Co. $ome more batterie$

K.

 

Great explanation Kieth, that makes a lot of sense. Also explains why I didn't find much acid spilled inside the generator. I will see if there is a way to adjust the voltage on the charger. Thanks Kieth.

 

JR, I had forgotten to ask you if you found any liquid inside the batt compartment... I guess that answers one question.
Another question, was it in 12v service, or are there two in series for 24v starting service?

In your pics it does look like it could be one of those "maintenance free", sealed, AGM type car batteries. If so, that could explain why no liquid.. If it truly IS a sealed AGM batt, there won't be any "liquid" sloshing around inside even when new. It is all absorbed into a dense mat of fiberglas held in close contact with each plate, and each cell is sealed to the outside world with a rubber relief valve to let out the overcharge gases.
Personally I've had more trouble with sealed, AGM(absorbed glass mat) car batteries because if they ARE being overcharged, you can't really tell until something goes BANG or they don't crank the engine, which is usually the case. Sealed/Valve Regulated, Lead-Acid AGM batts have a low tolerance for chronic overcharging, as their float/recharge voltages are critical for standby service life. They just dry-out, and there is very little water in them to begin with... They can even crack the case and catch fire from the plates swelling up(smaller PowerSonic type batts seem to be more prone to that malady).

(BTW, I'm taking another chance on sealed batts in my CTD with Red Top Optima's)

Trying to get the right "float" voltage on any standby starting battery is sometimes tough. It is pretty much walking a tightrope between them crapping out due to undercharge (sulphation) or overcharge (+plate corrosion).

Our plant has had quite a bit of battery troubles on the diesel firepumps(a b5.9 and an 855 bigcam Cummins) They've blown them up enough over the years that nowdays, the mechanics tend to just replace one dual redundant 24v pair of 8d batts on an annual basis. These OEM firepump controllers have built-in batt chargers with really crude voltage regulation(1970s vintage). Each engine has its own Motorola alternator, but they both have that darned little 1amp, battery destroying, poorly regulated, "trickle charger" that overcharges both of those batts.

K.

 

Kieth, it was/is a maintenance free lead acid battery made by AC Delco. If I peek inside the batt with a flashlight I do see liquid (very little), I will double check that in the morning.

That batt is a 450 Amp service 12V battery that is used to start a 12kW 2 cylinder Generac/Guardian standby generator. Only one is needed to start this generator. When its not running the battery charger is always active (assuming there is utility power available). If utility power goes out the generator starts and runs. The charger then engages a relay to draw power from the generator to continue to charge the battery. When utility power is restored it switches back. So the battery is in a constant state of charge minus a periodic engine startup.

 

There is a type of charging circuit that periodically stops charging and samples the battery to determine if it is fully charged. It stops charging if the battery is full. Years ago I had a charger made by HeathKit that used this circuit.

Edwin