Exploding Lead-Acid Battery

[hgordon]

Hi there,

This 12V maintainable lead-acid battery runs in series with another to make 24V to start a diesel fire pump. See photo.
The battery exploded from a gas and ignition source, and evidence points to a explosion when the battery was not starting the diesel.
i.e. simply sitting and being float charged.
There must have been hydrogen gas and an arcing ignition source on the cell cross plate as shown in the photo.
What I am confused about is why this would happen??
I checked the other three batteries (2 more for backup starting) and the electrolytes cover the lead plates, even the exploded battery still has electrolyte over the lead plates.
If anyone has any knowledge on this - would be great.

Thanks,

 

[itsmoked]

Just use the

to directly post your pictures.

Defective battery, possibly contamination or bad bonding of a plate. When current is demanded something turns red-hot and a long float can certainly make the perfect gas cloud.

Are you sure all cells are filled over the plates? Just one being low greatly increases the potential problem. A single cell can have bad bonding to the plates. This causes that one cell to be much lower capacity than the rest of the normal cells in the battery. That results in the bad cell having much lower capacity than the rest. In charging it will be fully charged before the rest and start gassing, transporting it's water into gasses that vent causing that one cell to bare its plates.

Glad no one was injured. It's a good reminder to always wear face protection around batteries and to know where the eye-wash station is located.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hgordon]

Thanks Keith,

I just went to site, 3 out of 6 of the cells were covered in electrolyte, the other 3 have long cracks down the plastic cell wall which the acid would have leaked from, so it is too hard to tell if they were submerged or not. From what I can tell the end of the cracks is where the acid level is - so indicates the cells were submerged.

So do you think the explosion requires the battery on load (diesel cranking) to make the ignition source?
See photo, it appears the cast-on-strap is where the ignition source was.

The battery is constantly on a float battery charger - which can make a good gas cloud?
No one was injured made a mess on the concrete with acid.

 

[ScottyUK]

The plate buckling is a sign of several different possible problems including deep discharge or charging at too high a rate, and could have given rise to stress on the discoloured inter-cell joint which is a credible ignition source for the explosion. Equally it may simply have been a poor joint.

 

[itsmoked]

hgordon; I'm with Scotty here in that I bet the battery was being thrashed in some manner. Overcharging can be pretty common. (Hope that wasn't my fire system battery charger design - LOL)

That blown battery strap is definitely the ignition source. Yes, it typically would've taken a start to light it up. To me the inter-cell connection looks pretty lame. A rivet that includes some plastic... <shudder>

L.A. batteries greatly prefer cyclic charging over float charging. A smart charger that shuts off and lets the battery coast for a week or two then does a top-off would make LAs happier. But, with fire equipment you tend to get what's approved and have little say in what you actually get.

The battery manufacturer's data sheet will state the float voltage. The temperature is critical in that respect. If the battery is in a warm place and the charger doesn't compensate it will off-gas and dry out quickly.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hgordon]

Thanks guys, I am trying to write a small report on this and am reading some different articles.
There is mention of sulfation a lot and how it reduces battery capacity and life but nothing about if it relates to gassing i.e. sulfation does not seem to contribute to gassing.
The way I see it now is that they are related? Hard sulfate reduces the acid content therefore voltage of a cell.
Therefore the cell is now at a lower capcacity and when it is being charged, the reaction of removing the leadsulfate stops prematurely and starts to gas the water instead?
It stops prematurely because the hard sulfate needs more voltage say 14.4V + to remove it from the plates. the float charge of 13.5V is not enough.
Seems like a logical theory but I cannot find anyything to support it.

Thanks,

 

[itsmoked]

Sulfation is the standard aging-out process of a battery. It removes participating plate area, less plate area, less cell capacity.

That said, sulfating of the plates of a battery is almost always a uniform process. One plate or one cell is not going to spontaneously sulfate. If it did then definitely you'd have individual cells losing capacity and then the situation I described above would take place. One cell massively over charging and hence boiling-off and electrolyzing the water.

Sulfating doesn't generally occur on fully charged or even floated batteries. I would expect fire equipment emergency batteries to always be charged and to not sulfate, at least for several years ~5+. Discharged batteries left in a discharged state sulfate at an alarming rate. Some gelcells will fully sulfate overnight. Flooded batteries like yours sulfate more slowly. Typically if left for a month or two in a discharged state or a week or two if left 'flat'.

The thing about sulfating is that all the cells will do it at about the same rate. This means your entire battery loses capacity relatively uniformly. To a battery charger it will just think it's charging a smaller battery and gassing will not particularly increase in any meaningful way.

To remove sulfation you use an equalizing cycle. That greatly over charges a battery hopefully breaking the much harder sulfate bonds. Equalizing batteries is a bit traumatic to batteries and is usually done with informed human assistance.

In your case I would first make sure the charger is not bonkers, set wrong (obscenely common) or the battery temperatures are not normal nor compensated for. Next I'd check that the batteries in an emergency service setting are monitored and logged and that they get annually or semiannually tested. They should have their specific gravity checked and logged cell to cell. These three points will 95% of the time lead to the problem.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[hgordon]

Thanks itsmoked, that's very helpful, I am looking at different cause and effects and which ones are realistic for this scenario.
I don't think sulfonation is a cause, also no visible buildups can be seen in the photo.
Thanks,

 

[ScottyUK]

You might want to look into the reasons why the plates have buckled. The evidence is there in the battery, have a read up on what it is trying to tell you.

 

[hgordon]

So looks like buckling is caused by overcharge or overdischarge, or using it in a low charge state, as well as non-uniform distribution of current over the plates. Low electrolyte probably creates some buckling as well.

So believe it or not another battery as exploded at another site. This is a sealed wet LA battery ("maintenance free"). All the cells were covered with electrolyte. But the difference in this battery is there is some white solids build up between the plates in all cells, which I am thinking is lead-sulfate buildup.
The batteries are kept at a float charge rate of 27.5 V (two batteries in series,) Same as other battery that blew, same charger model too. Which I think is a typical float charge voltage (13.8V per battery, 2.29V per cell). If anything is noticable from the photos please let me know. Thanks,

 

[ScottyUK]

Have you ever carried out an equalizing charge on the battery? You may need to disconnect the load during equalisation because the battery voltage will be a few volts higher than when on float, unless you're confident the load can handle the higher voltage.

 

[itsmoked]

Something is seriously wrong here.

I've only ever seen three batteries explode. One was a defective battery in a vehicle being jumped that ruptured. The other two had someone welding over them. I also had one of my diesel dual batteries on the side of Mt Whitney short a plate. This dumped the other fully charged battery into it and the 200A alternator kicked into overdrive into it too. We saw steam coming from the engine compartment pulled over and shut down and we could hear the battery boiling from 20 feet away with the insulated hood shut. It did not rupture or explode.

How old are these batteries?

What make are they?

Are they the same model?

What is the average temperature they are subjected to?

Does the temperature fluctuate much on a day to day basis?



Keith Cress
kcress -

http://www.flaminsystems.com

 

[hgordon]

Yeah it is strange as my boss has not had this occur in his career which is like 15 yrs.
Now there has been two over 3 weeks..
The 1st battery was 4 yrs and the 2nd 4.5 yrs old. Different brands, 1st is Super Charge and 2nd is Century.
We are meant to replace them every 4 years as per the standard.
The pump rooms are large and I did not notice any heat, and it was a sunny day. The pump rooms need proper ventilation so the diesel engine does not heat the room too much, <18degC above ambient. Highest temperature is 25-30 deg C in summer but recently 20deg C max.
Temperatures do drop down to maybe 14-15 deg C at night.
We look after 100's of fire pump rooms in Auckland City that run off diesels so 2/100's isn't too bad but it is strange.
This battery blew on diesel start up with a bang and a buff of smoke.

Another question - if cells touch eachother and create a short-circuit, they are usually under the electryolyre level so can they really ignite the H2, O2 gas?
Surely the spark needs to come from above the liquid?
Below is the battery charger - looks to have a high charge and low charge rate.

 

[hgordon]

I believe in both cases the inter-cell welds are loose and have created the spark.
Possibly the weld is bad or the vibration of the diesel next to the batteries has fractured the weld due to fatigue.

 

[ScottyUK]

You may be right about the source of the spark, it's hard for us to judgefrom photos.

The sulphate formation is indicative of poor charging conditions. I think on that charger 'high rate' is probably the current-limited mode and 'low rate' is the float charge at constant voltage. An equalise charge is different, with a higher target voltage - not something you see on most small chargers.