Batteries Don't Explode

[DFL1010]

Not mine, thankfully. Certainly made a bit of a noise when they went.

 

[RichardS]

Unlikely it was topped up, filler caps are flush and hidden under label.

I don't think that it's a sealed battery.

Richard

 

[DFL1010]

I don't think that it's a sealed battery.

Richard

Well, it sure ain't now.

 

[yotter]

I replaced my batteries in the winter, they have caps at top of each cell so can be topped up. They came with a plug in a vent hole (during transit), this is removed and a thin pipe attached (vent pipe I assume). I wonder if the plug was not removed if enough pressure would build up to cause an explosion is the batteries were gassing during charging?

 

[RichardS]

I replaced my batteries in the winter, they have caps at top of each cell so can be topped up. They came with a plug in a vent hole (during transit), this is removed and a thin pipe attached (vent pipe I assume). I wonder if the plug was not removed if enough pressure would build up to cause an explosion is the batteries were gassing during charging?

The answer is yes. However, we don't know whether that was the case in Paul's photo. I suspect that it was not but until the vent operation is confirmed we cannot be sure.

Richard

 

[AntarcticPilot]

I'd be very interested to strip that battery down to see what happened. As others have said the vent pipe is connected and the battery exploded from the inside. This is not necessarily a hydrogen explosion. A dead short within the battery with vaporised lead may induce a similar pressure rise. If hydrogen inside the battery was ignited by starting currents it would suggest that the plates were exposed. When/how often was the water topped up? The over pressure looks like it may have been in the third cell from the bottom of the photo. Interesting one to look into.

Could be a two stage thing. Initial smallish bang from a hydrogen explosion, which distorts the plates to give a dead short, resulting in a much bigger steam explosion. I wouldn't have thought there was enough volume for a hydrogen explosion to be the main event.

 

[Juan Twothree]

This happened aboard an angling boat we were called out to. Only they didn't tell us why they couldn't start their engine.

It was only as we were coming back into the harbour that one of the occupants mentioned that the acid on his skin was starting to sting a bit.

 

[pvb]

One observation I'd make is that AGM batteries have a much lower risk of exploding. The boat in question is a Bavaria from around 2012, and I believe that Bavaria routinely fitted AGM batteries at that time. I'd guess that the Banner flooded battery was installed by someone to replace an AGM.

 

[Bilgediver]

I had often wondered about this, however I recently discovered it was quite true. A group of divers had come to our marina to launch a RIB but found the battery was flat in the RIB. The battery was removed and placed close to the Land-rover in order to try and charge it via booster cables. There was an explosion which lifted the whole top off the battery with flying debris injuring one person who required hospital treatment.

The thing that annoyed me about the battery which was identical to one on my boat was that the plates were only half the height of the battery presumably to give the low maintenance by the fluid level having further to drop before uncovering the plates. I think I would prefer full size plates and topping up plugs.

If you have a long life fluid filled battery then just familiarise yourself how to top it up. On some the indicator unscrews. I suspect the low fluid level in this battery might have allowed an internal spark.

 

[pyrojames]

Could be a two stage thing. Initial smallish bang from a hydrogen explosion, which distorts the plates to give a dead short, resulting in a much bigger steam explosion. I wouldn't have thought there was enough volume for a hydrogen explosion to be the main event.

With Hydrogen, you will get approximately an 8 times expansion when it goes off. In a confined space, it will go off extremely quickly, but it needs a spark, or unusually high temperatures (well in excess of the melting point of lead). For an internal explosion in a sealed battery, there is most likely to have been and internal spark. As for H2 explosions, even with the caps open, the flame speed will be to high for the caps to vent the explosion pressure. Seeing as the explosion occurred on cranking the engine, I'd suspect an internal electrical fault that couldn't cope with the current demand and fused. As I said, I'd love to be able to go through it in detail.

 

[penberth3]

With Hydrogen, you will get approximately an 8 times expansion when it goes off. In a confined space, it will go off extremely quickly, but it needs a spark, or unusually high temperatures (well in excess of the melting point of lead). For an internal explosion in a sealed battery, there is most likely to have been and internal spark. As for H2 explosions, even with the caps open, the flame speed will be to high for the caps to vent the explosion pressure. Seeing as the explosion occurred on cranking the engine, I'd suspect an internal electrical fault that couldn't cope with the current demand and fused. As I said, I'd love to be able to go through it in detail.

Disagree. An external explosion will follow the gas back to it's source, i.e. inside the battery. I've heard about it happening through the vent of a "sealed" battery. The vent wasn't designed to stop flame.

 

[penberth3]

This happened aboard an angling boat we were called out to. Only they didn't tell us why they couldn't start their engine.

It was only as we were coming back into the harbour that one of the occupants mentioned that the acid on his skin was starting to sting a bit.

Hmmm, wiring like a rat's nest, I'm not surprised they had a problem!

 

[pyrojames]

Disagree. An external explosion will follow the gas back to it's source, i.e. inside the battery. I've heard about it happening through the vent of a "sealed" battery. The vent wasn't designed to stop flame.

A flame might propagate back down the vent line, but this would mean that there was enough accumulated hydrogen outside the battery box/locker to be spark ignited. Under those circumstances, I would expect over-pressure damage in other areas of the boat as well, unless the vent line vented close to the spark. I would hope that the vent line went to atmosphere and not to the engine bay!

 

[JumbleDuck]

Disagree. An external explosion will follow the gas back to it's source, i.e. inside the battery. I've heard about it happening through the vent of a "sealed" battery. The vent wasn't designed to stop flame.

Chemists please correct me when I go wrong ...

What's produced in the battery is H2 + 1/2 O2. 1 mol (2g) or hydrogen and 1/2 mol oxygen (16g) occupy 1.5 x 22.7 = 34 litres at stp. The enthalpy of combustion of hydrogen is 286 kJ/mol, so when those 2g go bang they release 572 kJ from 34 litres of mixture at STP, which is 16.8 kJ/litre. Making a wild guess that the void space in the top of a battery is 1 litre and that if the vent gets bunged up it can reach 2 bar before caps pop off, that's 33.6 kJ available in a battery, which is about 1/30 of a stick of dynamite (~1MJ) or about 1g of black powder.

[Maths updated and better value for energy in blackpowder used. Thanks, PJ]

 

[pyrojames]

Your chemistry is OK, not sure about your maths! 1.5 x 22.7 = 34.... and then you don't have 2 bar in the battery, because its vented, so you only have 12.6kJ in total. However. you then need to look at the specific heats of H2, H2O, O2 and N2 to calculate the pressure rise and thermal expansion, and account for any heat losses and mixing with air.

From playing with hydrogen in the lab, its products ie water (and N2 if there was any) get to around 2400 K once the hydrogen has been consumed, and rule of thumb in the lab was an 8 times expansion in air. You might get a bit more in the battery, if it not well ventilated, but not when the battery ruptures.

 

[JumbleDuck]

Your chemistry is OK, not sure about your maths! 1.5 x 22.7 = 34.... and then you don't have 2 bar in the battery, because its vented, so you only have 12.6kJ in total.

D'oh. Don't know how I managed that. I was thinking of the "blocked vent" case. As I have said before, I had a cell fail in the DS battery and a charger which thought "Only 10V? This battery needs charging" and kept on pumping 3.8A though it. The battery didn't explode, thank goodness, but it did pop off the covers, so I presume it's designed by Herr Bosch to run above 1bar if needed.

However. you then need to look at the specific heats of H2, H2O, O2 and N2 to calculate the pressure rise and thermal expansion, and account for any heat losses and mixing with air.

Steam table would probably do it, bu a bit laboriously. Really needs a Moller diagram to read temperature against specific enthalpy and specific volume. Or just accept that it will be a bit of a bang ... but will it be a battery-destroying bang?

 

[vas]

this scary thread is a good push for LiFePO4
I also had a battery explode on me while I was rebuilding the boat but happened while I was away with the charger on...
Good thing I don't see any pics of T105 exploding watering kit and watering them every month or so

 

[starfire]

This is what happens when you have an electrical fire, earlier this week. Both onboard jumped in & are unharmed

 

[Graham376]

I don't think that it's a sealed battery.

Richard

Look at the photo, the flush filler plugs are clearly visible by the handles, normally hidden under the label.

 

[Homer J]

I found this thread distinctly alarming. How best to avoid this happening? Are some batteries safer?