BATTERY EXPLOSION 1

[vmac100]

Good day all.

I have a bank of batteries (165pcs) serving my 150kVA HITEC rotary UPS. This machine has been down for a while, but the batteries were being charged through the rectifier.

Yesterday, one of the batteries exploded. What I have done right now is to remove the rectifier from service and stop charging the batteries.

Does anyone have any ideas why this explosion occured? The ventilation in the battery room is okay.

All ideas will be appreciated. Thanks

 

[wbd]

How old are the batteries? When was the last time a through visial inspection was done (assuming the jars are clear)? What I'm thinking that there may have been some internal shorts and if you were in a high charge, generating lots of Hydrogen gas, there could have been a spark.
The positive plate grid structure is the most age sensitive component. These plates tend to "grow" and cause internal shorts. Another possibility is that the container failed, I'm thinking around the flame arrestor, creating a path which would create a explosion hazard.
Have you contacted the manufacturer?

 

[vmac100]

The batteries are four years old.

 

[jtkirb]

we have seen problems with broken joints, bad plates, etc causing arcing or other problems. You may have to do a full inspection and load check to find further problems.

JTK

 

[itsmoked]

Yes I believe what happens is a particular battery's plates start to crumble and two plates get bridged with debri. When this happens the battery is essentially shorted thru that bit of debri. The debri being a high resistance essentially explodes creating an ignition source inside a battery. POOF!

Here's a shot of those results:

 

[waross]

Hey, I like the picture, itsmoked.
I have seen two failure modes for batteries.
1> Heavy or short circuit current. The electrolyte boils and steam pressure blows the case. The battery is most likely to blow out one end (or both ends). That is the greatest area for the steam pressure to act on.
2> Hydrogen explosion. Much more violent. More damage to the battery top. The first one I saw was in an old car. The battery was leveled at the top of the plates. The hood of the car was peppered with tiny dents from the inside out made by the force of the broken bits of plastic that used to be the top of the battery.

I have a battery explosion about every 14 to 16 months in a residential genset. (Not the same set) Typically 18 KVA to 50 KVA Gensets. Automotive batteries. The older sets without battery chargers never explode. The newer sets, starting about 7 or 8 years ago have battery chargers.

My theory is that as the battery starts to fail there is more leakage current internally that discharges the battery when it is sitting. With a charger, the charger supplies the leakage or internal discharge past the time when the battery should be replaced. Eventually, the internal leakage current increases to the point were it starts overheating. This overheating may be in a fairly localized area. There's probably a lot of hydrogen being developed, and the heat has evaporated some of the electrolyte so there is more volume for the explosive air-hydrogen mixture. With the battery in poor condition the starting voltage is low and that leads to increased starting current.
BANG. Get the baking soda and clean up.
That's my theory. Comments?

 

[itsmoked]

#2 Sounds like a likely scenario... Have to think about #1...

The pictured battery was in a house boat that had a solar panel running thru a charge controller. So it sat there being charged forever.

When the skipper went to start the vehicle a large scary blast was heard.

So it was a large current draw that triggered it. I suspect a whisker between plates that may have shorted a cell. That leads to the other cells being massively over charged. When the key is turned the short becomes a fuse.

Good lessons here as to the caution that should be given batteries, that most of us probably normally give little respect to.