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[JeffVolp]

While this isn't X10 related, I wanted to share this to alert others to use caution around lead acid batteries.

Some of you may know that we have a large UPS that powers a 15A "electronics circuit" in our home.  That circuit is isolated by a big 20A X10 filter, and it powers our computers and most other potential noise generators and signal suckers.  The UPS uses a bank of four large deep-cycle marine lead-acid batteries to carry a typical load for several hours.

Recently the UPS started giving an intermittent a low battery warning.  The electrolyte level in all batteries was fine.  Voltage measurements uncovered no shorted cells, so I was not sure what the problem could be.  I transferred that circuit back to utility power to bypass the UPS, and started to unplug the UPS to investigate the problem further.  As I unplugged the UPS, one of the batteries went BLAM, bounced both caps off the ceiling, and sprayed electrolyte from one cell that had cracked open.

Unplugging the UPS (the outlet is about 6 feet away from the battery) caused the UPS to switch on, and at that instant the battery blew.  Obviously, hydrogen gas in the battery had exploded, but I still don't understand why.  The vent caps were on all batteries.  They were not undergoing any fast charge at that point that might produce hydrogen.  My only guess is that particular cell was failing, and perhaps a spark was generated internally when the UPS switched on..

I since have replaced that one battery, and there have been no low battery warnings since then.  So clearly something was going wrong with that battery.

I had read warnings about being careful attaching jumper cables to a battery to avoid sparks near the battery to avoid a possible explosion.  In this case there was no spark near the battery, just a sudden increase in current draw.  It is just something to consider when working around lead acid batteries in the future.

Jeff

[Brian H]

I had one blow up in one of my cars.
Was a supposed to be maintenance free type. Though it had a way to access the top of the cells.
Well it was low on electrolyte.
When I tied to start the car. A big BANG.  My thoughts a spark inside a cell ignited the hydrogen gasses.
Top and one side was split.
Car want dead as there was no +12 volts.
Electrolyte sprayed all over the inside of the hood.
Car paint is not made to have electrolyte on it. The paint on the inside of the hood came off. Cleaned it off before the primer was also gone.

Auto parts store indicated they had seen many exploded car batteries and my experience was not rare. 

[dave w]

Dang!
I think I will be sure to don safety googles anytime I need to touch a car battery.

[JeffVolp]

I was sitting at the computer answering email during lunch yesterday, and heard a terrific crash.  I thought maybe one of the ceiling fixtures fell, but no.  Then I checked the pantry, but I couldn't find anything that had fallen there.  When I returned to the computer I found it was finishing booting up.  Ah ha...  So I headed downstairs and found the top of another lead acid battery had blown off, and acid was spreading across the floor.  After a quick run to the local grocery store for a big box of baking soda, I spent much of the afternoon cleaning up the mess.

Except for the cells that drained, the three good cells still had water covering the plates, so the water level wasn't low.  The battery was over 4 years old - dated 3/14 - but another one is dated 6/13.  The three good batteries read about 13.3V, and even the one blown apart still reads 12.6V.  So all were fine before the blast.  (In the past I had to replace batteries when a cell shorted.)

The UPS does an automatic self-test every two weeks to check battery capacity.  When it does that it transfers the load over to the battery.  Since power to the computer was interrupted, I suspect that is when the battery blew.

Jeff

[Brian H]

I got an indication on my APC a few days ago.
Self test passed. I noticed the LCD battery level display dropped to about 3/4 as soon as the test was run. Powering about 200 Watts of the rated 600 watts. Put a 400 watt bulb load on it and unplugged it. Battery level dropped to the about to shut down warning in maybe a minute. New one is here just warming back up from being outside.
Mine is a sealed lead acid battery with no filler type caps.

[JeffVolp]

Mine is a sealed lead acid battery with no filler type caps.

This is a big 2200VA APC unit I picked up during the dot com bust.  I converted it to run off a bank of 4 deep discharge marine batteries (48V series) that can be recharged from a solar array in an emergency.  (This UPS can do a cold-start if AC power is off.)

Every time I go into that room I check the LED indicator, which has shown full capacity.  The usual failure is a shorted cell, but this time all batteries appear to have been fine before the blast.

All connections were still solid and had to be loosened with a wrench.  I read on-line that sometimes there is a marginal connection between cells that can spark under load.  That's probably what happened.

I waited over an hour at Walmart today while they were deciding whether to issue the core return credit, which they eventually did.  The UPS is back in service again, but this time all batteries are in a large plastic bin.

Jeff

[brobin]

Over the last 5 years I've noticed that batteries aren't made as well as they used to be. All of the auto & boat service people I've spoken to agree the batteries rarely make to 4 years and they are seeing more cracks and splits.  I've noticed the same with smaller UPS/Alarm batteries as well.
Car batteries used to come with 100 month warranties (just returned one to Costco at 62 months) but now only the "best" offer a 36 month warranty. 
You might want to consider AGM instead of regular lead acid batteries. A little more expensive but perhaps safer. You may need new chargers if you do though.

[JeffVolp]

You might want to consider AGM instead of regular lead acid batteries. A little more expensive but perhaps safer.

I'm familiar with gel cells - replaced the standard 12V lead acid battery in our Toro electric trimming mower with a set of 6 Gates gel cells over 20 years ago, and it is still running.  It doesn't run as long on a charge as it did years ago, but all cells still read 2V.

The AGM batteries I looked at cost about 3 times the price of a standard 24DC deep-discharge lead acid battery.  The guarantee isn't much better either.  But maybe it is something to consider in the future.

Since this has happened twice now, I hope the plastic bin will contain the mess if it happens again.

Jeff

[racerfern]

1. My understanding is the difference between lead-acid batteries and cheaper ones is the amount of re-cycled lead in the batteries, vs. new. It makes sense that batteries don't last nearly as long since more of everything is re-cycled nowadays.

2. A battery wholesaler once told me the difference between some private label batteries is the label. A 36 month battery will cost you more than the 24 month or 12 month. They're all the same battery, you're paying for the warranty.

It makes me curious if it would make sense to build a battery bank out of 18650 batteries for some applications. https://www.makeuseof.com/tag/18650-battery/
My understanding is that the big battery backups are basically a big stack of 18650 batteries soldered together, but obviously much more complicated circuitry.

[dave w]

My understanding is that the big battery backups are basically a big stack of 18650 batteries soldered together, but obviously much more complicated circuitry.

FWIW blather follows.
Li-ions are very persnickety in the way they are charged and discharged. A "battery" (multiple cells) of 18650 cells must be balance charged or they can (explosive) vent and perhaps ignite.  A typical 16V laptop battery contains at least four 18650s in series, with each battery connected to a charge management PC board. For more current, a second bank of four is used, and so on. During charging, each cell is monitored individually for over charge conditions.

I tore apart a 20V, 10 amp, Weed Eater string trimmer battery and found it quite complex. Although part of the complexity was from discharge current monitoring circuitry to "turn off" the battery in the event of a motor jam or stall.

I have fun buying old computer batterie from thrift stores and harvesting the good cells. And then converting NiMH or NiCD devices to Li-ion. But in my conversions I mount the Li-ions on the outside of the device so I can remove them individually and charge them in a four slot Li-ion charger.

For the DIY,  Ebay has tons of Li-ion charge management boards for multi cell applications.