Friday, February 03, 2006

Sometimes "good" batteries do bad things

Well, after several years now of working with SLA batteries, I still haven't learned nearly all my lessons!

I hooked one up to the power supply this morning that I received from the IT group at work (I have them trained to bring me all of the old UPS batteries that they don't want anymore). This afternoon, my family called me and said that there was a really bad smell coming from my office. It turned out that it was coming from that battery. It was having a difficult time venting through its built-in valves and seemed to be getting ready to expand rapidly (burst!). I wasn't about to touch it (let alone pick it up), but I did reach over to carefully unplug it. I let it cool down for a while until I figured it wouldn't follow through with its explosive intentions and I picked it up for photographing. As I type this almost 3 hours later, it's still quite warm.

Anyway, here are some of the lessons I learned:
  1. Never believe sticky notes placed on batteries unless you write them.
  2. Never hook questionable batteries up to an unintelligent source of power.
  3. Be extremely careful charging batteries indoors near things that can be damaged by heat, acid vapors, smoke, explosion, etc.
1. When I received this battery, it was in the pile that was being handed out to replace batteries in ailing UPS units around the company. The UPS at my desk had been complaining and I had requested a new battery for it. This is the one I was given. I put it in, but it did not work. This should have been my first clue that something was wrong! The "Good" sticky label on top obviously fooled someone else before it got me. Since there are no battery testers around (or at least no people in the IT department who use them), once things get mixed up, no one really know what is what. Shh, don't say anything, but I'm pretty sure that I've received several that have never been in service before. At any rate, I figured it was just dead from sitting around so I took it home to charge it up and see how "good" it really was.

2. I didn't test it on my smart charger to see if it would take a charge, was shorted or anything. I hooked it to my Amateur Radio 12 V 15 Amp power supply along with the other dozen or so batteries I usually have floating there. The power supply doesn't have a built-in meter, but I keep one that I made connected inline with the batteries so I can see what is happening. The needle jumped as it always does when hooking up a battery that has not been on charge for a while. As the voltage quickly rose to the level where the supply floats, the ammeter went down to a normal level. Nothing seemed amiss. I left for work.

I believe that something caused the cell to start drawing more power than it could handle and it began to heat up badly. My power supply is happy to deliver as much power as it takes (up to its 15 Amp limit) to keep a connected load at 13.8 volts. The casing bulged under the pressure which the valves didn't seem to release. Perhaps it was just that it was warm enough due to the internal problems that it deformed fairly easily even though the valves were doing their job and venting the gas that was building up inside.

I really don't know yet what caused the failure. I'll look around eventually and try to find answers, but if anyone knows right off and could point me in the right direction, I'd love to hear from you!

I'm no longer sure that a simple power supply is a good way to keep SLA batteries charged. Although I haven't had any fail while they were connected (this one was bad before I connected it), it seems to me that the possibility exists for this to happen. I'll have to do some more research and see what others think.

3. Thankfully, nothing tragic occurred. No fluid made it out of the battery in liquid form, but plenty of gas escaped and made the house smell pretty bad. It was also rather difficult to breathe comfortably in my office for about 15 minutes after I started the fans going. Had I not cut off the power and stopped whatever reaction was occuring, I'm not sure there would have been much left of my house.

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