Well I went out to the garage this morning to get on my XB500 and head to work when I saw my battery charger was still running and there was an odd odor. The charger should not have still been running since it had been charging for well over 10 hours (and normally only takes 3-4 hours to fully charge) and I noticed the smell was coming from my 48v battery pack so I took it out and opened it up and discovered all 4 cells were blown. Here was the worst one:
Luckily I am still under the 6 month battery warranty so I shouldn't have to pay anything to get the replacements. I am hoping I can get 20AH replacements since the 500 comes with 12AH standard, I will pay extra if needed but I really would like the 20AH ones so I could get to work and back without needing to charge at work.
So, my first question is does anyone know how I could track down what caused the batteries to blow? If they didn't just go bad themselves then maybe the charger is on the fritz? How would I test the charger and is it possible to test it without hooking it up to the battery pack?
I have also heard about batteries overheating and since I live in Arizona I am worried maybe the heat had something to do with it. When I rode home from work yesterday it was around 100F out, at what temps should I be worried about damaging the batteries?
I had one more battery added outside the battery pack box to go to 60v and it looks just fine and has no bulges at all, that kind of makes me think it was just the other batteries that were bad and maybe the charger and the remainding battery is ok, is that a good assumption?
Thanks in advance for any input.
Hi Danga,
you now have first hand experience of a thermal runaway.
the standard charger doesn't temperature compensate the maximum charge voltage.
basically, the amount of current applied to a battery that is shunted by the "gassing" reaction increases with both voltage and temperature.
long story short (if you are really interested i can post the actual chemistry behind it) if the charger doesnt temperature compensate, the current in the constant voltage 2nd stage never falls below the "fully charge" threshold.
The charger therefore never shuts down and the batteries cook.
nothing suffered an "instant" failure, as it was a design flaw that caused the charger to cook the batteries.
a useful failsafe you could use is a timer on the charger.
unfortunately i cant recommend any particular temperature compensated charger as i never found one (though i didnt look all that hard, i changed to lithium, for this reason as well as a myriad of others).
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
The charger could also be bad. You could test it with a VOM. The voltage shouldn't get beyond 14.6V/battery. At that point, for a three-stage charger, the current should start to taper, when the current drops to a fairly low value, voltage should drop back to the float level.
The pack could also have gotten out of balance, triggering the thermal runaway.
I am a strong proponent of parallel charging, using a jumper plug to switch the pack to series for operation. You can then use a standard 12V charger and avoid many of the problems of battery balance that come up with SLA batteries, as discussed in the thread:
http://visforvoltage.org/forum/3166-seriesparallel-switching-charge-parallel-part-2-simplified
and my earlier comment:
I've had this working via PowerPole connectors, using a dummy plug to re-wire the pack as series for operation, and another plug that ties the 12V charger in to each battery in parallel for charging. It avoids multiple charger problems, such as varying cut-off points.
The maximum current draw is around 20 amps on my scoot, well under the 30A capacity of the PowerPole connectors I'm using, though you could get heavier capacity plugs for larger systems. The additional resistance due to the eight-fold passage through the plug and the extra 10ga wire in the path is quite slight, less than the original undersized 14ga "stock" pack wiring.
http://s200.photobucket.com/albums/aa122/mf70/Pack%20rewiring/
It's an either/or operation: parallel when charging and series when running, via the jumper plug.
Mark