Why Do I Blow Up So Many Batteries?

[flypigs]

I recently had yet another set of off-the-shelf batteries blow up (overheat and swell, not explode). This time was a set of three 10.5ah SLA batteries, that I believe are PowerSonic brand.

But this is the 3rd set in about 3 years:

First a set of 8ah's on our 12.5 model (w/ a stock Oset charger).

Then a set of 10.5's on a 36v model (I then replaced the Oset charger with an ebay 36v charger)

Then this set of 10.5s on one of our two 36v models.

To the best of my knowledge, I haven't left these things on charge more than overnight, or 24 hours. I tested both of the two chargers we have (1 Oset and the one I bought on ebay) and both are putting out about 41v.

There aren't many things in common with these events:

3 different bikes

2 or 3 different chargers

A couple of different brands of batteries

Do I need to rig up a timer so these never charge more than a couple hours?

Pete

Edited August 6, 2012 by flypigs

[thats_a_five]

Wow, clearly these batteries are overheating. I have no direct knowledge of the Osets so don;t know if you charge them on board or out of the bike. For sure I would make sure they can get good ventilation then charging. Spread them apart for better air.

You say your charger is putting out 41 volts. Normal 12 volt chargers run about 13 volts. 3 batteries in series would mean 39 volts.

Have you tried charging one at a time with a 12 volt charger? I know that would take a long time but if it works you could make up a charging rig to charge in parallel.

[flypigs]

The Oset batteries charge while they remain mounted in the bikes. The 3 batteries are wired in series and the chargers that come with the bikes are labeled as 36v (or 24v for the smaller bikes). Both the Oset brand charger and the aftermarket charger are labled as 36v's, but both were almost identical in output at 41v.

IIRC, those chargers start at a higher voltage and drop down to trickle, but I don't know what the threshold is for the dropdown, or how I could measure the trickle rate.

Pete

[thats_a_five]

OK, thanks for the info. You should be able to measure the charge rate with an ammeter in line.

Is this happening soon after installing or after some amount of time or number of charges? Could be that the batteries just have a certain life span.

If this is happening to your bike and not others, I would check the wiring diagram to see if there is an on-board voltage regulator or zener diode that has failed.

Maybe not the best alternative but you might consider getting a cheap light timer to turn the charger on and off hourly to give the batteries time to cool while charging.

[gwhy]

those batterys do look a tad unhappy, I cant think of any single thing that could cause this when you have had different setups. If the charger is giving out exactly 41v ( this is one thing to check ) a fully charged sla is around 13.6v so 3X13.6 is 40.8v that means you will end up with a 0.2v trickle/topup charge when the battery is fully charged , the thing is most sla chargers are not smart and have just a fixed set output voltage then as the voltage of the battery increases with charge this in turn will reduce the charge current. The problem with charging sla's in series ( or any battery ) with a non-smart charger ( a fixed output voltage ) is that if a battery becomes tired, cells within the battery can become short ( instead of a 12v battery it now becomes a 10 or 8 or 6v battery ) and it could be this that is causing your problem, you will no longer have a 0.2v trickle/topup charge it could be more like 3 or 4 v which will not do any of the batterys anygood , once a battery is fully charged the excess charge current is got rid of in heat from the battery. Definatly get your self a cut off timer or invest in a smarter charger.