Need help with battery diagnosis and repair

[JeffD]

Hi All,

So I rode to work and plugged in my battery but it didn't charge. I ended up riding home the old fashioned way...ughh! I would really like to get my bike up and running again now that the weather is showing signs of improvement.

Unfortunately, I'm not very electrically technical so I'll need to rely on the forum experts to walk me through my next steps. Thanks in advance for your help.

I bought my 48V 12Ah Rectangular NiMH from ebikes.ca last April. I've put over 3000 miles on my bike.
I pulled some of the black heatshrink off my battery pack so I could give a little inspection and found that one or more cells looked like they had leaked or something.




What does this mean? What happened?
What are my next steps?

Any advise is greatly appreciated.
JeffD

 

[deardancer3]

Do a visual and electrical inspection of the pack. Any cell with an unusual looking shape or deformity will have to be replaced. inspect the case and try to determine the cause of the failure.

count the number of bad looking cells, take some more pictures and contact the vendor to determine if the pack needs to be replaced or if it can be repaired. From the picture, looks like your pack might have overheated? from charging or having a high internal resistance and a big load?

did you have any performance problems or differences with your pack recently? did you ever drop it?

I think your vendor is in vancouver, so not too far away.
d

 

[dnmun]

looks like your charger cooked it. i would recommend you email justin, he and zev know more than anybody else about the big nimh. i suspect you have been leaking from overcharging for awhile and the cell finally vented so much it won't conduct any current at all any more. if you don't know how to repair them, i ssupect zev will and they can check your charger too. seal ruptured and it vented from overcharge. do you know what the voltage was on the charger when it shut off the last time? shoulda not gone over 56.4V.

 

[dogman dan]

It does look like Justins nicad pack that got ruined by a charger on the epic ride. Is 3000 miles close to the expected lifespan for nimh? Maybe the pack has just reached it's lower end of expected lifespan and died of natural causes? That is a lot of riding. I'd be a bit leery of depending on that thing now, if a repair was made. Mabye get a new battery of some kind, and repair that one for use on a lower volt bike? For a longish commute, fretting over a battery is a real drag.

 

[monster]

get a multimeter and measure the voltage of the pack and of all the individual cells then get back to us with the results. i've cooked most of my packs at some point but they are usually ok. nimh is very resiliant. probably more likely the charger has broken and the battery is just flat. the battery looks fine i don't see any rust/scorch marks. if you cooked it dead then there would have been electrolyte condensing off all the surrounding surfaces and the whole room would have stunk of chemical smell.

 

[dnmun]

i think he had the one cell in the corner vent, maybe it is a dead charger. justin had his lithiums in parallel then and the charger didn't get a clean termination signal. still recommend you email justin, he knows more than all of us put together.

 

[JeffD]

Thank everyone for you comments, opinions and suggestions.

I'll see what kind of voltage is on the pack and the batteries as Monster suggested but I'm guessing the battery is completely flat at this point.

• At first glance I don't see any cells that are disformed.
• There is no smell from the battery at this time. It did get warm/hot during the charge and rides. The charger won't kick in until it detects that the battery has cooled enough to begin charging.
• I've never dropped my battery but I've crashed a couple times (hasn't everyone?) Nothing major...it was not like I crashed and then it stopped working.
• I'll also follow up as dnmun suggested with an email to Justin/Zeb @ ebikes
• "do you know what the voltage was on the charger when it shut off the last time?" - no my charger doesn't disclose that info to my knowledge.

Safety concerns: What is that crusty stuff that leaked out of my battery? Is it toxic? Am I in any danger of my pack expoding? When my wife saw it last night she made me move it outside. :lol:

Thanks again and I'll post an update in a couple days with new pictures.

 

[monster]

unless it got so hot you couldn't touch it i wouldn't worry. 60*C = some reduced performance & cycle life. 100*C = dead. it sounds like just the charger is dead. most electric bike chargers i've had seem to die after only 6 months.

if your battery is too small for your motor then this will also cause reduced performance & cycle life. that battery is probably safe at about 1000watts. do you have any meters to tell you what your demanding from it?

check the fuse also

 

[dnmun]

if you have voltmeter, just put it on the charger leads or you can measure the pack while charging. usually a 40S nicad will charge up through the 48V nominal point to about 1.41V/cell or 56.4V where the voltage drops as the charge increases. this is called dV/dt detection and the charger should be smart enuff to see it. but for nimh, the voltage drop as you overcharge is not as strong as it is for nicad and sometimes the charger loses the ability to see it (as the cells get older i suspect).

one of the interesting things about nicads is that the temperature actually drops when you start charging them from discharged state (endothermic), and they start getting hot when they are getting overcharged, so both endpoint detection methods (delta voltage or delta temp) involve the cells taking an overcharge hit each time they are charged. the venting is of hydrogen produced when there is nothing left to charge up inside, and the metal cylinders can contain it somewhat but eventually they leak and dry out which is how the die. usually. you actually have alotta miles on that pack.

 

[monster]

you would expect it to last longer than 150 cycles thats probably only half or third of its life. that is assuming you have not been canning it! it should still have some AH even after 500 cycles

 

[OneWayTraffic]

With a Cycle analyst what I'd do is put the charger on a timed power outlet. With modern self terminating timers this should be just a precaution but timers are only about $10.

Anyway most Nicad and Nimh problems in charging relate to knowing when to stop. Charging is the easy part.

If you have a Cycle Analyst and you should then one can calculate the time needed to replace the Amp hours used easily. So if your battery has used 6Ahr then put no more than 7-8Ahr back in before the timer switches off. The extra is for efficiency loss etc. Then the overcharge should be well within the ability of the cells to handle it without venting.

http://www.gtechno.com/cas/cascf.htm

for my source (Nicad based but Nimh is similar)

 

[Drunkskunk]

Safety concerns: What is that crusty stuff that leaked out of my battery? Is it toxic? Am I in any danger of my pack expoding? When my wife saw it last night she made me move it outside. :lol:

Thanks again and I'll post an update in a couple days with new pictures.

That crusty stuff is NiMh: Nickol Metal Hydride, as well as somesome dryed solvents, and electrolytes. Its not exactly anything I would want to eat, but it's not going to kill you if you touch it. It will stain, and it will corode metal, and might even etch glass if left long enough, so try to keep of anything you want to keep. Its Toxic, but handling it isn't going to hurt you.

There should be no danger of your battery exploding, but fire is always a danger with a high wattage battery so don't keep it someplace it could get wet and short out.

after 3000 miles, it should not have died like that, but cells sometimes fail. replacing just the bad cell would make it work again, but it would never balance easiluy as the new cell would preform diffrent from the older cells. at this point, its probably better to replace the whole battery.