Battery dead? Kona eUte

[jakehrosenberg]

Thanks again to everybody who helped get my Electric Kona Ute back on the road, https://endless-sphere.com/forums/viewtopic.php?f=3&t=73710&hilit=kona+ute

Now I have a new problem. My battery pack won't charge above about 13.5V. Here's the specs on the battery: Samsung 18650 Lithium Ion batteries, 24-volt x 13Ah. And attached are a picture of the pack, as well as what I guess is the BMS (pardon my sons artwork). The charger is putting about 29V into the BMS, but with the charger hooked up, the battery pack still never gets above 13.5V. Each bank of 18650s reads about 1.9V, and all 7 are pretty close to the same voltage. It's possible that the BMS has a couple of components that are melted which leads me to believe that the batteries are possibly OK and it's just the BMS that's toast. How would I confirm that? Do I just wire the charger directly to the battery and watch it real closely? Could I replace the BMS with something like this http://tinyurl.com/h346gs9 ? I don't want to sink too much money into this current setup because, as previously noted, it's seriously underpowered and I'd like to save up to repower it. That being said, I'm willing to put the $18 into it to keep it on the road while I wait, and if I do repower it I could possibly put these components on a lighter bike.

Thanks!

 

[amberwolf]

Each bank of 18650s reads about 1.9V, and all 7 are pretty close to the same voltage.

THen the cells are toast and need to be replaced. You might be able to individually recharge the groups with a single-cell charger, but after having dropped that low they'll never be the same and could be a fire risk.

It's possible that the BMS has a couple of components that are melted

I don't see any melted parts, but if so then that's toast too, unless you know or can find what caused it, and know what the components were to find replacements and have the skill/tools to repair it.

 

[jakehrosenberg]

Thanks amberwolf, I guess I was hoping that I could just charge it up, replace the BMS and milk it along for a little while, but it sounds like that's not the case.

 

[izeman]

the question is: how's your electric knowledge and what tools do you have to fix it?
first good thing is, that you seem to have a DMM and measured the cell's voltages. that's the correct start.
do you have an adjustable power supply? something that can be set to 4.2V and max 2A current?
if so you can remove the BMS's balance plug and start charging individual cell strings through it. ideally you would use a 2-pin header and stick it into the plug. take care of polarity! and start with a low current such as 100 or 200mA. you can then raise it as soon as the string has reached around 2.7V. but don't exceed 2A (maybe 3A), as the plug is rated for 3A max and the wires are a little thin.

 

[izeman]

btw: if you don't have a bench power supply you make look through your old cell phone chargers. eg nokia used 3.7V directly. it's good enough to lift the string's voltage to a value where the BMS should start charging again and won't overcharge the batteries if you forget to remove it. charging will take A LONG time that way. they are around 300mA output.

 

[jakehrosenberg]

btw: if you don't have a bench power supply you make look through your old cell phone chargers. eg nokia used 3.7V directly. it's good enough to lift the string's voltage to a value where the BMS should start charging again and won't overcharge the batteries if you forget to remove it. charging will take A LONG time that way. they are around 300mA output.

Thanks izeman! I don't have a power supply, and just enough knowledge to be dangerous. Maybe I'll try the cell phone charger idea and see how that goes. So I assume I want to get all the cells up a little bit, then hook it up to the regular charger and hope that will finish them off? What voltage should I be looking to get them too with the cell charger?

 

[izeman]

exactly. bring them ALL up to a voltage where the BMS identifies them as "not undercharged" and then let the BMS to the charging.
i would guess that low voltage cutoff would be something between 2.5-2.7V. with 3V you should be on the 100% safe side.