Old Ping Battery - Is my BMS Busted?

[MojoSlim]

Aloha,

BACKGROUND:
Built my ebike in 2012 (500w Cyclone mid-drive kit, 24v 20ah LiFePo4 on a standard Montague Paratrooper) with lots of help from Jim Olsen at Cyclone USA and lurking these forums. Rode it as a daily commuter to work in 3 states and haven't really had any issues since building. I moved back home to Maui in 2020 and the bike recently sat in storage for over a year after the Lahaina fires. and I am just now getting back the bandwidth to clean up the bike and get it running again on a new part of the island.

TOPIC OF MY POST:
I am having what appears to be battery or BMS issues. After pulling the bike from storage and connecting the battery to the charger (stock metal ping charger that came with the battery) the charger would immediately cycle on and off, with the 2nd LED light flipping back and forth from red to green - this had never happened before. Eventually, the timing between on/off(red/green) cycles became larger, to the point where the charger finally stayed solid green, at which point I assumed the battery was charged.

I didn't immediately install the battery back on the bike due to ... reasons, and finally did about a month later - no juice/no power light indicator on my archaic half twist shift throttle with red/yellow/green light battery indicator. Removed battery pack from its homemade case and placed back on charger... same on/off cycle, then finally goes green after overnight charging. Immediately test it on the bike, and what I would consider light load/lowest gear, immediately see throttle charge indicator drop from yellow to red - back off the throttle and back to green - not normal for the previous 12 years riding it. ???? Back to the house and back on the charger.

Out of the case and my waterproof wrapping, this is the first time (I'm ashamed to admit) that I have noticed the red light(s) on the BMS. After a bit of online sleuthing, I have learned that these lights indicate a full charge on the individual battery cells as well that the on/off cycling is that BMS attempting to balance all the cells (thanks to Basic Care and Trouble Shooting of a LiFePO4 E-bike Battery). On the BMS while charging, I have 1 solid red light (far left) and no other lights light up - this after leaving it on the charger for about 36 hours.

The charger is showing LED 1 Red and LED 2 Green for long periods with an occasional cycling of "charging." with a Multimeter, I checked the voltage output of my charger at 29.5-30V, where the battery plugs into the motor (red/black wires) at 27.5V. I also disconnected from the charger and unplugged the BMS and checked each cell getting the following voltage readings:

3.348
3.372
3.388
3.385
3.351
3.393

The numbers of each cell appears to be fairly close/balanced, or am I interpreting it wrong? So I'm wondering if my battery is really out of balance? The BMS looks a little....brown/heat damaged in some areas. Should I leave it charging for way longer (up to a week as the referenced Eric Hicks article suggests might be needed)? Might my BMS be damaged and needing replaced? I'm not very experienced with the electrical stuff - I'm a tinkerer/mechanically minded person, but I try to keep things easy as possible. Why is the charger staying green (indicating charge) but only 1 light on the BMS is lighting up. The battery indicator on the bike dropping while under load could just be bike being completely out of tune, needing badly a cleaning/lubing and tune-up. Would it be detrimental to hook it back up to the bike in this state and run it for a while to see what the range is that I get, or better to leave it on the charger for a long time to see if more BMS Lights show up. (sorry for all the what-ifs). I'm not too keen on the idea of buying a new battery, not just for the scarcity of 24V batteries on the market today, but especially with the nigh impossibility of getting a Lithium battery shipped to Hawaii.

Any and all insight would be greatly appreciated.

Mahalo nui,

MojoSlim

 

[amberwolf]

Most likely one or more cells are just unable to support the load. It's likely that some of the cells are self-discharging, or else it shouldn't be shutting down before you even use it, just sitting around.

If you've left the pack on the charger until the charger never restarts and all the BMS leds are out (or all lit, however that one works), then the pack is generally as "full" as it's going to get, because the BMS has disconnected the cahrger so it can't put any more into the cells, whenver the charger is not running.

Balancing just makes them all the same voltage--they are all still different capacities and resistances, so they all behave differently.

The ones that fill up first are usually the lowest capacity.

You can let it finish a charge, disocnnect from charger, then measure all the voltages. Then let it sit overnight off the charger, and see which cells are lower in voltage than the previous readings--those are probably self-discharging.

You can test for a BMS problem (balancer stuck on drianing a cell constantly) by measuring across each balancer resistor while it's just sitting there not charging and has no leds on. If there are any voltages across the reisistors, then those are stuck on, which means the little transistors for that channel failed shorted. Pretty rare failure, so unlikely.

You can test the whole pack by putting it on a load (bike, whatever) and measuring each cell's voltage (at the bms connector, for instance, measuring between each wire on that), as you put a little bit of load. Any cell that drops more in votlage than the others is in worse conditon than they are. If they all drop a lot, they're just worn out or too old.


BTW, if you only have six voltages of less than 3.4v each, but it's a 24v battery that reads 27.5v total, there are probably other cells you haven't measured yet. 3.4v x 6 is only 20.4v, so there are probably two more cells.

 

[fechter]

Try measuring the voltage across the cell that's lighting up while charging and discharging (putting a load on the battery).

If you're lucky, it could just be way out of balance and be recoverable. Leaving it on charge for a few days would get it closer.
If you're not lucky, that cell could be toast and not recoverable. You could try looking for new cells.

 

[MojoSlim]

To update this thread, after leaving the battery charging since my OP, I now have 7 of the 8 lights on my BMS solid, with the 8th switching between solid and blinking (mostly solid). I'm hoping that after another night I'll have 8 solid lights. I'll make sure to re-update if/when I get the 8th solid light and go for a ride. If the battery is indeed recovered/recoverable, I'll resume being incredibly impressed with the longevity of this 13 year old battery!

Most likely one or more cells are just unable to support the load. It's likely that some of the cells are self-discharging, or else it shouldn't be shutting down before you even use it, just sitting around.

If you've left the pack on the charger until the charger never restarts and all the BMS leds are out (or all lit, however that one works), then the pack is generally as "full" as it's going to get, because the BMS has disconnected the cahrger so it can't put any more into the cells, whenver the charger is not running.

Balancing just makes them all the same voltage--they are all still different capacities and resistances, so they all behave differently.

The ones that fill up first are usually the lowest capacity.

You can let it finish a charge, disocnnect from charger, then measure all the voltages. Then let it sit overnight off the charger, and see which cells are lower in voltage than the previous readings--those are probably self-discharging.

You can test for a BMS problem (balancer stuck on drianing a cell constantly) by measuring across each balancer resistor while it's just sitting there not charging and has no leds on. If there are any voltages across the reisistors, then those are stuck on, which means the little transistors for that channel failed shorted. Pretty rare failure, so unlikely.

You can test the whole pack by putting it on a load (bike, whatever) and measuring each cell's voltage (at the bms connector, for instance, measuring between each wire on that), as you put a little bit of load. Any cell that drops more in votlage than the others is in worse conditon than they are. If they all drop a lot, they're just worn out or too old.


BTW, if you only have six voltages of less than 3.4v each, but it's a 24v battery that reads 27.5v total, there are probably other cells you haven't measured yet. 3.4v x 6 is only 20.4v, so there are probably two more cells.

Mahalo e amberwolf for your reply. And thanks for the catch on my missing cell voltages. I have 8 wires going from/to the battery/bms. Black and red on the outsides with 6 in the middle. I totally skipped over a set, but perhaps the method I'm using is not correct or sufficient to test all the cells. I placed the probes of my multimeter on the 1st two copper contacts on the battery side bms connector, then moved both probes over, one by one, but that only gets me 7 readings. I'm not sure how I might go about getting the reading for an 8th cell, because yes, they do not add up to the complete 27.5v total, even with the 7th reading (also 3.3-3.4ish).

Regarding testing the whole pack, as you described above, after connecting the battery to my motor, would I then disconnect the BMS cables and test as I described in my previous paragraph? Thanks again for your help.

Try measuring the voltage across the cell that's lighting up while charging and discharging (putting a load on the battery).

If you're lucky, it could just be way out of balance and be recoverable. Leaving it on charge for a few days would get it closer.
If you're not lucky, that cell could be toast and not recoverable. You could try looking for new cells.

aloha e fechter. Mahalo for your reply. Hopefully I am lucky, as you hypothesized, as I mentioned above, I'm (potentially) close to having all 8 lights on my BMS solid. As I mentioned, getting any kind of battery with the word "Lithium" in it to Hawaii is tough, though I know not impossible (amazon ships me power tools with ...gasp...lithium batteries), just more hassle than most shippers want to deal with; a long accepted issue with living in the islands.



Aloha,
MojoSlim

 

[fechter]

Once you get all the cells lit up, disconnect the charger and wait about an hour, then measure the cell voltages. If they're all about the same, you're good to go. Bad cells will tend to start dropping voltage right away.

 

[amberwolf]

Mahalo e amberwolf for your reply. And thanks for the catch on my missing cell voltages. I have 8 wires going from/to the battery/bms. Black and red on the outsides with 6 in the middle. I totally skipped over a set, but perhaps the method I'm using is not correct or sufficient to test all the cells. I placed the probes of my multimeter on the 1st two copper contacts on the battery side bms connector, then moved both probes over, one by one, but that only gets me 7 readings. I'm not sure how I might go about getting the reading for an 8th cell, because yes, they do not add up to the complete 27.5v total, even with the 7th reading (also 3.3-3.4ish).

if it's an 8s pack (which istounds like) but the balance wires only have 8 wires, then the last cell is probably between the main battery - wire and the most negative balance wire.

Regarding testing the whole pack, as you described above, after connecting the battery to my motor, would I then disconnect the BMS cables and test as I described in my previous paragraph? Thanks again for your help.

if you're testing under load, you'd leave it all connected just like normal so you can measure to be sure what voltages you get in a completely normal situation. any of them that drop more than ohters for the same load are less capable than the rest.