48v Li-Ion battery problem

[dylan]

Hi Guys
I have a problem with my battery pack, 48v Li-Ion from BMS battery about 18 Months old
Previously running perfectly from new, then one night just cut out halfway home
Wouldn't even spin the wheel with no load, just dead
It now gets me about 1 mile down the road & cuts out dead, no power, measuring 0 Volts
I charge it up & it runs normally until it does the same again & I have to pedal home
it has probably done about 200 recharge cycles
Normal usage is a guess at 25% power used then put on charge when I get home (if this makes a difference)
any ideas what's wrong & is there a way of fixing it or someone who can repair it rather than buy a new battery pack?
Appreciate any advice
Thanks
Dylan

 

[dylan]

Just checked the voltages
Fully charged 50.1v
road bike with very gentle power use for approx. 1 mile then it cut out - no power at all
voltage is 15.8v
just plugged it in to recharge again

 

[Ykick]

You're gonna need to measure individual cell voltages. Open 'er up, post some pics if you're not sure what/where to probe channel voltages.

Most likely a cell is dropping below ODDV (over discharge detection voltage) and you need to find which one and then determine if it can be re-balanced or if it's damaged beyond repair.

 

[dnmun]

no, not damaged, just unbalanced. post up a picture of your battery and BMS and keep it on the charger until it reaches full charge and then measure the cell voltages on the BMS where the sense wires plug in. put your voltmeter probes into the solder where the individaul pins are soldered to the pcb.

 

[d8veh]

Just checked the voltages
Fully charged 50.1v
road bike with very gentle power use for approx. 1 mile then it cut out - no power at all
voltage is 15.8v
just plugged it in to recharge again

50.1v is much to low. You have one or more low cells. You'll have to open it up to get at the BMS to measure the cell voltages to find out what's going on. Probably a knackered cell. Which battery is it exactly?

 

[dylan]

hi Guys
I really appreciate your help & advice - thank you
I have opened the battery (see attached pic)
I have measured the voltages as follows:
Pack = 50.3v after being on charge all night
Charger green light is on & fan on charger goes off when green light goes on
negative DVM lead on negative battery output connector
positive DVM lead on BMS PCB soldered pin on white connectors starting from the MOSFET end
1 = 0.4
2 = 3.2
3 = 6.7
4 = 10.3
5 = 13.9
6 = 18
7 = 22.2
8 = 26
9 = 30.2
10 = 34.4
11 = 38.3
12 = 42.2
13 = 46.4
14 = 50.3

 

[d8veh]

That gives cell voltages of
0.4
2.8
3.5
3.6
3.6
4.1
4.2
3.8
4.2
4.2
3.9
3.9
4.2
3.9

It doesn't look good, but might be recoverable enough to get some more use out of it. You need to charge the low cells to the same as the rest. You can use any USB charger or other 5v charger, or any that's for a 3.6v lithium battery. If you use a 5v one, you need to keep checking to make sure you don't go over 4.2v. It'll take a long time to get that 0.4v one up. You charge the low cells through the balance (white) leads. If the first one os 0v, you use the first two to charge cell 1, but if it's 0.4v, you have to use the battery pack ground for the negative charge lead. To charge the next cell, you use wires 2 and 3, and so on.

 

[d8veh]

I just read again and I see that it's a 48v battery, which normally means 13 cells. You have 14 results, so it could be that your 0.4v is actually 0v. I can oly count 13 channels on your BMS. The remedy is the same. Charge the low cells or discharge the high ones.

 

[Ykick]

What d8veh said. I agree, you're probably not measuring a cell voltage on that one end. Be very careful with the meter leads but try to probe across each "pair" of channel wires to verify the individual cell voltages. Although it looks like the cell @ 2.8V is probably the lame duck.

Figure out a way (again without shorting anything since they're close together) to rig an old USB or cellphone charger to the low cell. But be warned, those chargers float well above 4.2V so you either need to monitor it carefully so that it doesn't go over voltage on the cell or do what I did and rip an old cellphone battery apart - remove the BMS attached to the old cellphone battery and wire it into your 5V supply which will then protect Li-ion cell from overcharge condition.

There's a good chance the battery pack will come around if you bring up the low cell.

 

[dylan]

thanks guys
I have found a variable voltage charger, Set it to 4.5v (choice was 3, 4.5, 7.5v) & made some charging connections
I am charging pins 2 & 3 first (positive on pin 3 as it measured positive)
I am monitoring voltage across the pins as it charges & disconnecting charger to measure the cell every 30 mins or so (currently 3.6v & rising)
will I have to get all cells to exactly the same voltage or just the low one up to around 4?
will the BMS equal out the voltage of all the cells with normal charging once the low one is sorted?

 

[Ykick]

It will probably do some meaningful balancing once the duff cell is back into working voltage range. Leave it connected to the bulk charger a long time and check voltages to monitor to see if it's balancing.

 

[macnore]

Hi. I am new to this forum and I too have issues with my 48v Bionx battery. At first the range was great (50-70 km) . But on my last two trips a lot less (15km and 17.5respectfully). After the first fail I spoke to the dealer and he asked if I was sure. So on my next run (17.5km) I used only 25% assist. At that point I took the battery to the dealer. So far they have updated the firmware on the battery and will charge it through the winter for me. They will call in the spring and both myself and the dealer will take it for a test drive (me first). I am hoping that updating the controller will also help. Their diagnostics said the battery was fine. Only the firmware update was required.
Frankly I expected more from the battery although I have it engage at a very low speed and use the throttle to get me started if I have not geared down to a lower gear. I would like to get more speed out of the bike I can peddle up to 40-45 km on a good stretch of road and in town with limited bike paths I feel I am a road hazard at 32km, holding up traffic and pulling in to the parking lane and out again to allow other drives to get by.

 

[d8veh]

thanks guys
will I have to get all cells to exactly the same voltage or just the low one up to around 4?
will the BMS equal out the voltage of all the cells with normal charging once the low one is sorted?

It'll probably be much quicker, and you'll get more capacity, if you charge them all to about 4.15v.

 

[dnmun]

they will not balance until you charge the pack to over 4.20V/cell where the BMS will start balancing the cells. you need to increase the charger voltage to force it to balance.

 

[dylan]

hi Guys
I'm now in the process of charging each cell individually to as near to 4.2 v as I can
this will take a while...!
if this doesn't work where is a good place to get a replacement 48v 10ah battery pack?
last time I got it from BMS battery - low initial cost in $ USD but after shipping & import duty at the UK end, not so cheap...!
is there a UK battery builder that could either repair my battery pack or build a replacement cheaper than BMS Battery?

 

[d8veh]

Cyclecharge are a non-profit supplier, so they should ne cheap. Go to the UK Pedelecs forum and send a message to Morphix, who runs the Cyclecharge scheme. Woosh have the nice downtube ones at a very reasonable price.

 

[lbz5mc12]

I have a 48V 10Ah one from bms battery and it quit working right after about a year. I had a local guy look at it and he said all the cells are bad.

 

[dnmun]

you do not have to charge each cell individually. just use the reguglar charger and make sure it is set with an output voltage equal to full charge voltage at a minimum.

if you have one cell go above 4.20V while charging then use a power resistor and drain charge off of the high cell to keep it from overcharging up to HVC.

or use a light bulb to drain the charge off the high cell.