Battery problem. Diagnose?

[MP3test]

Hello,

I have a LFP-4810S-LT battery (48V/10AH). The charger is HP8204L3 (golden motor's dedicated).

When trying to charge it, the charger works for really short time and turns off (width a green light i.e. the battery should be charged). When attached to the bike (MP3) the indicators show low power. So the sort charging time reflects in low power. Haven't tried if everything will result as a sort ride time as I didn't wanted to push it by hand.

But the lights at the bike grip are just the red and yellow with yellow turn off after really short time, so I guess the power is really low.

The question is - how to diagnose the problem? Is the battery died for some reason? To be honest, I haven't charged it for almost a year which may be lead to its dead. Do you have any experience with such a situation?

[Bikemad]

These batteries should be charged every 6-8 weeks if they are not being regularly used to prevent the voltage from falling too low, so it's possible that one or more of the battery's cells may have been damaged if it has not been charged for a whole year. 
Hopefully, if you're really lucky, it might just be due to one of the cells holding its voltage over time much better than the others, and this could cause the cells to be unbalanced and the BMS may be disconnecting the charger when the highest cell reaches the maximum cell voltage (3.65V) well before the other weaker cells have all been able to reach a similar voltage.

Leave the battery on charge until the green light comes on and then measure the voltage at the power output socket (with the key turned to the "ON" position) while the charger's green light is on. If it is a lot lower than 58V then leave the battery on charge for 24 hours (to hopefully allow the cells to become more evenly balanced) and then check the output voltage again.

If the voltage has increased significantly over the 24 hour period but is still not above 57V, I would suggest leaving it on charge for even longer to see if the cells will balance even more, allowing the battery voltage to increase nearer to the expected charge termination voltage (58.4 V).

However, if the voltage does not noticeably change (and is still a lot lower than the 58.4V charging voltage) you may have to dismantle the pack to enable each of the cell voltages to be checked individually to try and locate the cause of the problem.

Alan
 

[MP3test]

Thank you for your answer.

Well I know the "6-8 weeks" rule, but I initially proved that it is not so important as after I ordered the battery 3 years ago I haven't time to assemble the bike again almost for a year
Then it worked perfectly and I was able to drive 40-50km (25-30 miles) per charge. Then in the winter I had a plan to build electronic powermeter and had to measure the voltage while the battery is self discharging for some stats, but then I forgot about that project until I rebuild yesterday the bike and was surprised by what I shared.

I charged the battery once however I didn't noticed how long it got for the charged to auto switch off. I noticed the grip meter problem and that's why I drove just 1-2km (1 mile). Then at home charged again to see what happens the charger worked just for some minutes i.e. like the battery is charged.

So one of the possibilities is that the battery is good, but the power meter (just 3 leds - red, yellow green) is not measuring well for some reason.

Now I measured the unplugged battery (after left alone for several hours) and the voltage is 57.24V which is pretty good and is not a sign of a bad battery... Now I plugged in to the charger to see when it turns out what the voltage will be. But as far as I recall (can't find my notes from the past) this was the normal voltage of a fully charged battery.

So my plan is to try to drive it tomorrow for longer time to see if it will shut down earlier than usual.

Is it possible that a shortened wire somewhere in the bike is causing what I've seen today (voltage drop)? Actually I am not sure if the voltage is low. After the battery is charged now I will attach it and will measure the voltage at the lights wire that comes out in the grip. As far as I remember it was about 53V.

[MP3test]

And an update:
- the charger was off
- turned on again, worked for several seconds and turned off again

Measured the battery immediately and the voltage was 58.2V with slightly lowering by 0.01 per 5 seconds.
Then the stable voltage is 57 and something.
Yet again looks like a good battery.

Attached to the bike and measured the voltage coming from the lights connector and it was 57.24 again slightly lowering by 0.01V per some seconds.

Only red and yellow lights turned on (on the grip power meter) and while checking the voltage above, the yellow light turned off, so only the red is on, like the battery is out of power. So having 57.24 at lights connector and at the same time the grip showing out of power is indication that there is something wrong with the power meter, not the battery, is that right?

But is it just a power meter problem or is it a sign of a bigger problem in the electronics? Or may be I have to check the setup of the motor controller - I don't remember what were the possibilities but if while experimenting I've set it as it is using 60V power, it will not light the leds on the grip for full power in that situation.

[MP3test]

Now after some hours, the voltage of unplugged battery dropped to 54.4 which I remember was OK (is it?).

There is no 60V setting for the controller so this is not the case of power meter showing red light... Must be something else.

[Bikemad]

Attached to the bike and measured the voltage coming from the lights connector and it was 57.24 again slightly lowering by 0.01V per some seconds.

Only red and yellow lights turned on (on the grip power meter) and while checking the voltage above, the yellow light turned off, so only the red is on, like the battery is out of power. So having 57.24 at lights connector and at the same time the grip showing out of power is indication that there is something wrong with the power meter, not the battery, is that right?

I must admit that it does sound like the battery meter is playing up and is not indicating the correct battery level in relation to the measured voltage.

My GM 48V 10Ah LiFePO₄ battery charges to just over 58V and drops to around 57V within 5~10 minutes of disconnecting the charger (with the bike's power plug still unplugged) but I don't recall it dropping a further 2.5V over just a few hours.
I have just checked my battery voltage (which hasn't been plugged in or used since it was last charged in June) and it is now reading 53.5V.

If your battery was ordered 3 years ago, it must be a lot older than mine which I've only had for just under a year.

So my plan is to try to drive it tomorrow for longer time to see if it will shut down earlier than usual.

I hope your range is still about the same, and not considerably lower than it used to be.



Alan
 

[MP3test]

This is something useful I found in another forum - someone has measured and logged the voltage depending on Ah drained from the battery:

From that log here are representative resting voltages after some rides with the amount of Amp-hours used;

52.8V 2.8Ah
52.7V 4.1Ah
52.4V 6.7Ah
52.2V 7.3Ah
51.8V 8.3Ah
51.5V 9.0Ah

Mine currently is at 54.2V charged yesterday, so it's way above an empty bat, while the light at the grip shows red. But my main concern is not to have some wire shortened at the grip to cause the faulty power meter. Nothing blew so far, so may be just the meter has it's own mind for some reason