Battery voltage drop when connecting to eBike

EbikeTinkerTime · Nov 4, 2024

Hi All! I am trying to troubleshoot an issue with my eBike/Moped and as a novice I was wondering if anyone had any troubleshooting tips! Thanks in advance.

Symptoms:
1. When ignition is turned to "On" position, the motor does not run. There are two LEDs on the controller and neither turn on. The speedometer display does give off a low backlight glow but is overall very dim and cannot view any of the displayed information. The lights do not turn on. The horn does not work.

Troubleshooting Steps:
1. Took battery (60V 26Ah) out and placed on charger for several hours.
2. Measured voltage across battery's connector (61.6 V).
3. Placed battery inside eBike and plugged in battery's connector to eBike's connector.
4. Measured voltage across eBike's circuit breaker in "off" position (61.6 V).
5. Measured voltage across eBike's circuit breaker in "on" position (10.9 V).
5. Repeated this step with the second eBike's connector (eBike has space for two battery packs) and measured similarly drop in voltage across the second circuit breaker.

From some background research online, I am wondering if the problem is related to the battery pack and more specifically the battery management system (BMS).

docw009 · Nov 4, 2024

Your description suggests it's shutting down under load. That's usually from a series group that is very weak, with enough voltage sag to trip the BMS low voltage alarm circuits. The other series groups have good charge. This is called an unbalanced battery,

It's reading 62V, but a 60V 16S lithium battery ought to read 67,2V at full charge. You can look at your charger label. The full voltage is printed on it,

I would put the battery back on the charger for about six hours to see if gets any higher in voltage, Take the usual cautions, no charging while unattended, etc, If it's still stuck at 62V, the battery is unbalanced. Not really repairable.

glennb · Nov 5, 2024

I’d guess it’s 15S. But .still, 61.6V is ample to power up the controller.

You asked for troubleshooting sdvice … unplug everything and start from there. So, one connection only, that between battery and controller. If the result is the same, disconnect battery and connect charger to the controller, with a fuse in series unless the charger already has a fuse. If you’re seeing the same issue, it ain’t the battery at fault.

glennb · Nov 5, 2024

By “issue”, I’m referring to the voltage drop when controller is powered on.

E-HP · Nov 5, 2024

EbikeTinkerTime said:
From some background research online, I am wondering if the problem is related to the battery pack and more specifically the battery management system (BMS).

Whether it’s the BMS or bad cell groups, the remedy will involve opening the battery case to access the BMS. Once the BMS is accessible, you’ll be able to confirm whether the BMS is bad, or if it’s working properly and shutting down the pack due to a bad cell group.

fechter · Nov 5, 2024

It’s behaving like the BMS is tripped. Either a bad cell group bad connection or a bad BMS.
I’ve had some that would reset if you charged briefly though the discharge (controller) wires.
You will probably need to take things apart enough to take individual cell group measurements.

Portugaline · Nov 7, 2024

Well sometimes ESC capacitors initial charging current trips the overcurrent protection. If it happens, just leave the battery connected for a few trip-cooldown cycles, until the capacitors are fully charged and do not trip the protection anymore. Or use some anti spark solutions to charge the ESC capacitors before plugging the battery in.

Give it a try

EbikeTinkerTime · Nov 8, 2024

docw009 said:
Your description suggests it's shutting down under load. That's usually from a series group that is very weak, with enough voltage sag to trip the BMS low voltage alarm circuits. The other series groups have good charge. This is called an unbalanced battery,

It's reading 62V, but a 60V 16S lithium battery ought to read 67,2V at full charge. You can look at your charger label. The full voltage is printed on it,

I would put the battery back on the charger for about six hours to see if gets any higher in voltage, Take the usual cautions, no charging while unattended, etc, If it's still stuck at 62V, the battery is unbalanced. Not really repairable.

Thanks for the tips! I took a look at the charger and you are correct (specs: 67.2 V, 5A).

I charged the battery for ~6 hours and then re-measured the voltage across the battery connector reading 61.6 V, so no change compared to before.

That being said, the battery charger is not behaving as I would expect. Per the battery charger label, there are two LED's to indicate charging status, LED 1 (Red) indicates Power on and LED 1 (Red) + LED 2 (Green) indicates charging/cut-off state (lithium battery).

Regardless of whether the battery is connected or not connected to the battery charger, both LED 1 and LED 2 stay on the entire time. The battery charger fan also does not appear to have turned on at any point. I did measure the voltage across the battery charger and that is reading 67.2 V. I also checked the battery charger's fuses and they both appear to be good.

EbikeTinkerTime · Nov 8, 2024

glennb said:
I’d guess it’s 15S. But .still, 61.6V is ample to power up the controller.

You asked for troubleshooting sdvice … unplug everything and start from there. So, one connection only, that between battery and controller. If the result is the same, disconnect battery and connect charger to the controller, with a fuse in series unless the charger already has a fuse. If you’re seeing the same issue, it ain’t the battery at fault.

glennb said:
By “issue”, I’m referring to the voltage drop when controller is powered on.

Thanks! I stripped the eBike down quite a bit so I will reassemble it (at least through the controller) and try this suggestion of plugging the battery charger directly to the eBike.

Battery voltage drop when connecting to eBike

EbikeTinkerTime

1 µW

docw009

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glennb

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glennb

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E-HP

100 GW

fechter

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Portugaline

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EbikeTinkerTime

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EbikeTinkerTime

1 µW

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