New Ebike disaster, battery dead?
 

Hello all,

New to the forum and to the Ebike world. I recently purchased a rather inexpensive Ebike online to test the water and to see if I can give up my car at least partially. After two weeks of waiting, I am all excited to see a package arrive and there it is! A completely different bike than the one I ordered! Can't even find any information about the brand, but the manual says it has a 250 W motor and a 36 V 10 AH battery. After endless emails back and forth with the seller, they refunded me the full amount and said I could keep the bike. Not bad.

Today, I took it out for a spin for the first time and the battery turned off immediately after the motor kicked in. I played with the On and Off switch and turn it back on them same happened. Went home and plug it in, and its marking 75% full. What could be causing the problem? Is that a fuse failing? Is the battery defective? I would greatly appreciate any help.

If you never charged it at all, a new battery ships around 50% charged. In addition, it could be unbalanced which is when a few cells in the battery are lower in voltage. Normally, they are all close. Ebike batteries have safety circuits that check for low voltage and an unbalanced battery will shut off early, even if the gauges say partial charge, It's ironic, but the cells that power the safety circuits get unbalanced if the battery is left to sit for months,

Most batteries will rebalance if you recharge them to 100% and then give it some extra time to even out. Battery charging is best done when attended, but since that's impractical, do it somewhere where things are safe if the unthinkable happens and the battery catches on fire, I try to keep mine mine outside when charging.

Thank you for the response. I charged the battery to 100% yesterday. When to start it today and it seem dead, all the controls were non responsive as if no power, plug the charger in and it says its full? Any ideas?

try removing and reinsert the battery (if it is removable) If not removable, figure out how to disconnect it, then reconnect it.
Still not working? Since you got it for free, take it to a knowledgeable shop to diagnose for a small fee. It could be a bad battery or controller. It could be a loose connection or a faulty component or a short. Check the wire connector going into the hub axle.Maybe re-seat it. .

I hope these help

You'll have to show a photo or describe the bike.

Also, store and charge the battery in a place where you wouldn't mind having a fire.

The Forum won't allow me to post a picture until I have 10 post :(.

I initially ordered a black fat tire mountain bike, to fit my long legs, I am a 6" foot male, but instead I got this ladies cruiser in white :). Good thing gender isn't a thing these day. The battery is in the rear cargo rack and came disconnected. All the wiring is running through the main frame tube to the back. I don't have a throttle only pedal assist. The hub motor is in the back wheel.

I will try disconnecting the battery today and check the connectors. I keep reading about the fires, is that common?

Not common, but not fun and more likely with a problematic battery (if that's your situation).

When you buy a mail order bike, you need to assume the duties of a bike mechanic and know how to assemble it and tune it up. Not that hard for most hands on people.

When it's a mail order ebike, you need to have some electrical skills and knowledge. Owning a voltmeter becomes mandatory, as well as being able to spin the dial and know what it's doing. A healthy respect for electricity is important. The 48V in an ebike won't hurt you or me, but it could kill a crawling toddler who puts everything in his mouth. You also should realize the 36V or 48V in an ebike battery still has an instantaneous 1000watts behind it that can melt your probes if you cross them.

First thing is to verify you have voltage at the terminals of the battery. If it's a 36V battery, it will actually be 42.0 volts at full charge. The bike should run if you have at least 32 volts.

Your bike worked once, so that's encouraging. These cheap bikes, in my opinion, are simple enough that they should work. Most of the time, it's a bad connection. Is it a horizontal or a verycal rack battery?

Alright, I unplugged the battery this weekend and ran some tests. The problem is definitely the battery, even when disconnected from the bike it turns OFF off on its own. I called two local ebike shops and they won't touch Chinese stuff "because it is nothing but trouble." I guess I am gonna have to pull it apart and test the cells. Or just just get a new one.

Nothing but trouble. Have it recycled. Buy a new one and get a new charger too.

I am fighting similar case but on my own bike
 

Would be interested to know what you found, my battery was left a long time unused, about 4 months, but connected to bike.
When I plugged in the charger it went to fully charged (solid green light in my case)
My battery has a push tester it also showed 5 bars.
I measured 21v on the 43v nominal battery.
My research tells me my BmS will cut out at 2.75V power cell. 21v is less than 2v.

I have opened the pack. My battery has 4px 12s nominal 3.7v per cell.
Each cell was only at 1.6v but all cells were low.
Currently I am trying to charge back cell by cell through the bms wires with a small 18650 single cell charger. I've got 7 of the 12 fine so far and the cells seem to charge back up.
I suspect I have a bms system failure.
My smart charger is so smart I don't know what it is doing. There is some kind of communication needed with the bms before it will turn on.
I am hoping if I can partially charge the pack the bms might decide to start charging again.
With the available documentation it is so hard to know if issue is in cells, bms or the charger.

Get a tester on the main terminals, the charger terminal, and the fuse terminals.
This will show what's where.

Now open it and get a tester on the BMS.

I suspect there will be over 40v to the BMS, as the charger port is clearly giving full voltage to the charger, but it won't be allowing it out to the bike terminals.

Cheap Chinese batteries may have a duff BMS, bit of a lottery, I've fitted costly 8-mosfet ones in both my 48v batteries.

Fixed?! I am fighting similar case but on my own bike
 

Mikey thanks for reply

I think I got it kick started, the system seems overly complicated and the documentation and feedback support from mfr is very poor basically nonexistent.
If Bafang want to service the diy market they need to make some info available.


The product looks like it is good quality, mosfet Toshiba battery 2600ma and bms has 40A hand written on it for a 20a Max discharge rate battery pack.

How did I 'fix' it?

Open the pack
Disconnect bms.
Measure each 4p cell at 1.6v(cell minimum in spec is 2.75v)
Charge each 4p cell to 3.6v for the 12 series cells through bms cabling. This took 3 days.

Reconnect Bafang 5p smart charger and bms, voila, I get a red light and it seems to be back to life with 2 bars on battery LED indicator
This BMS has sleep and deep sleep modes but I am guessing I went beyond that point?

If I had an external power supply I could have avoided a lot of breaking things apart and just bulk charged from b+ and b- monitoring bms voltages manually.

I am praying that I have a rejuvenated pack.

I will be a wet blanket and say that 1.6V per cell is well below minimum voltage for a lithium cell. Best case, the cells will just lose some capacity. Worse case, the cells are at risk for internal short circuit.

I think 2Old said it best. Use, charge and store that battery in a place where you wouldn't mind a fire.