Have exactly same battery. Bms jbd 30A will do just fine.
M820 Bafang - LIGHTCARBON LCE930 Frame (lightweight)
- Thread starter mike_kelly
- Start date
Hi! Very nice build! I was wondering what size of the dropper you use here? I ordered a KS 900i 125mm and worried it might be too high for me, I'm 5'3.
i’m interested to see how you go with the battery build
Hey guys, I noticed that the lower rear shock bolt is a bit loose inside the rearshock. Are there any replacement I can purchase in Aliexpress? I tried 2 hardware (fox) already, and there is still a very minimal movement. SPecially when picking up the frame.
hi borris, im getting the same issue now, but it seems it's the provided m8 bolt. Did you sandwich it inside the bolt? or inside the hardware? I'm getting vertical rattle, specially when picking up the bike.
I have been using the JBD Bluetooth Smart BMS 20A for over a year without any problems.
temon10
Well-known member
size of this bms small??
Hi all,
Looking for some help. I have an LCE930 frame with a Bafang M820, one year of use, never a single issue until now.
Here's what happened:
- Went for a ride, came back with 19% battery
- Washed the bike (no pressure washer), left it in the sun to dry
- Forgot it outside overnight
- Next morning: display completely black, won't turn on
- Plugged in the charger: display came on once, showed 19% (correct pre-wash value), so I turned it off to let it charge
- Came back a couple hours later, unplugged charger → black screen again
- Reconnected charger, waited until green light → still black, nothing
- Disconnected motor and battery, inspected all connectors: no visible corrosion, no damage, all seated
- Battery charges to 100%, less than one year old
I found Migli54's post earlier in this thread about the black plug next to the yellow plug on the motor not being seated hard enough, and Crackerman confirming the fix. but i don't think this is my case as I've already reseated the plug multiple times.
Thanks!
Looking for some help. I have an LCE930 frame with a Bafang M820, one year of use, never a single issue until now.
Here's what happened:
- Went for a ride, came back with 19% battery
- Washed the bike (no pressure washer), left it in the sun to dry
- Forgot it outside overnight
- Next morning: display completely black, won't turn on
- Plugged in the charger: display came on once, showed 19% (correct pre-wash value), so I turned it off to let it charge
- Came back a couple hours later, unplugged charger → black screen again
- Reconnected charger, waited until green light → still black, nothing
- Disconnected motor and battery, inspected all connectors: no visible corrosion, no damage, all seated
- Battery charges to 100%, less than one year old
I found Migli54's post earlier in this thread about the black plug next to the yellow plug on the motor not being seated hard enough, and Crackerman confirming the fix. but i don't think this is my case as I've already reseated the plug multiple times.
Thanks!
no expierence with m820 yet but i had similar problems on my mates m510 bike
on his the motor casing screws got loose and the paper seal was dried out, this made it possible for water to enter and fuck up his power board (where all the plugs go in)
it was 25,- on ali and after replacing it and the paper seal and some loctite and grease it worked fine again.
just saying it could be something like that
what bafang canbus cable you running ? some have the 1t4 canbus cable but dont use all the ports. if water enters one connection you are ducked.
not what u want to hear but todo some proper problem solving you need to dissambly the bike and check everything.
even something simple like a speed sensor cable that is to tight can duck your controller. i had that happen myself. it was to short and it broke first try as the suspension cycled. it caused a internal short and burned a controller
look for damages on all cables, maybe it was stuck somewhere and finally after some rides it decided to stop working?
i never wash my bikes with water tho
good-luck!
on his the motor casing screws got loose and the paper seal was dried out, this made it possible for water to enter and fuck up his power board (where all the plugs go in)
it was 25,- on ali and after replacing it and the paper seal and some loctite and grease it worked fine again.
just saying it could be something like that
what bafang canbus cable you running ? some have the 1t4 canbus cable but dont use all the ports. if water enters one connection you are ducked.
not what u want to hear but todo some proper problem solving you need to dissambly the bike and check everything.
even something simple like a speed sensor cable that is to tight can duck your controller. i had that happen myself. it was to short and it broke first try as the suspension cycled. it caused a internal short and burned a controller
look for damages on all cables, maybe it was stuck somewhere and finally after some rides it decided to stop working?
i never wash my bikes with water tho
good-luck!
Goff
Active member
Hi
The fact it powers up with the changer is a good thing, it’s the bms doing what should do, you most likely have water in the battery, sometimes they will reset by themselves, you should remove the battery and check for signs of moisture
Thanks both, really appreciate the detailed input.
@kaaskopf — good shout on the motor casing. I had a look and the paper seal still seems properly glued and I don't see any signs of water inside the casing itself, so I don't think that's it in my case. What's more suspicious though: the cables exit through the headset area, and the dropper post cable grommet up there is pretty beaten up. I haven't pulled out all the electrical cables yet, but it's very possible one of them got damaged somewhere along the routing — maybe pinched by the suspension cycle, like you described on your own controller burn. Sounds like the only way to be sure is to strip the bike down and inspect every cable end-to-end. No way around it.
On the 1T4 / unused ports point — that's a good one I hadn't considered. I'll check what exactly I have and whether any unused port is open to moisture.
@Goff — small correction on my original post, sorry if I wasn't clear: it only powered up with the charger that very first time. Since then it stays black whether the charger is plugged in or not, including after a full charge to green light. So the BMS "wake" theory doesn't quite fit anymore. That said, pulling the battery out and checking for any moisture inside is on my list anyway before I go deeper.
Going to tear it down this weekend and inspect everything cable by cable. Will report back with what I find. Thanks again!
@kaaskopf — good shout on the motor casing. I had a look and the paper seal still seems properly glued and I don't see any signs of water inside the casing itself, so I don't think that's it in my case. What's more suspicious though: the cables exit through the headset area, and the dropper post cable grommet up there is pretty beaten up. I haven't pulled out all the electrical cables yet, but it's very possible one of them got damaged somewhere along the routing — maybe pinched by the suspension cycle, like you described on your own controller burn. Sounds like the only way to be sure is to strip the bike down and inspect every cable end-to-end. No way around it.
On the 1T4 / unused ports point — that's a good one I hadn't considered. I'll check what exactly I have and whether any unused port is open to moisture.
@Goff — small correction on my original post, sorry if I wasn't clear: it only powered up with the charger that very first time. Since then it stays black whether the charger is plugged in or not, including after a full charge to green light. So the BMS "wake" theory doesn't quite fit anymore. That said, pulling the battery out and checking for any moisture inside is on my list anyway before I go deeper.
Going to tear it down this weekend and inspect everything cable by cable. Will report back with what I find. Thanks again!
I’ve experienced a specific glitch with my M820 that might be happening to you as well (though it could be something else entirely).
If you’re using a custom-built battery with a Smart BMS, go into the control app and cut the power to the motor for at least 5 seconds. Once you restore the power, try to start the motor immediately.
If you don't have a Smart BMS, you’ll need to physically disconnect the motor from the power source. After reconnecting it, try to start it up right away.
To this day, I still haven't figured out what the root cause is. I’ve replaced the motor controller, the 1T1 cable, the display, and the remote buttons... nothing helped. I read somewhere that a faulty torque sensor (TQ sensor) caused similar issues for someone else, but I’m not sure if that’s the case here too.
Quick update — you were onto something.
I stripped the bike down to the bench: motor, battery and display loose, all cables visually perfect, battery at 93%. Reconnected everything on the bench and tried to power on — dead. Then I did your trick: disconnected the battery, waited 5 seconds, reconnected, hit power immediately → it booted. Turned it off, tried to turn it on again normally → dead. Did the disconnect-reconnect-boot trick again → works every time.
So the pattern is 100% reproducible: normal power on = dead, disconnect battery → wait 5 sec → reconnect → press power immediately = boots fine. Every single time.
All cables look perfect, no corrosion, no damage. It's clearly not a hardware connection issue since the trick works reliably. Feels like some kind of controller or BMS state that doesn't reset properly on a normal power cycle.
Did you ever figure out the root cause on yours? And is the disconnect-reconnect trick something you still have to do every time, or did it eventually sort itself out?
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I have this same issue. No idea what the reason is, but luckily I have smart bms so I can do it from phone. First I did not like it, but now when I got used to it, it is like a soft lock for the bike. No way any "normal" person could figure this out.
If you don't have smart bms, maybe you can have a hidden switch somewhere?
Had the same with M820 motor. IMHO some kind of firmware issue. Had to reconnect the power every time to ride the bike.
Solution is simple. You have to ride the bike and drain the battery completely to 0% until the PAS is gone.
Than leave the bike to turn off. Next day charge the bike and it resets some parameters and works OK.
Goff
Active member
You need to try another battery, any 36 volt ebike battery will do.
I’m not expert but have done a lot of trial and error, I did have more of major electrical problem with mine that was caused by the cable getting damaged at the head set and caused a short due rubbing on the fork steerer and to replace the controller twice in the motor. I have a few bafang motors, displays, diy batteries so it’s an only way to eliminate what is happening, displays and cables are not that expensive so it pays to have spares.
It was driving me nuts having to connect to the BMS app every time, so I wired up a NC (normally closed) switch and tucked it near the motor side cover. Now, whenever I need to get the bike going, I just hold it down for a few seconds, let go, and I'm good to ride!
Never tried that before!
Does that reset fix it for good, or is it just a one-time thing?I should add that for the last few months, everything was working flawlessly—it basically fixed itself—but about two weeks ago the issue came back, and it's annoying as hell.
If his problem is the same as mine, none of those fixes will do squat! It doesn't matter if you swap the battery, use a lab power supply, or try new cables, displays, and buttons. I’ve even ruled out any loose connections or contact issues... The problem is buried somewhere in the motor’s electronics, and even after swapping in a brand-new controller, it was still acting up (which totally blew my mind).
Despite all the headache, I’d hate to get rid of this motor. Yeah, it’s loud, but paired with FakeTaxi and the LCE930, it’s absolutely badass. It just rides like a dream!
So. You use fake taxi. Does, those have the same problem use the same firmware ?It was driving me nuts having to connect to the BMS app every time, so I wired up a NC (normally closed) switch and tucked it near the motor side cover. Now, whenever I need to get the bike going, I just hold it down for a few seconds, let go, and I'm good to ride!
Never tried that before!
I should add that for the last few months, everything was working flawlessly—it basically fixed itself—but about two weeks ago the issue came back, and it's annoying as hell.
If his problem is the same as mine, none of those fixes will do squat! It doesn't matter if you swap the battery, use a lab power supply, or try new cables, displays, and buttons. I’ve even ruled out any loose connections or contact issues... The problem is buried somewhere in the motor’s electronics, and even after swapping in a brand-new controller, it was still acting up (which totally blew my mind).
Despite all the headache, I’d hate to get rid of this motor. Yeah, it’s loud, but paired with FakeTaxi and the LCE930, it’s absolutely badass. It just rides like a dream!
It was driving me nuts having to connect to the BMS app every time, so I wired up a NC (normally closed) switch and tucked it near the motor side cover. Now, whenever I need to get the bike going, I just hold it down for a few seconds, let go, and I'm good to ride!
Never tried that before!
I should add that for the last few months, everything was working flawlessly—it basically fixed itself—but about two weeks ago the issue came back, and it's annoying as hell.
If his problem is the same as mine, none of those fixes will do squat! It doesn't matter if you swap the battery, use a lab power supply, or try new cables, displays, and buttons. I’ve even ruled out any loose connections or contact issues... The problem is buried somewhere in the motor’s electronics, and even after swapping in a brand-new controller, it was still acting up (which totally blew my mind).
Despite all the headache, I’d hate to get rid of this motor. Yeah, it’s loud, but paired with FakeTaxi and the LCE930, it’s absolutely badass. It just rides like a dream!
In order to solve ''not turning on 2nd time M820'' problem I have tried changing display, on/off switch and controller board from the motor itself. Somehow data is transferred/synced when You connect 1 new component.
One of the forum members had exactly the same problem and mentioned that discharging the battery all the way down helped. It also helped in my case.
Probably some battery level values are resetted during full discharge.
Pozdrawiam
Thank you for your reply. I searched all over AliExpress but couldn't find anything. I also contacted Bafang, and they said that only the bike manufacturer has this cable. LightCarbon hasn't replied yet to let me know if they'll send it to me.
xtraman122
Well-known member
These cables should be readily available on Ali/Aliexpress. If anything you may need to contact a seller like Fieldebikes and just chat with them, show them the connectors you need and they should be able to guide you in the right direction.
Thanks for the tip. I contacted Fieldebikes last week, and we found the cable I need. They should be sending it this week.
Thanks for your help
So i had a new issue. I have been planning to change bearings in the linkage. Not because of bad bearings, only because it is already ridden over 5000 km on stock bearings. Old ones are still smooth.
Yesterday I noticed big play on the left side chainstay/seatstay bearing, like 2-3 mm. So opened it up and it was not the bearings. It was the bearing cup that is supposedly glued to the seatstay that was loose.
I glued it back with loctite 480, it seems to hold. Not ridden it properly yet though.
I checked the bearings at the same time, I am surprised how good they are still. Feels like new.
Yesterday I noticed big play on the left side chainstay/seatstay bearing, like 2-3 mm. So opened it up and it was not the bearings. It was the bearing cup that is supposedly glued to the seatstay that was loose.
I glued it back with loctite 480, it seems to hold. Not ridden it properly yet though.
I checked the bearings at the same time, I am surprised how good they are still. Feels like new.
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