Bafang m820

[clix]

I don't agree with this, actually I try to spin higher cadence with this because the motor seems to be working better that way.

Well, ok. High cadence is a bit arbitrary. What is high for some, is not high for others. Spinning at 90rpm is most of the time fine, especially with higher battery percentage. But higher, 120 for example, there is a very noticeable drop in power. For some this is not an issue at all.
When things get steep, I like high cadence. Not for long periods of time, but for few seconds, to get over the steep bit. In this situations I notice, that things can be improved. Especially, because at lower cadence there is SO MUCH torque. I would prefer If this curve would be shifted a bit to higher cadences.

 

[ficorama]

Well, ok. High cadence is a bit arbitrary. What is high for some, is not high for others. Spinning at 90rpm is most of the time fine, especially with higher battery percentage. But higher, 120 for example, there is a very noticeable drop in power. For some this is not an issue at all.
When things get steep, I like high cadence. Not for long periods of time, but for few seconds, to get over the steep bit. In this situations I notice, that things can be improved. Especially, because at lower cadence there is SO MUCH torque. I would prefer If this curve would be shifted a bit to higher cadences.

power drop above 120rpm is normal, it happens with all engines. however, the m820 is not a full power engine!

 

[clix]

power drop above 120rpm is normal, it happens with all engines. however, the m820 is not a full power engine!

You don't have to explain anything to me. M820 is not a bad motor. It has more than enough power and also a lot of torque at low cadence. But, my experience is, that at higher cadencees, torque tapers off a bit faster than with the competition. That's it...

 

[ficorama]

You don't have to explain anything to me. M820 is not a bad motor. It has more than enough power and also a lot of torque at low cadence. But, my experience is, that at higher cadencees, torque tapers off a bit faster than with the competition. That's it...

what competition?

 

[clix]

what competition?

Other lightweight motors. Fazua, tq, Bosch sx,..

 

[ficorama]

Other lightweight motors. Fazua, tq, Bosch sx,..

did you drive them all?

 

[ficorama]

Other lightweight motors. Fazua, tq, Bosch sx,..

what firmware are you using?

 

[clix]

what firmware are you using?

FW attached, but I don't think there is anything wrong with my unit.
Anyway, here is last years review of different ligthweigth motors. One of them is forestal, that has EON drive, (bafang M820 brother).
https://www.bike-magazin.de/komponenten/e-bike-motoren/leichte-e-bike-motoren-im-test-fazua-tq-forestal-specialized-ep8rs/
Near the bottom of the review, there is power curve:

Few things to note (and some to speculate):
-Forestal uses 52V (14s), battery and BAFANG ligthweigth battery is 43V(12s, this one I also have).
-basicaly, due to the "back E.M.F". and particular motor design(armature design, number of stator poles,..), each motor has max RPM. Also higher the voltage (with the same motor design) higher the max RPM
-most of the people on here are saying, that 36V/43V/48V M820 motors are identical, apart from FW. Then, it would be reasonable to believe, that EON in forestal has the same motor internals. That would indicate, that with 43V battery, M820 higher cadence performance is even sligthly worse than the one in the picture.
-I would also asume this is the reason forestal went with 52V battery, to help with the assistance at higher voltages
-upper graph also corelates quite a bit to my experience with M820. And as the battery drains, voltage is lower, and the performance at higher cadances becomes worse. I also notice this.

so, overall, not a bad motor, but also not the best.

 

[mike_kelly]

I doubt seriously that the Bafang motors are all the same and it is just firmware. The relationship between rpm and kv is linear. So if you had a constant kv, due to the same motor, a 36v motor would run 36/48=.75 or 25% slower.
You can't change that in firmware.

 

[ficorama]

FW attached, but I don't think there is anything wrong with my unit.
Anyway, here is last years review of different ligthweigth motors. One of them is forestal, that has EON drive, (bafang M820 brother).
https://www.bike-magazin.de/komponenten/e-bike-motoren/leichte-e-bike-motoren-im-test-fazua-tq-forestal-specialized-ep8rs/
Near the bottom of the review, there is power curve:
View attachment 139814
Few things to note (and some to speculate):
-Forestal uses 52V (14s), battery and BAFANG ligthweigth battery is 43V(12s, this one I also have).
-basicaly, due to the "back E.M.F". and particular motor design(armature design, number of stator poles,..), each motor has max RPM. Also higher the voltage (with the same motor design) higher the max RPM
-most of the people on here are saying, that 36V/43V/48V M820 motors are identical, apart from FW. Then, it would be reasonable to believe, that EON in forestal has the same motor internals. That would indicate, that with 43V battery, M820 higher cadence performance is even sligthly worse than the one in the picture.
-I would also asume this is the reason forestal went with 52V battery, to help with the assistance at higher voltages
-upper graph also corelates quite a bit to my experience with M820. And as the battery drains, voltage is lower, and the performance at higher cadances becomes worse. I also notice this.

so, overall, not a bad motor, but also not the best.

View attachment 139812

everything is on paper. but forestal motor is 60nm and m820 is 75nm. I don't think any comparison makes sense here! According to their specifications, the forestal motor weighs 1.95 kg and the m820 weighs 2.3 kg. so there are differences.

 

[ficorama]

I doubt seriously that the Bafang motors are all the same and it is just firmware. The relationship between rpm and kv is linear. So if you had a constant kv, due to the same motor, a 36v motor would run 36/48=.75 or 25% slower.
You can't change that in firmware.

the engine from forestal and the m820 look the same from the outside, as I wrote in the post before, the information and the weight alone indicate that the engines are not the same.

@clix I don't know if your FW is road. I tried e-mtb and e-road firmware. in terms of strength equally. and as far as driving characteristics are concerned, the road fw is much lazier in its reactions! there is no overrun either. so maybe that bothers you. maybe you should try 36v emtb fw to see if there is a difference.

 

[clix]

@mike_kelly , @ficorama , if someone would actually open different voltage motors, and check the windings and gearing, that would be great. I would be very interested.

I attributed different weight between the EON and M820 to different material being used in the gears, axle(more aluminum and or titanium?), but presumed that mechanically and electronically they are identical.

 

[ficorama]

Hi guys. yesterday while driving I saw 620W in boost on the screen.
battery full 11s 46.2V.

that's serious power for such a small engine.

 

[Adam Anderson]

M820 on an electric gravel now in BAFANG's booth in China Cycle

Electric gravel bike compatible with bafang m820 #electricbike #ebike #egravel #ebikes

 

[voigtkampff]

M820 on an electric gravel now in BAFANG's booth in China Cycle

Electric gravel bike compatible with bafang m820 #electricbike #ebike #egravel #ebikes

is it equipped with bottle cage range extender? could it be that bafang made it officially supported option?

 

[Adam Anderson]

is it equipped with bottle cage range extender? could it be that bafang made it officially supported option?

there is only one battery as the bottle is.

 

[voigtkampff]

there is only one battery as the bottle is.

Please elaborate. Is this awkward-looking, blockish bottle actually a watter bottle not a battery or there's no downtube battery and the only battery is this blockish bottle?

 

[Adam Anderson]

Please elaborate. Is this awkward-looking, blockish bottle actually a watter bottle not a battery or there's no downtube battery and the only battery is this blockish bottle?

this is the battery, and the only power source on the bike. TBH, I think the design is nice. BTW, there are conversion kits company offering this bottle battery, too.

 

[souftosouf]

Hello guys ! What's the difference between 36, 43 and 48v battery ? what made you choose one instead of the other ?

 

[Adam Anderson]

Hello guys ! What's the difference between 36, 43 and 48v battery ? what made you choose one instead of the other ?

to get long range, try the 48v 15ah for sure.

 

[Freda]

Hello guys ! What's the difference between 36, 43 and 48v battery ? what made you choose one instead of the other ?

You will not notice any difference when using it. There seems to be firmwares available for all three.

36V is most commonly used, so third party batteries and range extenders are widely available.
43V is Bafang speciality, many motor+battery kits are 43V, but you cannot find other batteries/extenders for this.
48V is also commonly used, so third party batteries are available. Also needs smallest amount of current, but difference is small.

I chose 48V because of the lower current when making DIY batteries. If it matters or not, I am not sure.

 

[patdam]

You will not notice any difference when using it. There seems to be firmwares available for all three.

36V is most commonly used, so third party batteries and range extenders are widely available.
43V is Bafang speciality, many motor+battery kits are 43V, but you cannot find other batteries/extenders for this.
48V is also commonly used, so third party batteries are available. Also needs smallest amount of current, but difference is small.

I chose 48V because of the lower current when making DIY batteries. If it matters or not, I am not sure.

For complete. bafang batteries (43V) are more expensive but the BMS can communicate with HMI and you can displayed battery and cells status. 48V batteries needs less ampére than other 2 for provide same power (less °)

 

[blazo]

Hello! I have a question. I ordered m820 motor (48v version), and I have good 52v 14s battery(58.8v max) laying around. Do you know if I can use it with the m820, anybody tried ? I saw in other forums that people are using 52v battery with different bafang motors, but couldn't find any info about m820 motor. Motor is coming with this display Bafang DP C245. Thanks for any info If it is possible, I would like 14s, because I prefer it over 13s, I have other bikes on 14s, chargers bms etc in house.

 

[ficorama]

Hello! I have a question. I ordered m820 motor (48v version), and I have good 52v 14s battery(58.8v max) laying around. Do you know if I can use it with the m820, anybody tried ? I saw in other forums that people are using 52v battery with different bafang motors, but couldn't find any info about m820 motor. Motor is coming with this display Bafang DP C245. Thanks for any info If it is possible, I would like 14s, because I prefer it over 13s, I have other bikes on 14s, chargers bms etc in house.

Hello. the only possible problem is engine overheating. I used an 11s battery on a 36v motor. the engine overheated a lot, it is starting to lose power. especially on bigger hills. with a 10s battery, I haven't noticed it so far.

 

[ficorama]

Has anyone had an e09 error on their m820?

 

[Freda]

Hello! I have a question. I ordered m820 motor (48v version), and I have good 52v 14s battery(58.8v max) laying around. Do you know if I can use it with the m820, anybody tried ? I saw in other forums that people are using 52v battery with different bafang motors, but couldn't find any info about m820 motor. Motor is coming with this display Bafang DP C245. Thanks for any info If it is possible, I would like 14s, because I prefer it over 13s, I have other bikes on 14s, chargers bms etc in house.

I got a 36V firmware in my motor on delivery. When I connected 48V battery(charged to 46V at the time), I got "high voltage" alarm and motor would not start. I don't know the upper limit for 48V firmware, but at 58,8V there is a risk it is too high and you can't start the motor.

 

[temon10]

I'm using this 2.3 firmware on my latest build. Seems less battery consumption than my other bike on 3.2 firmware.

This is my latest build with Tantan E67 frame with 540Wh DIY internal battery.

Display shows 70km with 57% battery left. But actual distance on strava about 65km with 1100m elevation gain.

I'm using 21700 5000mah LG Cell

Later will test with extender. I make 2 extender 360Wh and 180Wh.

 

[Freda]

I'm using this 2.3 firmware on my latest build. Seems less battery consumption than my other bike on 3.2 firmware.
View attachment 140882

This is my latest build with Tantan E67 frame with 540Wh DIY internal battery.
View attachment 140883

Display shows 70km with 57% battery left. But actual distance on strava about 65km with 1100m elevation gain.
View attachment 140884

I'm using 21700 5000mah LG Cell
View attachment 140885

Later will test with extender. I make 2 extender 360Wh and 180Wh.

Are these extenders with the same cells? You will use more current then the cells can handle on full power.

 

[temon10]

Are these extenders with the same cells? You will use more current then the cells can handle on full power.

same cells

 

[voigtkampff]

I'm using this 2.3 firmware on my latest build. Seems less battery consumption than my other bike on 3.2 firmware.
Display shows 70km with 57% battery left. But actual distance on strava about 65km with 1100m elevation gain.

These numbers are beyond my comprehension. I use like 60% of my 480Wh battery to ride 45km with similar elevation, all in E/T mode. How is your 43% even possible, do you have some super strong legs and constantly ride > 25kmph disabling the power assist?