Bafang m820

[mike_kelly]

The battery looks fully charged in the photo?

 

[borysgo2]

The battery looks fully charged in the photo?

Battery is 59% charged at about 5Ah 45V (about 3,77V per cell) . Full capacity is 9Ah and charger voltage is 49.2V so I think it should topped up normally. Will see tomorrow.

Edit
Just wondering if there is any build in fuse in the battery or charger.

 

[Dado]

Battery is 59% charged at about 5Ah 45V (about 3,77V per cell) . Full capacity is 9Ah and charger voltage is 49.2V so I think it should topped up normally. Will see tomorrow.

Edit
Just wondering if there is any build in fuse in the battery or charger.

Why 49.2? If u have 12S, should be something close to 4.2V per cell (so 50.4V), not 4.1V.

 

[borysgo2]

Why 49.2? If u have 12S, should be something close to 4.2V per cell (so 50.4V), not 4.1V.

Bafang charger that comes with btf014 is 2A 49.2V. I think I'll take the hammer tomorrow and will get it open.

 

[Dado]

Bafang charger that comes with btf014 is 2A 49.2V. I think I'll take the hammer tomorrow and will get it open.

Hmm, can be it is on purpose, not to charge to full. Just according charging characteristics, if you ending at 4.1V it is only 80% charged.

Measure charger with voltmeter, what you get.

 

[clix]

Bafang charges its 12s 410wh battery to 4.1V per cell. I would assume, that they are trying to improve battery life a bit. Higher voltages degrade battery faster.
And by charging to only 4.1, you don't really, lose 20%. More like 2%-4%. At the higher voltagea around 4.1, curve is quite steep, and the voltage drops quickly.

 

[Waynemarlow]

Most chargers will top out at 4.2V but with a bit of equalisation by the BMS after full charge current has stopped, will drop the volts back to around 4.15v, at which stage most home voltmeters are not precise enough to accurately show 4.1 or 4.2 over 12 series cells.

 

[Dado]

Bafang charges its 12s 410wh battery to 4.1V per cell. I would assume, that they are trying to improve battery life a bit. Higher voltages degrade battery faster.
And by charging to only 4.1, you don't really, lose 20%. More like 2%-4%. At the higher voltagea around 4.1, curve is quite steep, and the voltage drops quickly.

Hello Clix.
I was also taking care of my batteries in the begining, then I found out, I hardly charge battery 100 times during lifetime.

And here is charging characteristic, show me that 2 to 4%.

 

[Dado]

Most chargers will top out at 4.2V but with a bit of equalisation by the BMS after full charge current has stopped, will drop the volts back to around 4.15v, at which stage most home voltmeters are not precise enough to accurately show 4.1 or 4.2 over 12 series cells.

Drop to 4.15V is not because of balancing. (Also many BMS are balancing only during charging). Thats the natural behaviour, if you rest cell a while after charging, you still get a drop. See previous charging graph.
Voltmeters are not accurately? Uf, what I gonna learn here...

 

[borysgo2]

Charging problem - a bit of the update, drained the battery to 3% left. Battery not charging, charger outputs 49.3Vdc for a 2-3seconds and than turns the output off, green light stays on. I checked the cables yesterday and they are OK. Error code 09 stored in display diagnostics. Looks like BMS does no allow battery to charge.

How deep 2170 cells usually can be discharged?

 

[Waynemarlow]

if you rest cell a while after charging, you still get a drop.

I wonder what that is in regards to our battery packs ?

Could it be the BMS balancing out each cell to the common lowest voltage, by burning off energy through a resistor creating heat,( after the charging cycle has switched off ) after all our chargers are not “bottom up” complex chargers.

 

[Dado]

Charging problem - a bit of the update, drained the battery to 3% left. Battery not charging, charger outputs 49.3Vdc for a 2-3seconds and than turns the output off, green light stays on. I checked the cables yesterday and they are OK. Error code 09 stored in display diagnostics. Looks like BMS does no allow battery to charge.

How deep 2170 cells usually can be discharged?

Hello Boris

Indeed something is wrong with charging. Either BMS wont allow to charge (charging FETs are closed) or defect of charger (charging detection, when you writing it shut off output after few seconds). ;(
You should be able to charge up to 49Volts.

I would try another 12S charger with full voltage output - 50.4V
But could be, that Bafang BMS is set to cut of charging at 4.1V - which is not a good idea.

And again the issue with depth of discharge - is set too high when you writing at 3% you have 3.38V at cells. You wont do anything with this. If you not charging to full and also not discharging deep enough you wasting lot of battery capacity.
You can freely discharge down to 3V per cell. Is allowed to discharge even to 2.6V (then you decreasing lifetime). I am setting for races low voltage cutoff to 2.8V on Innotrance controller. BMSes have usually safety cut off at 2.7V

Error 9 - is not related to charging. Seeing it for first time though. Something with phase winding (shorted or high resistance? Just guessing. There can be a self test diagnoses after power on). Clear that error and check if show up again in the future, or to inspect phase wires and connectors inside motor. Can be just some one time fault.

 

[borysgo2]

Thanks Dado
It looks that I will build my own battery. Can you recommend bms (which will work with bafang system) with can bus so I can see % on the display?

Samsung 50E have about 35mOhm of internal resistance so about 70mV at 2A discharge so 3.3V a cell looks like a waste indeed.

Tomorrow another update.
Thx

 

[Dado]

Yes, I also dont like this high cut off voltage with CAN bafangs motors. With UARTS you could set anything downt to 2.8V if I remember right.

And from discharge characteristics, I can tell you, you wasting 0.6Ah (13%) comparing to cutoff at 3V per cell. (at 3A average discharge current per cell)

You will not easily buy BMS with Bafang CAN comunication (it is proprietary protocol and you would run into same issue again). Dont worry, Bafang motors will start also without "smart" battery (you can cable any 12S battery and would take also 13S). But then power limitation is starting too soon. You would see SOC % - but is not as accurate as when BMS is estimating it ;(
When I see original Bafang battery charging is set to 4.1V I would not want such a battery.

Anyway, this is a good topic, I am just working on a device, which would trick Bafang BMS and should be possible to discharge deeper and without power limitation. But still lot of testing in front of me.

It is about implementation, where you set high and low voltage cutoff - and therefore we have relative SOC and absolute SOC. When ending at 4.1V you have relative SOC 100% and absolute SOC is here cca 80%.

 

[clix]

Hello Clix.
I was also taking care of my batteries in the begining, then I found out, I hardly charge battery 100 times during lifetime.

And here is charging characteristic, show me that 2 to 4%. Also what u mean by "voltage drops quickly"?

View attachment 128332

I was looking at the discharge graphs, where the first 0.1V dropps rather quickly. (disregard 3.9V start voltage, that is due to internal resistance.)

Source: Test of Samsung INR18650-35E 3500mAh (Pink)

But now that you pointed it out, I am not sure if this is acrurate way of estimating capacity. Even if you charge to only 4.1, the first 0.1V migth still drop quickly. Based on your charging graph, It does look like cca 15% difference between 4.1V and 4.2V charging voltage.

Anyway, if we actually check the datasheet of Samsung INR18650-35E, it looks like samsung states different charging voltages, depending on the application: (imo, they still propose lower value for more charging cycles, BT F014.410.C states 600 charging cycles, whitch would corespond with 4.1V)

 

[Dado]

I was looking at the discharge graphs, where the first 0.1V dropps rather quickly. (disregard 3.9V start voltage, that is due to internal resistance.)

Source: Test of Samsung INR18650-35E 3500mAh (Pink)

But now that you pointed it out, I am not sure if this is acrurate way of estimating capacity. Even if you charge to only 4.1, the first 0.1V migth still drop quickly. Based on your charging graph, It does look like cca 15% difference between 4.1V and 4.2V charging voltage.

Anyway, if we actually check the datasheet of Samsung INR18650-35E, it looks like samsung states different charging voltages, depending on the application: (imo, they still propose lower value for more charging cycles, BT F014.410.C states 600 charging cycles, whitch would corespond with 4.1V)

Indeed you need to look at charging characteristic, how much energy you push in till cut of voltage 4.1V.
Notice your graph discharging is at 7A - so a big voltage sag and this is almost maximum for 35E. You are not discharging at this rate with legal ebike motors (up to 5A max per parallel cell - talking about 4P or 5P batteries 18650, average discharging current at normal ride is much less).

You can follow that Samsung guidelines, it is because of longer life time of LiIon cells. Depends what is your priority. Electric cars are also not charging to full 4.2V per cell.

 

[mike_kelly]

You have to make your choice. High performance or long life...

 

[borysgo2]

I wouldn't be concern about 4.1V vs 4.2V , more of the juice is wasted down bellow the voltage chart. In my case at 3.389V no load battery is at 3% left. Let me say at 35mOhm@2A load a cell we have circa 3.32V, let me say 3,3V.
So If we discharge cells let me say to 2.9V we are gaining easily 1Ah.

Now, another question is how is the battery % estimated with generic BMS, I presume M820 motor have some kind of map Voltage vs % of Charge and where does the power limitation kick in.
Let me say that power limitation is voltage dependent and kicks in at 3.4V. So 3.4V*12= 40,8V.
So if we use 13S battery instead we will get 40,8V/13=3.14V to work with the cell. In theory it should be better used than 12S.

 

[Dado]

And the truth is, you wasting more capacity by ending charging at 4.1V then difference between lvc 3.3 and 3V.

Yes, If not using Bafang BMS battery, bafang is estimating over some default rainbow table (this is the reason why u see SOC % raising after you stop riding) Battery is charging out of thin air - I am joking it is a special bafang feature. This estimation was there since my first bafang motor.

Using one up battery series cell allow you to discharge deeper. SOC will be showing bad though. I used to ride M600 at 43V firmware and 48V battery. But we going out of M820 topic...

Seems M820 can be a popular motor... any new observations, user experience?
I am awaiting here new boot3.1 controller (rev.B). M500 and M600 already on boot3.x

 

[borysgo2]

Good morning.
A few screenshots from today.
In the diagnostics of controller I am getting 0108 fault code or two codes 01 and 08, i do not know, maybe that is why my battery is not charging. Bike drives 100% OK.

The other thing I found is set of parameters in section 6012, did anyone tried to change battery voltage to 48V or try to map the table for SOC % of the battery ?

Unfortunately that section is not translated do EN and my Chinese is pretty bad

 

[Dado]

Not sure if this is error code 01 and 08.

Been trying to overwrite parameters in register 6012, but seem like read only. Leave mouse above chinese label, you get some aditional info tooltip (in english).

 

[borysgo2]

I think is sorted.
Wire inside charging socket was barely soldered to the pin so it snapped inside. When I was maneuvering the cables it was showing continuity but after all cables fitted in the frame it was not connecting at times.
In case someone is going to replace charging socket with standard DC plug I made schematic for the charger to turn ON.
NTC 16kR @ 10DEG can be replaced with 15k or 10k resistor. ID resistor is 4k7.

 

[clix]

Does anybody have any information regarding official bafang range extenders? Few months ago, there was discussion, how bafang is developing 36V and 42V range extender, but no news since than.

 

[El Topo]

Does anybody have any information regarding official bafang range extenders? Few months ago, there was discussion, how bafang is developing 36V and 42V range extender, but no news since than.

Not sure if that helps, but this M820 frame is sold with a 360Wh range extender in a fake bottle. I have no idea, if that is the official one or an in-house-development.

E1029 Bafang M820 | YISHUNBIKE

700C Carbon E-Gravel Bike Frame w/t Mid Drive Bafang M820 – Carbon E-gravel Bike Frame– Full Internal Cable Routing– Bafang M820 Mid Drive System– Integrated Battery 360wh– Extender Battery 360wh– Dropout 12*100mm & 12* 148mm

www.yishunbike.com

 

[Pinkee]

Hi all, just finished building up my 820.

did anyone find a spider solution to the 1piece sprockets? I change my sprockets frequently and would prefer a 104bcd spider.

Cheers all.

 

[Freda]

Hi all, just finished building up my 820.

did anyone find a spider solution to the 1piece sprockets? I change my sprockets frequently and would prefer a 104bcd spider.

Cheers all.

I got a spider with my motor with 104bcd. I don't know where you can buy the original, but for example Miranda makes them for bosch motors that might fit:

E-bike Spider Bosch G4 DS Super Boost BCD 104 Aluminium for E-BIKE

mirandabikestore.com

 

[Dado]

There will be soon one piece chainring from Bafang.

 

[patdam]

There will be soon one piece chainring from Bafang.

View attachment 128501

in 28 teeth ? you will sold it ?

 

[Dado]

Dont have it. It is new chainrings for M560.

 

[Adam_TrailBK]

Hello,
I have a problem with a strange sound after the engine warms up (see video). The croaking sound appears after the engine warms up. Even if I then turn off the engine and go without support, the sound does not stop. Changing gears (pedaling cadence) does not affect the sound. Does anyone else have it? M820 - croaking sound