Bafang Motor H840 RM G0900.750.D/DC

[Arnaud WOODALPS]

Hi all,

I'm converting a bike to electric, with a H640 48V RM G0900.750.D/DC hub motor from Bafang, a grin Baserunner controller hidden in a Hailong battery case, a T17 torque sensor, and a 600C display from APT. I was seaching for info about the H640 motor (750W), notably the number of pole pairs and the gear reduction to set the correct parameters in the Grin controller.
As I did not found anything on the forum and elsewhere, I have opened the motor to be sure.

There is 10 pole pairs (20 magnets) and a gear ratio of 1:5 (15/30/75 teeths)

I just wanted to share the info, I hope it will help.



I'm still struggling to make the correct connection between the Higo mini connector of the APT 600C UART display with the Baserunner harness, I don't have the info about the pinout on the display connector. If someone has details, I'm interested.

This e-bike conversion is for my father. I also buit wooden bikes, but i do not yet have a dedicated ebike model. Just a glimpse of my wooden bikes :

This is the gravel. I will will use the MTB model for the Ebike conversion.
My brand is WOODALPS, this is just a secondary activity.

 

[Mikelon]

Hello,

Could you please tell me the size of the axle on the H640 750w G0900 hub motor ?
Is the axle 14mm x 10mm ? I am thinking of buying this motor for myself.
Or is the axle 12mm x 10mm ? It looks like a 12mm axle to me. Bafang should have upgraded the axle to 14mm for the torque level this motor can provide with the right controller. MAC and BMC motors are using 14mm axle on their geared motors of the same power level for years now.

Thank you in advance!

As a thank you from my side, as you requested information, I have attached my pinout picture I created for the APT 600C display connector. This is a correct pinout for 600C display, specifically with UART protocol.
However, be advised that Baserunner controller from Grin obviously support KM5s protocol.
And your 600C display has UART communication protocol. So, it's not a guarantee that even if you connect everything correctly, that the display and controller will work correctly, because of the different protocol.

 

[Arnaud WOODALPS]

The axle is 14mmx10mm. The nut is quite big (you will need a 22mm wrench). I've purchased a slightly smaller nut as I will use a torque arm.
Thanks for the info about the display. I purchased the 600C display from Grin, and thought it would be compatible, as it is clearly detailed in the description on Grin website (600C Integrated Handlebar Display and Switch) that it operates on KM5s communication protocol. In fact, it is compatible, but only if their Main9 Superharness is used (and this is not clearly described on their website), but they don't sell it alone yet, so I'm a bit stucked on this project. I will try to setup the system headless until I can purchase the SuperHarness.

And their pinout is different from the one you have shown, probably because it is not UART Protocol, even if the display name is also 600C.

 

[Mikelon]

Thank you very much for your reply, regarding the axle size. Finally Bafang has realised that a thicker axle is necessary, I am glad about it.
Years ago, MXUS has manufactured their 3K-Turbo direct drive 3000w (nominal !) motors with only 14mm axles. Many users have broken the 14mm axle, as the motor is so powerful. But then eventually MXUS has realised their huge oversight, and they have upgraded the axle on 3k-Turbo motors to 16mm.

Regarding your 600C display: if you have bought it from Grin website, then of course it has KM5s protocol, and a pinout which has been specified by Grin team themselves.
As you probably understand: I thought that your 600C display had a UART protocol because you mentioned in your post, I quote: "APT 600C UART display". 600C UART displays are usually used for Bafang mid drive (BBS02, BBSHD etc.) and for some Bafang hub motor controllers. And for Bafang controllers, UART protocol, and Bafang 1t4 wiring harness, the pinout I provided would be certainly correct. But not for your 600C display from Grin, because that display is customized. The 600C display from Grin not only has a different pinout, but also a custom firmware in it, which enables the display to by used even with 72v batteries.
600C UART displays with standard firmware for Bafang controller can only be used for 52v batteries for now.
But everything is clear now for both of us.
I hope that eventually you will be able to buy a wiring harness separately from Grin.
Good luck with your project!

 

[Narbthetoeless]

Hi all,

I'm converting a bike to electric, with a H640 48V RM G0900.750.D/DC hub motor from Bafang, a grin Baserunner controller hidden in a Hailong battery case, a T17 torque sensor, and a 600C display from APT. I was seaching for info about the H640 motor (750W), notably the number of pole pairs and the gear reduction to set the correct parameters in the Grin controller.
As I did not found anything on the forum and elsewhere, I have opened the motor to be sure.

There is 20 pole pairs (20 magnets) and a gear ratio of 1:5 (15/30/75 teeths)

I just wanted to share the info, I hope it will help.

View attachment 349635 View attachment 349636 View attachment 349638

I'm still struggling to make the correct connection between the Higo mini connector of the APT 600C UART display with the Baserunner harness, I don't have the info about the pinout on the display connector. If someone has details, I'm interested.

This e-bike conversion is for my father. I also buit wooden bikes, but i do not yet have a dedicated ebike model. Just a glimpse of my wooden bikes :
View attachment 349639
This is the gravel. I will will use the MTB model for the Ebike conversion.
My brand is WOODALPS, this is just a secondary activity.

I bought the same motor and also use a baserunner but with a CA 3. Would you be willing to share a few screen shots of your parameter settings on the phaserunner suite? Are you using the temperature parameter? I seem to have a bit of an issue with overcurrent faults. I can’t seem to find an explanation. Also I think Grin make a new adapter wire for your setup. (You probably know this)

 

[Arnaud WOODALPS]

I bought the same motor and also use a baserunner but with a CA 3. Would you be willing to share a few screen shots of your parameter settings on the phaserunner suite? Are you using the temperature parameter? I seem to have a bit of an issue with overcurrent faults. I can’t seem to find an explanation. Also I think Grin make a new adapter wire for your setup. (You probably know this)

I try to show you the parameters tomorrow.
They effectively have an adapter, the superHarness that I should use with the 600c display I bought from Grin, but they only sell it as part of a kit (controler + motor + display + sensor +...). So I still can't finish my bike. I will maybe order a CA3 to be able to use my bike, and order a superHarness when it will be available for purchase.
From what i understand, the H640 bafang motor doesn't have a temperature sensor.

 

[Arnaud WOODALPS]

I bought the same motor and also use a baserunner but with a CA 3. Would you be willing to share a few screen shots of your parameter settings on the phaserunner suite? Are you using the temperature parameter? I seem to have a bit of an issue with overcurrent faults. I can’t seem to find an explanation. Also I think Grin make a new adapter wire for your setup. (You probably know this)

Hi, the main parameters for my motor / battery configuration are detailed below.

 

[ShardCollector]

Hello and thank you for the info!

Bafang claims that the motor is compatible with 7 - 11 speed cassettes, but doesn't give any measurements or cassette standards.
So, my question: is it Shimano HG? Or some other standard?

A guide to freehub body and cassette compatibility

Can’t figure out what freehub body you need for a certain cassette type? This will help.

velo.outsideonline.com

Edit: My Bullitt has the choice to change dropout to traditional 10x135 mm quick release or 12x142 mm thru axle. Some site claims that Bafang needs 138-142 mm O.L.D. size, but clearly it doesn't fit the 12 mm thru axle dropouts? Do you think it would fit the 135 mm quick release ones?

https://www.larryvsharry.com/da/dropouts

Sorry for so many questions! It would be nice if Bafang told these things straight on their page!

 

[Nixunen]

There is 20 pole pairs (20 magnets) and a gear ratio of 1:5 (15/30/75 teeths)

20 magnets is 10 polepairs not 20.

 

[Bomb24]

20 magnets is 10 polepairs not 20.

Does it mean that when using a H640 motor with a KT controller, the P1 value should be 50 (and not 100) ?

 

[ebikebuilder]

Inside the Bafang G0900 750W Motor: Teardown, Analysis & Temp Sensor Mod!

Join me on the ebikebuilder channel as we crack open the Bafang G0900.750.DC (9T) 750W rear hub motor! In this video, we're doing a full teardown to explore its internal construction, identify key components, and uncover some potential challenges with this popular motor.

What we cover in this video:

1. The Teardown Process: See how to (carefully!) open the G0900 motor. You'll need specific tools like a flathead screwdriver, a mallet, and a T25 Security Torx bit. Heads up: It's not the easiest motor to disassemble without potentially causing cosmetic damage.
2. Internal Component Analysis:
   • Gearing: We identify the 15T / 30T / 75T internal gear ratios.
   • Nylon Gears: A close look at the 30T nylon planetary gears (12.5mm wide, 63mm diameter) and the major finding: these are currently VERY difficult to source replacements for!
   • Clutch: Examination of the unique clutch assembly, marked 'BF RM G0900.750DC' (with counter-clockwise arrow). Notably, it features 6 splines connecting to the shaft, unlike the single parallel key commonly seen on other Bafang fat bike motors – another part that seems hard to find on platforms like AliExpress.
   • Phase Wires: Comparing the phase wires to other Bafang models (G60/G62). They seem thicker than the G60's 12AWG, possibly closer to 11AWG like the 1000W G62.
   • Rotor & Magnets: The internal rotor measures 25.66mm wide. This is significantly narrower and suggests smaller magnets compared to many other Bafang fat hub motors.
   • Bearings: Main shaft bearings identified as 16003-2RSM; the bearing inside the planetary gear carrier is a 6001RZ.
   • Stock Controller: Mentioning the stock 20A controller that came labeled as 25A.
3. Key Findings & Potential Issues: The difficulty in sourcing replacement gears, clutch, and likely other internal parts is a significant disadvantage currently. The narrower rotor might also impact heat dissipation and peak torque compared to wider fat bike motors.
4. Recommendations: Based on the teardown and parts availability, I recommend most users run this motor with its stock controller setup. Pushing it hard with aftermarket controllers (high phase amps) risks damaging the hard-to-replace gears, especially without thermal monitoring. This motor is best left to advanced users if modifications are planned.
5. Temperature Sensor Installation: Watch step-by-step as I install a temperature sensor, soldering it to the negative pad and the white wire's pad on the internal PCB.
6. The Goal: This mod repurposes the white wire (originally for speed signal) to output the motor's internal temperature reading. Essential for preventing overheating when using aftermarket controllers like a Flipsky VESC!

Why add a temp sensor? Monitor your motor temps accurately, push performance safely, and avoid overheating meltdowns!

Coming Soon: Watch for the follow-up video where I connect this modified Bafang G0900 to a Flipsky controller and show the temperature reading in action!

 

[ebikebuilder]

Edit: My Bullitt has the choice to change dropout to traditional 10x135 mm quick release or 12x142 mm thru axle. Some site claims that Bafang needs 138-142 mm O.L.D. size, but clearly it doesn't fit the 12 mm thru axle dropouts? Do you think it would fit the 135 mm quick release ones?

this motor is not compatible with a through-axle rear dropout bike frame. the motor has nutted axles. its made for 135m to 143m dropouts , or something like that.

I used AI to approximate characteristics of the motor, not sure if this is correct but it seems about right:

Okay, let's use your empirical data (top speed, voltage, wheel size, and the 5:1 gear ratio) to estimate the motor's Kv and Kt, and then calculate the approximate phase amps needed for the rated torque.
1. Calculate Motor Kv (RPM per Volt)

• Wheel Speed: 35 MPH
• Wheel Diameter: 29 inches
• Voltage: 53.7 V (unloaded)
• Gear Ratio: 5:1
• a. Convert MPH to Wheel RPM:
  • Wheel Circumference = π * Diameter = π * 29 inches ≈ 91.106 inches
  • Inches per Mile = 12 inches/foot * 5280 feet/mile = 63360 inches/mile
  • Wheel Revolutions per Mile = 63360 / 91.106 ≈ 695.45 revs/mile
  • Wheel RPM = (Speed in MPH / 60 minutes/hour) * Revolutions per Mile
  • Wheel RPM = (35 / 60) * 695.45 ≈ 405.7 RPM
• b. Calculate Motor RPM (before gearbox):
  • Motor RPM = Wheel RPM * Gear Ratio
  • Motor RPM = 405.7 RPM * 5 = 2028.5 RPM
• c. Calculate Motor Kv:
  • Kv = Motor RPM / Voltage (at no-load)
  • Kv = 2028.5 RPM / 53.7 V
  • Kv ≈ 37.8 RPM/Volt

So, the estimated Kv of your Bafang G0900 motor (before the gearbox) is approximately 37.8 RPM/Volt.
2. Calculate Motor Kt (Torque Constant - Nm per Amp)
There's a direct relationship between Kv and Kt for BLDC motors.

• a. Convert Kv to SI units (radians per second per Volt):
  • Kv (rad/s per Volt) = Kv (RPM/Volt) * (2π radians / revolution) * (1 minute / 60 seconds)
  • Kv (rad/s per Volt) = 37.8 * 2π / 60 ≈ 3.958 rad/s per Volt
• b. Calculate Kt:
  • Kt (Nm/Amp) ≈ 1 / Kv (rad/s per Volt)
  • Kt ≈ 1 / 3.958
  • Kt ≈ 0.253 Nm/Amp

The estimated torque constant (Kt) of your motor is approximately 0.253 Nm per Amp of phase current.
3. Calculate Phase Amps for Manufacturer Rated Torque

• Manufacturer Rated Torque: 80 Nm (This is almost certainly torque at the wheel, after the gearbox).
• Gear Ratio: 5:1
• Calculated Kt: 0.253 Nm/Amp
• a. Calculate Motor Torque needed (before gearbox):
  • Motor Torque = Wheel Torque / Gear Ratio
  • Motor Torque = 80 Nm / 5 = 16 Nm
• b. Calculate Required Phase Amps:
  • Phase Amps = Motor Torque / Kt
  • Phase Amps = 16 Nm / 0.253 Nm/Amp
  • Phase Amps ≈ 63.2 Amps

Conclusion and Important Considerations:
Based on your observations and the 5:1 gear ratio, to achieve the manufacturer's rated 80 Nm of wheel torque, your VESC would need to deliver approximately 63 Amps of phase current to the motor.

• Accuracy: This calculation relies on the accuracy of your unloaded speed measurement and voltage reading. Real-world factors like friction were ignored in the Kv calculation, so the actual Kv might be slightly higher, and Kt slightly lower.
• Peak vs. Continuous: The 80 Nm rating is likely a peak or intermittent torque rating. Continuously demanding 63 phase amps might overheat the motor. Manufacturer ratings often push the limits.
• VESC Settings:When setting phase current limits in the VESC tool:
  • Motor Current Max corresponds to this calculated phase amperage (e.g., set it around 60-65A if you want to target that peak torque).
  • Motor Current Max Brake would be for braking phase amps.
  • Remember to also set appropriate Battery Current limits (Battery Current Max and Battery Current Max Regen) which will typically be lower than the phase current limits, depending on your battery's capabilities.
• Thermal Management: Start with slightly conservative phase amp settings (maybe 50-55A) and monitor motor temperatures closely during demanding use (like hill climbs or strong acceleration). If temperatures stay reasonable, you could gradually increase the limit towards the calculated 63A, but always prioritize not overheating the motor.

This calculation gives you a very good starting point for configuring your VESC's phase current limits to approximate the motor's rated torque capability.

 

[Rebellion.Bike]

Great info on this post, thanks everyone.