Help! Bafang 36v hub motor for fat bike.

Matmuze

Finding my (electric) wheels
Mar 19, 2019
6
0
Hi guys, I got myself one of these trendy fat cruisers that come equiped with high torque bafang hub motors. Mine says exactly RMG06 36V (10) on the hub case, no power rating engraved, but the bike is sold as 250W.

I am looking for someone who is knowledgable about these motors, as I can hardly find any info online...

Now I think its time for upgrades, my controller is a 36V/15 amps + 36V battery, and I would like to up the ante, to 48V/20amps + 48V or 52V battery.

From what I gathered, a motor is not tied to a particular voltage, only battery and controller is...

I just wanted to make sure that this fact is actually correct, and that nothing differ between a 36V and 48V bafang hub motor despite being engraved on the case...

Also I tried to find out what the code (10) in brackets actually means, I have seen many models with the same code with 36V/48V and 250/350/500W written on the case, no 750W tho... does this give any indication of what's inside the motor ? Does it mean that all models are the same and that only the 750W one is actually physically different ?

Funny enough, I've also found 36V/250W motors with a different code (13)...

Any insight would be much appreciated.
Cheers, Mat.
 
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vfr400

Esteemed Pedelecer
Jun 12, 2011
1,788
405
Basildon
Code 10 is the winding speed. If it's the same as the convention for the Bafang BPM, its 310 rpm, which is around 22 mph for a conventional 26" wheel. Increasing the voltage increases the motor speed and decreases the efficiency at low RPM. It also causes your controller to run at maximum power more of the time, which can be bad because controllers are only rated for half there maximum power.

Before you do anything, you should confirm your motor's max speed with the wheel off the ground. Actual speed will be around 10% more than nominal because your battery will run close to 40v when fully charged, so expect around 350 rpm.

I don’t think it's a good idea to go higher than that with a bike like yours. If you want more power, you should increase the current rather than the voltage to something like 22 amps, but only if you know that your battery has that capability.
 

Benjahmin

Esteemed Pedelecer
Nov 10, 2014
1,367
850
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West Wales
The (10) is the winding code and denotes the maximum rpm of the motor. Don't know the codes, maybe some one else will say. If you go 36v to 48v you will increase that rpm by 25%. If you overvolt be careful on increasing the maximum controller current.


Crossed with vfr's post, I bow to his far superior knowledge.;)
 

Matmuze

Finding my (electric) wheels
Mar 19, 2019
6
0
Thanks guys for the answers. I feel like my question was only partially answered though... Would a 36V (10) hub motor be in effect be the same as a 48V (10)... I'm asking because other vendors sell a "250W" version of a very similar bike with a 48V version of that motor and a 48V/20A controller. So in case the two motors are the same then simply upgrading my controller + battery would be legit right ? Why would I be "overvolting" if I were to send the same amount of juice to the same motor as this other bike manufacturer ...?

More importantly for my curiousity, if two hub motors (36V and 48V respectively) are indeed different, what is it exactly that distinguish them two, I mean electronically speaking...

Thanks in advance if you know the answer.
 

Matmuze

Finding my (electric) wheels
Mar 19, 2019
6
0
Ok, so I looked at posts related to the Bafang BPM and I was able to find loads of information about the motor, thanks for the tip.

From what I understand, 36V (10) and 48V (10), would actually be very different. It would mean they share the same winding speed, but at different voltage, so if they both spin at 325 rpm at their designated voltage, then the 48v motor would actually run at 245 rpm at 36V.

Which means that if I were to change for a 48V (10) motor instead of overvolting a 36V (10) one, it would actually not increase the top speed, only the power efficiency would be increased.

So if I am seeking to increase the top speed with a 48V battery/controller, my only options are thus overvolting a 36V (10) or fitting a 48V (8 or lower) with higher RPM.
 
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vfr400

Esteemed Pedelecer
Jun 12, 2011
1,788
405
Basildon
These codes and winding speeds are a bit of a mystery because there doesn't seem to be any consistency. Normally, the code would be the number of turns of wire on each pole, so all code 10s would turn at the same speed when at the same voltage. Many other motors use that convention.

With the BPM motor, there is definitely a difference between the 250/350W version and the 48V one. My guess is the wire diameter, but I've never measured it.

Quite often, the sellers will tell you the rpm, but you can't trust what they tell you.

Sellers don't normally care too much about efficiency, so it wouldn't surprise me to see a 48v code 10 in a fat bike. You still get the 30% increase in torque over the 36v one but your battery will go down disproportionately faster at speeds below 15mph.

It's much better for the controller and motor if their peak efficiency, which you get at about 75% max rpm, coincides with your modal travelling speed. I can't see a fat bike sustaining any more than 20 mph with that motor, so the max speed of the motor should not exceed 26 mph. That's about 325 rpm on a normal 26" wheel or maybe 300 rpm if you have 4" tyres.
 

Matmuze

Finding my (electric) wheels
Mar 19, 2019
6
0
Man, that's actually the oposite of what I've read online, and also the specs on the bafang website indicates a different winding speeds between 36V/48V (325, 245 rpm respectively), which seems to be the winding speeds at a simular voltage, I'd logically guess 36V...

If that turned out to be the case it would mean the winding speed indicated on the hub would actually be the RPM at their designated voltage...

Now I'm even more confused than at the beginning...

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