Sent the wrong BPM motor need advice!

[nasium]

I ordered a BF BPM 48v 500w 26" front motor and got a BF BPM 48v 500w 20" front motor from an Aliexpress vendor.

The motor says: BF BPM 48v 500w 20(13) Am I correct this is a motor for a 20" wheel?

This is to be laced into a front 26" wheel 7spd beach cruiser. What kind of performance should I expect?

I'm more interested in torque than speed will this motor still work for me?

 

[brumbrum]

Correct me if i have read this wrong, but if you bought a bare motor it can be laced into any size rim as long as you have the right length spokes. The number you have put in brackets i.e (13) denotes the rpm of the motor. This will define how fast or slow the wheel will turn at a given voltage and will affect maximum speed.

 

[izeman]

There is nothing like a 20" motor or a 26" one. A motor just has a certain rpm at a certain voltage.
And the rpm has to match you voltage and your wheel size to acchieve the wanted speed.
So it COULD be that "their" 20" laced wheel motor runs at a higher rpm than the 26" one. But that's only guessing.

 

[motomech]

I ordered a BF BPM 48v 500w 26" front motor and got a BF BPM 48v 500w 20" front motor from an Aliexpress vendor.

The motor says: BF BPM 48v 500w 20(13) Am I correct this is a motor for a 20" wheel?

This is to be laced into a front 26" wheel 7spd beach cruiser. What kind of performance should I expect?

I'm more interested in torque than speed will this motor still work for me?

I've studied BPM nomenclature till my head hurts and still don't really understand it. That's why these days, we recommend the BPM CST from BMS Battery which is known to have a no-load speed of 270 rpm @ 36V.

I think this is what your label means;
The no-load speed in a 20" wheel @ 48 V is 230 rpm (code 13).
Extreemly low speed motor, here are some different wheel size/ battery Volts combos;
26" whl @ 48 V = 16.5 mph.
700 whl @ 48 V = 17 mph
26" whl @ 66 V = 21 mph
700 whl @ 66 V = 22 mph

I guess there is no sure way to know without testing it's no-load speed.

 

[nasium]

Thanks for all the replies..

Motomech,

You say it's an extremely low speed motor in a 20" so then it's a motor with more torque? If that's the case do you think it will have good torque in a 26"? It could be a good fit since I don't want speed.

I really don't want to have to deal with shipping this back to China if I don't have to.

 

[flangefrog]

Nasium - it's a myth that with two identical motors with a different winding (e.g. 8 turns, 12 turns) one will be capable of high torque (low speed) and the other high speed (low torque). It is true that if you used them with the same battery and controller with no settings changed that is what you'd find. But actually, the motors have a different amount of speed per volt and torque per amp. The two motors will be capable of exactly the same speed and torque but the 12 turn one will require 1.5x the voltage (12/8) and 2/3 the current (8/12).

Usually a 20" motor would have less turns which means it has more speed/volt and less torque/amp. A good guess to make it perform the same as a 26" motor is 1.3x (26/20) the voltage and .77x (20/26) the current you would use for the 26" motor.

What this means for your situation is that as long as your battery has enough voltage to make the motor spin fast enough for your desired speed, you can simply adjust your current limit to get the same amount of torque as the 26" specced motor.

The code BF BPM 48v 500w 20(13) should mean 20" wheel and 13 turns. Based on this table the Kv (RPM/V) will be around 6.65. Using this data a 48V nominal battery will give you a no load speed of 319.2RPM (48x6.65) which is roughly 24.7 mi/hr depending on your tire circumference.

 

[friendly1uk]

Well they have sent a faster motor than you asked for. You have recieved something in the region of a 230rpm motor. It seems most people want something even faster than a 230 in a 26" wheel, choosing the 270rpm cst or 300rpm code 10 bpm. So while you have recieved something faster than you asked for, most of us would of asked for something even faster than that.

You should probably be thankfull

 

[motomech]

Nasium - it's a myth that with two identical motors with a different winding (e.g. 8 turns, 12 turns) one will be capable of high torque (low speed) and the other high speed (low torque). It is true that if you used them with the same battery and controller with no settings changed that is what you'd find. But actually, the motors have a different amount of speed per volt and torque per amp. The two motors will be capable of exactly the same speed and torque but the 12 turn one will require 1.5x the voltage (12/8) and 2/3 the current (8/12).

Usually a 20" motor would have less turns which means it has more speed/volt and less torque/amp. A good guess to make it perform the same as a 26" motor is 1.3x (26/20) the voltage and .77x (20/26) the current you would use for the 26" motor.

What this means for your situation is that as long as your battery has enough voltage to make the motor spin fast enough for your desired speed, you can simply adjust your current limit to get the same amount of torque as the 26" specced motor.

The code BF BPM 48v 500w 20(13) should mean 20" wheel and 13 turns. Based on this table the Kv (RPM/V) will be around 6.65. Using this data a 48V nominal battery will give you a no load speed of 319.2RPM (48x6.65) which is roughly 24.7 mi/hr depending on your tire circumference.

Based on this table the Kv (RPM/V) will be around 6.65. Using this data a 48V nominal battery will give you a no load speed of 319.2RPM (48x6.65) which is roughly 24.7 mi/hr depending on your tire circumference

That is for a code 26[13].
Is there no difference between a 20[13] and a 26[13]?

 

[999zip999]

Is this laced in a 26in. rim ? You have a link ?

 

[flangefrog]

Nasium - it's a myth that with two identical motors with a different winding (e.g. 8 turns, 12 turns) one will be capable of high torque (low speed) and the other high speed (low torque). It is true that if you used them with the same battery and controller with no settings changed that is what you'd find. But actually, the motors have a different amount of speed per volt and torque per amp. The two motors will be capable of exactly the same speed and torque but the 12 turn one will require 1.5x the voltage (12/8) and 2/3 the current (8/12).

Usually a 20" motor would have less turns which means it has more speed/volt and less torque/amp. A good guess to make it perform the same as a 26" motor is 1.3x (26/20) the voltage and .77x (20/26) the current you would use for the 26" motor.

What this means for your situation is that as long as your battery has enough voltage to make the motor spin fast enough for your desired speed, you can simply adjust your current limit to get the same amount of torque as the 26" specced motor.

The code BF BPM 48v 500w 20(13) should mean 20" wheel and 13 turns. Based on this table the Kv (RPM/V) will be around 6.65. Using this data a 48V nominal battery will give you a no load speed of 319.2RPM (48x6.65) which is roughly 24.7 mi/hr depending on your tire circumference.

Based on this table the Kv (RPM/V) will be around 6.65. Using this data a 48V nominal battery will give you a no load speed of 319.2RPM (48x6.65) which is roughly 24.7 mi/hr depending on your tire circumference

That is for a code 26[13].
Is there no difference between a 20[13] and a 26[13]?

I'm not sure, but unless a 20" or 26" marked bafang has different gearing (and I'm pretty sure they don't) then they should be identical because 13 is the number of turns.

 

[nasium]

Lots of great and interesting info! So it all comes down to voltage and current to make this work. I think this motor will work out just fine. Time to build my first wheel.

 

[izeman]

Lots of great and interesting info! So it all comes down to voltage and current to make this work. I think this motor will work out just fine. Time to build my first wheel.

why don't you connect it to the controller and measure no load rpm? then you can be sure.