Waynemarlow wrote: ↑Nov 24 2019 8:33am
Not replying for Buba, but I have both the 48volt and 36volt motors and have tried both on the same bike ( just replaced the motor and not the whole unit ).
The 36 volt on a 36 volt battery is a great motor for anybody on the road wanting to just commute at lower pace, that's what it was designed for.
The 48 volt unit on 48 volts has a mass of torque ( I think better than most commercial bikes ) but because of that torque, you end up simply running a cadence too high due to the way the motor assists ( the torque just accelerates the bike without you really realising it ) at lower cadence levels and once you get into that 80 rpm cadence level, the motor just starts to back off. You end up having to change to a lower gear in rapid succession to get the best out of the motor. Once you learn that, on road its probably not a bad option for the commuter who wants to get to work without having a sweat on, hence Buba's reference to a 52T front chain ring.
For off road and for active cyclists, 80rpm cadence is too low. the 36volt unit on 48 volts will willing pull into the 90's before it backs off which makes it a good compromise, less torque but torque spread over a wider cadence rpm which suits the off road cyclist who constantly has to range up and down in cadence. Its a good solution and puts it into the commercial off road ebike bracket.
As to 52volts well I'll leave that to Buba to respond to although I may well convert a battery over to try it as 52volts transforms the Bafung motor soonish.
Let us quantify the difference between the motors:
Kv =
RPM /
Vp
Where
Kv is the motor velocity constant,
Rs is the rotational speed in RPM and
Vp is the
peak voltage.
So the
Kv constant for the 48 V motor is
83.33 ≈ 4000 / 48. And the
Kv constant for the 36 V motor is
111.11 ≈ 4000 / 36.
Using the
Kv we can get the torque constant and thereby the relationship between current and torque:
T = 60 / 2 *
pi *
Kv
Where
T is the torque,
pi is pi and
Kv is the previously mentioned motor velocity constant.
So the
T constant for the 48 V motor is
0.115 ≈ 60 / 2 * pi * 83.33. And the
T constant for the 36 V motor is
0.086 ≈ 60 / 2 * pi * 111.11.
So this means that due to the controller being limited to around 16 A we can get approximately 34 % more
peak torque from the 48 V motor. But this extra torque quickly goes down to levels at or below the 36 V motor. It is only truly noticeable at startups and low range situations. The 36 V motor will provide more torque in a greater operating range and will quickly outperform the 48 V motor if using a higher voltage battery. I wanted to do a nice graph showing the difference but I think it is clear as is.
Clearly there are two different characteristics between the two motors. Choosing the right motor depends on several parameters, e.g., user preference, riding conditions and bike hardware.