Help with using GoldenMotor hub motor as a generator

[ctk]

Hi

We are a group of students in Sweden, want to make an stationary bike generator with a hub motor. The setup would be in a way to put up the back wheel on a stand and use the hub motor in the back wheel.
I read on the forum that because of the clutch, it's not possible to drive the generator as it is by pedaling, therefore, some sort of adjustment is needed like flipping the wheel and bringing the gears to the other side but we are not sure whether that's the case in HBS36R also? Besides that, we have some questions regarding the characteristic curves of the motor(generator) in order to plan for the other parts regulating the voltage.

Our questions are:

- We don't need to generate more than 300W probably, so what hub motor do you suggest? We are not sure whether we can use minimotor 250W or not, since it's at the limit. So we aimed for HBS36R 500W, 36V instead but we are not sure about this.

- Is it HBS36R, that is used in 901-R? and does it have this clutch problem also which needs to be solved? Moreover, do you see any difficulty if it's gonna be used as in a 20" rim? (since the generator seems to be welded to the rim).

- Is the characteristic curve in the link below represents the HBS36R 36V, 500W also? (since it seems it's only for 750W (P2) and 1000W (P1) models). Does the curve represent the situation when we are running it as a generator and how can we interpret it? For example let's say if we run the generator at 100 rpm, what voltage level and power output can be extracted? etc etc.
https://www.goldenmotor.com/hubmotors/HBS-36V500W%20Performance.pdf

Thanks for your help in advance.
Nima

[Bikemad]

Hi Nima andto the forum.

Only the minimotor (902) has the internal freewheel device (unidirectional clutch) so it is not really suitable for your proposed use.

I think that the HSB36R should be a good choice, but I don't know if it is the same as the 901-R, or whether it has simply replaced it.

The 20" Magic Pies (with the exception of the Magic Pie Edge) come with a solid cast alloy wheel assembly that is also part of the motor, but I'm pretty sure that the HBS36R comes with a conventional spoked rim, but you might want to check this with your proposed supplier.

I have not seen any performance curves showing the generated output, so I don't know how it will compare.

However, my instinct tells me that it would probably be a reversal of the dynomometer figures, i.e. the current and voltage would increase with rpm (dependant upon the load) and only ~80% of the input power would be available on the output (as ~20% will still be lost due to inefficiencies within the motor).

At 100 rpm, the output power will ultimately depend upon the motor's KV (rpm constant of the motor) and the amount of current being produced by the motor working as a generator.

Spinning it at 100rpm with no load on the output will produce a steady voltage but no actual power is being produced as no work is being done.
Spinning it at 100rpm with a heavy load on the output will reduce the voltage and increase the current. Although this will ultimately produce more power, it will also require at least 25% more power to actually drive the generator than it will be producing.

The Performance chart you have linked to appears to be for the HBS-36 500 Watt motor, and based on those figures, I would estimate the voltage produced at 100 rpm to be approximately 10 volts under no load conditions, but I don't know how much the voltage will sag when a heavy load is placed on it.   

The "P1" and "P2" columns on the performance data sheet relate to the "Power In" and "Power Out" figures, not the motor model.

Alan