How do Pedelec systems work?

[flecc]

If they are Hall effect motors, the Hall sensor signal rate to the controller circuit automatically indicates speed Rooel, the same as the Wisper one and many others. The controller can then dictate a cut-off speed, not issuing phase current beyond a certain pulse speed.

The pedelec disc type that beeps mentions only applies to some hub-motor bikes, I think the minority now, since if the pedelec ring is on the BB spindle as it often is, it has the disadvantage of limiting power at high pedal rates in every gear, not just top.

Most like Wisper, and eZee where limited, use motor Hall sensor feedback to the controller.
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[rooel]

From what flecc says I think we can assume the Sram Sparc motors are a Hall sensor type, and therefore, when they sense a certain speed cut the power supply. Presumably they also sense varying speeds between 1 mph and 15 mph and cause the motors to respond in a manner similar to what happens with a pedelec sensor system.

I wonder if all this explains, too, a minor problem I have had after installation of lithium batteries: occasionally if the wheel speed is suddenly retarded (by the brakes, or even going up the up side of a speed hump) while the pedals are still being turned (which means the motors are still in operation) the motors stop and the battery gauge/power supply lights go out. The only way to restart the circuit is to unplug and replug the power supply. I have dealt with this problem by ensuring that I am free-wheeling (thus cutting the motors) a split second before braking or mounting a speed hump, and when I forget, a push-to-break/push-to-make switch in the power supply enables me to reset the system instantly. As I did not notice the problem with NiMh batteries it may be something to do with the higher voltage of the lithium battery (when fully charged is 21 volts against 18 volts with the NiMh) - I think too that when the lithium batteries fall to 18 volts the problem does not arise.

 

[flecc]

Those cut-out and restart characteristics are exactly the same as the eZee ones, cut-out on the eZee due to overload causing a drop in voltage to below safe levels.

It seems unlikely to be the cause on the Sparc/Lithium, but it may be a protection circuit operating in the same way, maybe an excess current protection, the load current rising when driving against the brakes.

However, it could just be be a voltage drop cutout in the same way, given our knowledge of how much lithium cell voltage can drop on the eZee Li-ions, to under 32 volts from a nominal 37 volts when driven under excess load conditions.
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