How does the controler limit 'speed' ?

[JohnD]

I understand how a controller can manage voltage and amps to control power (under my school friend Ivy Watts ) but how can the controller limit 'speed' ?

Unless the controller knows how many RPM the motor is doing and also knows the diameter of the wheel it is fitted to - but this seems very complex.

 

[onmebike]

Its a simple case of setting up at the factory. It doesn't actually know what speed you are doing, it is set to a maximum of 15mph in the same way as you can hold it at a set speed of say 8mph with the throttle.
Inside the controller there will either be a variable resister or set value resisters to control the maximum speed, altering these will either increase or decrease top speed within the range of battery and motor.

 

[Mussels]

I'd guess hall sensors in the motor provide the controller with the speed and could be used to limit the speed, that seems more complicated than it needs to be so I expect it's a simple current control.

 

[NRG]

Talking about hub motors, it doesn't as such its how the motor is wound with a set voltage in mind that determines the RPM or speed of the motor. Typically motors of the same type will be available but wound for different RPM/Speed to suit a particular wheel size. This is what determines the speed. The controllers job is to provide a variable three phase pulse width modulated (PWM) signal to the motor windings to turn the motor up to a 100% duty cycle IE maximum RPM...but it can only feed the motor with whatever the supply voltage is, no more. Hope that makes sense!

 

[NRG]

I believe Hall sensors in the motors (talking hub again) are used primarily for position sensing and direction of rotating sensing. I think they can also be used as a feedback mechanism for sensing speed and motor torque, so maybe there are two ways of governing speed. The simple mechanical approach with sensor-less motor/controller combination or a more sophisticated controller and motor with Hall effect sensors...

 

[flecc]

Makes sense to me, that's exactly how it is on most e-bikes. That's why they commonly go faster when freshly charged and the speed gradually declines as the battery empties and it's output voltage drops.

My bikes speed range is about 15 to 16.5 mph depending on charge level, but if the battery is used hot off the charger, the initial top assist for about half a mile is 17.5 mph, but if I fully empty the battery, the speed towards the end is 14.5 mph.

A few do have controller speed control, bikes made for the US market are controlled that way when exported to Britain, the original eZee F series models being one example. 20 mph on voltage control but limited to 15 mph by the controller for Britain.
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[Straylight]

My '08 Wisper also has the speed capped at the controller, as it has the option to uncap it via the green button, don't know whether it's still limiting to 19/20mph, or if this is simply the limit of the motor.

 

[flecc]

Wisper are another example like those eZee F series, limited by controller. They say that continues and although losing the option button, the derestrict information will be available to consumers for "off-road" use. The derestricted speed is voltage limiting, not controller.
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[eTim]

If the controller is limiting the speed, does this mean it is wasting energy in doing so and that energy is lost in the form of heat?

 

[flecc]

If the controller is limiting the speed, does this mean it is wasting energy in doing so and that energy is lost in the form of heat?

Heavily limited bikes I've known like the Torq 1 have more range when limited so obviously no waste. I assume the limiting is done on the phase pulse frequency, merely capping that.
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[eTim]

Heavily limited bikes I've known like the Torq 1 have more range when limited so obviously no waste. I assume the limiting is done on the phase pulse frequency, merely capping that.
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Ok thanks Flecc, straight over my head already . To my simple mind I thought that the battery would be producing more energy for the motor demand and the controller might 'waste' some of the energy in the form of heat to limit energy supplied (for different markets).

Is there a FAQ putting it into relative laymans anywhere?

 

[flecc]

Ok thanks Flecc, straight over my head already . To my simple mind I thought that the battery would be producing more energy for the motor demand and the controller might 'waste' some of the energy in the form of heat to limit energy supplied (for different markets).

Is there a FAQ putting it into relative laymans anywhere?

I don't know of any conprehensive one, and the many variations between designs means a generic one wouldn't be too reliable.

On this battery and motor point though, the general principle is that an appliance like a motor or controller draws what it needs according to it's design factors like intrinsic resistance. The designer aims to use factors like that resistance to produce useful power.

Sometimes further limiting is used to reduce what an appliance like a motor draws at it's normal design level, for example like reducing it's normal speed. This can be by crude methods like a resistor wasting some of the supply as heat as was often done in the past, but obviously such cheap methods are undesirable and rarely used these days. Using the speed of rotation of the motor to merely switch off when appropriate is much more efficient.
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[lemmy]

Using the speed of rotation of the motor to merely switch off when appropriate is much more efficient.
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With my Panasonic system Kalkhoff, I find that in 8th gear I am rarely cycling at below 15mph. Since the power is well below peak at that point, does that mean that I am saving that power or is it simply being dissipated?

I have found with the Panasonic system that is has taken me several months to really get to know it and how to maximise its value. I find it very rewarding to use now, sometimes dropping down to 3rd gear and riding up the steepest hills round my way with seemingly zero effort if I'm knackered.

It reminds me a bit of my little 400cc four Honda which had a power band from from 7500 to 10000rpm. Difficult to master but hugely useable and rewarding when you do.

 

[Fiddler]

Ok thanks Flecc, straight over my head already . To my simple mind I thought that the battery would be producing more energy for the motor demand and the controller might 'waste' some of the energy in the form of heat to limit energy supplied (for different markets).

Is there a FAQ putting it into relative laymans anywhere?

Many years ago I built an E car used a fork lift controller thyristor control . Easy to understand . You couldn't just switch on the thing would blow up . So the feed was pulsed .that is it was switched on and off so many times a second say 30 . Each switch on / off was a very short time .Switch on / off longer and the car goes faster . . DC system has to have the electronics to do the pulsing . Household dimmer uses the 50 on and offs . Easy ! A later E car had all that electronics in a box the size of a half a loaf of bread . No thyristors but power transistors . But I liked the buzzing of the old style control .
Before that it was the clicking of contactors on trolley busses and old milkfloats