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I am considering buying an electric bicycle using brushless DC Hub Motor. What is the difference between 24V Vs 36V motor? Is it related to the maximum torque produced by the motor? If yes, what does that mean to a bike rider?

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Author cross posted here. –  Caleb May 17 '11 at 12:11
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2 Answers

Again, it's the same as with battery powered power tools. Usually the higher the voltage the more powerful the motor is and the higher battery Volt-Ampere-hour (not Volt-Ampere alone) rating is.

More powerful motor will usually (but not necessarily) mean higher torque and that will mean climbing steeper hills at higher speeds and accelerating faster. Higher battery Volt-Ampere-hour rating will mean you have more energy in the battery and can go further on your bike.

All of the above implies that both cases have the same energy efficiency which is not always true - motor controllers and other circuitry can have different efficiencies on different bike models. You should get details on the specific models you compare and pick the one you like more.

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As far as motors go, usually the higher the voltages the more efficient they run. However there is a trade-off because usually the higher the voltage, the less efficient the battery is! Different systems may balance these factors at different points depending on how they expect the system to be used and what parts they have access too. I don't think you will be able to strictly say one is better than the other, you will need to compare the specs and a whole package and figure out what package suites you best.

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Why would a battery be less efficient with higher voltage? It's just a bigger number of same low-voltage cells, isn't it? –  sharptooth May 19 '11 at 9:41
    
Yes, but but batteries are physical objects subject the restrictions imposed by classical physics and real world matter :) Multiple smaller cells bring increasing overhead in psychical packaging. There are of course various trade offs at various size factors depending on battery technology, but in very general terms the less meta packaging you have to do the more battery you get. –  Caleb May 19 '11 at 9:47
    
Agreed. I guess the worst problem is with charge equalizing over the cells. And this might be a problem for a demanding application like a bicycle. –  sharptooth May 19 '11 at 9:55
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