Dropping from 36V motor to 24V motor for more speed?

[The S Man]

Apologies in advance...Complete Newb with 3 weeks experience!
I have an eco expedition 36V 250W e-bike which I love.
Like everyone else I would like more power when using it off road,
and easily keeping it legal when on the road.
Has anyone any experience of fitting a lower voltage motor to give more speed, rather than overvolting.
I thought if I could pick up a 24V hub, I would try to connect it into my existing 36V system.
No need to change anything else hopefully. Then when back on road a quick 5 minute swap will leave me road legal again.

 

[Alan Quay]

I run a couple of 24v motors at 36v. Both SWX type. They spin faster, as they are wound to go at about 15mph at 24v. Unloaded they will spin 50% faster, around 22mph. In the real world though, they only get to about 19 (ish). You don't get much more torque though, as the extra power is all given over to higher RPM.

Just to be clear, this is called over volting.

To get more torque you need to increase the current.

 

[Swytch Bike]

Hi, you're right in that using a 36V battery and controller with a 24V motor will give you a higher top speed. This is because a 24V motor is wound in such a way giving a motor constant where the back EMF reaches 24V at a particular rpm, which is usually deliberately set at around 25-35 kph.
It's important to realise that there is a trade off between the amount of torque you get out of the motor, and the top speed you get.
If you swap a 36V motor to a 24V motor then you will notice a reduction in the performance at the low end of the speed range, at the expense of getting a higher top speed. You are not just getting extra speed at the top end "for free".

Not to mention that you risk damaging the motor by putting more current through the 24V motor coils that it has been designed for...

If you want more power, then I would recommend going for a 36V 500W or 36V 750W controller with your existing system (assuming what you have at the moment is a 250W controller), just be careful about how much power you can get away with pushing through the motor without burning out.
If you really want to get a higher top speed, then consider a new 36V motor that is designed to have a higher rpm at 36V , these are available from any of the major chinese manufacturers just by consultation, Shengyi Xiongda etc. can make custom hub motors with a winding configuration to give you whatever is your required top rpm. You can obviously mess around with mismatching the motor voltage and battery voltage but I wouldn't recommend it.

 

[Deleted member 4366]

The power comes from the controller and battery. If your motor has too much speed for the power given to it, it will run inefficiently without going any faster.

With any motor, it's very important to know its max rpm at any voltage, so that you can run it at the correct speed and power. The starting point must be the rpm of your present motor. What is it? Does the controller restrict the speed?

 

[The S Man]

Thanks everyone for the replies