Minimum Operating Voltage

[koolkev]

What is the minimum input voltage for the inverter/motor? I am thinking of recycling a motor in another car but want the pack to be as small as reasonable to keep the price/space down.

 

[nlspace]

It depends upon the weight, tire size and gear ratio of your car, and how quickly you want to accelerate, and what top speed you require.

The motor has embedded permanent magnets in the rotor, so the inverter must be able to supply a higher voltage than the back emf in order to put current through the windings. A higher speed creates a higher bemf and requires a greater supply voltage.

For example if a laef motor could drive the car to 90 mph with a 400V pack, then it might drive your car up to 45 mph with a 200V pack.

check out the DIYElectricCar (.com) forum for builds that others have done.

 

[goldbrick]

I agree about the BEMF limiting the spin speed with an H-bridge type direct drive but with an inverter I'm not convinced that is still a limitation since the inverter can probably generate any required voltage (although with less current) from the DC source.

And OP, if voltage is a concern, you can always modify the number of cells in series vs in parallel to increase the voltage. This will come at the expense of max current and range since there is obviously no way to magically make more capacity in the battery.

 

[LeftieBiker]

And OP, if voltage is a concern, you can always modify the number of cells in series vs in parallel to increase the voltage. This will come at the expense of max current and range since there is obviously no way to magically make more capacity in the battery.

Yes, and this is the preferred approach for smaller pack & EV builders, because higher voltage gives you more power, and some of that power can offset the reduced range from the smaller capacity. There are few calls for "Less power! Less power!" It's why most E-Bikes are now 48 and even 52 volts.