# Traversing Hills



## Alchemist (Apr 16, 2009)

I had a conversation with someone discussing EV motors and the subject of addressing hills came up. It was mentioned that DC motors are challenged when having to climb steep grades or long hills and that AC motors are better suited for that task.

I searched and did not find any info on this. Can anyone please enlighten me on this issue please?

Thanks for your time!

Ernie


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## madderscience (Jun 28, 2008)

It has more to do with the continuous Horsepower rating than whether it is AC or DC. 

You need to do the math to figure out how much horsepower you will need to maintain speed up a given incline with a vehicle of given weight.

Once you know that, you can size your motor and controller to be able to sustain this amount of power for enough time to get you over the hill (with margin to account for real world uncertainties and whatever your worst case scenario is)

Then, its just a matter of gearing the vehicle to put the motor in its 'happy place' on its torque/RPM curve for pulling that kind of load at the speed you want to go. 

AC motors can usually rev to a higher RPM safely vs. the DC ones, and AC generally has regen capability included, but AC can easily cost 2X to 3X what a similar-sized DC system can, horsepower wise.

As one data point, my 126 volt, 3400lb toyota MR2 conversion with an advanced DC 9" motor and a 500A curtis controller will hold about 30mph on a 12% hill, pulling 300 amps off the battery. That is in 2nd gear, with an overall gear ratio of about 8:1 to the wheels (23" diameter). If I floored it, I might it get to 33 or 34 mph on that hill. In my case, the best way to improve the performance would be to take off some of the battery weight, for example by going to 8V traction batteries instead of 6V, or (better yet) going to lithium.

Good Luck.


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