A question on gearing on EV's.

[Joe_Oh]

I hear that many electric cars have one gear. That's easy to understand. But I read about some EV's that can have custom gears installed to have achieve increased speeds.

But at the same time, I hear that having any sort of transmission used with an electric motor isnt nessesary. Maybe I'm just thick, but would even a manual 3 speed tranny help to improve the end speed of a EV? You can have all the torque from the EM you want, but in the end it can only help so much when it comes to speed.

If a car engine wanted to go 55mph with first gear the engine would be reving at something like 9000 rpm. That would kill the engine in no time.

So why not apply the same tranny idea to an EM by use of a CVT? It would be fewer rpms and volts needed to get that highway speed we all know and love.

But then again, maybe I'm just stuck in first in this field myself.

Thanx-

 

[kibble]

I thought most EV's used CVT's? They do in hybrids.

 

[carbon]

i'm making an electric kart (not exactly a full scale EV) and i'm using seven gears from a bike. i dont know what it'll do, but they might keep the rpm low on the motor. an electric motor only draws as much power as it needs, so gears will only decrease the load and prolong battery life. because of the ratios involved, i'll only really use gears 1-3, but the other 4 are good for extreme top speed runs

 

[wingnut]

Part of the reason gas motors need a gears is because they don't make torque until the RPMs get above a certain point. An electric motor will make as much torque at stall as does at full RPM. In practice, if you pick the motor and the gearing that will get you to the speed you want to get to, it will already have enough power to give you reasonable acceleration with the same gearing.

 

[Joe_Oh]

it's not so much acceleration, Its the attainable top speed that I'm interested in. I know that more volts means more max rpm. but even a 72 volt system (72 rpm per volt) will get me 5,184 rpm max with the motor I want. That sounds good and all, but 1st gear in my truck is maybe 35mph before the engine starts to stress out.

It's the torque that moves heavy weight ahead, and the rpms x gear ratio that determines the end speed of the vehicle.

I think that's right-

 

[wingnut]

Don't bother comparing electric motors to gas. They're too different for the comparison to be meaningful. You've already picked the motor so just pick the gearing you need to achieve the speed you want and then see if the acceleration is adequate. Of course there's more involved in attaining the desired top speed. The motor has to be producing enough power at the rated RPM to overcome wind and rolling resistance. Then you have to factor in the weight of the vehicle against any hills where you plan to be driving. It's never as simple as Volts * RPMs/Volt