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EV Conversion: Locking the Transmission in Second Gear

by Ove
(Stockholm, Sweden)

If you decide to keep the transmission, but also lock it in gear, I've heard of locking it in any from first to third, but let's say second gear, and then using electric reverse since the gearbox is locked and the shift stick removed so you can't put the gearbox in reverse gear; why don't you just get rid of the gearbox all together?

Does it have to do with the gear ratio of the second gear, this being better than just bolting the motor to the driveshaft directly?

If this is the case couldn't you just get a smaller more compact and lightweight gearbox, which only job is to change the ratio between the motor and the wheels; much like what is done in radio controlled cars?

Hi, Ove -

That's the new Ford Focus Electric in the video up there - two gears, forward and backward.

On with your question.

So with the usual disclaimer that this is the EV Kindergarten Class, and that you might be better off asking your grown-up questions over at the EVDL or DIY Electric Car Forums...

1. You can dispense with the transmission altogether, gearbox and all, and just power the car directly from the motor, but it will require a larger motor. Since most conversions already have transmissions in them, people often opt to use the existing gearbox and a smaller electric motor. You can do whichever you like.

2. Yes. People lock it into second gear because it's the most favorable gear ratio for 0-35 or whatever. The "around town" gear and the "freeway" gear. If by "better" you mean "more efficient", then yes, it's better than going directly to the driveshaft. Gearboxes were invented for a reason, after all; ) It's a tradeoff of weight vs. the expense of a bigger motor.

3. I heard a similar argument recently for using a motorcycle gearbox in an electric car conversion. The answer? The torque required to move a heavier vehicle like a car would just demolish your compact, light gearbox.


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Shifting Gears in Electric Car Conversions

by Bryan

Can I shift gears to meet both city and highway speed limits in my conversion? I keep reading about pinning in second or third gears. In my case I need 25 to 60mph.

Hi, Brian -
This got me thinking...why do we shift gears, anyway?

Well, in an ICE car, we shift gears to get up to speed smoothly, efficiently as possible, and keep the engine from stalling.

But your series DC electric motor (the most popular kind) won't stall, even if you start it out from a higher gear, so that's not us. In an electric car, the controller does some of the work the ICE-machine's transmission does.

The controller acts like a big dimmer switch that "controls" the output of the motor based on information gathered by the "pot box", which gets its information from the foot on the accelerator.

Not to say that the transmission doesn't help, but the truth is, you don't really NEED that transmission. It's just more convenient to leave it where it is and use it.

So yeah, you can do what others have done, and leave yourself one lower gear (not the lowest) for city driving, and one higher gear for freeway driving. You don't really "need" to shift into the freeway gear, but I guess it'll save your lead batteries, if you use those.

The smart guys over at the EV Discussion List agree you'll need a bigger motor if you're going to go tranny-free.


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