# Motor selection



## MattsAwesomeStuff (Aug 10, 2017)

> Is the RPM that is listed the max or can it go much higher?


Since these are motors that plug into the power grid, that is the speed they rotate at 60z, or nearly thereabouts.

However, since they are motors that plug into the power grid, that might be the max rate they're designed to spin at.

Bearings might fail, and the structure of the rotor might tear itself apart. On a guess, anything reasonably sized should be good for at least 4000-5000rpm. Giant motors, having a larger radius, will have a higher edge speed at higher RPM and probably can't sustain that. But anything you'd fit into a car is probably okay to be spun faster.



> For example, how would these motors fair?
> https://www.ebay.de/itm/Sicmemotori-...QAAOSwEMxa2FgE
> https://www.ebay.com/itm/Marathon-AC...-/283096441764


Well that second motor is the size of a pallet and probably weighs as much as a car.



> And if the RPM is in fact to low, would using the old transmission of the car solve my problems?


A transmission has gears that change the rotation speed. If it has overdrive gears (gears that speed up the output) then that would work, if they're geared high enough (which they probably aren't). Usually most (sometimes all) of the transmission's gears are for slowing the rotation speed.


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## jonescg (Nov 3, 2010)

Don't be afraid to spend more on the motor than you originally planned. It is the single component which delivers both joy and reliability every single day. It's worth getting it right.

I spend $12,000 on the motor for my electric race bike.

Worth. Every. Cent.


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## Duncan (Dec 8, 2008)

jonescg said:


> Don't be afraid to spend more on the motor than you originally planned. It is the single component which delivers both joy and reliability every single day. It's worth getting it right.
> 
> I spend $12,000 on the motor for my electric race bike.
> 
> Worth. Every. Cent.


I spent $100 on my first motor - probably more power than your bike motor bit a wee bit heavy for a bike


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## jonescg (Nov 3, 2010)

Duncan said:


> I spent $100 on my first motor - probably more power than your bike motor bit a wee bit heavy for a bike


Yeah, you don't get 175 kW to the rear wheel with an electric motor weighing 40 kg unless you spend a fair bit of money...


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## Duncan (Dec 8, 2008)

jonescg said:


> Yeah, you don't get 175 kW to the rear wheel with an electric motor weighing 40 kg unless you spend a fair bit of money...


But you can get close to 400 Kw for $100 if you can live with a 100 kg motor


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## jonescg (Nov 3, 2010)

Sounds like a beast Duncan - what was it? And what did it get installed in?

As for the original post - my point is, don't compromise too much on your motor. It's going to be what makes your EV experience possible. Don't go overboard either, but then again, nobody ever complains about too much power to the ground.


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## Duncan (Dec 8, 2008)

It's in "Duncan's Dubius Device"

https://www.diyelectriccar.com/foru...dubious-device-44370p15.html?highlight=duncan

I blew my first motor up after five years - I'm pretty sure it was my fault and I had damaged one of the armature coils

Got a replacement - exactly the same model for $150 - it's in the car now

Just got a "Fine" from the Sheriff of our Hot Rod Club - apparently it's against club rules to beat ALL of the supercharged V8's at our annual drag races with an EV
(Two of the motorbikes did beat me)

I am overloading it a tadge - it was
1400 rpm, 200 amps and 48 volts in the forklift
So I'm feeding it
1200 amps and 340 volts and it's doing 5300rpm at the end of the 1/8th 

So I picked up a "Spare" - the model that replaced mine in the forklifts (about 20 years ago) - that cost me $200!

Would not be any good in a bike (too heavy) but great fun in a car


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## Emyr (Oct 27, 2016)

Jubo said:


> Now my question is, I see quite a few motors with those two requirements but with low RPM (sub 2000).
> Is the RPM that is listed the max or can it go much higher?


A motor engineering/servicing company should be able to replace your bearings with ones rated for higher speed and advise you on your options for sealing.

The folks over at http://forums.aeva.asn.au/viewtopic.php?f=41&t=1237 have had interesting results from reconfiguring the wiring of some AC motor designs, getting many times the original power rating. This would allow you to use a smaller, lighter aluminium-cased 10-20kw motor rather than a monster with a 66kw rating on a mains supply.

Remember that industrial motors' nominal power is usually for 24/7 operation indoors with limited airflow, whereas cars tend to only use max power for only a minute or two while accelerating, then use 10-20kw to cruise with plenty of airflow.


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