# AC Electric Bicycle Motor



## Greenflight (Sep 13, 2007)

Most conversions of power tool motors use cordless tools, so the motor is generally a permanent magnet DC motor operating at around 15-25V, which is pretty good for that kind of application.

Also- a lot of devices (treadmills and stuff) just use small series-wound motors that can operate on either DC or AC instead of using dedicated AC induction motors.


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## xrotaryguy (Jul 26, 2007)

I suspected that the saw motor could have been from a cordless device. thanks for the info.

So, if I were to use a treadmill motor that's rated at 120vac and 18 amps, would it be safe to assume that I could also run it at 24vdc and 75 amps?

120 vac x 18 amps = 24 vdc x 90 amps = 2,160 watts


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## Mr. Sharkey (Jul 26, 2007)

No, wrong on several counts.

The internal resistance of the armature and field windings (assuming series wound here) will determine how much current a motor will draw at a lower voltage. (calculations based on simple resistance, a motor, being a dynamic device with internal inductance would return different but similar actual, measured values.)

120 v / 18 a = 6.66 ohms.
24 v / 6.66 ohms = 3.6 amps.
24 v * 3.6 a = 86.4 watts.

If you were able to load the motor (running at low voltage, and therefore a lower RPM) with sufficient drag to cause it to draw 75 amps, it would probably burn out, as the armature and filed windings are constructed with small, high resistance wire. The excessive current would cause a lot of heat to be generated, resulting in destruction of the motor.

If you intend on running a motor at a voltage far outside of it's design parameters, expect low performance and failures to be the rule.


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## xrotaryguy (Jul 26, 2007)

Aah, so the motor would need to be rewound. That being the case, I would imagine that numerous other changes would need to take place. that's not worth it. I guess the best thing to do would be to find a way to feed it the correct amount of voltage and amperage and then gear the drive train accordingly.


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## Greenflight (Sep 13, 2007)

Just to clarify, I wasn't suggesting that you use a treadmill motor... I was just using it as an example of the kind of motor often used in AC appliances. 

It's probably not ideal for any kind of EV drive train... I don't know enough about them to say for sure.


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## aeroscott (Jan 5, 2008)

these are universal motors ,thay have name plate rating of 120 volts,ac/dc. the volts need to be high,thay run vary strong on 120v dc but hard on the switch. about 2hp


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## xrotaryguy (Jul 26, 2007)

I've been poking around a bit more. The cordless drill or saw motor really looks like a better candidate. many of them are an 18 volt configuration, so I could run a trio of 6 volt batteries. Amperage is a bit of a concern still though. 

The tread mill motor would probably be better as an accessory drive motor on an electric car with a 120v battery pack.


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## houseoffubar (Nov 18, 2007)

One last thing, Some of the bicycle motor kits are AC, and you could buy a controller from one of these, and run an AC motor, such as the skill saw( assuming the correct volt, amp, rpm ranges. Eric


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## Mr. Sharkey (Jul 26, 2007)

Not sure about the particular bicycle kit you saw, but generally, when the subject of "AC drive motors" is discussed, the controller is a three-phase AC inverter. This isn't going to be of much/any use with a simple universal, series-type DC motor, so be sure you aren't mixing your AC apples and DC oranges before laying out any long cash for hardware.


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## aeroscott (Jan 5, 2008)

an ev friend said that skillsaw is a series wound motor the same as in many dc ev's.most high power ev's are running at least 72 volts.some bikes are running 72 volts .motors of low voltage have less efficiency then higher voltage ones.


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## xrotaryguy (Jul 26, 2007)

Mr. Sharkey said:


> Not sure about the particular bicycle kit you saw, but generally, when the subject of "AC drive motors" is discussed, the controller is a three-phase AC inverter. This isn't going to be of much/any use with a simple universal, series-type DC motor, so be sure you aren't mixing your AC apples and DC oranges before laying out any long cash for hardware.


Hmmm... the electric bicycle motors that I see most often are of the DC permanent magnet type. Perhaps some of them are AC. I haven't seen any though... or I wasn't paying attention to motor type at the time. Of course, the reason that I am doing this is to avoid "laying out any long cash," so hopefully I'm in the clear there


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## xrotaryguy (Jul 26, 2007)

aeroscott said:


> an ev friend said that skillsaw is a series wound motor the same as in many dc ev's.most high power ev's are running at least 72 volts.some bikes are running 72 volts .motors of low voltage have less efficiency then higher voltage ones.


Hmmm... interesting. running 72 volts on a bicycle could be tough. A trailer might provide enough room for a half dozen small 12v batteries though.


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## Hi Torque Electric (Dec 23, 2007)

Hey Rotary

I have a few small 24 volt PM DC drive motors that I've used to make small projects. If you can't find a motor that you feel is a good motor choice let me know and I'll get you some pics of one. Not sure what you're looking to pay (or what I'd need to charge for one)(they've all been used for my own consumption) but would be willing to work with you to get one in a bicycle for testing there. I might be able to find one with useable brushes and that still runs okay as is for a better deal than if I had to replace parts and put time into it. These motors come with a keyed (mates to the shaft) nut that is easy to machine and weld a sprocket to as well.
Anyway, when I read this thread, I just had to chime in with info on these little motors I've been getting pretty cheap. The data tag states .6HP at 24 volts and I've run them at 36 (without advancing) and they're pretty well built and I've been thinking they'd be a great bike motor.
Just my two "little motors" worth.
Cya
Jim Husted
Hi-Torque Electric


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## Greenflight (Sep 13, 2007)

Okay, here's a few more cents from me... If I were to build an electric bicycle, I'd probably buy one of these...

http://cgi.ebay.com/Electric-Bicycl...ryZ75210QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


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## aeroscott (Jan 5, 2008)

vary cool motor,with on board controller(inverter).i have learned to call dc bruchless motors ac motors.becouse its run buy an inverter and can not run on dc without it.so i mean i lump ac and dc brushless together.ps that skillsaw motor should be good for over 6kw intermittent ,wormdrive might not be good ,thay run at over 12000 rpm stock.hot rod bike!


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## xrotaryguy (Jul 26, 2007)

Hey guys, thanks for all the suggestions and offers. I actually stumbled (actually, I've been hunting pretty hard) across an used 24v EV Warrior bicycle with an extra 36v motor for $100 total. The bike itself is in pretty rough shape, but the motor runs great. I can't wait to put that 36 volt unit in something and really have some fun.  

For now, I just need to transfer all of the 24v stuff over to my mtn bike so that I can make the 7 mile commute from my kid's school to my school in under 45 minutes.


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