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Discussion Starter #1 (Edited)
Hi everyone.

I'm trying to make an electric scooter, but I'd like to avoid hub motors. I came across a video in which an old alternator is used as the kart's motor. However, I'm still questioning the feasibility.


I like the idea of using an alternator because of its cheap power and compactness. The question is, given any old alternator, how would I find out its specs? Voltage, amps, regenerative braking? Are all alternators the same 'under the hood'? Would I expect an alternator from a bigger motor to be more powerful?


Every video I've come across has told me that an alternator is just a three phase motor, so I'd assume it'd work with a matching three phase speed controller. I just hope that it's that simple.

This is my first build. I'd just like some wisdom!
 

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The spec of the car probably makes more difference for the rating of the alternator than the engine size. Look for a luxury car/SUV with a large-screened entertainment/nav system, heated/cooled/motorized seats... the more gadgets it has, the heavier the electrical load, so the alternator should be more powerful.

If you look at alternators in a car parts supplier's catalogue, they may mention the rating (in watts or amps) if a particular model used different parts for different spec levels. For my Peugeot Boxer van (Dodge ProMaster in USA), I can find alternators rated from 70A to 150A, so at 14V that's about 2kw or 2.8hp which is plenty for a single person vehicle.
 

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I agree with Emyr that alternator size is related to vehicle equipment rather than engine size. The highest-capacity 12V alternators are likely in trucks for commercial applications, and cars for fleet use such as taxis and law enforcement, although luxury cars are presumably similar. 200 amp units should be available, although 150 amp is likely more common.

Auto alternators typically have a 3-phase stator, but unlike most 3-phase motors (which have induction or permanent magnet rotors) the rotor is wound and powered (through slip rings) so that it can be easily operated by controlling the rotor current and simply rectifying the output. That means that a controller/inverter for a PM motor might work, if simply running the rotor winding at full power all the time is acceptable.
 

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I think the control and power electronics might be easier if you use a 24v alternator off a truck. For a given power, double the voltage but halve the current. Less current means cheaper wiring and switching.
 

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I think the control and power electronics might be easier if you use a 24v alternator off a truck. For a given power, double the voltage but halve the current. Less current means cheaper wiring and switching.
I agree, although the available selection will be much narrower.

I think it's reasonable to assume that, like the use of cheap brushed DC motors in EV conversions, the alternator can probably stand operation at a somewhat higher than designed voltage and speed, at the expense of reliability.
 

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There are cars (i think vw touareg or whatever its called) with 3 phase bldc motors on radiators for conditioners. You could probably gear it down and use it for a bike, not as much for scooter
 

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PHP:
There are cars (i think vw touareg or whatever its called) with 3 phase bldc motors on radiators for conditioners. You could probably gear it down and use it for a bike, not as much for scooter

Look up Austin Brown's projects, which inspired me to buy a Denso ES27 compressor from a Lexus GS. There's a thread somewhere here that I need to update...

The ES27 is a ~8kw motor running on 30A at about 280V. That doesn't really match any commonly available IPM-compatible controllers. Those that can handle 300V will be scaled and priced for 100kw, so ~300A. Those scaled for only 30A won't handle much over 100V.
 

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What did you (or are planning to) use as a motor controller? Does it work at lower voltage higher current? What kind of power is it supplied with (2 wire DC, 2 wire AC, 3 phase AC)?

PHP:

Look up Austin Brown's projects, which inspired me to buy a Denso ES27 compressor from a Lexus GS. There's a thread somewhere here that I need to update...

The ES27 is a ~8kw motor running on 30A at about 280V. That doesn't really match any commonly available IPM-compatible controllers. Those that can handle 300V will be scaled and priced for 100kw, so ~300A. Those scaled for only 30A won't handle much over 100V.
 

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What did you (or are planning to) use as a motor controller? Does it work at lower voltage higher current? What kind of power is it supplied with (2 wire DC, 2 wire AC, 3 phase AC)?
Single-phase ("2 wire") AC power seems unlikely to exist anywhere in any vehicle, except to supply a convenience outlet for 120 V AC appliances.
A motor is only supplied with DC power if it either has a commutator and brushes ("brushed DC motor"), or it is packaged with a motor controller/inverter (so the motor gets AC power).
 
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