Quote:
Originally Posted by serialk11r
Alternators aren't good for motor conversions because they have too many poles for any off the shelf motor controller to handle. At least that's what I thought when I was trying to figure out if it was feasible. A more minor problem is that alternators also tend to have inefficient thick laminations.
Replacing the whole alternator with a permanent magnet motor would be my preference, but getting it to work with the serpentine belt and adding a second tensioner are kind of annoying.
It might be easier to make a custom rotor for the alternator with less pole pairs but you need to know your physics.
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From what I've seen the # of poles is similar to the ctlrs used in bicycle hub motors serialk11r.
I'm sure the guys over at Endless Sphere will be happy to advise on this.
Ye the laminate thickness and the fact that you need to power the rotor are inefficiencies.
I wonder if the newer alternators still use such thick laminations?
Permanent magnet motors have the issue of cogging or drag while coasting serialk11r.
You know; Eddy currents in the laminates induced by the magnets.
With an alternator you can simply cut power to the rotor till you're braking.
Other thing is; being able to control the rotor field strength by varying voltage makes the motor efficient over a much wider rpm range.
This, and the coasting ability, may well make them more efficient than PM motors overall and avoid the cost of those expensive magnets! (more research reqd)
(Here's some amusing video of a alternator powered bicycle out dragging everything but an Audi Quatro!
Quote:
Originally Posted by serialk11r
As far as voltage and stuff goes, it's pretty simple, just match the maximum torque on the alternator pulley. Rough estimate is 1kW at 1400rpm idle (2x crank speed) = 7 Nm for a smaller alternator, double for some newer cars. Set the motor controller's current limit to whatever produces that torque. A larger pulley will give you proportionally more up to the limit of the belt and tensioner.
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Exactly what I was thinking!
Keep it low power so you just need on/motor or off/alternator and skip all the tied to throttle electrics.
Er... the bigger the alternator pulley the LESS torque it puts into your ancillary belt, but higher rpms...