Alternator as motor during acceleration?

[Logic]

Found this post
where a guy's talking about 8000 W from a normal alternator, when accelerating, with a ctlr and extra batteries. (100vdc)

Old post and the guy seems to have faded away. Site's dead etc.

I know newer cars have one way bearings on the alternator to use any rotational momentum it might have.
That wont work with this.

Then there's the 100 volts thing.
I'm guessing its a small pack if its only for acceleration but lithium isn't cheap or weightless.

Thoughts?

https://www.diyelectriccar.com/threa...s-motor.80547/

https://youtu.be/7iM6Oa8uh0k

[freebeard]

eAssist

Eight kilowatts is on the order of 10HP. The GM eAssist had 15HP and required a serpentine toothed belt for bidirectional power transfer.

[Logic]

Originally Posted by freebeard

eAssist

Eight kilowatts is on the order of 10HP. The GM eAssist had 15HP and required a serpentine toothed belt for bidirectional power transfer.

Good point freebeard.
One would need tensioner pulleys before and after the alternator/motor at the very least. (if you dropped the voltage to 48-50 volts)

Def not as easy as a one way bearing and perhaps just cutting power to the alternator rotor and the aircon clutch during acceleration.

[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.

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.

[freebeard]

One could bypass the battery pack with an electric turbocharger, but the heat kills the magnets.

[oil pan 4]

It's been tried. Didn't really work.
The hybrid drive motors usually ends up being around 30hp and the battery packs being at least 1kwh, the trend appears to be settling on about a 2kwh pack.
A vehicle alternator is only going to make about 11hp if one could do 8kw.

[Logic]

Originally Posted by oil pan 4

It's been tried. Didn't really work.
The hybrid drive motors usually ends up being around 30hp and the battery packs being at least 1kwh, the trend appears to be settling on about a 2kwh pack.
A vehicle alternator is only going to make about 11hp if one could do 8kw.

Ye there are a good number of electric assist, starter alternator, mild hybrids out with the required belts and tensioners one might salvage from a scrap yard.
Challenge is the ctlr/electronics to hook it up to the throttle..?

Thx for the 2KWh info oil pan.

My thinking is that as long as there is some power output and the ctlr is cheap; one is winning some economy.
ie:
With a low, parasitic drag cancelling, output you don't need to control power to/from the 'motor': It can just be either on/motor or off/alternator, which should be a hell of a lot cheaper than a ctlr linked to the throttle etc and requiring lithium batteries etc.

ie: Get the cost down there to about the cost of a circuit that cuts power to the rotor and aircon pump clutch with a vacuum switch (or something?) when accelerating.

[serialk11r]

Controllers are cheap. https://kellycontroller.com/controllers/brushless/

You want a small amount of net regen, so the pedal needs to be pressed a good amount before electric assist kicks in and otherwise it's charging the battery to provide power to the car. One way to get this is have some simple circuit to change the electric throttle signal in accordance with battery voltage (lower voltage, reduce throttle).

You can have a reduced capacity 12V battery or not to save space/weight for the hybrid battery. You want a DC-DC converter able to supply 12V power. 13.5V combined with a LFP battery is what I would go with.

The hardest thing other than mounting the motor or converting the alternator is honestly going to be the tensioner. You'll have to do a lot of measuring and adjusting to create a mount for the tensioner and get it aligned to the belt.

[Logic]

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.

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!

https://www.youtube.com/watch?v=7g8BRyLaQgg

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.

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...

[serialk11r]

Hub motors run at very low speed. Alternators run at 17000rpm. Huge difference.

Just look at the numbers for permanent magnet motor losses. It's not that bad, and you won't be spending a lot of time at high engine speed regardless. 10kW motor has a no load power consumption of 300-400W at maximum speed.

Alternators have field weakening, but they are so inefficiently designed from the start that it's not a big difference. They have inefficient cooling fans, significant rotor power consumption, and 4x the iron losses for the same magnetic field strength.