CNW 3-Phase Alternator as Starter?

Has anyone tried running a 3-phase alternator as a brushless DC motor? Should be able to muster somewhere south of half a kW. Dunno if that'd be enough to e-start the motor, but it might be worth the experiment. Polyphase motor controllers at 12V/80A are readily available at very low prices. (CNW 3-phase alternator not so low!)

davamb said:

Has anyone tried running a 3-phase alternator as a brushless DC motor? Should be able to muster somewhere south of half a kW. Dunno if that'd be enough to e-start the motor, but it might be worth the experiment. Polyphase motor controllers at 12V/80A are readily available at very low prices. (CNW 3-phase alternator not so low!)

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CNW doesnt make any stators. I think that one is a standard RM24.

davamb said:

Has anyone tried running a 3-phase alternator as a brushless DC motor? Should be able to muster somewhere south of half a kW. Dunno if that'd be enough to e-start the motor, but it might be worth the experiment. Polyphase motor controllers at 12V/80A are readily available at very low prices. (CNW 3-phase alternator not so low!)

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No.

Thanks Gort, thought it was CNW OEM only, but there's a standard RM24 Lucas 3-phase.
Even in-stock here in Aus:
Time to dig out my old 3rd year electrical machines books and bone-up a bit on polyphase synchronous engines. Think it'd make an interesting experiment.
Worst comes to worst, I end up with a 3-phase alternator. That is, if I don't fry the windings in the process. Still, might be ok if the duration is short.

If I understand (and I may not), you are wanting to "reverse" the alternator and use it to start the engine? There would be insufficient torque by a huge amount. Consider how an E-start functions - a dedicated electric motor that spins rapidly and is geared down to gain sufficient mechanical advantage to spin the engine at cranking speed. The alternator would be trying to spin the motor without benefit of any gearing reduction. It will just hum for second (or less) and burn out.

davamb said:

Has anyone tried running a 3-phase alternator as a brushless DC motor? Should be able to muster somewhere south of half a kW. Dunno if that'd be enough to e-start the motor, but it might be worth the experiment. Polyphase motor controllers at 12V/80A are readily available at very low prices. (CNW 3-phase alternator not so low!)

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Wouldn't you be running into the same problems as Alton - trying to start the engine with the alternator woodruff key - something it was never designed for?
How would you travel for kick-back protection?
I'm not saying I know the answers - just a couple of things that sprang to mind.
Cheers

Yeah, good point Mike, the amount of torque may be way short of what's required. I was thinking I could mock it up using the lathe to hold the rotor and make a mounting plate/frame for the stator. Fine, but how to actually measure the torque? Also, depending on where the rotor is "parked" with respect to the rotating magnetic field, there may be only a fraction of the available maximum induced torque available. That's something that's not really an issue with a motor that runs through a reduction box.

Dunno about the Alton Rob, but yeah, hear what you're saying with the Woodruff key. Unlike the primary gear there's no taper fit of the rotor to the crank end to distribute the torque coupling. Kick-back shouldn't be a problem as far as I can see, the rotating magnetic field will pick up the rotor's fixed permanent magnet fields in the case of slippage.

Well, it was an interesting thought experiment while it lasted. Thanks brains trust. I'll skip the high-power electrics in future and stick to microelectronics and firmware design.

robs ss said:

Wouldn't you be running into the same problems as Alton - trying to start the engine with the alternator woodruff key - something it was never designed for?

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Potentially yes but the original setup has a higher surface area engagement than the Alton but I would still torque down the nut and use blue loctite so less likely to come undone.

Typical gearing of motors to cranks on large twins is between 27 and 30 to 1 ratio. Power is typically 0.7kw with upgrades to 1.0 or 1.2kwh.

I run an Alton starter, never had a problem with the woodruff key.

Continuing on with the thought experiment...... I kind of doubt that you would ever get enough torque to turn the engine over without a speed reduction geartrain.
On a further tangent, the challenge reminds me of the Volvo diesel engine in my first sailboat. It had a combination generator and starter. Not a bad starter, but in generator function it had a pathetically low charging rate. Probably a good example of the compromise usually involved in getting a device to do more than one thing.

alots a small displacement dual purpose Japanese 2 strokes had combo alternators/ starters . My TC185 has one, its huge compared to a normal setup.

When I was trouble shooting my Alton and it’s sheered woodruff key, I did some analysis in the starter system. In order to start a 4 stroke engine, you need to be able to spin the engine up to 100 rpm as quickly as possible. From a dead stop, it takes about 150 ft.lb of peak torque to accelerate a typical Norton engine. Assuming that the torque to overcome inertia begins to drop at about 50 rpm, but still requires power to overcome compression, you will need at least 1.2-1.4 KW to crank the engine.

The most powerful 3-phase alternators I have seen that match the Lucas form factor are in the 210-240 watt range. So even gearing the alternator would not be enough to crank the motor to start it.

FWIW

Derek Wilson said:

The most powerful 3-phase alternators I have seen that match the Lucas form factor are in the 210-240 watt range. So even gearing the alternator would not be enough to crank the motor to start it.

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In the Navy, I used to work on small Ford 4-cylinder gas-powered starter/generators with 24V batteries. The batteries weighed around 40 lbs, the whole rig weighed in just over 200 lbs. The motor would start the engine using battery power, then the engine would turn the same motor into a generator to start aircraft with.

Reminds me of "jump starting" a dead Tesla with a diesel generator...

Generally, a DC motor spun is a DC generator and vice versa. That's very different than an AC alternator. You would first have to provide the correct AC current. Since there are multiple windings involved with both single- and three-phase stators, you would have to provide multiple overlaid AC current providers timed correctly to make the stator into a motor. Then there is the problem of the nominal 18 ga wires to the stator - smoke much above 8 amps. Finally, getting it to start turning in the right direction could be a challenge. That's all before it likely is not strong enough to turn a Norton or any other Lucas equipped engine. AC motors are generally not fields winding and a permeant magnet armature for many good reasons!