Bill, you are a tiny bit ironic about good looks of a car alternator on a classic ??
Myself not very knowledgeable about stepper motors or brushless to this day I hooked up a small stepper motor to my lathe , set 2000 rpm and got up to 60 V DC from it on rectifiers - but no usable power when connected to a 6 V 35 W bulb and no more voltage showing. It is sort of a short with that bulb. So I don´t see much use of a stepper for generator, so instead better get a brushless servo motor like these in my photos below.
I got the big , longer type these days, was express shipping from China at € 40.- -they would not do snail mail. So it is € 90.- plus taxes.
The performance was very impressive from the three phase rectifier, while still waiting for the bike regulator to arrive :
14 V on a 60 W quartz bulb at 1360 rpm - 1090 at crank speed
14 V on a 100 W quartz bulb at 1480 rpm - 1180 at crank speed
14 V at 120 W bulbs at 1580 rpm - 1265 crank speed
I blew two quartz, a 60 W plus a 100 W connected - but not safely, so both destroyed by unreliable contact and overvoltage.
I can only later tell higher power readings with the regulator, limiting voltage to 14 V at high revs, so for the while we have to wait for the next shipping.
That is a lot more electric power than I need , I´ll have a big magneto anyway.
When you look at the massive 15 mm shaft, 14 mm at the pulley drive fit, you can figure out what it does as a motor. I don´t care the least what this type does in this role but am only interested in generated power. So this is a good tell-tale for what to expect from any motor as a likely generator. The smaller shorter brushless below has a 8mm shaft, quite powerful , see numbers at the start of this thread. The new type is 14 mm shaft and almost excessive for my needs. For judging the "load" on the dynamo sprocket: Contrary to some comments this cannot possibly be much as I could easily hold the motor in the lathe in the right hand while getting the revs from the reflex digi tachometer in left hand with 120 W load. After all, 200 W is just a quarter of a hp at best, negligible.
Cooling might be a factor to keep in mind, but then , I guess power will be well below 300 W anyway, so only part of this will go up in heat. As no electronics are inbuilt in the motor 100 degrees should be no factor - unlike in the regulators in typical car alternators. There you waist part of the generated electric power for sustaining the magnetic field in the rotor. With a permanent brushless this is done away but you turn some of the power into heat in the motor coils and the simple regulator. Well, you can´t have it all, a simple brushless motor - or a brushed alternator with regulated field supply. This does not worry me much looking at modern motorcycles with mainly brushless type permanent magnet alternators, millions of them on the road. Generators behind covers mounted on the engine. So an air cooled small brushless on top of the gearbox with some temperture conductive contact should be allright, the Altons with identical tech are proven, with lower power when ungeared I guess. And they operate in all sorts of bikes from the timing gear drives, having certainly an easier life there compared to the triplex chain/ESA drama.
The new motor was skimmed in the lathe for 68 mm o.d. because I had the cases already done for common 68 mm motors. When you look closely 68 mm is the absolute minimum diameter with it as the 3 mm threads of the long bolts just started to get exposed. So I made new bolts with 6 mm nuts which were made to be heads of the bolts . These were loctited onto 3 mm rods with threads at both ends. One of the heads has to be filed flat to the front flange so as to clear the engine case. The new front flange was extended for two ball bearings - 15/32/11 mm - and suitable for an o-ring fit in the engine case bore.
Conclusion : These China brushless motors look all the way like great alternatives to the very expensive Altons - for those who love to do some machine jobs on the lathe and mill. Once this is done you need no longer worry about expensive repairs or replacements as you can get low price spares from China any day and have all components exactly to your liking when doing the job yourself. So I am looking forward to reading your stories here with experiments and real road reports.
Vic
stepper motor test:
new longer brushless :
rear end extension - for ignition pickup ?
front end 14 mm pulley shaft
turned down 68 mm , shortened rear cap, front twin ball bearing flange extension: