One horsepower is 746 watts. That's easy enough. That makes no allowance for efficiency factors, typically low in small alternators.

The motorcycle alternator is differently designed from the automotive alternator. On the motorcycle (I'm sure there are exceptions) the flywheel carries permanent magnets past the stationary coils of the alternator - the "stator". Whenever the engine runs those magnets cause alternating current to be produced in the stator. The faster the engine turns, the faster the magnets pass the coils and the more current is generated. That alternating current - AC - is rectified by diodes in the regulator. The resulting direct current - DC - is used to power the motorcycle and recharge its battery. As the battery reaches full charge the voltage tends to rise. The regulator senses this. Remember those rectifiers? Some of them are silicon controlled rectifiers - SCRs. They are so arranged as to shunt some of the current, and they are controlled by the regulator. When the regulator decides the output voltage is high enough it turns on those SCRs and shunts enough current to control the output voltage. Because the regulator is electronic it literally controls the AC cycle by cycle.

Automotive alternators are different, in that they do not use permanent magnets. Instead they use electromagnets. The voltage regulator controls the current through those electromagnets. When the output voltage rises high enough the regulator reduces the current through the electromagnets, which in turn reduces the output current. Since the current is controlled differently, they don't have nor need the SCRs. Automotive current loads are much more variable. Cars have more lights, they have windshield wipers, heater blowers, air conditioner compressor clutches, electric window defrosters, and so forth. Some even have electric power steering. They also have a lot more room to mount parts. And for the yobs with high-powered audio systems, the current demands are incredible.

It might be possible to redesign the voltage regulator on the motorcycle to use switching transistors instead of SCRs. Then it might be possible to switch off the current instead of shunting it. But I suspect then there might be some pretty high-voltage spikes to control, which might burn the switching transistors.

It might be possible to redesign the voltage regulator on the motorcycle to use switching transistors instead of SCRs. Then it might be possible to switch off the current instead of shunting it. But I suspect then there might be some pretty high-voltage spikes to control, which might burn the switching transistors.


Yea, maybe, but the HP of swinging the magnets thru the flux fields & creating a Voltage would still be spent,, dangitt,,

Darn good explanation, C. Thaks again

I remember seeing pictures of your build as I was thinking of what to do with my bike. Can't wait to see the newly finished product!

Diamond Jim!!!! are ya back???
So happy to hear from you.

Diamond Jim- I think I'm going to keep using my HD fishtail.  It's not the perfect looking pipe but it's still got edge and it sounds amazing.  "Chopper" describes both the way my bike looks and sounds!

UPDATE 2/7/10

I'm wiring up the electrics at the moment.  I cut out plates to mount the components.  Here's the plate with the starter relay and the fuse panel.



Back side starter relay


Front side fuse panel


Here are the two plates I made mounted to the frame.  The plate underneath the seat is gonna hold the ignitor box.



The ignitor box in position on the top plate.


Routing of the wires (in cloth sheath) towards the front of the bike.


The supply to the front of the bike goes to the spark plug (top sheath) and the starter button (bottom sheath)


Hooking it up to test the lights.  The yellow/white wire hanging over the rail there comes from the starter button and is going to be plugged into the relay once I've got everything in place.  

Battery is going to go in a box behind the engine and under the swingarm.

The electric system here basically works.  I'm getting power to the head and tail lights, starter button, ignitor box, and coil.  My starter, ignitior box, and battery are working (tested them in Verslagen's savage) but I'm not getting enough juice through my starter.  Likely a combination of the main cables being too small to carry the current and having too much resistance in the engine from not being properly lubed yet.

looks good.
we should set up a socal ls650 meet up when your bike is done.

Great progress on the bike, I lost this thread in time some how.