TOPIC:

About 12 years ago I could have answered this, but in the modern age of laptop diagnostics I've lost the hands-on edge.

I know Lou can answer it.

I've got a small engine with a single lighting and a single ignition winding (12V CDI). Unlike the attached drawing, I don't plan to run a battery or starter on this bike.

I'd like to add lighting to my bike, but just can't seem to make myself order the $30 reg/rec from fleabay. Is there a way to do this easily that will provide about 30 to 50 Watts of regulated 12V for lighting?

Saki Jockey wrote:

I'd like to add lighting to my bike, but just can't seem to make myself order the $30 reg/rec from fleabay. Is there a way to do this easily that will provide about 30 to 50 Watts of regulated 12V for lighting?

There are two general topologies of electrical system types that take two kinds of regulators:

1) cars use an alternator with a terminal that allows a current source to vary the current flow in the primary winding of the alternator, which controls the current delivered to the electrical system from the secondary winding. Regulators for these are simple, I have built them before.

2) bikes typically require the use of SCR's on the output of the alternator and the regulator has to control the SCR's. This is a little more complicated than case #1.

But, the SCR topolgy makes the alternator simpler (a permanent magnet on the flywheel spinning inside the winding). The car alternator requires both a fixed (stator) winding and a spinning armature winding.

Bike systems trade a simpler alternator design for a more complicated regulator design.

It requires a control system that regulates the system to 14V by increasing or decreasing the firing angle of the gates of the SCR's which rectify the AC coming from the output of the alternator.

I suspect somebody here has built them, I haven't built the SCR type.

Let me get this straight, you have the bike which that diagram is for? But you want to run with no battery, no starter, and no regulator and no rectifier?

That drawing is very unclear. It does not distinguish between wires that are simply crossing over versus wires that are actually connected. It shouldn't be too hard to figure out, though. But it is impossible to know how much extra power is available for lighting based on that diagram. Also, without regulation, you have to match the lighting load vary carefully to the alternator. This usually menas the light will be very dim at idle and very bright (and possibly burn out) at higher RPMs. This is a common problem on mopeds and scooters and dirtbikes.

Also, if you are going to use any switched lighting like brake lights or flashers. They will likely not work without a battery. There will simply be too much load added when the brake light is applied. To remedy this, mopeds and scooters usually have a dedicated winding in the alternator just for brake lights. Maybe the yellow winding can be used for that?

I put some notes on the drawing. I'm sure that the line going from G of the reg to B/W of the flameaut switch is an error. I x-ed out the errant lines. G should go to G only.

Also, the alternator is a mystery as to why they have a yellow winding in addition to the white winding unless there is an option for lights on this bike. Since the main winding is grounded, the alternator can really only be rectified to a half-wave. This is common on some Honda dirtbikes as well.

If the regulator is truly a regulator and not just a rectifier (where the battery acts as a regulator) then it will likely have to use a battery anyway in order to have a more stable voltage to regulate.

However, if you want to ditch battery, regulator, starter, and run a simple light, I think it's do-able if you can get the right light, and the right ballast resistor. I'll post that as well.

The idea here, is that the ballast increases resistance as the RPMs increase over time so the bulb won't blow on an extended ride. Choose a bulb that gets blown after a few seconds of sustained high RPMs, then apply the appropriate ballast. Maybe get a ballast resistor from an old chrysler or chevy and play with the multiple taps. It'll probably have to be in the 1/4 to 1/2 ohm range, or even less if you can find it. It will have to be in the 10 watt range or higher. But this will be a lot of trial and error without knowing what the alternator puts out.

I've seen this method used on some old Honda dirtbike. In order to work properly, the ballast has to be a true ballast, not just a big resistor. A true ballast increases resistance with temperature where the increase in temperature comes from increased current over a sustained period (like cruising at higher speeds). (For testing you can temporarily use a resistor to determine what resistance ballast you need.)

Another method would be to find a ballast and see what bulb works with it.

As I said it's a lot of trial and error and there's no guarantee that there is an easy combination to find.

If you have no luck, then we can get a better idea using a meter and steady power resistor to make some measurements.

Also, I would expect the yellow winding to be in phase with the white winding, but there's no guarantee on that either. Play with connecting the yellow winding with the white winding to see if it raises or lowers the power output.

another issue: If the alternator was meant to be rectified to half-wave only, then using it this way may overheat the alternator windings. The remedy for that is to use a lower wattage bulb and higher resistance ballast.