Mercy! Mercy! That Dang Nabed PERCY!

Electricity and the Bighorn Adventure

Before I started on the Bighorn adventure I knew that Electricity powered things

I knew that Electricity was like a water tower. Voltage was like the pressure in the tank created by all that water high above the ground. I knew that pressure was created by the forces of gravity acting on the tower and that amperage was like the flow of water out from the tank powering the appliances in my home. Ohm's law was one of those three part power equations where if you know two of the values you can calculate the third. I knew all that and I could have probably passed a high school science test with flying colors.

What I didn't really know was AC and DC current. If you remember your High School science one of the experiments was to wrap an iron coil with copper wire and then move a magnet over it and measure the current you induced. So what? You induced an AC electrical current. Big deal. That was my state of thinking about electricity until last week. It was scientific voodoo you couldn't see that made appliances work in today's world.

In a motorcycle there is a crank shaft attached to a piston going up and down inside a cylinder. Attached to the crank case beneath this cylinder is a crank shaft and this shaft runs through an array of coils positioned around the shaft. This is called the Stator. Surrounding the stator is a flywheel with magnets inside. Voila, the piston is not just making the motorcycle go but is also producing electricity... AC Electricity. The number of loops around each of the coils determines how much current they produce. In my motorcycle there are three coils. One of these makes juice that goes goes up to the CDI box and powers the coil. The coil juices the current up and sends it to the spark plug. The spark plug ignites a vapor of compressed air and fuel and BANG... The big piston goes up and down, the crankshaft goes around and around and the mechanical forces proceed via a clutch and gear train, to a chain and rear wheel sprocket.

Now that explains what the first coil is there for but what about the other two? Well, the second coil is there to tell the CDI box when to send the pulse to the coil. The first remember, created the current, the second coil tells it when to act. This depends on where the flywheel is in its rotation. You see just before the piston is in the perfect position to ignite the explosive mixture of air and fuel vapor, the second coil gives the signal and the big bang happens.

It is worth noting at this juncture that we are discussing AC current. Keep in mind that when the north pole of the magnets in the flywheel pass over a coil the current is positively charged and when the negative pole passes the current becomes negatively charged. This is called AC or alternating current. As far as the spark plug cares either type is fine. As far as the signal coil cares either one is fine. And if there was a coil to run the light that would be fine too. AC current powers the lights in your house after all. The difference between a house an a motorcycle is that a house is stationary and served by a power plant and a motorcycle makes its own power on the fly.

The problem with AC current is that a battery hates it. If your machine needs a battery a battery requires direct current and so the Third AC coil must convert the AC to DC or Direct current. It does this with a device known as a rectifier. This device rectifies the battery problem, at least to the extent of the current issue. There still remains a need to make sure the current stays within reasonable limits and doesn't destroy the battery or burn out the light bulbs.

Keep in mind that early cars and motorcycles had a hand or foot crank to get the AC current flowing. This was fine as long as the operators were willing to turn the crank or kick the engine over. Once operators got addicted to electric starters, the need for a battery became self evident. So this required rectifiers and regulators.

So now you know a bit more about AC and DC current and the need to understand why someone doing a rehab on a motorcycle needs a remedial knowledge of what is going on beneath the surface in order to get one running especially if it has been lying in a neglected state for the past half century.