Something I learned tonight.

[quicksilver]

Well I finally broke down and bought a HID light kit to install for my MC250B. When I went to check which wires are for the high and low beams, I found something interesting. With the bike off and key on, the small light above the regular lights read at 12.4, what the battery would be. With the bike running, 15+ volts.

Now I would consider that normal but what I found out is that with the bike running and supplying power to the head lights, I was only getting about 9 volts.

With doing some calculations, with 13.5 volts as the voltage and 35 watts for the lamp, the resistance that the bulb would be 5.285 ohm's. Now if I took the resistance and multiply it with say the 9.6 volts that I was reading, I would only get about 17 watts of light output. No wonder that light are not very bright.

Further along as I was monitoring the voltage, the fan kicked in and found that the voltage to the lights went to 12 volts. Go figure.

Although I didn't get a chance to finish the install, I did test one light and WHAT A DIFFERENCE!

[OverReved]

Aug 3, 2012 20:22:18 GMT -5 quicksilver said:

Now I would consider that normal but what I found out is that with the bike running and supplying power to the head lights, I was only getting about 9 volts.

You'll get those sort of low voltage readings if you have more than one load in series.
If you inspect the wiring on basically everything on a car or motorcycle it is all parallel wiring which doesn't cause one component to rob another of potential voltage. You'll also notice there are a ton more fuses on higher dollar bikes because they are wired in parallel and require more protection points for current flow because they are all wired to potentially supply full battery current.

Aug 3, 2012 20:22:18 GMT -5 quicksilver said:

With doing some calculations, with 13.5 volts as the voltage and 35 watts for the lamp, the resistance that the bulb would be 5.285 ohm's. Now if I took the resistance and multiply it with say the 9.6 volts that I was reading, I would only get about 17 watts of light output. No wonder that light are not very bright.

The resistance of a light bulb is variable in relation to the heat load on them. For instance you may have a bulb that reads 1 ohm of resistance not installed. This same bulb may read 25 ohms of resistance when it is installed and running. You can determine the bulbs resistance while it is running by calculating it from both voltage and current draw of the bulb. As the bulb heats up it's resistance also increases which directly affects current draw and its light output. Light output is a result of resistance to current flow.