Post
by jesmed » Thu May 15, 2008 8:25 pm
When I rebuilt my CP77 as a newbie in 2005, the electrical system was a major headache. Eventually I got it sorted out, and I count myself fortunate that my dynamo now puts out close to 14 volts after rectification (I've seen many posts here from people complaining of low output at their rectifiers). Even so, I've learned to check my battery voltage every time I ride, both before and after. I've learned that 12.65 volts or above before starting means I'm good to ride; below that there's a good chance I'm going to be walking home.
It was a pain, though, to remove the seat every time for a voltage check. So I wired up a short pigtail from the positive battery terminal with the other end crimped into an insulated butt connector that hangs out just below the seat. Now I can check voltage by inserting a voltmeter probe into the butt connector, touching the other probe to ground, and getting a battery voltage reading without removing the seat. (Yes, it would be safer in case of a short to wire the pigtail downstream of the fuse).
But the before-and-after voltage check still didn't save me when I had some intermittent electrical problem on the road, lost charging output without knowing it, and had to walk home. So I poked around online for a simple voltmeter to hardwire into the system, and didn't find much of use. I didn't want some big round gauge hanging off my handlebars, and smaller dial gauges looked like they would be too hard to read. I did find an idea that looked useful, and I adapted it for my CP77. I found a web post from someone who had taken a simple LED voltmeter from an auto parts store and wired it into his Goldwing (or something) console. I copied his idea and found an el-cheapo LED voltmeter (specifically a Calterm 66318 Battery & Alternator Voltage Analyzer if you want to Google it, available at auto parts stores and also online from Ace Hardware and True Value hardware) and wired it into my system. I zip-tied it to the my right handlbar, wired the black to ground and red to the black terminal of the key switch. (That was after first making the mistake of wiring the red directly to battery positive, forgetting that of course the meter would be permanently on, thus draining the battery when not running).
So far it's working well. The LEDs are hard to read in bright light, but are readable in partial shade, and give me a good quick indicator on startup and shutdown that my charging system is working properly. (Note: It does NOT give a correct indication of open-circuit battery voltage. Since the meter is wired through the key switch, it is OFF when the key switch is off. When I turn the key switch on, the meter comes on, but the battery is now draining through the coils, so I get a voltage reading that's lower than the open-circuit voltage--thus not useful for determining the actual state of charge of the battery. I still have to use an external voltmeter to get that open-circuit battery voltage. But once the engine is running, the meter does give a correct [more or less] reading of the charging system output).
Yes, it's kind of a hack. If you're a purist and don't want an LED dongle zip-tied to your handlebar, ignore this post. I offer this suggestion for those who, like me, care more about function than appearances, and don't have more than $10. Enjoy.
