Dead on the road

[RsvlFeej]

(Because a running engine makes the alternator spin, which produces electricity to power the electrical systems -- and the battery is no longer needed to run the electrical systems.)

Not my experience with this bike. A loose battery cable kills the bike, even if running; it will not run straight from the alternator. I don't believe you can even bump start this bike if the battery is completely flat, but have no personal experience to back that up.

 

[audiowize]

After my fatal experience (burning out my motorcycle rectifier), a mechanic explained that the battery on motorcycles are often placed after the electronic components that are not expecting a current at the battery to exceed a given amount. A car's alternator produces AC current, and has diodes that rectify this into an oscillating DC current. It is then 'smoothed' out by the battery being used as a sort of filter. These oscillations could include spikes at harmful levels to the motorcycle's components, as they were designed around a rather limited alternator output. As general advice dictates, it's okay to jump from a car battery, as long as the car is not running, as to not expose your motorcycle's components to the automotive alternator's output.

Yes, the alternator produces AC, yes the diodes rectify this into bumpy DC. Batteries have incredibly low internal impedance, and most rectifier spew is well sunk by the battery.

These statements are also true of a motorcycle's electrical system.

Sensitive components in our bikes run on lower voltages that are regulated. Even the crappiest voltage regulators available are far quicker than the oscillations that appear from diode switching in the rectifier.

 

[TomInPA]

Three hours into a trip on my '04 FJR to LA, I pulled into a gas stop. Bike had been running perfectly. Filled up and went to start the FJR; nothing. Tried everything; no gauges, no lights, no starter, nothing. Took the cover off the battery and jumped wired it from a car. Started right up and ran fine, but as soon as we puled the cables off and it died instantly. Repeated the process with the same results. Towed the bike and spent the night in a hotel. Got the bike back home today. Battery checks in at 13v and shows full on the charger. I have been working on bikes for a long time, but this one has me totally baffled. Any thoughts from the collective wisdom?

Well, it looks like the forum has solved every problem but yours. Did you have a chance to load-test the battery? I had an interesting failure a couple weeks ago that was similar. Stopped the bike and refueled, then cranked the bike to start and got a half a spin then nothing. The gauges usually sweep when starting, and they were still stuck halfway, and no power anywhere. I knew immediately a cable had come off the terminal, and took off the top panels to fix that. Sure enough, it was just loose enough to lose power. Cleaned it up and snugged it down, and the bike fired right up.