Question about ST1300 charging system

If you have a bike with a low battery and a non functioning alternator, you can jump start the bike (i.e. using another bike's battery) or maybe even push start it, pop the clutch in gear, and start her up that way. It will run until the battery is exhausted. If you can turn off the headlights, the bike will run farther. Just for the record, there are a lot of old (aka vintage) bikes that raced with a small battery used to fire the coil/plugs only. No lights, very little drain on the battery.

If you were to suddenly cut the cable leading from the battery while the bike is running you would probably fry the electronics on the bike. The battery stabilizes the voltage and serves to store what is not used by the bike and accessories that is generated by the alternator. So, running a bike w/o a battery is not a good idea.

(SMSW beat me to it, but I'll leave this here...)

If the charging system is up to snuff, the bike will continue to run just fine as long as the engine does. However... DO NOT RUN THE ENGINE WITHOUT A BATTERY. The battery serves a second purpose, which is to soak up spikes and fluctuations in the electrical system that would otherwise cause damage. Even a battery that won't take a charge will still do its other job.

What your [-]Husqvarna[/-] [-]Hyosung[/-] Harley-riding friend probably ran into was a failed charging system, where the bike ran on battery power until the battery died and that was all she wrote. (Saw that firsthand with a friend's Jeep a couple of weeks ago.)

BTW, I measured my battery voltage yesterday afternoon before and after starting, it was 12.6V at rest, ~14.2V at idle, and limited to 14.25V above 2k RPM or so. Do those numbers sound about right?

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If you're trying to determine the health of your battery, you want to see what its voltage is when the alternator isn't turning. 12.6 at rest sounds fine, and if it stays above 10 while you're cranking the starter, it's fine.

Anything you measure with the engine running is the charging system voltage. The ideal figure is 13.8, and anything under 14.3 is fine.

--Mark

This is exactly what I suspected - that the battery basically acts as a buffer while the alternator is properly functioning with engine running. Thanks for the replies guys.

Blrfl said:

(SMSW beat me to it, but I'll leave this here...)
What your [-]Husqvarna[/-] [-]Hyosung[/-] Harley-riding friend probably ran into was a failed charging system, where the bike ran on battery power until the battery died and that was all she wrote. (Saw that firsthand with a friend's Jeep a couple of weeks ago.)
--Mark

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Some years ago (roughly 80) my father and his brother drove across the country in a Model A Ford. The generator failed, and they were able to keep going, as the story was told by turning off all the lights and using the battery to power only the ignition system. They got the battery charged during the day, and drove at night - with Dad or his brother standing on the running board holding a flashlight so they could see the road.

Peter

Good story. Did anyone ever tell you about having to back up a hill in a Model A Ford so gas could still get to the carburetor? I've heard that story more than once -note that I'm not quite that old (yet), but I have heard the story, wasn't there ,,,

Update: My bad - going off on a tangent here, but it was the "Model T", not "Model A" that had no fuel pump and the carburetor was gravity-fed.

I can tell you from personal experience with my Buell 1125R, the bike would not run once the battery was used up. In my case it was a bad charging system.

Now cars on the other hand, prior to all the electronics would run off the alternator or generator alone once started. However, if the RPM's dropped to low where the alternator or generator was not putting out enough voltage the car would die because the plugs wouldn't fire. The beauty in old technology vs new technology.

All correct disconnecting the negative terminal on the battery is a quick way to tell if your alternator is working or not if you don't have a meter handy.

Don B said:

This is exactly what I suspected - that the battery basically acts as a buffer while the alternator is properly functioning with engine running. Thanks for the replies guys.

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On the Harley and many cars the alternator dose not put out at idle, turning to slow. Also most bike alternators can't keep up at high RPMs so actually charging less as you go higher past the high output RPM, usually 2500 to 3000 RPM.

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I have a nightmare battery experience. The wife's Can Am battery failed with a bad cell. She ignored the battery failure light hoping it would go off. Well, the rectifier failed then the stator melted. The Spyder feeds the battery directly from the stator and the battery runs the rest of the Can AM electrical systems according to the wiring diagrams. Haven't looked at the wiring diagram for the ST but 2 battery cell failures have only resulted in a non starting bike. Since this failure I added a voltmeter wired through the Quartet 9 pin outlet since there is no battery warning light. It looses .4 volts through the quartet harness but it keeps me informed about charging and battery. Lesson learned the hard way.