[tylernt]

leaving the car running won't make a diffrence for a motorcycle. ... 2 alternators working together is not a problem, each one will just not work as hard. They only put out what is needed,

Um, no. I have read several reports of motorcycle regulator units being fried when jumpstarting from a running car. A permanent magnet motorcycle alternator puts out 100% all the time and the regulator simply shorts the excess current to ground to bring voltage within spec. The car's alternator can put out so much more current (amps) than the regulator can sink to ground, that it burns up. You might get lucky if you don't leave the jumpers connected for very long, but it's real iffy.

If you know for sure your motorcycle is equipped with a field-effect (brushed) alternator and has no shunt regulator, only then can you safely jumpstart from a running car.

Why would you want to jumpstart from a running car anyways? The car battery certainly doesn't need any help. It has so much excess capacity for a bitty motorcycle starter, that the alternator's output is wholly unnecessary.

 

[tylernt]

where is the danger of a battery exploding while jump starting if not from the multiple alternators.

The danger in jumpstarting is the hydrogen gas, vented by the dead battery, generated when the good battery rapidly charges the dead one. A spark from unhooking the jumper cable can ignite it and cause an explosion. This is why you make your last connection at an unpainted ground point away from the dead battery, and also break the circuit there after jumpstarting.

 

[tylernt]

Exactly my point, with TWO alternators connected the dead battery will have much more charging ability at it's disposal to draw from. And in your words the alternators will only put out what they are asked for. The single alternator is designed for charging the battery in the vehicle it's installed in, not to work in tandem with another. Thank you for the assistance in making my point.

I am in complete agreement that the jumpstarting car should NOT be running. I think we're on the same side here. :biggrin: