Don't jump start a bike off a car battery

[Colt4530]

Originally Posted by nwujames

<<CORRECTION>>Don't jump start your bike off of a car that's turned on - the amperage difference will fry your bike's battery, and maybe the electrical system too.

That's absurd. Both are 12 volt nominal systems. Just because a car alternator CAN generate 60 or 70 amps (the typical size) does not mean it can force that much into your motorcycle, though the bike will pull nearly that when cranking. The current flow is determined by the voltage. Since they're both 12v systems, ......

Most bikes can be jump started from a car without the engine running because the battery has enough capacity to maintain voltage while the bike is cranking.

[Nate]

One more time, folks, it has nothing to do with the differences in amperage capacity of a car battery/charging system versus a bike's. Let me say this again, the advice probably applies mostly to us with older machinery where the regulator/rectifier unit was not designed nor constructed to handle any amount of reverse voltage. A car's alternator can put a significant AC voltage into the electrical system. Connect that to an electrical system that is not designed or constructed for that kind of reverse polarity voltage and the unprotected/not robust enough components will be damaged.

All solid state components have a reverse voltage threshold that when exceeded will cause the component to fail. It's probably no more complicated than that.

[nwujames]

Wow - this thread is going to live forever.

[jsin607]

yea, thats a long thread about nothing
i jump started my bike off a running honda civic last week, and i could hear the civic struggling to provide enough power for my bike

oh, and one time i jump started a 24v rig with 2 cars running at the same time.

[fastback]

Long live this thread.


Not A/C. Alternating Current (AC).

[esornivram]

Originally Posted by Frankt07

i believe what might happen is the same as connecting a generator to your house while the light company is still powering it. the power company will push the generator voltage and current back and blow something.
same thing with the motorcycle and car charging systems. the cars system is designed to put out over 100 amps in most vehicles due to all teh electronics. all we have is a few dozen amps.
we can jump start off of a car battery, but the car must be off

the DC starters have an uniquec ability, they can take all the amps you can give it till it melts, usually the brushes burn up,out . i lost starter in my 82 750 spectre starter that way using an car battery, not on/in a car, I did have engineer tell me using the car jumper cables was more of problem than the battery, but spare bike battery with car cabless is ok.

[esornivram]

Originally Posted by Colt4530

That's absurd. Both are 12 volt nominal systems. Just because a car alternator CAN generate 60 or 70 amps (the typical size) does not mean it can force that much into your motorcycle, though the bike will pull nearly that when cranking. The current flow is determined by the voltage. Since they're both 12v systems, ......

Most bikes can be jump started from a car without the engine running because the battery has enough capacity to maintain voltage while the bike is cranking.

actually current flow is with held by resistance or the load, and an non moving dc motor has very very low ohms,especial when counter electrive force is also zilch, put any power source than can supply lots of amps to it and at start you toasted ,smoked something

[bosscat]

But the amps don't get pushed by the source they get drawn by the load. That would be why a bulb wouldn't take all the amps available only what it draws when on. And why a car battery with 1000 CCA doesn't hurt a car that only needs 500CCA, it just gives it a bigger reserve.

Still though a car battery should be able to jump it with no problem with the car not running, and with alot less risk of overcharging the bikes battery. A running cars voltage is actually around 13.5-14.5 volts. And a bikes battery doesn't take a lot to boil it out with it's small size. Better to leave the car turned off.

BTW- no electrical degree, but I did spend a few years assigned to the battery shop while in the Navy

[CycleDude]

Originally Posted by bosscat

BTW- no electrical degree, but I did spend a few years assigned to the battery shop while in the Navy

Oh thank God! I thought you were going to say that you did stay at a Holiday Inn though.....

BTW, this thread is over a year old.

[Obsidian16825]

We haven't had any problem with jumping off a GL1000 with a pickup truck. The bike's battery is ready to be replaced. It's just too old. It took running the truck's engine up to 2,000 rpm last time to get enough charge through the bike's battery to turn the starter fast enough and fire up the tired four-banger, which wakes up one cylinder at a time, and smokes from it's left pipe for several minutes. If the beast isn't run every day, it just won't start on its own. I know, we need battery tenders.