Hello,
Can I jump by motorcycle battery from my car ? Someone said that you weren't supposed to. I thought they were both 12 volt.

 

Yes you can but I would not make a daily habit of doing it. Instead try to slow charge (1amp or less) your bikebattery for 8 hours. If the battery will not takeor holdcharge its time for a new battery.............BG

 

I definitely wouldn't do it with the car running unless you want to risk frying your electrical components. You're fine jumping it from the car battery as long as the car isn't running...

 

Can someone explain why not.
I'm no electrician, but I have a decent understanding of things.

A car puts out no more or less voltage than a bike. Sure the car battery can supply more amperage, but you only 'take' the amps you 'ask' for.
If your bike will turn over on the bikes battery when charged, then it shouldn't cause any problems.

This has to be old voodoo...

 

It has to do with the alternator and the amps it forces throught your battery.

[IMG]local://upfiles/3159/51AE0980F7FC4D23BC29678FFBBC3AC7.jpg[/IMG]

 

So you are saying that it is forcing the battery to recharge at too quick of a rate?

Thanks for the reply.

 

It is OK to jump start with car, but I would limit it to emergencys only. The slower you recharge a battery the longer it will last. So anything you can do to limit the current during a recharge, such as not having the car running for less voltage, trickle charging etc., the better.

 

Did it once & fried the self canceling turn signal module. Maybe coincidence. but ir cost me $70 bucks for that jump.

 

i'm not sure about new harleys, but my 81 low rider put excess output from the alternator to ground. alternator put out about 27 amps. (this happens in the regulator) your car can probably put out around 100 amps. if car voltage regulator is "set" higher than the bike regulator the bike regulator will put excess to ground. (about73 amps too much.) if car isnt running this doesn't factor in. make sense?

 

Nutsandbolts,

Thanks for the reply. It doesn't make sense to me because amps just aren't floating around. When a device (starter for instance) draws power, it draws as much as it takes based upon the resistance created by its motor. As the motor spins up, it draws less power than on initiation because its got some internal intertia now. A headlight will draw a fairly constant value if you take out the minor changes for heat fluxuation.

I don't know what a bike battery can put out, but I'll guess it's at least 100 amps (If you think about it for a second, at 120 volts thats only ~10amps. A 10 amp @120v motor isn't that strong). Putting anything to ground would be a direct short and would draw far more current than most of the wiring, if not all could handle.

I'm thinking either its the charging the battery too fast (probably not likely though) or maybe a carryover from a time when bikes had 6-volt systems. It could also be that jumper cables are huge and the clamps may short out on things like the frame or battery box.

I'm going to see if I can find the answer somewhere, because it bugs me. I'm not saying its not true, I just want to know why.