Jumping with a car on/off

could someone explain why the car needs to be off ?

 

I don't see a reason why, unless someone is concerned about the alternators of the two vehicles "fighting" once the bike is running.... (which isn't really a thing). Again, 12V is 12V. Neither regulator is going to try to shunt the other and overload things - that's not how alternator regulators work.

 

i know that and you know that, just trying to clear things up
consider it our civic duty

 

AFAIK, you want the charging car on and maybe even reving a little to get good alternator output to charge the target vehicle. You'd want the target off to minimize drain on the battery and maximize charging. You only try starting that car once there's some charge in the battery since you don't want to pull starting current over the jumper cables.

 

I knew you knew that.

 

I’ve never needed to rev the car for the bike.

 

So, we're mainly needing to hear from Raskal, for more information...

 

shit,... I've been called out

okay, mostly I said that because I was parroting information I had heard previously like a brainless fool I am

logically;

If a car is running, it is producing more voltage and amperage than when off.
The voltage should be fine for the bike assuming the car's alternator is working correctly
The bike should not draw more amperage than it needs, so that should be fine
If there was an issue with the bike's battery, it *may* negatively affect the car's electronics

Lastly I have heard that bike manufacturers don't suggest it, but I can't find anywhere that's actually written. Maybe it's newer bikes only

I think in summary, there should be no need for a car to be running to jump start as a bike's requirements are far less than a car's battery abilities, so why have the car running?

in the future, I shall try to think before mindlessly spewing out rehashed information. I will probably fail at that, but I will try

 

Why have the car running? So the current that is drawn is being drawn from a steady, replacing, supply... not from a battery that may or may not be drawn down enough to ALSO not have enough juice

 

Here's something I haven't seen stated. When a 12V battery is sitting there, it will have about 12V of output (give or take, YMMV). If you start the car, the nominal charging voltage is 13.8V. That's what you need to charge the bike battery (or at least, that's more effective to charge the bike battery than 12V).

 

no, not you personally buddy, that old wife's tale just needed a little attention. i just did the same thing with clutch basket bolts.
all i can add is don't make the last connection at the battery, i found that out the hard way

 

If you are referring to revving the car for more amperage to be put out from the alternator; alternators on cars haven’t finctioned like that in around 25 years. There are a lot of computers that pulse width modulate the alternators on the vehicle based on what the battery soc ( state of charge) is. That would be when the ECM tells the alternator to adjust what it producing. Hence the reason the vehicles from the last 25 years or so do not need to be revved up for a parasitic drain I.e. jump starting a motorcycle which pulls depending on the size of the vehicle not even a 1/4 of what it would take to start the bike. Because the bike is actually pulling the amperage not the voltage.

 

When you started this thread, I thought "Oh shit,... this is cause what I wrote"
Then I started doing reading about this subject to try to back up the spew I laid out
I still don't think there's a need to have a car running and still feel (with no basis) that it shouldn't be

My truck's battery is a 710 CCA, the bike is 210 CCA. Assuming the truck's battery is in good shape, it has plenty of capacity to start the bike without needing the altenator

The only practical thing I've learned in all my reading was make the last connection of the jumpstart to a chassis location, not the battery, just in case the battery is leaking hydrogen and a spark from the connection happens and it blows up. Not real likely, but it could happen I guess

 

I’m not saying you HAVE to have it running. I just generally do

 

My main point was that you're not going to hurt anything by having it running, and, in some cases, you'll have a better result. Some jumper cables are pretty light, and/or have crappy connectors, and the extra voltage of a running engine will make up for some of the loss over the cables.

As I mentioned before, there's nothing about the running system that going to hurt anything on the bike. There is, though, I suppose, the non-zero chance that the person connecting the jumper cables will drop a cable into a moving belt or catch their hand on a running fan. So, from that perspective, a non-running engine is safer for the human.

 

Now THAT
Is an answer I can totally agree with

 

I have to jump start my KZ750 every now and then by jumping onto the kick start lever. Does it matter if my car is running when I do this?

 

Not really; as was in previous post it’s honestly not hurting anything unless you hook something up wrong or something is incorrect....

 

Fair play.... just got that one when I looked at it.