Can you jump your battery with your car?

Hey all,

I wanted a straight answer on this and found all sorts of differing answers after a Google search.

IE: Never do it...You'll fry the electrical system - Sure...but with the car's engine off - No way, the voltage is different - Yeah, they're the same...12 volts!

Uggh!

I'm also curious/worried because I did jump the battery last week after nuking it while trying to start. I hope i didn't fry anything as the XJ hasn't been put back together after cleaning.

 

I would do it without the car running.
Its just a lead acid 12v battery.
Leave your run-down battery connected to get it re-charged.
Do a load test on the battery after it is charged.

 

I have done research on the topic and was frustrated with the different answers i got also. I will tell you that i have used a portable car jumper to start my bike several times without any problems. Just make sure your bikes key switch is off when you connect to a car battery or portable jumper unit.

 

I've done it quite a bit, either from my car (while not running) or from a booster pack. As far as I know it won't hurt any thing, they are all 12v sources, the only thing stopping you from putting a car battery in the bike is the physical size

 

I've had bad luck jumping from a car battery. Burned out the regulator/rectifier on two different bikes. I was told there is too much amperage potential available in a car battery vs a motorcycle battery(700 amps vs 50 amps). That greater amperage potential tends to overload the regulator/rectifier assembly and burn it out. Its hard to explain but i have had to replace two of them before, I'll use another MC battery to jump start next time or wait for my battery charger to finish.

 

I do it all the time, with the XJ and my GSXR. Typically to be safe ill turn the light on, and make sure then engine is off. Never fried anything!

 

If you are concerned about hurting your MC and only have a car available to jump then hook up the batteries together and let the car battery transfer power to your MC battery for at least 10 minutes then disconnect the car battery and start your bike from just the bike battery.

As long as you are just using the car battery to charge your MC battery I don't see a problem.

 

Sorry to hear about your experiences, but the "amperage potential" explanation doesn't exactly hold water. Current flows based on voltage and paths to ground. If you were to reverse + and -, then I could easily see the car battery supplying sufficient current to overwhelm the bike battery and blow the regulator. As long as + goes to +, though, the current from the car battery is not going to go anywhere it shouldn't and the regulator is simply going to see 12V on the regulated side... how much current is behind that 12V at that point is irrelevant.

FWIW, I've also used car batteries many times to jump start my bike, with no problems at all. On the other hand, I did once blow the rectifier in my car when I accidentally installed a battery with the terminals swapped.

 

So, since I had the car running while jumping the battery on the MC, it could have harmed my electrical system?

 

From what I've heard, while running your alternater puts out voltages higher than 12. If it spikes its possible to blow something... but even then, I used to jump my bike with a running car, and never cause any problems.

Dont start worrying UNLESS you actually have problems.

 

Good advice. And apply the "uncle Ernie rule" if it ain't broke don't fix it.

 

You guys are the best! Thanks for the sage advice.

 

A way to visualize this is to compare a battery to a dam. The height of the water is like the voltage, and the size of the reservoir or length of the lake behind the dam is like the amperage.

Are these batteries really just 50 (reserve) amps?

 

Agreed. Voltage is potential, amperage is capacity to sustain the potential. Batteries are not rated in amps, they're rated in amp-hours.

So, a 50 ah battery can deliver 1 amp for 50 hours. a 500 ah battery can deliver 1 amp for 500 hours. Even though they're both 12V batteries.

Your device will only "draw" the amps it needs. The LED in your car radio doesn't fry because it has a 650 ah battery behind it.

Actually all batteries can provide infinite amperage (up to the limits imposed by internal resistance).

Standard automobile voltage is exactly the same as our motorcycles.

Hook up backwards though and something will cook.

 

Contrary to all "electronics theory" wisdom ( I am an electrical engineer by education) I had the experience of 1. never being able to jump my motorcycle with either my Honda civic battery or the Toyota sienna . And I some how blew a fuse doing it with the sienna. Yes they are all 12v with more than enough amps to start. However I did always have better luck with a portable starter - if it is fully charged, the bike starts right up.
There are a lot of reasons i can think of.
1. There is an intermittent short of a reasonable resistance in the electrical system that blows the fuse with enough amperage available to it.
2. My coils are bad and so require higher cranking amps which only the starter can provide.
3. Jump cables are bad.
I know the theory - but what's better is I know it works with the portable starter. You can over analyze. Just keep doing something reasonable and it will eventually work. With things like motorcycles, you either have the experience or not to know what the cause is. Sometimes you will never know even with experience. Sometimes the cost of finding out what exactly is wrong is too high compared to trying an alternative. So the scientific method doesn't always help. Sometimes the advice you get on google is from people who are biased by their own experience. Sometimes it just helps to be adventurous - just don't replace the fuses with a splice because its blowing too often or do some boneheaded thing like that.

 

my truck has 2 850 CCA batteries, backed up by an alternator that is regulated at 14.5 volts. i have jumped my quads, bikes, ANYTHING.

if you have a 12 volt battery that reads 12 volts, its only 75% charged. the few extra volts will not hurt anything. i bet the bike charges somewhere around 15 anyway, i know my suzukis and honda all do/did. you could hook it up to a camper house battery pack, wich would be around 4000cca's, but it wont fry anything. the bike will take what it needs for amperage, the rest just sits there waiting.

the best way i initially learned the whole voltage amperage thing was:
VOLTS = PSI (pressure)
AMPS = Gallons Per Hour (flow)