Myth busted: Jump-starting your bike from a car battery

[Zerosum]

I was always told by my Dad that if you tried to jump-start a motorcycle off a car's battery, the higher amperage of the car's electrical system would fry all of the bike's electronics.  So, for all these years, jumping off a car battery was positively verbotten in my book.

Then, yesterday afternoon, I find that my Hawk's battery was dead.  I left the stupid rear parking light on.  So, I go back into the office and mention my plight to an electrical engineer.

"Is your bike a 12 volt system?"

"Yeah"

"Then you can jump it off a car.  Your starter motor doesn't car about the incoming amerage, it'll only draw what it's designed to draw."

So, I gave it a try, half expecting my Hawk's CDI box to explode.  Sure enough, it started right up!  

Huh.  All these years I've believed in my Dad's myth.  I think he must have gotten that in his head back when bikes with 6-volt systems were common.  Now that WOULD blow something up, according to my coworker.

Maybe you all knew this already, but it was news to me!  

[UFO]

V = IR

[1KPerDay]

If I have to jump from a car battery I do it with the car not running. The battery alone will have enough juice to jump the bike. Someone told me once there's less chance of trouble this way; dunno if it's true but I have perpetuated that belief.

[DavidLSI]

If I have to jump from a car battery I do it with the car not running. The battery alone will have enough juice to jump the bike. Someone told me once there's less chance of trouble this way; dunno if it's true but I have perpetuated that belief.

+1

[bomber]

your Dad is laughing.

;-}

[Papa Lazarou]

I did fry the ECU/ CDI on my Tbird doing just this.....

[1KPerDay]

I did fry the ECU/ CDI on my Tbird doing just this.....

Car running or not?

Was it some funky British 17 volt car battery?  

[Papa Lazarou]

car running

[frayne48]

I have jumped bikes from cars with no problems.

[Papa Lazarou]

I have jumped bikes from cars with no problems.

For me-old bikes yes, those with computer thingies-no.

[Leanintree]

Never had any issues, but only with the car not running. Used to have to do that every spring before I learned about the wonders of a Battery Tender.

Oh, and given a choice, not off of a pickup, particularly a 3/4-1ton that might be packing a spare battery in series. Always jump a bike off of the smallest battery available.

Used to weird me right out... going from rr-rr-rr-...clickclickclick... to  RR-RR-RR-RR-RR-RR-RR-RR-RR-RR-RR-RR VROOOM!!! BANG!!!  <----flooded backfire  

Leanintree

[scottzilla]

If I have to jump from a car battery I do it with the car not running. The battery alone will have enough juice to jump the bike. Someone told me once there's less chance of trouble this way; dunno if it's true but I have perpetuated that belief.

Yup, that's what I do too.

[Zerosum]

If I have to jump from a car battery I do it with the car not running. The battery alone will have enough juice to jump the bike. Someone told me once there's less chance of trouble this way; dunno if it's true but I have perpetuated that belief.

Huh.  I'll keep that in mind.  The car was running when I jumped it.  Everything on my Hawk still works.  

[tigertom1965]

Forgive my ignorance but.......Your bike has a parking light????

I thought the lights went out when the key was off?

I know I could possibly leave the hazards on but a parking light?

[Medic09]

Forgive my ignorance but.......Your bike has a parking light????

I thought the lights went out when the key was off?

I know I could possibly leave the hazards on but a parking light?

In addition to the 'lock' position on the ignition lock, there is often (usually? always?) a 'park' position.  The 'park' position on older bikes left the taillight lit; on my '01 Sprint it leaves a little white light up front and the taillight lit.  Every bike I've owned (AFAIR) has had some arrangement like this.  Yours doesn't?  

[tvpierce]

12 volts is 12 volts.  Extra amps won't hurt the bike.

[tigertom1965]

I haven't tried it to see if the lights stay on. I will try that tonight when I get home.

[1KPerDay]

It's a holdover from the European bikes... in some/most countries they do (or did) require that bikes parked on the street have their parking lights on.

Or so my dad tells me.

I for one wish my hazards would work with the ignition off. But that's another story.

[Zerosum]

Forgive my ignorance but.......Your bike has a parking light????

I thought the lights went out when the key was off?

I know I could possibly leave the hazards on but a parking light?

Yeah.  I hate it.  It's the last notch on the ignition switch before "off."  You can take the key out and the rear lamp stays on.  I don't ride my Hawk that much, and I sometimes forget about it.  On a bright sunny day, you don't even notice.  Some time after '88, Honda must have figured out that this was a battery-killer.

[Mydlyfkryzis]

There can be a problem. On bikes that use a Zener Diode regulator, the basically work by shorting the excess voltage to ground. If your zener diode is, say, dumping at 14.6 volts, and the car, running, is putting out 14.8 volts, the diode will try to regulate the voltage by diverting current to ground. since cars have a pretty large charging capacity, the voltage regulator in the car will increase current output, trying to maintain 14.8 volts.  Most motorcycles have a 30 amp or less charging system. The car keeps adding current until the fuse in the motorcycle circuit blows or the zener diode burns up.

If you jump your bike from a non-running car, the battery is never over 14 volts, so it is safe.

If you have a none zener diode system, then it doesn't matter.

If the car regulator is putting uot less then the Zener diode short to ground voltage, then you won't hurt anything.

So depending on the bike, the actual rating of the Zener Diode, and the output of the car, you may or may not fry your charging system.

You will not fry the other electronics as they use the smae voltage as Car electronics.

For those who say 12 Volts is 12 Volts, I remind you that even a 12V battery isn't 12V. And charging systems run between 14 and 15 volts on a properly operating system. If the car is putting out 16 volts, or 15.8 or something else, you may fry the bike regulator or electronis.

For safety, just make sure the car motor is not running and you will never ruin any electronics.

If the engine on the car is running, then, good luck, you are taking a chance.  

[1KPerDay]

Does anyone understand what this duck is saying?  

[black hills]

Oh, and given a choice, not off of a pickup, particularly a 3/4-1ton that might be packing a spare battery in series. Always jump a bike off of the smallest battery available.
backfire  

Leanintree

Umm..that would be a 24v system wouldn't it??

[black hills]

He meant to say in parallel...but you are correct, series would make it 24v.

Yes, you are correct
on the other hand it doesn't matter if it has 1,2, or 10 batteries. As long as they are connect parallel and the engine is not running you are going to get somewhere between 12-13 volts. 12 volts is 12 volts (remembering that if the engine is running you are running somewhere around 14+ ) It's really not as magical as it seems.

[PhilBiker]

I wasted the rectifier in my bike by jumping from running cars.  It's not a myth to me.

[Doug Just Doug]

Does anyone understand what this duck is saying?  

Yes, but I'm fluent in Ork. Zener Zener!

[thatguy]

I've replaced a few ECMs that died coincidentally    when they attached a jumper cable from a running car.Do yourself a favor when jumping an FI bike.Attach the cables with the bikes ignition off and the ECM fuse disconnected.ECMs are not cheap.

[Zerosum]

I've replaced a few ECMs that died coincidentally    when they attached a jumper cable from a running car.Do yourself a favor when jumping an FI bike.Attach the cables with the bikes ignition off and the ECM fuse disconnected.ECMs are not cheap.

Will a modern FI bike even start withouth the ECM?    ECM stands for Engine Control Module, right?

[thatguy]

No they won't.Yes it does.I meant only during the connection phase.You'll need to reinstall the fuse to start it.Every training class I've attended stresses voltage spikes,no matter how small the total can be fatal to an ECM.

[EricD10563]

Car not running never had a problem been doing it for years. I don't think there is a need for the car to be running, plenty of juice with a car battery.

[UFO]

Okay, lots of talk about jumping using a running car?

Who here (raise your hand) thinks this makes ANY sense to do?  Bueller?  Your car isn't designed such that the engine needs to be running to...start its own engine!  

Just hook it up to a car battery, start the damn bike, disconnect.  End of thread.  Sheesh.

[1KPerDay]

Or ride your bike often enough to keep the battery charged. Or buy a battery tender.

[basco]

Or push start it.

[Leanintree]

Or push start it.

That's REALLY not as much fun as it sounds if you happen to ride a boat-anchor...

[black hills]

That's REALLY not as much fun as it sounds if you happen to ride a boat-anchor...

Not sure what qualifies as a boat anchor, but I've had no trouble bump starting the following:

V45Magna
VFR
VTX1800
CBR954

[Mr Sunshine]

If I have to jump from a car battery I do it with the car not running. The battery alone will have enough juice to jump the bike. Someone told me once there's less chance of trouble this way; dunno if it's true but I have perpetuated that belief.

Doesn't matter...I'd do it with the car running so I can make sure to recharge my car battery so I can start it later.

[1KPerDay]

Doesn't matter...

sez you...

[Scoop]

I was a bit concerned about jumping my new R1200RT as I figured that any BMW must have some sort of sensitive electronic something that will fry if shown booster cables.  But the manual has only a one-liner warning, "jump from a battery with the same voltage as the bike".  So, as has been said, there should be no issues jumping a bike from a 12 v system.  But, as has also been said, a running car will be putting out about 15.2 v and could cause some issues.  If you are worried, you can always take the "surface charge" off of a car battery by turning on the lights or running the fan motor for a second before you hook the battery up to your bike.  This will pretty much ensure that you are boosting with 12 volts.  

[radman]

Does anyone understand what this duck is saying?  

Yup.  And I agree with him, especially on ECM equipped bikes.  Even cars are more and more susceptible to over-volts from car starting units-a fact of life in the Great White North.

[Uncle Bob]

at the bike shop we had a 1500 CCA battery jumper, used it hundreds if not thousands of times.  That is double, if not triple the capacity of most car batteries.

Cars running shouldn't make a difference, but then, I can't imagine why you would do it to begin with.

IMO, I think most 'stories' about things blowing up is people simply getting the polarity wrong.  I can't tell you how many times, both cars and bikes, we had to repair damage for that (although they rarely admit it at first)

The story is always the same...."so anyway, A FRIEND OF MINE went to jump the bike/car and...."

[EricD10563]

Or ride your bike often enough to keep the battery charged. Or buy a battery tender.

What he said.

[Black Ice]

This is news?  

[ragtoplvr]

Here is my spin, and I work in automotive electrical reman

If you have a serviceable battery,  make sure it has the correct amount of water.  Not a big concern now, but if winter never jump a frozen battery.  It is probably toast anyway.

There is a alternator thing called a load dump.  It occurs when a heavy load is removed, it can be over 100 volts.

Normally a good battery will absorb enough of it.  When your bike battery is discharged it can not absorb it.

Some but not all alternators are protected against load dump.  Some BMW have a protection device on the alternator.  It can be fried by the bigger car alternator.

Some motorcycle regulators will attempt to dissipate excess voltage, usually to their demise.  I know of no list telling which kind you have.

A fully charged lead acid battery will partially charge a discharged lead acid battery, engine does not need to be running

A part way charged battery can absorb spikes and load dump much better than a dead one

A discharged battery can not protect against reverse connection, so OBSERVE the polarity, or do not jump.

With both engines off, keys off ect, connect jumper cables, and wait at least 5 minutes for some charging.  Time is your friend here

Then start dead bike.

Disconnect cables

Find a new to you twisty road.

Rod

[trapp120]

I've jumped numerous street bikes, dirtbikes and quads from car battery - running. Have not seen an issue with the electrical, or any adverse effects.

[chornbe]

"Then you can jump it off a car.  Your starter motor doesn't car about the incoming amerage, it'll only draw what it's designed to draw."

Exactly. Amps are drawn not force-fed. Path of least resistance and all that.

[chornbe]

Forgive my ignorance but.......Your bike has a parking light????

I thought the lights went out when the key was off?

I know I could possibly leave the hazards on but a parking light?

Some bikes have a parking light on a different key position than ignition or aux or off, etc.

[Bjorn Toulouse]

Over the years I've repaired quite a few bikes with damaged electrical components due to jump starting from a car, although jumping from a car is not a big deal. 12 volts is 12 volts.

In virtually every case the problem was traced to a ham-fisted maroon shorting out the + jumper connection. The proximity of frame rails and other grounded bits to the + battery terminal makes the use of car size jumper cables somewhat dicey in many instances.

The "arc weld" marks on the frame rail reveal your stoopidness, and no, it ain't covered under warranty!


Rex

[whoaru99]

...IMO, I think most 'stories' about things blowing up is people simply getting the polarity wrong.  I can't tell you how many times, both cars and bikes, we had to repair damage for that (although they rarely admit it at first)

I agree. It's usually not jump starting per se that caused the problem, it's much more likely that someone screwed up that is the real problem.

[HaChayalBoded]

Here's a tip for your Hawk GT, ALWAYS, put back that stupid little battery cover thingy. Even though its a little light piece of plastic, it apparently offers just enough of a load bearing for the fender to not have the other two tabs crack and break off.


Ask me how I found that out....

[Zerosum]

Here's a tip for your Hawk GT, ALWAYS, put back that stupid little battery cover thingy. Even though its a little light piece of plastic, it apparently offers just enough of a load bearing for the fender to not have the other two tabs crack and break off.


Ask me how I found that out....

   That's interesting... because that part is currently on a shelf in my garage!    I'll have to put it back on!

[Justin]

Bottom line: Unless you like expensive repairs just leave the car off when jumping from a car battery. When the car is on the charging system is putting out a lot more volts than just the battery alone.

[tigertom1965]

I do have parking lights on my R1200RT.

I think you turn off key and then press and hold left blinker (within so many seconds of turning off bike) for so many seconds and on they come.

Or some other such nonsense.

To turn them off you must turn on bike again.

Why do they make it so difficult?

[highside]

It never ceases to amaze me how many people do not know how to jump start a car. Improper technique can damage a car's electrical system. If your jumping a bike from a car the risks of doing it wrong are magnified. I think that is where this myth comes from.

I agree that there is no need for a car to be running to jump another vehicle. A car battery is perfectly capable of starting a car without the engine running.  

[tigertom1965]

I thought you hooked up the positive to the positive and the negative from the car battery to ground on the second car.

You are not supposed to hook up battery to battery right?

[Justin]

I thought you hooked up the positive to the positive and the negative from the car battery to ground on the second car.

You are not supposed to hook up battery to battery right?

You can do it either way. The negative terminal on the battery is hooked up to the chassis ground anyway...

[birdrunner]

You can do it either way. The negative terminal on the battery is hooked up to the chassis ground anyway...

however, by doing this ground last, and onto a grounded part of the car instead the battery pole, any spark that happens, happens away from any gases your battery MIGHT be producing.  It's a safety thing.

[highside]

You can do it either way. The negative terminal on the battery is hooked up to the chassis ground anyway...

Im no electrician so i couldn't explain why, but i have jumped a LOT of cars and I have found that better results are achieved by grounding on the chassis or motor than on the negative terminal, especially when the battery is thoroughly drained.

[Scoop]

Im no electrician so i couldn't explain why, but i have jumped a LOT of cars and I have found that better results are achieved by grounding on the chassis or motor than on the negative terminal, especially when the battery is thoroughly drained.

The only reason for connecting the negative to the chassis is, as was mentioned above, to prevent a spark that might occur on closing the connection from igniting the hydrogen gas produced by the battery.  Other than that safety issue, it makes no difference where you hook it up.

[black hills]

The only reason for connecting the negative to the chassis is, as was mentioned above, to prevent a spark that might occur on closing the connection from igniting the hydrogen gas produced by the battery.  Other than that safety issue, it makes no difference where you hook it up.

+1 if you follow the negative cable on the battery it goes to the chassis or engine

[cworley5150]

I jump start bikes from time with no problems.

[highside]

+1 if you follow the negative cable on the battery it goes to the chassis or engine

Your probably right that it wont make a difference, cept that for most cars I have jumped the battery terminal is so corroded that a better connection can be made elsewhere.

[black hills]

Your probably right that it wont make a difference, cept that for most cars I have jumped the battery terminal is so corroded that a better connection can be made elsewhere.

+1  most new cars have a nice cast lifting eye somewhere near the top of the engine, works great for a jumper cable

[Bravo12]

Back in 1994, the R/R (and eventually the alternator) went bad in my 1989 GS500E shortly after jumping it from my buddy's running car.  Since then, if I need to jump it from a car battery, the car is off.

[black hills]

Back in 1994, the R/R (and eventually the alternator) went bad in my 1989 GS500E shortly after jumping it from my buddy's running car.  Since then, if I need to jump it from a car battery, the car is off.

+1 12v is 12v no matter the size of the source, but when the car is running you are no longer dealing with 12v. With the car running you have 12-16v, there in lies the problem.  

[county]

My Buick has the battery under the back seat.....they put positive and negative terminals under the hood for convenience.