Jump Start

[NewGlide]

I know this has probably been covered here, but if your battery were to die on an EFI, could you, would you jump it off with a car?

[ANNIEFATS]

I have boosted my 05 EFI Fatty, with my truck, not running of course.
With the vehicle running, the output from the alternator, is too high for the bikes.
I have not had any issues since boosting my bike.
I hope this helps.
Todd

[IBARider]

No problem jumping from vehicle... running or not.  In fact, I've charged up bike battery with vehicle running.  The voltage is definetly not too much and it will only give as many amps as demanded by bike.  I never knew the origination of 'car puts out too much'?? 
 

[ANNIEFATS]

Wow, I heard the warnings, but never wanted to try to prove it wrong.
Thanks for the info, IBARider.
You learn something everyday.
Hopefully I will be able to retain it until tomorrow!

[Ape_do]

Good thread. My question isn't worth a new thread, so I'll respectfully throw it in here:

How 'bout a bump start on an EFI? I grew up dumping the clutch on just about every bike I've owned, but never tried it with an EFI. Does the start button open any other sensors?

[Jeffd]

If your battery is dead a bump start will not get an efi running. On my work bike any time the battery would go very low it would barely run.

[truck]

I've seen it done on a Evo Ultra where the battery wasn't strong enough to spin the starter.

[starrider]

I had a battery no start problem...Tried to jump it off the tow truck battery (not running) ...and it would not turn...So finally with the truck running and reving the engine...that got it started. Not saying that is the right way ... just saying thats what got it started. The next day...went and picked up a new battery.

03RK carb

[Coyote]

I watched a guy get a jump start off a tractor trailer rig. Made for a cool photo. 

[ANNIEFATS]

I have also bumped started my 05 EFI Fatty.
Had myself and a couple of buddies push the bike with my wife on it to pop the clutch.
The battery was to low to spin the starter, and rolling the bike down the driveway wasn't enough
to get it to start.
We had to push it down the street a bit to get it to fire.
I don't think someone could do it on there own unless you had a steep incline and some good speed.  JMO.

[HotRock]

And the new models with the "fly by wire throttle" maybe present a new problem when the battery is dead.  HUH?

[Justpassingas]

I've done both types of jump starts on my 98 EFI RK with no problems....with jumper cables off my truck when the battery was dead (motor wasn't running in my truck) and this past summer when my starter went south I pushed jump started it also and popped the clutch....

[eglideic]

 How is it possible to bump start an EFI (electronic fuel injection ) bike with a dead battery? How does the motor get fuel?

[bobrk1]

Don't have the car running, was at a bike rodeo and a bro's battery died when it got over to them the bike would spin over but not start, the truck was running I told him the ign. can't handle all the amps a car or truck puts out and he fried his crane ign, at least we had a friend with a truck to put it in LOL.

[FLTRI]

How is it possible to bump start an EFI (electronic fuel injection ) bike with a dead battery? How does the motor get fuel?

It will not start if totally dead, however, as the post mentioned it did not have enough to turn over the engine indicating is was not totally dead. The EFI system will run on 9-12 volts with very little amperage. If the charging system is working and it is a bad/old battery, once the engine gets started it'll run.....at least till the batter has nothing left in it cause the alternator will not run the engine totally by itself.
HTH,
Bob

[Phu Cat]

I have fried my regulator twice by jumping off a car that was running, but never by jumping from a car with it's engine off.  Agree with 'Fats:   the output from the alternator, is too high for the bikes.

PC

[NewGlide]

Thanks for the info fellas

[CrazyRay]

Yep, you can push start the efi bikes. Have done it several times. The batteries prolly had enough juice for the vitals, but they would not even try to crank.

[Garry in AZ]

Okay, I have seen this topic many times over the years, and I have always hesitated to get involved, simply out of respect for everyone elses opinion, but I'd like to make a point. For the last 30+ years, I've made my living dealing with all kinds of 12 volt systems. 
Because of my experience, I will very respectfully disagree with those who say that you can't jump start a bike with a running automobile. You certainly can, if you are reasonably careful.
The facts and physics of the issue are quite simple, an electrical device cannot "draw" or "absorb" more current than it was designed to use. Current can not flow in a circuit if all the points in the circuit are at the same voltage. You cannot have current without voltage, and you cannot have voltage without current. They are inextricably connected, and that's the physics of it.
Current flow is determined by the difference in electrical potential (voltage) between the two points. If the difference is very high, a lot of current can flow. However, if the maximum voltage of the device suppling the energy (the running car for example) is within the design tolerances of the device being charged, (and the bike surely runs on the same voltages as a normal car) there cannot be an excessive amount of current flow in the circuit.
Ohms Law tells us the current equals voltage divided by resistance, (I=V/R) so the car operating withing the same voltage range as the bike, can't hurt the bike by connecting the charging system. If the car is left shut off, the voltage is lower, so the difference between the charged battery in the car, and the "dead" battery in the bike is reduced, and less current will flow, and the battery will charge more slowly, which is generally a good thing. But you can actually draw a car battery down significantly by using it to charge another battery. For this reason, I like to connect the cable with the car off, wait about 5 minutes, and then start the car and just let it idle for another 5 minutes before disconnecting the cables and trying to start the bike. This technique minimizes the current draw on the whole circuit, and has never once caused any damage to either system. If the bike still does not start, shut the car off, and reconnect the jumper cables. With the car off, then try to start the bike. By the way, you might not realize it, but most car alternators barely develop 10 amps of current at an idle...

Now, if you accidentally cross the cables, even for an instant, that can pop the diodes in a regulator, in the bike or the car. Or, if after a jump start the regulator is found DOA, it could be why the battery went dead in the first place. Also you should not try to start the bike until the car has had a change to charge the battery for a few minutes. This technique will reduce the current flow between the charger and the "chargee". Why? Because as the bikes battery voltage rises, the difference in potential is reduced, and the current flow is reduced with it.
Jumping a bike with a semi tractor would need to be done very carefully, as most heavy duty diesels use a 24 volt system not 12.

With respect... not wanting to start any arguments... these really are the facts.

Garry

[Coyote]

Actually I can see the possibility of damaging the bike if the car is running. When the car is running, it's actively charging and if the cars voltage regulator is even slightly higher than that of the bike, it could damage the bike's much smaller regulator by forcing a higher voltage back on it. Both regulators would try to regulate to their set point but obviously the car would win.

[HIPPO]

I know this has probably been covered here, but if your battery were to die on an EFI, could you, would you jump it off with a car?

Yes, no problem if done properly and with the car not running.

If you are worried and have time just charge the battery with the car. It also helps to do this for a few minutes when the jumper cables are marginal, to minimize the draw through the jumpers with a completely dead bike battery.

[HIPPO]

Good thread. My question isn't worth a new thread, so I'll respectfully throw it in here:

How 'bout a bump start on an EFI? I grew up dumping the clutch on just about every bike I've owned, but never tried it with an EFI. Does the start button open any other sensors?

There may be a small window where the battery still has enough to bring proper fuel pressure up but not spin the starter.
It would take someone smart enough to stop trying the starter in time. The way the AGM batteries fail it isn't going to happen, unless it is a case where someone left the key on and the battery is just discharged rather then failed. Or theoretically a charging system failure, but then the bike isn't going far anyway.

The one word answer.
Depends.

[HIPPO]

Garry, yes but there are exceptions. Presumably one does not know the vehicle the bike is jumped off in BFE.

Picture a old pick up truck in the middle of the desert. Say as luck would have it the thing unknown to you is grossly overcharging.

With the engine running you can jump it to the bike and blow any electronics that are not over voltage protected simply by turning the bike on and supplying power to them. Don't even have to try and start it.

Not arguing with the various laws. Just saying that they apply until they do not apply.

And this is not even going into the old alternators that sometimes had significant AC riding on top of the DC. Not even sure what this might or might not do. 

[someday69]

hey and what if you jump your bike from an electrick car.....with huge batteries....oh,,never mind,,,it would still be 12volts...
          I tried to bump start my 02fxd from the top of a montana mountain...and could'nt get the darn trany to get past second gear...and never got it started..(but that was because the battery was toast,,,because the stator/regulator was toast.)...but I could'nt get it into third???...maybe bad techneek...that was one long night out there though...

[Phu Cat]

could'nt get the darn trany to get past second gear

Put a little pressure on the bottom of the shifter and roll the bike backward a little (assuming you're on a down hill).  You'll find the tranny is then unloaded and snicks right into 3rd gear.

PC

[Phu Cat]

Coyote, I see Garry's points, all correct regarding Ohm's law, current flow, voltage, etc..  I also see your point regarding the car's slightly higher regulator voltage being a problem. But since both regulators are charging 12 volt systems, are car regulators voltage systems generally higher???  I wouldn't think they would be.

I respect your opinion as I've seen you answer some tough questions here, so fill me in on what I'm not understanding about the difference on car regulators.  (Over the last 25 years I've had two HD regulators go bad a week or two after jump starting from a running car.  I originally proposed the idea years ago that regulators might get trashed from a running car jump is because the sign waves from the alternator might be close enough to being in synch they'd arch thru the regulator's insulation..  I'm full of ideas about how trashing the regulator might happen, but short on fact.

PC

[Garry in AZ]

Hi PC,

The AC waveforms from the bikes (or cars) charging system are converted to DC current by a diode bridge, (otherwise known as a rectifier) before the voltage is regulated. For this reason, it's not possible for the individual waveforms from two different charging systems to ever become phase aligned and increase in voltage, they are removed long before the charging systems ever get connected.
This is not a perfect process, and some energy is lost as heat, which is why regulators have cooling fins. Also, in all cases a small amount of 3 phase AC ripple remains on the DC voltage, but it's generally insignificant.  One exception to this is when one or more of the diodes in the rectifier bridge is shorted, and then as Hippo said, you can get a bunch of AC ripple which has the effect of lowering the available DC voltage and if the vehicle has a radio, there will be a lot of whine in the sound.

Cars, trucks and bikes that use a 12 volt battery all have voltage regulator set point maximums within a few of tenths of a volt (14.2 - 14.5) to prevent overcharging the battery. Remember, the regulators output voltage has to be higher than the battery voltage to cause current to flow. New cars actually have the field coil current controlled by the computer, which automatically develops a historical reference of your driving habits, RPM ranges, battery temp, average electrical loads... and only allows enough current development to cover those needs. This is all done in the interest of fuel economy, believe it or not.

Although a modern cars charging system is much more sophisticated than what our Harleys use, the general principles, and voltages are very similar. I hope this really condensed version of what happens helps.

Garry

[Coyote]

Coyote, I see Garry's points, all correct regarding Ohm's law, current flow, voltage, etc..  I also see your point regarding the car's slightly higher regulator voltage being a problem. But since both regulators are charging 12 volt systems, are car regulators voltage systems generally higher???  I wouldn't think they would be.

I respect your opinion as I've seen you answer some tough questions here, so fill me in on what I'm not understanding about the difference on car regulators.  (Over the last 25 years I've had two HD regulators go bad a week or two after jump starting from a running car.  I originally proposed the idea years ago that regulators might get trashed from a running car jump is because the sign waves from the alternator might be close enough to being in synch they'd arch thru the regulator's insulation..  I'm full of ideas about how trashing the regulator might happen, but short on fact.

PC

The charging systems are DC (well after rectification) so the sync thing is not an issue. Charging systems for vehicle batteries are basically charging to a voltage. Depending on how the charging regulator is designed it might be damaged if it's designed to source OR sink to a set point voltage. Since the system on a bike is fairly low capacity (in amps that is) it probably could not fight against a car system. Also, since every regulator set point voltage is slightly dependent on the tolerance of parts used to build it, it's a given that one regulator might be targeting 14.3 volts, and another 14.4 volts. Not much difference but if you connect two different regulators that are 0.1 volts apart, they can exchange a lot of current trying to correct. If the car regulator was on the low side, you would probably not have an issue as the bike could never win. But if the car regulator was on the high side, it would do it's best to pull up the voltage on both the car and the bike. The bike regulator might be damaged trying to do the same. Most likely the damage would occur if you were using good quality jumper cables with a minimum of resistive losses. All of this depends on how the regulator is designed. It could survive this if designed correctly but most of the electronics on our Harley's are pretty marginal to start with. The automotive industry seems to do pretty well though. Probably why you don't see these failures on cars.

[FLTRI]

In other words, if you are stuck in the middle of BFE and there is an other 12volt vehicle available to jump from do it without the other vehicle running.
Otherwise it is not reccommended, especially if there is a proper charger available.

[Phu Cat]

Great explanations Garry and Coyote.  I understand wheatstone bridges, but can't get that goofy idea of the ac ripple out of my mind.  Thanks for the info.

PC

[ANNIEFATS]

Good thread. My question isn't worth a new thread, so I'll respectfully throw it in here:

How 'bout a bump start on an EFI? I grew up dumping the clutch on just about every bike I've owned, but never tried it with an EFI. Does the start button open any other sensors?

Looks like your question, was well deserved of a new thread.  Great question.
Even better explanations guys.
Thanks.
Todd