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There is absolutley nothing wrong with leaving the car running while jumpstarting. The altenator on most cars only produces a 100 amps max at full output which is very hard to achieve . meanwhile car batteries themselves are capable of producing easily 5 times that and your bike battery is most likely rated at 100 + cold cranking amps. also the cars charging system only puts out the required voltage and amperage needed to get the system to maintain 12.5 volts. So go ahead and leave it running it doesn't matter.
For that matter I have actually used my bike to jump start my truck before.
 

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Seeing as you can burn up a bike battery if you charge it at anything over 2 amps I'd say its quite possible a car could cause some electrical gremlins if a bike's charging system isn't quite in peak condition.
 

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The Cruising Gunsmith
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ok i'll start tomorrow by trying a new battery. i hope thats all it is, but that thing the tach was doing was really wierd i hope i didn't mess up my electrical system.
As a general warning about bike (and car) electrical systems: the battery functions as the large filter capacitor which helps to filters the high voltage pulses coming from the output of the generator/rectifiers.

If you run the systme without a battery, or if the battery has an OPEN cell, the high voltage pulses that hit the electrical system can really toast some hardware.

In most cases of a bad battery, it has a weak or shorted cell, so it doesn't happen. But, if the battery has a high impedance cell, you can really do some damage. When you jumpt start, the good battery in the other car is in parallel with the weak one so all is OK. When you disconnect the jumper, you can get what's called a "load dump" condition and get a high voltage pules on your system if your battery is really bad.
 

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Seeing as you can burn up a bike battery if you charge it at anything over 2 amps I'd say its quite possible a car could cause some electrical gremlins if a bike's charging system isn't quite in peak condition.
If that was true that would mean the bikes charging system would not produce over 2 amps when charging the battery...... I hate to say it but if that was the case you wouldn't be able to run all your lights at night without killing the battery. because the headlamps and the taillamps will easily draw 2 amps therefore the battery would die. I don't know what the charging system is capable of but its got to be higher than 2 amps
 

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The Cruising Gunsmith
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If that was true that would mean the bikes charging system would not produce over 2 amps when charging the battery...... I hate to say it but if that was the case you wouldn't be able to run all your lights at night without killing the battery. because the headlamps and the taillamps will easily draw 2 amps therefore the battery would die. I don't know what the charging system is capable of but its got to be higher than 2 amps
That is correct: on my bike, a typical "max load" with high beam, running lights, ignition, etc is probably about 12A. As you said, the alternator must be able to output more than that or the battery would go dead.

But remember that a car's charging system is sized to handle a battery in the 60 - 100 A-hr range and a bike battery is maybe 15 A-hr. many car alternators can output 100A, whuile bike alternators are probably in the ballpark of about 20% of that..

If you jump a battery, they are in parallel. If the bike battery has a shorted cell, it will pull the voltage down on both systems. The car's electrical regulator will tell the car's alternator to output all the current it can to try to force the system voltage back up to about 14V....which means it will crank that 100A into the battery. And if left for any length of time, it could burn out the car's alternator and make the bike battery explode due to overheating because it can't get the shorted cell to charge back up so the system voltage stays low.

If the bike battery is only discharged or only has a weak cell, the system voltage will come back up to 14V and be OK.
 

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Luv my big boy toys
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That is correct: on my bike, a typical "max load" with high beam, running lights, ignition, etc is probably about 12A. As you said, the alternator must be able to output more than that or the battery would go dead.

But remember that a car's charging system is sized to handle a battery in the 60 - 100 A-hr range and a bike battery is maybe 15 A-hr. many car alternators can output 100A, whuile bike alternators are probably in the ballpark of about 20% of that..

If you jump a battery, they are in parallel. If the bike battery has a shorted cell, it will pull the voltage down on both systems. The car's electrical regulator will tell the car's alternator to output all the current it can to try to force the system voltage back up to about 14V....which means it will crank that 100A into the battery. And if left for any length of time, it could burn out the car's alternator and make the bike battery explode due to overheating because it can't get the shorted cell to charge back up so the system voltage stays low.

If the bike battery is only discharged or only has a weak cell, the system voltage will come back up to 14V and be OK.
Ditto, which is why you should jump off of a non running car.
 

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Remember that just like a car with a manual transmission, you can always "push start" your bike, too. I left my key turned to the auxillary position when I went into work the other day, and when I realized I'd left the key in an hour later and came out, the battery was dead. Went upstairs, got a guy to give me a push for 30 feet or so, and then dumped the clutch and gave it a little gas. Started right up.

My car's battery went bad back when I was broke and in college. For two weeks until my next paycheck, I had to park facing downhill wherever I went so I could get a rolling start and then dump the clutch to start the engine. Ahhhh, memories. :D
 

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Why jumpstart a ninja 250 from a car?
I just bring it up a small incline, then run down as fast as I can, put it in first and let go of the clutch.

Works after the second or third try. That pretty much does it.
 

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Wannabeabigbike Owner
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no

Sure its not that he had the car running when he jumped it that killed the battery?.
Even if the car was running, it would be putting out about the same 14-14.5v as the bike's alternator, so obviously the system can take it or the bike's own system would screw it up! The only way a running car jumping the bike battery should do any harm was if the car's regulator was bad, allowing IT'S alternator to put out more. It would probably take 18v or more at least, to do any harm. ALL electrical component in the automotive industry (yes, we fall there, under the same DOT regs) are rated with a HIGH safety factor. That includes everything from wire sizes used in manufacturing to light outputs.
 

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That is correct: on my bike, a typical "max load" with high beam, running lights, ignition, etc is probably about 12A. As you said, the alternator must be able to output more than that or the battery would go dead.

But remember that a car's charging system is sized to handle a battery in the 60 - 100 A-hr range and a bike battery is maybe 15 A-hr. many car alternators can output 100A, whuile bike alternators are probably in the ballpark of about 20% of that..

If you jump a battery, they are in parallel. If the bike battery has a shorted cell, it will pull the voltage down on both systems. The car's electrical regulator will tell the car's alternator to output all the current it can to try to force the system voltage back up to about 14V....which means it will crank that 100A into the battery. And if left for any length of time, it could burn out the car's alternator and make the bike battery explode due to overheating because it can't get the shorted cell to charge back up so the system voltage stays low.

If the bike battery is only discharged or only has a weak cell, the system voltage will come back up to 14V and be OK.
Well I learned something today... my grade 12 physics is long gone... I can't remember anything about electrical circuits LOL

Even if the car was running, it would be putting out about the same 14-14.5v as the bike's alternator, so obviously the system can take it or the bike's own system would screw it up! The only way a running car jumping the bike battery should do any harm was if the car's regulator was bad, allowing IT'S alternator to put out more. It would probably take 18v or more at least, to do any harm. ALL electrical component in the automotive industry (yes, we fall there, under the same DOT regs) are rated with a HIGH safety factor. That includes everything from wire sizes used in manufacturing to light outputs.
It's not the voltage we're worried about, it's the potential amperage difference.
 

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Wannabeabigbike Owner
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No

That is correct: on my bike, a typical "max load" with high beam, running lights, ignition, etc is probably about 12A. As you said, the alternator must be able to output more than that or the battery would go dead.

But remember that a car's charging system is sized to handle a battery in the 60 - 100 A-hr range and a bike battery is maybe 15 A-hr. many car alternators can output 100A, whuile bike alternators are probably in the ballpark of about 20% of that..

If you jump a battery, they are in parallel. If the bike battery has a shorted cell, it will pull the voltage down on both systems. The car's electrical regulator will tell the car's alternator to output all the current it can to try to force the system voltage back up to about 14V....which means it will crank that 100A into the battery. And if left for any length of time, it could burn out the car's alternator and make the bike battery explode due to overheating because it can't get the shorted cell to charge back up so the system voltage stays low.

If the bike battery is only discharged or only has a weak cell, the system voltage will come back up to 14V and be OK.

NO CURRENT SOURCE "PUSHES" or "CRANKS INTO" anything!! Current is DRAWN by the load! Current capability (like the 100A you are refering to) is only a capability IF that much were drawn by the load! Current should be thought of as an available supply. You only use what you attach to it ASKS FOR. Voltage on the other hand IS there all the time AND hits whatever is attached to it. If you put a load like the bike at 12A draw during starting on a source capable of giving 1000A, the you would ONLY pull 12A, not the 1000! BUT, if you put a system that will take only say, 16-17 VOLTS before it gets toastie, then you attach that to a car whose regulator is blown and putting out 18-20v, then ZAP. Of course if the regulator was blown the CAR would be frying all ITS parts too! This ain't magic guys, it's simple electronics formulas and LAWS of physics. They don't change. They work on bikes, airplanes, cars and space ships, as well as your Walkman. (they still have those?) I, and several others on here have Electrical Engineering degrees and backgrounds. I am not denigrating those with different opinions, but there are things that works differently according to the applications, and there are those that do not! Electricity is a DO NOT.
:shock:
 

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NO CURRENT SOURCE "PUSHES" or "CRANKS INTO" anything!! Current is DRAWN by the load! Current capability (like the 100A you are refering to) is only a capability IF that much were drawn by the load! Current should be thought of as an available supply. You only use what you attach to it ASKS FOR. Voltage on the other hand IS there all the time AND hits whatever is attached to it. If you put a load like the bike at 12A draw during starting on a source capable of giving 1000A, the you would ONLY pull 12A, not the 1000! BUT, if you put a system that will take only say, 16-17 VOLTS before it gets toastie, then you attach that to a car whose regulator is blown and putting out 18-20v, then ZAP. Of course if the regulator was blown the CAR would be frying all ITS parts too! This ain't magic guys, it's simple electronics formulas and LAWS of physics. They don't change. They work on bikes, airplanes, cars and space ships, as well as your Walkman. (they still have those?) I, and several others on here have Electrical Engineering degrees and backgrounds. I am not denigrating those with different opinions, but there are things that works differently according to the applications, and there are those that do not! Electricity is a DO NOT.
:shock:

This is true, i work on vehicle electrics a lot.
And also remember even if a car alternator were to say be able to put out 90amps, that would be at a high rpm, not a car idling.
at idle it may produce say 1/4 of that, not its max available output.
and it would take a long time to overcharge even a bike battery, unless the cars regulator is faulty in the first place.
 

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The Cruising Gunsmith
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NO CURRENT SOURCE "PUSHES" or "CRANKS INTO" anything!! Current is DRAWN by the load!
Let's see.... 33 years as an electrical enginerr, designed multiple battery charging and control systems.... I think I know how current works. The charging system in a car is CV (constant voltage) with a regulator that adjusts the current drive to the field winding in the alternator (based on the system voltage) which increases the secondary winding current proportionally. The system reg voltage is between 13.5 and 14.5V, and anytime the regulator senses lower than this it cranks the secondary current just as hard as it takes to get the system voltage up to spec. The battery is connected from the alternator/rectifier output to ground. If a battery has a shorted cell, it will NOT get up to 14V and the alternator control loop will run wide open and output maximum current (which is typically 70 - 100 A). That will generate a lot of heat and could damage the alternator/rectifiers.


Current capability (like the 100A you are refering to) is only a capability IF that much were drawn by the load!
You have no clue how a charging system works. In a car elect system the battery is the load (if if has a low or shorted cell) and the alternator will pump as much current as it takes into it to try to get it back up to 14V. That will create HORRENDOUS internal heating if left to run wide open. Study how a CV charging system works and get back to me.

BTW: even if the battery is perfectly OK: after you start your engine, the battery is a "load" for some time as the alternator is pumping current back into it to replace what was taken out during starter crank.

Current should be thought of as an available supply.
Current is a flow of electrons. In this case, the alternator is pushing them into the battery to try to force it's cell voltage up.


If you put a load like the bike at 12A draw during starting on a source capable of giving 1000A, the you would ONLY pull 12A, not the 1000! BUT, if you put a system that will take only say, 16-17 VOLTS before it gets toastie, then you attach that to a car whose regulator is blown and putting out 18-20v, then ZAP.
You can't seem to comprehend that a defective battery will pull down the system voltage and then becoem the load drawing the current.

Of course if the regulator was blown the CAR would be frying all ITS parts too! This ain't magic guys, it's simple electronics formulas and LAWS of physics. They don't change.
I am quite certain they haven't changed since I got my degree in electrical engineering or when I designed the IC control circuit that went into a few zillion Chrysler products and controlled the battery charging system.
 

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The Cruising Gunsmith
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This is true, i work on vehicle electrics a lot.
And also remember even if a car alternator were to say be able to put out 90amps, that would be at a high rpm, not a car idling.
at idle it may produce say 1/4 of that, not its max available output.
OK. So, how long do you think it would take to toast a typical 14 A-hr bike battery when the alternator is forcing 22A through it because the shorted cell keeps telling the voltage regulator that the battery voltage is low? That battery will get cooked in a HURRY.

and it would take a long time to overcharge even a bike battery, unless the cars regulator is faulty in the first place.
NO. You are assuming the bike battery has six good cells whose voltage will come up when charged allowing the reguilator to taper off the charging current. If you have a shorted cell, that leaves only FIVE cells and their sum voltage won't get up to 14V so the regulator will keep overcharging the hell out of the five functional cells.
 

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The Cruising Gunsmith
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Even if the car was running, it would be putting out about the same 14-14.5v as the bike's alternator, so obviously the system can take it or the bike's own system would screw it up! The only way a running car jumping the bike battery should do any harm was if the car's regulator was bad, allowing IT'S alternator to put out more. It would probably take 18v or more at least, to do any harm. ALL electrical component in the automotive industry (yes, we fall there, under the same DOT regs) are rated with a HIGH safety factor. That includes everything from wire sizes used in manufacturing to light outputs.
NOPE. You jump a defective battery from a good working sytem and you can toast all kinds of things, not the elast of which is the bike battery you will be cooking as the car's regulator tries in vain to get the defective battery up to the correct voltage.

You can't get that the bike battery becomes PARALLEL to the entire auto's electrical system the moment you jump to it? If that battery won't charge up, it loads the whole charging system down.
 

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OK. So, how long do you think it would take to toast a typical 14 A-hr bike battery when the alternator is forcing 22A through it because the shorted cell keeps telling the voltage regulator that the battery voltage is low? That battery will get cooked in a HURRY.


NO. You are assuming the bike battery has six good cells whose voltage will come up when charged allowing the reguilator to taper off the charging current. If you have a shorted cell, that leaves only FIVE cells and their sum voltage won't get up to 14V so the regulator will keep overcharging the hell out of the five functional cells.
So if the battery was already junk, how can you hurt it?

If its healthy, it would not be hurt.

do you see the point, or is the forest lost to you by too many trees?
 

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... this is why I never comment on anything to do with the electrical system LOL

12 volt power pack it is for me!
 

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[QUOTE

I am quite certain they haven't changed since I got my degree in electrical engineering or when I designed the IC control circuit that went into a few zillion Chrysler products and controlled the battery charging system.[/QUOTE]

Since Chrysler has not sold zillions in total, you prove right there you have no idea what you are talking about.
 
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