Explain jump starting from a started car is bad for your bike

[SD Hornet]

From what I can tell, that is not possible due to the way the regulator is designed. The RR dumps the AC output of the alternator to ground. The dumping circuit is protected from the DC side of things by means of diodes.

At worst, the RR will be dumping the entire output of the bike's alternator to ground. With that said, it will typically be the entire output at idle, rather than the peak output.

Or, some misguided soul that does not have a battery charger, jumpstarts from a running car and revs the bike steady to 3 or 4k while keeping the car's system attached to speed up the charging process.

 

[Carlo]

'Has nothing to do with the alternator AC output.

Here's the potential problem in a nutshell. If the bike's VRR "dump point" (when it starts to send current to ground) is lower than that of the car's VRR, then there's the possibility that the bike's VRR will then be dumping all the current from the higher capacity car alternator and the attempt to dump much more current than it was designed for means it can overheat and suffer a melt down. Will it always happen? No. Is it possible? Hell yes. To be perfectly safe, you'd need to know a lot more information about both the bike and the car than is practical to know. So, the simple, safe thing to do is have the car's engine off.

That answers my question. Sort of.

The current being dumped is the result of the car's system possibly putting out a significantly higher voltage (which is what I was guessing at), then the bike's system will attempt to regulate that voltage by trying to dump as much current as the car's system can put out.
Since all batteries are pretty much the same in how much voltage they can tolerate, it's likely that even though the car's system can put out twice as much charging current as the bike's system, it's probably putting out the same voltage.

I'm going to go measure the voltage at the battery of my truck with the engine off, idling and at high revs.
My guss is that it will match the 13.5, 14.2 and 14.7 volts I'm reading on my Aprilia under those conditions.

That said, if you don't know what the voltage output of a car is, it's best to leave it off if you can get away with it.

 

[LS1Bandit]

If the set/dump point of the car's VRR is higher than the bike's VRR, then it's possible.

You seem to keep glossing over the issue that the designs of the regulators that "we" have looked at so far prevent that from happening. So far I haven't been shown/told any regulator design where this would actually happen. I have a really hard time believing that the dump-style regulators wouldn't have diodes preventing it from dumping power from the non-generator side. The basic design philosophy of that style regulator would almost dictate that it needs to be built that way.

 

[Duffil]

You guys can probably argue this point until doomsday.
My two cents are this: Short of some serious inattention or operator error, you'll be fine. I've had customers drop machines off with bricked batteries, and I usually just hook a small battery up with jumpers and put the bike where I need to, and then replace the battery when I get to it.
I see the bigger issue being OVERHEATING the R/R by running the bike with a bad battery after jumping it, causing the bike's system to overwork itself.

I probably just opened up a bigass can of worms...

 

[the grinch]

I have a really hard time believing that the dump-style regulators wouldn't have diodes preventing it from dumping power from the non-generator side.

I am curious to know (if or what) the breakdown voltage of the diode has any effect on all of this. I haven't read the whole thread so forgive me if I am off base or bringing up a subject that has been considered. Also, I am certainly not very strong in finer points of motorcycle electronics.

 

[LS1Bandit]

I see the bigger issue being OVERHEATING the R/R by running the bike with a bad battery after jumping it, causing the bike's system to overwork itself.

Actually, this is another case where intuition can lead you astray. The r/r actually works hardest when there's *no* load, not when there's a heavy load. When there's a heavy load, it doesn't need to shunt much (if any) power. When there's no load, it needs to shunt the entire output of the generator.

I believe the part that you *do* need to worry about when running a bike on a freshly-dead battery is the stator. The dead battery will cause it to have to put out a max (or near max) current. And with the relatively-undersized stators on most sprotbiles, that can cause problems, even potentially melting/shorting some of the windings.

 

[Burning1]

I am curious to know (if or what) the breakdown voltage of the diode has any effect on all of this. I haven't read the whole thread so forgive me if I am off base or bringing up a subject that has been considered. Also, I am certainly not very strong in finer points of motorcycle electronics.

Probably not. Even if the voltage coming off the car is greater than the dump voltage of the regulator, it's going to be significantly lower than the voltage put out by the generator running at full tilt.

 

[Starshooter10]

so, I need to chime in on this one.

So, speaking in electrical terms here...

I understand that when running a standard cars charging system can produce ~14.5V
but IIRC they (being your alt) dont produce jack at idle, jsut enough to run the ECU pumps injectors ETC.

a bike is the same thing, at idle you dont get jack, with some revs up to ~14.5

both are 12V DC otherwise

now, if its the AMPERAGE your speaking of.

my truck puts out 80 and my vic put out almost 200 (P71 alt)
the bike puts out, well way less.

in terms of BATTERIES the bike is ~180 CCA. truck is ~650CCA and the car is ~1100CCA

with that being said shouldn't I have blown any bike that I've ever connected to my autos??

well it dosnt happen, why?

I'm thinking that most jumper cables would be a bottle neck (POS china brands)

but then again, my jumper cables I've used to start some heavy duty diesels before (on the car) (cummins power stroke ETC)

I have a hard time believing that running or not really makes a differance



going to the regulators, I can see that being an issue I guess but since its not comming from the sator to the battery (jumpercables go direct to the battery) wouldnt that mean your circumventing it?

and with a stators I know electricity is a black magic of sorts, but if you have magnets spinning around a coil of wire is it REALLY gonna make more heat if its *pushing* more electrons?

 

[Burning1]

and with a stators I know electricity is a black magic of sorts, but if you have magnets spinning around a coil of wire is it REALLY gonna make more heat if its *pushing* more electrons?

A stator only makes electricity when there is a complete circuit going from the positive side of the stator to the negative side. The more resistance in the circuit (E.g. there is only a small bulb running,) the less energy the stator will produce. The less resistance (e.g. a short to ground) the more energy it will produce.

More energy produced, means more resistance against rotation. It also means more heat in the stator coils. If demand for energy *and* the ability to produce energy are great enough, the stator will eventually burn out. My understanding is that the ability to produce energy has to do with the size of the magnets, the number of windings, and the speed of the stator. The size of the coil wire will have a big impact on how much energy the stator is capable of producing before burning out. Wire size is a trade-off though - heavier gauge for the same physical size means fewer windings, and less energy produced for the same size/weight. So a balance must be found between those factors.

 

[ST Guy]

You seem to keep glossing over the issue that the designs of the regulators that "we" have looked at so far prevent that from happening. So far I haven't been shown/told any regulator design where this would actually happen. I have a really hard time believing that the dump-style regulators wouldn't have diodes preventing it from dumping power from the non-generator side. The basic design philosophy of that style regulator would almost dictate that it needs to be built that way.

I can't point you to a particular design. However they're out there. And unless you know which is which, the simple thing is to leave the car's engine off.

As for the diodes, diodes work up to the current level's they're designed for. Beyond that they'll fry. That's the problem.

 

[ST Guy]

That answers my question. Sort of.

The current being dumped is the result of the car's system possibly putting out a significantly higher voltage (which is what I was guessing at), then the bike's system will attempt to regulate that voltage by trying to dump as much current as the car's system can put out.
Since all batteries are pretty much the same in how much voltage they can tolerate, it's likely that even though the car's system can put out twice as much charging current as the bike's system, it's probably putting out the same voltage.

I'm going to go measure the voltage at the battery of my truck with the engine off, idling and at high revs.
My guss is that it will match the 13.5, 14.2 and 14.7 volts I'm reading on my Aprilia under those conditions.

That said, if you don't know what the voltage output of a car is, it's best to leave it off if you can get away with it.

Voltage isn't the issue. Any small differences in charging system voltage output between a car and a motorcycle is insignificant. It's amperage behind the volts that's important.

Your bike (and other vehicles) battery should read only 12.8 volts at best. If you're getting higher readings, that's only because you haven't waited long ehough after shutting down any charging voltage to the battery so that the battery can stabilize. Wait at least one hour after unplugging the charger or shutting the engine off before measuring battery voltage. Otherwise you get a falsely high reading.

 

[ST Guy]

Actually, this is another case where intuition can lead you astray. The r/r actually works hardest when there's *no* load, not when there's a heavy load. When there's a heavy load, it doesn't need to shunt much (if any) power. When there's no load, it needs to shunt the entire output of the generator.

I believe the part that you *do* need to worry about when running a bike on a freshly-dead battery is the stator. The dead battery will cause it to have to put out a max (or near max) current. And with the relatively-undersized stators on most sprotbiles, that can cause problems, even potentially melting/shorting some of the windings.

As I understand it, with a permanent magnet type alternator, it's always putting out the max (for a given rpm). There's no thottling back due to load. If the extra "juice" isn't needed, the VRR dumps it to ground.

 

[ST Guy]

Probably not. Even if the voltage coming off the car is greater than the dump voltage of the regulator, it's going to be significantly lower than the voltage put out by the generator running at full tilt.

Not really. It all depends upon the specific bike and specific car in question.

And remember, voltage isn't the issue. It's the amps behind those volts. Voltage only applies as it relates to the trigger points of the two systems VRR's. If the bike's VRR starts dumping excess current before the car's VRR does, then it's possible to have a problem. Not always, but possible.

 

[ST Guy]

so, I need to chime in on this one.

So, speaking in electrical terms here...

I understand that when running a standard cars charging system can produce ~14.5V
but IIRC they (being your alt) dont produce jack at idle, jsut enough to run the ECU pumps injectors ETC.

a bike is the same thing, at idle you dont get jack, with some revs up to ~14.5

both are 12V DC otherwise

now, if its the AMPERAGE your speaking of.

my truck puts out 80 and my vic put out almost 200 (P71 alt)
the bike puts out, well way less.

in terms of BATTERIES the bike is ~180 CCA. truck is ~650CCA and the car is ~1100CCA

with that being said shouldn't I have blown any bike that I've ever connected to my autos??

well it dosnt happen, why?

I'm thinking that most jumper cables would be a bottle neck (POS china brands)

but then again, my jumper cables I've used to start some heavy duty diesels before (on the car) (cummins power stroke ETC)

I have a hard time believing that running or not really makes a differance



going to the regulators, I can see that being an issue I guess but since its not comming from the sator to the battery (jumpercables go direct to the battery) wouldnt that mean your circumventing it?

and with a stators I know electricity is a black magic of sorts, but if you have magnets spinning around a coil of wire is it REALLY gonna make more heat if its *pushing* more electrons?

Most cars will produce 14+ volts even at idle. And you might be surprised at the number of bikes that can do that as well.

 

[Burning1]

Not really. It all depends upon the specific bike and specific car in question.

And remember, voltage isn't the issue. It's the amps behind those volts. Voltage only applies as it relates to the trigger points of the two systems VRR's. If the bike's VRR starts dumping excess current before the car's VRR does, then it's possible to have a problem. Not always, but possible.

What I meant, is that the voltage coming off the car shouldn't be more than 14 or so volts, where the regulator is designed to dump 70+ volts coming from the bike's generator.

 

[Motech]

So much engineering theory and postulating...

Riders... The donor car is like a charger. It is not loading up the motorcycle RR or stator.

 

[LS1Bandit]

I can't point you to a particular design. However they're out there. And unless you know which is which, the simple thing is to leave the car's engine off.

Are you sure "they're out there"? If you can't point to any designs, how do you know? Is it based on that post by the "very, very, very bright guy"? If so, maybe he made a mistake and/or assumption without verifying.

As for the diodes, diodes work up to the current level's they're designed for. Beyond that they'll fry. That's the problem.

No. In this case there wouldn't actually be current flowing through them from the car. Sure they'll fry if you exceed the current rating in the "forward" direction, but there won't be a voltage differential in the reverse direction so there won't be current flowing through it to fry it.

 

[Duffil]

Actually, this is another case where intuition can lead you astray. The r/r actually works hardest when there's *no* load, not when there's a heavy load. When there's a heavy load, it doesn't need to shunt much (if any) power. When there's no load, it needs to shunt the entire output of the generator.

I believe the part that you *do* need to worry about when running a bike on a freshly-dead battery is the stator. The dead battery will cause it to have to put out a max (or near max) current. And with the relatively-undersized stators on most sprotbiles, that can cause problems, even potentially melting/shorting some of the windings.

Your logic is unsound. The way I understand a regulator to work is the same as an old mechanical regulator. It senses voltage...if you put full battery voltage to the field, you'll get about 17-24 volts depending on model, etc. In a mechanical regulator, there are points inside that open and close fast enough to regulate the amount of voltage at the field terminal, and, therefore the output of the alternator. One set of points would open at overvolt, and then another would close at undervolt, allowing for a set "regulated" output. I cannot see that a newer, electronic (transistorized) regulator would operate completely opposite. That is to say, running full power to the stator and shunting excess power to ground creating a shit-ton of heat in the process.

 

[ST Guy]

What I meant, is that the voltage coming off the car shouldn't be more than 14 or so volts, where the regulator is designed to dump 70+ volts coming from the bike's generator.

Methinks you're confusing AC and DC voltage. We're only talking about DC here.

If you look at an automotive/truck alternator, it will be putting out the same level voltage (more or less) that a motorcycle will. 50 to 90 volts AC. Or there'bouts. Then that AC voltage goes to the VRR where it's rectified (turned into DC voltage and then regulated at around 14 volts DC). The same thing happens in a bike. And for those who think that bike alternator don't put out a lot of volts, AC, my old '80's era Suzuki put out 90 volts AC across each of the 3 wire pairs coming from the stator.

For those who don't know, VRR stands for Voltage Regulator Rectifier. It's purpose is two fold. One, it rectifies AC current and turns it into DC current. Two, it regulates the voltage output to the battery and the rest of the bike's electrical system in the range of 14 volts. All 12 volt DC powered vehicles that use an alternator (as opposed to a generater which is so old school) have a stator and a rotor which together is called the alternator (puts out AC voltage only) and a VRR which then converts and voltage to DC and then regulates the voltage level. In many (even the majority of) bikes, the VRR is separate from the alternator because the alternator is part of the engine where it's very hot and oily and the VRR couldn't survive there. This makes discerning between the two easy. You have an alternator and you have a VRR. On other bikes, and in cars and trucks, etc., the alternator also houses the VRR. This is where some confusion arrises. It's still just called an alternator, but in actuallity, it's an alternator/VRR all in one. In any case, any alternator "system" has two main components: the alternator itself which only puts out AC current, usually at a much, much higher voltage than what the vehicle uses. And a VRR which then converts AC to DC and then drops and regulates that current. Where those two main commponents are located is up to the engineers that design the vehicle.

 

[LS1Bandit]

Your logic is unsound.

I believe you might be correct. After thinking about it on the ride in this morning, it occurred to me that I was likely falling victim to the same "repeating of hearsay" that I was effectively complaining about with the original discussion.

The reason you can burn out a stator under heavy load was well-described by Burning1 and was spot on. However what I forgot to consider was that in the case of the r/rs that we're discussing, they effectively create that same load when shunting power to ground. So whether the power is going to charging/running your system or it's being shunted to ground, it seems the stator should be under the same load.

What I need to ponder is whether/if a greater load can exist through the draw from the MC system (be it from additional loads or from a deeply discharged battery) than from the shunting of power. My intuition actually says that it *is* possible (which brings us back to the possibility of burning out a stator charging a dead battery), but I can't say that with confidence right now.

I've had my stator burn out 3 times on me, and I had been told (and blindly agreed) that it was because I was running a heavier-than-normal load (aux lights + GPS). I need to sit down and think about whether that's actually what was causing the burn-out.