Starter issues

[Patriot]

Still sits on shelf in garage. Never bothered with it.

mines the same way...

 

[Slonishku]

Old or not, I'm interested. A follow-up on the old motor would be great, as a confirmation that it wasn't a connector or some other peripheral piece of the motor itself.

On my way through Arches National Park a few weeks ago, it was around 105+ degrees, and I was cruising slowly through the park and stopping frequently. The last couple of times, it barely started, and I cut the tour of Arches short. I didn't want to get stuck out there in that heat.

No worries since, but no temps anywhere near that either.

 

[garyahouse]

Nothing I can add here, Woof, but I'm pulling for ya. Many of us are following along on your thread waiting to see whassup. I'm curious to know what your voltage is doing during this process. The jump start success gives me a couple clues... ground or weak battery. I know it's rare, but occasionally, new batteries have issues. For what it's worth, the local auto parts store can torture test the battery... I know it's frustrating, but you CAN do this. I'm hoping the solution won't be a new starter.

Gary

darksider #44

 

[RadioHowie]

Gary, didja happen to check the original date on this thread????

Foosh has had it fixed for 3 years!!!

 

[wfooshee]

But I'll address his jump start point anyway.

The bike could be at a point where the battery would turn the motor over three times and cry "Enough!!!" but I never had a problem jumping the bike off.

But it wasn't a battery problem. I STILL HAVE THAT SAME BATTERY IN THE BIKE RIGHT NOW!

But I never had a battery problem, I had a starter problem. The starter would suck the battery dry of electrons, but a car battery has plenty of capacity to feed my greedy starter, so jumping was never an issue (other than feeding 160 to 200 amps through my tiny FJR starter wires.)

 

[RadioHowie]

The starter would suck the battery dry of electrons, but a car battery has plenty of capacity to feed my greedy starter, so jumping was never an issue (other than feeding 160 to 200 amps through my tiny FJR starter wires.)

Foosh,

The section I emboldened leads me to a question I've often wondered about...

You say "feeding 160 to 200 amps through my tiny FJR starter wires" but is that actually true?

I mean, won't the starter only draw the amperage it needs, rather then the total amps available?

So even if you have a 500 amp power supply, and assuming the starter isn't malfunctioning, won't the starter ONLY draw the amount of current it needs to operate, rather than pulling all 500 amps available?

I ask because I've never been clear on current draw, i.e., does a device only draw the amount of current needed, or the current available? Again, assuming the device in question isn't faulty.

 

[ionbeam]

The starter would suck the battery dry of electrons, but a car battery has plenty of capacity to feed my greedy starter, so jumping was never an issue (other than feeding 160 to 200 amps through my tiny FJR starter wires.)

...I mean, won't the starter only draw the amperage it needs, rather then the total amps available?...won't the starter ONLY draw the amount of current it needs to operate...

All electrical devices can only draw what they need (can accept). Given a 1000 ohm resistor connected to 10 volts with 1 million amps available, the resistor can only pass 0.01 amps. A good starter has the current limited by the resistance of the armature windings. For a starter to pass 40 amps at 12 volts the winding resistance would be 0.3 ohms. The resistance is what sets the current flow in conjunction with the voltage potential. In automotive stuff the voltage normally swings a narrow range between 12.0 and 14.5 volts so resistance is the primary current regulator. :blink:

 

[Fred W]

The starter would suck the battery dry of electrons, but a car battery has plenty of capacity to feed my greedy starter, so jumping was never an issue (other than feeding 160 to 200 amps through my tiny FJR starter wires.)

Foosh,

The section I emboldened leads me to a question I've often wondered about...

You say "feeding 160 to 200 amps through my tiny FJR starter wires" but is that actually true?

I mean, won't the starter only draw the amperage it needs, rather then the total amps available?

So even if you have a 500 amp power supply, and assuming the starter isn't malfunctioning, won't the starter ONLY draw the amount of current it needs to operate, rather than pulling all 500 amps available?

I ask because I've never been clear on current draw, i.e., does a device only draw the amount of current needed, or the current available? Again, assuming the device in question isn't faulty.

Well' I'm not Foosh, but I did stay at a Holiday Inn Express once. :lol:

You are correct. Just because you hook up a power source (battery in this case) that has the capacity to supply huge amounts of current doesn't mean that it will. It's pretty simple electrical theory, and what matters here is the load resistance that is put on that power source.

In a lot of ways electrical theory is analogous to hydraulic theory, but people usually have an easier time visualizing the latter. A water source with a particular pressure (voltage) will only flow (current) a certain amount, dependent on the total restriction (resistance) of the entire circuit. So jump starting a bike off of a big high capacity car battery doesn't mean that you will get more current when you thumb the starter button, only that you can get more current if the load resistance drops. In the case of a starter that is starting to go bad, it is turning slowly and straining to turn the engine over, the resistance of that motor will be lower. How much lower?

When using a wimpy little FJR battery the internal resistance of the battery will self-limit the output current to whatever the maximum capacity of the battery is, even with a dead short across its terminals. That's what's happening when you see the voltage (pressure?) dropping when your starter is grinding away. You are losing the rest of the voltage inside the battery itself. As the pressure drops, obviously the flow will be limited also. But a car battery with higher ampacity ratings will not trend to self limit as early.

That's the only hazard of jump starting off a big car battery. Not that it will fry things due to the larger current. Just that it can.

 

[mcatrophy]

...

I ask because I've never been clear on current draw, i.e., does a device only draw the amount of current needed, or the current available? Again, assuming the device in question isn't faulty.

Simple answer: A conventional dc "shunt" motor will only draw the current needed to power the load.

More complex answer: When the motor is turning, it acts as a generator, trying to oppose the voltage feeding it. A theoretically perfect, lossless motor will turn at a speed so that its back EMF (electromotive force) is equal and opposite to the voltage of the supply. On a real-world motor, its speed will be slightly lower, its back emf will not equal the supply voltage, there will be a current draw given by the differences in the two voltages and the electrical resistance of the motor.

As the mechanical load increases, the motor slows, the current increases to provide the torque load.

From stationary, when the voltage is first applied (the starter solenoid is activated), the initial current is limited only by the circuit resistance (internal battery resistance, connections, leads, contacts, brushes, coils etc.). This current is much higher than the normal running current, and gives a very high torque that accelerates the motor and its load. As the motor speed increases, so does its back emf, reducing the current until the current is just sufficient to provide the torque of the normal load, at some speed below the "no load" speed.

To add to the complexity, this describes a conventional "shunt" motor, where the stator is either an electro-magnet whose coils are driven directly off the supply, or is possibly a fixed magnet, as opposed to a "series" motor, where the stator coils are in series with the armature. The latter type of motor has a very different characteristic, and is more suited to traction loads.

[edit] Ion & Fred got there first

[/edit]

 

[RadioHowie]

Mr. Beam, Mr. W and Mr. Trophy,

So, having a 500 amp capacity power source will NOT damage a device pulling power from that source just because there is an over-capacity of current available, assuming the current draw is within the capacity limits of the device and/or attendant wiring.

BUT, if there is something wrong with the device, as in Walter's original problem-starter, that would conceivably pull 120 amps instead of 30, because it was sick, then there could be a problem, because the bike's wiring or the starter's windings can't handle the current and something gets fried.

Is that pretty much a summary of the situation?

 

[SkooterG]

Is that pretty much a summary of the situation?

If you expect those guys to put it in terms 'tards like us can understand that Thou Doth Expect Too Much!

 

[RadioHowie]

Is that pretty much a summary of the situation?

If you expect those guys to put it in terms 'tards like us can understand that Thou Doth Expect Too Much!

Shouldn't you be out getting yourself "un-lost" from the Zombie Apocalypse? :lol:

But yeah, you're right. If I finally get an answer with words I can understand, then I'll be happy.

 

[ionbeam]

If you expect those guys to put it in terms 'tards like us can understand that Thou Doth Expect Too Much!

Hey, next time I'm out your way I can bring my technical illustrator

And my board of education to get your attention and keep you focused

Bring along a shop power supply

And teach you the fundamentals of electricity the way it should be -- learn or die :lol:

 

[mcatrophy]

Mr. Beam, Mr. W and Mr. Trophy,

So, having a 500 amp capacity power source will NOT damage a device pulling power from that source just because there is an over-capacity of current available, assuming the current draw is within the capacity limits of the device and/or attendant wiring.

BUT, if there is something wrong with the device, as in Walter's original problem-starter, that would conceivably pull 120 amps instead of 30, because it was sick, then there could be a problem, because the bike's wiring or the starter's windings can't handle the current and something gets fried.

Is that pretty much a summary of the situation?

Yes, a perfect summary. A good way to let the smoke out of what was perfectly good wiring, starter solenoid contacts, and pull the lead/sulphury compounds off the battery's plates. And ruin a good day's riding. Or three.

 

[wfooshee]

As for amps, recall from earlier in the thread, even though it's 3 years old, that my starter pegged my 160-amp test meter (post #80) and the shunt was too hot to touch after cranking...... Also, my starter's no-load draw was north of 75 amps (post #114!)

That's where my figure came from. Not that a car battery could supply an excessive amount of amps, but that my starter was demanding an excessive amount of amps.

 

[RadioHowie]

...and if you'd only continued cranking at the 160amp level, you'd have found out REAL quick what the weak points in the starting system were.

All you would have to do is trace down the smoke...after you put the flames out. :rofl: