Heated gear- less MPGs?

[SLK50]

I think you have a pretty good handle on how things work, Knifemaker.

Once inertia is overcome the alternator spins easily, putting out

maximum output at cruising speeds.

Demand ( load ) is constantly balanced against supply with the excess

turned off or shunted, depending on model.

Even if demand exceeds supply alternator output remains constant at

engine speeds above idle.

 

[mcatrophy]

...So, WHAT force is going to "slow down" that turning crankshaft when I turn on a light or plug an accessory in? To make the engine work harder and burn more fuel there had to be something physically trying to work against it.

That's the crux of my question here which still seems unanswered.

Sorry if I missed it.

The force is magnetic.

This pic shows the coils and the ring magnet that moves round the outer diameter of the coil assembly. (Click on image for larger view.)



Here's a thought experiment.

As you say, the magnet (actually a ring arranged N-S-N-S ...) is rotating round the group of coils. Initially we'll say the coils are open circuit, so no current can flow.

As a magnet passes a coil, the magnetic field of the magnet passes through the coiled wire and induces a voltage in the wire, basic magnetic induction. But there is no current because the coil is open circuit.

Now put a light bulb on the coil. As the magnetic field from the magnet induces a voltage in the coil, current will flow through the coil and through the lamp. Now, here's the interesting bit - that current flowing through the coil creates its own magnetic field.

As (say) the north pole of the magnet approaches the coil, the induced current creates a north pole at the end of the coil, opposing the approaching magnet. As the pole moves away from the coil, the induced current is in the opposite direction, creating a south pole that is tugging the magnet back.

The higher the current, the greater the magnetic field, the greater the force opposing the magnet's movement.

Does that help?

 

[garyahouse]

Interestingly enough, this is why the brake pads on my Toyota Camry hybrid last so long. When I step on the brakes, the hybrid system "flips the switch" which causes the generator to begin generating electricity. But when the generator is told by the computer to begin this process, it creates a drag on the engine when generation begins. This creates braking action, and the car begins to slow down, but is not using the actual brakes. The harder I step on the brakes, the more the computer tells the generator to produce more electricity, thus the more this "braking action" is applied to the engine, and the more I feel the car slowing down. Reason? the more electricity it produces, the more resistance it exerts against the spinning engine... it feels exactly like the brakes are being activated, but they're not. Most of the time, if I use the brakes gently, my actual brakes on the car don't get used much at all... because the generator is producing power to recharge the hybrid battery pack.

In a nutshell, it takes more horsepower to produce more electricity.

Maybe that will help somewhat.

Gary

darksider #44

ps, just in case anyone is curious, this Toyota hybrid braking system is seamless and cannot be felt. It feels exactly like a normal braking system.

 

[SLK50]

That's a good description, Gary.

Just to clarify a bit, your Prius uses induction to generate the

magnetic field, the FJR does not.

Therefore, resistance with little variance.

 

[Knifemaker]

...So, WHAT force is going to "slow down" that turning crankshaft when I turn on a light or plug an accessory in? To make the engine work harder and burn more fuel there had to be something physically trying to work against it.

That's the crux of my question here which still seems unanswered.

Sorry if I missed it.

The force is magnetic.

This pic shows the coils and the ring magnet that moves round the outer diameter of the coil assembly. (Click on image for larger view.)

Here's a thought experiment.

As you say, the magnet (actually a ring arranged N-S-N-S ...) is rotating round the group of coils. Initially we'll say the coils are open circuit, so no current can flow.

As a magnet passes a coil, the magnetic field of the magnet passes through the coiled wire and induces a voltage in the wire, basic magnetic induction. But there is no current because the coil is open circuit.

Now put a light bulb on the coil. As the magnetic field from the magnet induces a voltage in the coil, current will flow through the coil and through the lamp. Now, here's the interesting bit - that current flowing through the coil creates its own magnetic field.

As (say) the north pole of the magnet approaches the coil, the induced current creates a north pole at the end of the coil, opposing the approaching magnet. As the pole moves away from the coil, the induced current is in the opposite direction, creating a south pole that is tugging the magnet back.

The higher the current, the greater the magnetic field, the greater the force opposing the magnet's movement.

Does that help?

Yes it does. So your saying adding any "Extra" electrical load to to the bikes battery increases the magnetic field in the coils surrounding the fixed magnets and thus in effect turns it into a "magnetic brake"....putting more drag on the crankshaft. The more juice used the stronger the field produced and thus more "braking action".... Causing then the bike to burn more gas at a given speed.

Luckily I don't give a crap about my MPG figures and if I add any heated gear I'd likely consider the trade off of being warm on a cold day worth the extra price I'd be subjected to at the pump.

There do seem to be some contradictory posts on this. But I'll go with this one for now

 

[mcatrophy]

...

So you're saying adding any "Extra" electrical load to to the bikes battery increases the magnetic field in the coils surrounding the fixed magnets and thus in effect turns it into a "magnetic brake"....putting more drag on the crankshaft. The more juice used the stronger the field produced and thus more "braking action".... Causing then the bike to burn more gas at a given speed.

Luckily I don't give a crap about my MPG figures and if I add any heated gear I'd likely consider the trade off of being warm on a cold day worth the extra price I'd be subjected to at the pump.

There do seem to be some contradictory posts on this. But I'll go with this one for now

That's about it. Remember where you say "increases the magnetic field", that's the field generated by the current in the coils. The field generated by the rotor magnets remains constant, although at any given moment in any given position, the instantaneous field is the vector sum of the magnets' field and the coils' field.

As I said before, an extra 100 watts might change your range by perhaps 1/330th, or at worst 1 mile. Not exactly significant.

And, when you ask why a short circuited coil takes much less power from the engine than a loaded coil, even though the current and hence the coil's magnetic field are similar, I can give you the answer - but that's another lesson for another post if you really want to know

.

 

[Knifemaker]

I want to know, but I'm sure I'm not qualified to particularly understand the math.

The poster on the other forum simply said when they ran two heated vests they noticed a marked reduction in fuel economy. I called them on this, just asking to explain why this would be true. Their reply was not as exacting as yours and I felt unsure of their logic. I'm not an electrical engineer but do have some fundamental understanding of physics.

I figured there was some easy to understand principle at work here, like the "conservation of energy" or some such law I was not seeing that applied.

My response was instead the theory he was at the brink of taxing the system running two vests on a system that could just barely support it. Which I think may still be the case... As others reported no noticeable reduction in mpg figures when they used their heated gear. (As his included heated gear for his passenger but failed to make it clear what model motorcycle he discovered this on)

I appreciate the time you took to explain all this.

 

[JimNtexas]

This is an important question! Aren't most of us skimping on milage so we can save up enough down payment to trade in our FJRs for Smart Cars?

 

[mcatrophy]

I want to know, but I'm sure I'm not qualified to particularly understand the math.

The poster on the other forum simply said when they ran two heated vests they noticed a maker reduction in fuel economy. I called them on this, just asking to explain why this would be true. Their reply was not as exacting as yours and I felt unsure of their logic. I'm not an electrical engineer but do have some fundamental understanding of physics.

I figured there was some easy to understand principle at work here, like the "conservation of energy" or some such law I was not seeing that applied.

My response was instead the theory he was at the brink of taxing the system running two vests on a system that could just barely support it. Which I think may still be the case... As others reported no noticeable reduction in mpg figures when they used their heated gear. (As his included heated gear for his passenger but failed to make it clear what model motorcycle he discovered this on)

I appreciate the time you took to explain all this.

A brief search suggests the Bonneville has a generator output rating of 27 amps, or nominally 12 x 27=324 watts (I'm not arguing about 12 or 14 volts). I'd guess that there's not much available for heated clothing after lights, ignition, and on the later ones, fuel injection and ECU have taken their bit. But, of course, that in itself won't explain a big increase in fuel consumption.

The only possible reason I can see is that the rider is using a lower gear to keep the revs up to get the best out of the alternator

.

No problem with my time, I'm retired

.

 

[HotRodZilla]

Has anyone stopped to think that when its cold enough to actually use heated gear to its potential, its cold outside? This means the air is more dense and winter gas is probably being used...decreasing mileage.

All this "increased magnetic field" magician BS sounds like...well...BS. Gimme a break. Just because someone uses big words and you have no idea what they are talking about doesn't make it true.

 

[mcatrophy]

Has anyone stopped to think that when its cold enough to actually use heated gear to its potential, its cold outside? This means the air is more dense and winter gas is probably being used...decreasing mileage....

True, and probably by far more than any extra alternator load.

...All this "increased magnetic field" magician BS sounds like...well...BS. Gimme a break. Just because someone uses big words and you have no idea what they are talking about doesn't make it true.

Nope, doesn't necessarily make it true. Doesn't necessarily make it false, either

.

But somebody has to understand it

, or you'd have no electrical power for anything

.

Hey, I'm not trying to be "clever", the guy asks a question, I try to answer it.

Peace, man.

Sun's shining, I'm going for a ride.

 

[ionbeam]

...All this "increased magnetic field" magician BS sounds like...well...BS. Gimme a break. Just because someone uses big words and you have no idea what they are talking about doesn't make it true.

Then let me use little words and my blunt crayon: mcatrophy +1

 

[HotRodZilla]

I didn't say I didn't know what the big words meant. I was looking out for the dumb members of this forum...Like Howie, Bust, Don, and Skooter. Those poor losers have no idea what's going on.

Sheesh!! :lol:

 

[gixxerjasen]

Easy way to understand all of this without having to delve too far into the physics stuff. See if you can locate either a hand crank or bicycle generator. Try it and then start plugging things in. You'll notice that it gets harder and harder to turn.

I've seen this exact setup at a lot of science museums. They have a hand crank generator and you can flip switches to turn things on that are connected to the generator and allows you to feel the increased load.

 

[mcatrophy]

Easy way to understand all of this without having to delve too far into the physics stuff. See if you can locate either a hand crank or bicycle generator. Try it and then start plugging things in. You'll notice that it gets harder and harder to turn.
I've seen this exact setup at a lot of science museums. They have a hand crank generator and you can flip switches to turn things on that are connected to the generator and allows you to feel the increased load.

Thing is, Knifemaker wanted to know exactly what force was acting on the engine, simply showing that it did act wasn't going to crank his handle sufficiently.

At least, that's how I read it.

Hey, there's a pun in there somewhere

.

 

[gixxerjasen]

Yea, but there was some conversation in there about whether or not the load actually put drag on the engine requiring the engine to work harder.

I actually did very well in physics until we got to the whole electricity bit. My brain doesn't wrap around it so well. Trajectories and weight and inertia, I can visualize that. But all that stuff going on inside those electronics components can't be visualized. I got straight A's till we got there and managed to pull C's on those tests. Gave me a B average but still....

That said, some of the experiments like the one I was talking about at least put some of the concepts into a way that I had "Some" understanding of them. Just trying to help in ways that have helped me.

 

[ionbeam]

Modern diesel trains don't run directly off of the engine, they run off of a main generator driving traction motors at the wheels. This is done to eliminate the need for a transmission. Trains use dynamic braking to slow them down. A dynamic brake is when the traction motors stops being driven by the main generator, causing the free rolling traction motor to be come a generator, then the output of the wheel motor/generator is applied to a 'brake grid' which made of resistors to electrically load up the traction motor. Putting an electrical load (grounding) on wheel generators is capable of stopping a whole train without using mechanical brakes. (A lot has been left out, this is just an overview of how adding an electrical load to a generator causes the generator to strongly have the ability to brake the shaft from turning.) The cars previously mentioned are another example of a dynamic brake.

The opening post muses:

I guess I need someone to explain this to me. On another forum, a member posted that running heated gear lowers your miles per gallon.

I assumed that the stator is always putting out power, so there is no extra "drain" on the engine....thus fuel mileage would be not effected.

How would running more electrical accessories increase the load on the motor to effect fuel consumption?

The charging system in the FJR uses a R/R that dumps power to ground in order to maintain 14.x volts on the charging system. Virtually 100% of the charging capability is either being dumped to ground or consumed by the electrical doodads on the bike. Thus, turning on heated gear simply means that instead of dumping 36 watts of power to ground it is now flowing through the grips or vest. Therefore there as been no additional loading on the stator, the load has just been rearranged.

 

[mcatrophy]

...The charging system in the FJR uses a R/R that dumps power to ground in order to maintain 14.x volts on the charging system. Virtually 100% of the charging capability is either being dumped to ground or consumed by the electrical doodads on the bike. Thus, turning on heated gear simply means that instead of dumping 36 watts of power to ground it is now flowing through the grips or vest. Therefore there as been no additional loading on the stator, the load has just been rearranged.

[edit] Statement revoked.

Errrm - not on the Gen II (and I'd guess most later bikes). The output is switched on and off rapidly, the mark-space controlling the mean current from the alternator and hence the battery voltage. (I seem to remember we've been here before?)

The advantage of this type is reduced wasted power (more importantly less heat to dissipate), the disadvantage is that high voltages can be generated by the open-circuited alternator that must be tolerated by the switch. The latter is easier now with later technology. (And when the coil is shorted it takes little mechanical power as I hinted at above.)

With the short-circuiting regulator, current that would have over-charged the battery is effectively shorted to ground. This dissipates much less power than the older "shunt-to-a-load" type, where the power generated by the alternator (and hence power taken from the motor) is essentially constant regardless of the bike's electrical load.

[/edit]

I've found an article here that describes operation the short-circuit dump type of R/R here. It is something of a simplification, but that's probably a good thing

.

 

[ionbeam]

Errrm - not on the Gen II (and I'd guess most later bikes)...The advantage of this type is reduced wasted power (more importantly less heat to dissipate), the disadvantage is that high voltages can be generated by the open-circuited alternator that must be tolerated by the switch...

PM being sent about this. I deliberately didn't differentiate between the Gen's.

 

[mcatrophy]

Errrm - not on the Gen II (and I'd guess most later bikes)...The advantage of this type is reduced wasted power (more importantly less heat to dissipate), the disadvantage is that high voltages can be generated by the open-circuited alternator that must be tolerated by the switch...

PM being sent about this. I deliberately didn't differentiate between the Gen's.

Hmm - my senility is showing, I've altered my post above - apologies to all our readers.