smkettner
Well-known member
Nissan does say no to 4 down towing such as behind a motorhome.
Can't see it would hurt anything while driving.
Can't see it would hurt anything while driving.
It has been done.smkettner said:Nissan does say no to 4 down towing such as behind a motorhome.
Can't see it would hurt anything while driving.
NeilBlanchard said:Coasting is best when you need to carry speed, and regen is best when you need to slow down. Friction brakes are only for emergencies and the last few MPH when coming to a stop, when regen no longer works. If you come into a stop too hot, you have already wasted the energy, and you only heat up the brakes; which is a total waste...
While it is true that "neutral" in an EV doesn't involve disconnecting a transmission to an engine, it seems like a reasonable term to describe what actually happens in an EV: no magnetic field is applied to the motor's rotor, so it can spin without any forces being generated.kubel said:Correct me if I'm wrong, but the way I understand it, neutral isn't really neutral. If the front wheels are spinning, you are also spinning the reduction gears and the electric motor since everything is fixed. In any other car, putting the transmission into neutral or pressing the clutch will decouple the engine from the drive wheels, allowing the engine to run (or not run) independent of the motion of the wheels. Not so on the LEAF and other EVs...
So are there no fixed magnets in the LEAF's motor? Any place on line where they have an inside view of the motor?dgpcolorado said:While it is true that "neutral" in an EV doesn't involve disconnecting a transmission to an engine, it seems like a reasonable term to describe what actually happens in an EV: no magnetic field is applied to the motor's rotor, so it can spin without any forces being generated.
w4y said:TickTock said:You probably should actually read a post before stating it is false. My comment remains correct and yet doesn't contradict anything you stated (which is also correct).
You overestimate the efficiency of regen (Hint: It's not very efficient). There are plenty of anecdotal evidence (here, Tesla forums, etc) that suggests coasting during downhills is more efficient than regen in almost all cases.
In this case, coasting is the clear winner, as 54 vs 50 MPH does not increase drag coefficient very much (probably 5% more). Regen will be much lower than this.
Other case is if you mess up and shift to Reverse below the speed threshold which I think is 7 mph, the motor will nearly instantly attempt to change direction.kubel said:...Nothing mechanical happens when you "shift" (except when you go to park, the parking pawl engages if you're going slow enough).
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In the first scenario, your battery may have the same amount of energy, but you have stored up additional kinetic energy. In the second scenario, you have stored more chemical energy in your battery, but your kinetic energy is unchanged.TickTock said:It doesn't matter how efficient regen is, in this scenario it is still better even if only 1% efficient. I will restate my post thusly: You are cruising down a mountain, in one scenario you let the drag maintain your speed at 54 mph. You get to the bottom with the same energy in your battery as you had a the top. In the other scenario you let regen recover some of that energy and hold your speed at 50 mph. Now, at the bottom of the hill you have traveled the same distance yet have more energy in your battery than you had at the top. How is the first scenario (coasting) better for efficiency?
For a short hill and 1% I would agree so, yeah, you're right, it does matter. The difference in kinetic energy at 54 mph and 50 mph comes to .019kWh or ~1/4 gid. OP says the hill is 1/4 mile so his break-even point is if his regen at 50mph produces 3.8kW. If less then coast, if more then regen.RegGuheert said:In the first scenario, your battery may have the same amount of energy, but you have stored up additional kinetic energy. In the second scenario, you have stored more chemical energy in your battery, but your kinetic energy is unchanged.TickTock said:It doesn't matter how efficient regen is, in this scenario it is still better even if only 1% efficient. I will restate my post thusly: You are cruising down a mountain, in one scenario you let the drag maintain your speed at 54 mph. You get to the bottom with the same energy in your battery as you had a the top. In the other scenario you let regen recover some of that energy and hold your speed at 50 mph. Now, at the bottom of the hill you have traveled the same distance yet have more energy in your battery than you had at the top. How is the first scenario (coasting) better for efficiency?
The answer to which one leaves you with more total energy at the bottom of the mountain depends on the efficiency of the regen, the amount of aerodynamic drag and the length and slope of the mountain. If your regen is only 1% efficient (your number) and the mountain is short, then you likely are better off coasting.
dgpcolorado said:While it is true that "neutral" in an EV doesn't involve disconnecting a transmission to an engine, it seems like a reasonable term to describe what actually happens in an EV: no magnetic field is applied to the motor's rotor, so it can spin without any forces being generated.kubel said:Correct me if I'm wrong, but the way I understand it, neutral isn't really neutral. If the front wheels are spinning, you are also spinning the reduction gears and the electric motor since everything is fixed. In any other car, putting the transmission into neutral or pressing the clutch will decouple the engine from the drive wheels, allowing the engine to run (or not run) independent of the motion of the wheels. Not so on the LEAF and other EVs...
For those new to EVs, the rotor in the car's electric motor is directly attached, via a reduction gear system, to the wheels (front, for the LEAF). The rotor always spins when the wheels spin. When the battery is used to apply magnetic fields to the motor, a force is generated that causes the rotor to spin forwards or in reverse, depending on the field polarity. The magnetic fields can also be used to turn the motor into a generator so that the kinetic energy of motion causes electricity to be generated and returned to the battery; this is used for "regenerative" braking. If no fields are applied, the rotor (and wheels) spin freely, which we call "neutral". This can be achieved by selecting N on the shifter or by keeping the accelerator pedal positioned at zero power (= no magnetic field).
Regardless of whether or not magnetic fields are applied to the motor, the rotor always turns in one direction if the wheels are moving forward and in the opposite direction if the wheels are moving in reverse. Since the rotor is directly linked to the wheels, its speed of rotation is always proportional to the speed of the wheels.
Why would you think you would need a gear change to be in reverse?NeilBlanchard said:...
When you put the Leaf in reverse - is it really in reverse? There is no gear change ...
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This is an over-simplification. As Reguheert pointed out a couple posts up, it really depends on the length of the hill and how much regen. In the OP scenario, you can easily calculate this to be 3.8kW of regen (assuming the driver adds 165 lbs to the total weight of the car). If using regen to slow from 54 to 50 for a quarter mile results in 3.8kW or more, then it is a win to use regen. If not then coasting is better.NeilBlanchard said:So, when you need to carry speed to continue your drive, then coasting will always be better.
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NeilBlanchard said:So, when you need to carry speed to continue your drive, then coasting will always be better.
When you need to slow down, or limit your speed down a slope, then regen is better than friction brakes.
An interesting question. Yes, the LEAF motor uses permanent magnets (the Tesla uses a pure induction motor, so no permanent magnets and the rare earths needed to make them, but it is reported to be less efficient).jpadc said:So are there no fixed magnets in the LEAF's motor? Any place on line where they have an inside view of the motor?
TimLee said:Why would you think you would need a gear change to be in reverse?NeilBlanchard said:...
When you put the Leaf in reverse - is it really in reverse? There is no gear change ...
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Just because ICE vehicles had to use a transmission to accomplish reverse because an engine cannot spin in the reverse direction, does not mean an electric vehicle needs to do the same thing.
So in an electric vehicle changing the motor rotation and moving the vehicle backwards is reverse.
Similarly when Neutral is selected and the motor is not providing motive power, that is by definition Neutral.
In an electric vehicle there was no need for a clutch to accomplish Neutral.
It is better for the motor to stay spinning at the speed matching the speed the vehicle is moving.
Less stress when the motor is put back into providing motive force.
Only drawback is the slight drag from the single speed transmission gears spinning in the oil bath.
But that is small, and clutches are a chronic maintenance problem on ICE vehicles.
There was no justification to have one on an electric vehicle.
TickTock said:This is an over-simplification. As Reguheert pointed out a couple posts up, it really depends on the length of the hill and how much regen. In the OP scenario, you can easily calculate this to be 3.8kW of regen (assuming the driver adds 165 lbs to the total weight of the car). If using regen to slow from 54 to 50 for a quarter mile results in 3.8kW or more, then it is a win to use regen. If not then coasting is better.NeilBlanchard said:So, when you need to carry speed to continue your drive, then coasting will always be better.
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kubel said:Correct me if I'm wrong, but the way I understand it, neutral isn't really neutral. If the front wheels are spinning, you are also spinning the reduction gears and the electric motor since everything is fixed. In any other car, putting the transmission into neutral or pressing the clutch will decouple the engine from the drive wheels, allowing the engine to run (or not run) independent of the motion of the wheels. Not so on the LEAF and other EVs.
In other words, the "shifter" is entirely software controlled and is more like a mouse controlling what software does than it is a gear selector mechanically choosing gears. Nothing mechanical happens when you "shift" (except when you go to park, the parking pawl engages if you're going slow enough).
So, no damage will come- though I don't find it particularly beneficial myself. I never shift into neutral unless I'm screwing around or a purse nudges the shifter out of drive and I'm left puzzled for a half second as to why my car lost all power.
TickTock said:w4y said:TickTock said:You probably should actually read a post before stating it is false. My comment remains correct and yet doesn't contradict anything you stated (which is also correct).
You overestimate the efficiency of regen (Hint: It's not very efficient). There are plenty of anecdotal evidence (here, Tesla forums, etc) that suggests coasting during downhills is more efficient than regen in almost all cases.
In this case, coasting is the clear winner, as 54 vs 50 MPH does not increase drag coefficient very much (probably 5% more). Regen will be much lower than this.
It doesn't matter how efficient regen is, in this scenario it is still better even if only 1% efficient. I will restate my post thusly: You are cruising down a mountain, in one scenario you let the drag maintain your speed at 54 mph. You get to the bottom with the same energy in your battery as you had a the top. In the other scenario you let regen recover some of that energy and hold your speed at 50 mph. Now, at the bottom of the hill you have traveled the same distance yet have more energy in your battery than you had at the top. How is the first scenario (coasting) better for efficiency?
Regen really isn't that bad. It is true that you only recover ~39% (according to the Leaf Technicians workbook) of your kinetic energy when you regen to a stop but that is because you are losing energy to frictional losses - all of which are still present when you coast. Removing the frictional losses from the equation since those exist with or without regen, at least 61% recovered based on actual measurements (Hint: eschew anecdotal evidence). Finally, speed is, by a wide margin, the #1 contributor to range. Drag increases square law to speed (double your speed --> quadruple your drag). However, you are also going faster so your losses per distance only increases linearly so 54 mph will cost you 8% more energy than going the same distance at 50 mph.
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