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garygid
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 3:08 pm

Connect a battery to a resistor (heater), no movement, so no energy?
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EVDRIVER
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 3:16 pm

planet4ever wrote:
EVDRIVER wrote:The creep control is electronic and it uses extra power to do so
Are you sure about the second part of that statement? What I remember from my physics classes is that power is the rate of expending energy, and energy is force times displacement. I was careful to say in my statement earlier that the phase bias applies a force to the motor. But if the motor isn't turning, then there is no displacement, hence no energy, hence no power. It's been more than 50 years since I took my last physics class. Maybe I've forgotten, :? or maybe they've changed the laws. :shock:

What do you propose is holding the motor in place or causing it to "creep", a double unity chip? If you are climbing a hill in a low powered EV and it stops still in place because it can no longer climb are you telling me it is not consuming significant power to hold that position? It's just a magic rubber band of non-energy that does it all:) One can replicate this feature in any EV but pressing the accel pedal on a hill to the point where the EV holds position. I don't know what grade you received in that class but you may have been better off in an electronics class with ohm's law. You could also pull your LEAF up to a concrete wall with the bumper on the wall and push the accel pedal and with the car static and the wheels just before the break-loose point let me know that the kw meter goes unchanged.

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johnr
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 3:22 pm

planet4ever wrote:What I remember from my physics classes is that power is the rate of expending energy, and energy is force times displacement. I was careful to say in my statement earlier that the phase bias applies a force to the motor. But if the motor isn't turning, then there is no displacement, hence no energy, hence no power. It's been more than 50 years since I took my last physics class. Maybe I've forgotten, :? or maybe they've changed the laws. :shock:
There is no work being accomplished in that case, but there is power being used - although the motor isn't turning, the power being applied to the motor is still going somewhere - without the magnetic bias of a spinning motor, the power ends up being dissipated in heating the motor windings instead.
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suresnoi
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 3:25 pm

Note that keeping the car still in a slope, no matter in which direction, by the mean of the electric motor (and not the mechanical brakes) is clearly stated in the manual as a "don't". It is awfully inefficient, obviously.

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EVDRIVER
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 3:32 pm

Physics Grade D-
Electronics Grade F

Night classes opening soon....

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planet4ever
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 5:31 pm

johnr wrote:without the magnetic bias of a spinning motor, the power ends up being dissipated in heating the motor windings instead.
OK, I can believe that.
EVDRIVER wrote:Physics Grade D-
Electronics Grade F

Night classes opening soon....
I object! I still think I'm right on the mechanics. Shouldn't I at least get a B on the physics side? Now, as for electronics, I grew up in the dark ages. I don't think we even had transistor radios yet when I graduated from college. Sure, sure, I spent forty years programming computers, but I never pretended to understand the electronics in them. It was all just logic and math. So I'll accept the F in that course (which I never took).

Now, back to Visual's problem with his driveway ...
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Smidge204
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 5:43 pm

suresnoi wrote:Note that keeping the car still in a slope, no matter in which direction, by the mean of the electric motor (and not the mechanical brakes) is clearly stated in the manual as a "don't". It is awfully inefficient, obviously.
Much the same way as holding a car with a manual transmission on a hill using the clutch is a "don't" :lol:

Worst part is, since the parking brake is electrically actuated you can't really use it as a temporary surrogate for the foot brake - which I guess would apply mostly for manual transmissions again, but from what I heard on these forums the LEAF's brake pedal preempts the accelerator pedal input, so you can't ease off one while pressing the other. A manual hand brake would be perfect for that situation.
=Smidge=

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EVDRIVER
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 5:52 pm

planet4ever wrote:
johnr wrote:without the magnetic bias of a spinning motor, the power ends up being dissipated in heating the motor windings instead.
OK, I can believe that.
EVDRIVER wrote:Physics Grade D-
Electronics Grade F

Night classes opening soon....
I object! I still think I'm right on the mechanics. Shouldn't I at least get a B on the physics side? Now, as for electronics, I grew up in the dark ages. I don't think we even had transistor radios yet when I graduated from college. Sure, sure, I spent forty years programming computers, but I never pretended to understand the electronics in them. It was all just logic and math. So I'll accept the F in that course (which I never took).

Now, back to Visual's problem with his driveway ...

No, it always requires energy to counter an opposite force, how much more of a basic physics example could it be. If you don't agree, put your car on a slight hill and remove the brake, hold the car in place buy pushing the opposite direction on the back and let me know if you get tired. If not you are not using energy. Look up double unity devices, as much as some on U Tube want us to believe they exist, they don't.

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garygid
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Re: Rolling in reverse (backing up slope)

Fri Jan 14, 2011 8:42 pm

On flat land, in R, with feet-off, does the LEAF "creep" backward?
See SOC/GID-Meter and CAN-Do Info
2010 Prius, now for sale
2011 LEAF, sold in 2015
2018 Tesla Model 3
2014 Tesla S, Model 3 in 2019
PU: SDG&E
Solar PV: 33 x 225W -> 7 kW max AC
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AndyH
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Re: Rolling in reverse (backing up slope)

Sat Jan 15, 2011 8:16 am

Visual wrote:I haven't used the "hand brake", which is actually electronic, and it would help since it disengages automatically when you hit the accelerator (our Audi has the same setup), but the real question is most automatics don't roll in the opposite direction, even when you're on a slope, so it caught me by surprise.

I checked again tonight when I got back home, and it rolls about 2-3 feet then stops. Still a bit strange - its the kind of thing I'd expect on a manual (when you take your foot off the brake and your clutch is still in, it starts rolling until you let the clutch out).

Nothing I can't handle, just a little unexpected - will probably bother my wife more ;)
I have the same challenge with my wife's Pontiac Vibe/Toyota Matrix automatic. It's downhill into the garage. The car will roll forward even when the transmission's shifted into reverse. I have to hold the brake and bring in some throttle.

The car will stay in place when in park, and with the parking brake set, but will roll downhill in either direction until there's enough hydraulic pressure in the transmission to counter gravity.

Her previous car was a Saturn Vue and it behaved the same.

I've never had an automatic transmission - I need to find the Leaf's clutch and learn how to down-shift. ;)

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