Power use at a stop light

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smkettner

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Joined
Aug 10, 2010
Messages
7,501
Location
Orange County, CA
Does Leaf power the traction motor while stopped for a light? Since the Leaf will roll on its own power (idle?) with the brake off I am curious if that power is provided to the traction motor with the brake peddle holding the car.

Can Leaf be power braked? Apply power to the motor at the same time as the brake holds the car?
 
Most likely the LEAF will only power the motor when the brake is NOT pressed.

Take the foot off the brake, and a little power goes to the motor to simulate
the ICE car's now-familiar (to most) automatic transmission "creep".
 
even my Prius has "creep", it's all about "simulating" the experience of an automatic transmission on an ICE car. I think it's not really needed, but all of the mfrs
seem to do it...
 
Could be for safety. If you creep on a hill it is less likely to roll back after releasing the brake. If they allow power with the brake applied then there is no safety measure to cut power in an unintended acceleration so they may not allow power plus brake at the same time, the creep helps solve the roll back issue. And there is no mechanical e-brake to rely on like in a manual. Drive a stick Audi with an electronic parking brake and on a steep hill and see how it differs..
 
evnow said:
Anyone know - why the auto has creep ?
It's a function of the torque converter, which is the auto-tranny version of the clutch and pressure plate in a manual. It is basically a hydraulic coupling device--the auto tranny is never completely disconnected from the engine (as a mechanical clutch does in a manual), it is still spinning even when the car is at idle and stopped, and generating some torque from the circulation of the fluid inside, which is transmitted through the gears to the wheels (if the car is not in neutral). Depending on its "stall speed" setting, this "residual torque" may be enough to hold the car in place on a slight hill, or creep forward on the level if no brake is applied.

TT
 
If nothing else, this would be nice to know as the constant term in the power equation. But it would also depend on Environmental Control Settings a great deal. If you're heating the cabin in winter most of your idle energy is probably going into the coils.
 
if the Leaf is sitting still at a stop light - assuming that the climate control is OFF - in READY MODE, the only power consumption is being drawn from the lead acid battery (low voltage). the traction motor requires no high voltage current in the idle state.

in other words, leaf sitting still (climate control OFF) is no different than any car sitting with ignition in ACC

-n-
 
That doesn't explain the high Wattage shown at idle. (250W?)

What about the brake booster? The soft-start "tug" at the wheels to make it feel like an automatic?
Inverter leakage/losses?
 
23doctor said:
if the Leaf is sitting still at a stop light - assuming that the climate control is OFF - in READY MODE, the only power consumption is being drawn from the lead acid battery (low voltage). the traction motor requires no high voltage current in the idle state.

in other words, leaf sitting still (climate control OFF) is no different than any car sitting with ignition in ACC

-n-
So you are saying the creep is not powered until the brake is released?
So does the brake disable the throttle to prevent "powerbrake" ?

Where is the info from.... documentation or test drive?
 
I doubt very much that power is wasted running the electric motor against the friction brakes to provide the "creep".

The system is a control loop and the "creep" is electronically added at low/no speed depending on the position of the brake peddle. At some point the mechanical friction brakes are engaged and all power is removed from the motor. I'm sure that Nissan spent a considerable amount of time blending these things together and providing the "creep" of a automatic transmission car.

I personally wish they wouldn't have did this but it seems to make sense if you want the car to feel like a gas car.
 
garygid said:
In ACC the inverter (driver for the motor) would likely be OFF, but at a Stop, that circuitry would be ON.

Also, Brake lights will be ON, otherwise you would be "creeping".
But surely brake lights are powered by the 12v battery, which 23doctor excluded from his statement. As for the inverter, would it need more than a couple of watts if no power is going through it?
 
I suspect this:
When the LEAF is ON, the HV battery really powers everything, and the 12v battery might even be charging. The DC to DC converter will supply all the 12v power, powering the 12v buss while it is also "maintaining" the 12v battery that is on that same buss.

With the car OFF, the 12v buss will only be powered by the 12v (nominal) battery. Only then, will the 12v battery be supplying power ... to anything ON and powered by the 12v buss.
 
garygid said:
I suspect this:
When the LEAF is ON, the HV battery really powers everything, and the 12v battery might even be charging. The DC to DC converter will supply all the 12v power, powering the 12v buss while it is also "maintaining" the 12v battery that is on that same buss.

With the car OFF, the 12v buss will only be powered by the 12v (nominal) battery. Only then, will the 12v battery be supplying power ... to anything ON and powered by the 12v buss.


This is correct. The loads will be the alarm, acc switched loads, car communications, etc.
 
a little off topic, but regarding creep feature, you can always put on the parking brake while at the light. It will automatically shut off when you step on the accelerator (hill start mode).
This would be my first car without a clutch and I'm not used to keeping a foot on the brake
pedal at a stop light (on flat surface). I guess a little more power needed to engage the parking brake?
 
In manually turning the Parking Brake OFF and ON, there appeared to be a 1 to 2 second delay after activating the parking-lever (lever-switch) before the "parking-brake" LED (on the lever) went OFF or ON.

So, that might be the time needed to pressurize (or depressurize) the parking brake system?
 
There is a motor driven mechanical system to engage/disengage the rear wheel emergency brake (it uses the rear disk calibers and has a mechanical override in the trunk) and a similar system to engage/disengage the front wheel parking brake pawl (it's uncertain how/if this one can be manually overridden). Both take a certain amount of time to operate, thus the delay.

Tom


garygid said:
In manually turning the Parking Brake OFF and ON, there appeared to be a 1 to 2 second delay after activating the parking-lever (lever-switch) before the "parking-brake" LED (on the lever) went OFF or ON.

So, that might be the time needed to pressurize (or depressurize) the parking brake system?
 
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