Wh ????

It's a way of quantifying energy. 1 Whr is the equivalent of 1 watt of power for the duration of 1 hour.

 

Each little leaf car is enough recovered energy to run a 50 watt light bulb for one hour.

Tom

 

(here comes an equation dont flip out)

Power (P) = Work (W) / Time (t)

The units of P are Watts (W)
The units of W are Joules (J)
note: one joule is how much energy it takes to move 1 newton (.2 lbs) 1 meter (3 ft) forward.

The units of t are seconds (s).

So the equation in units is

Watts = Joules per second

if you make time into units of hrs (3600 s) and bring the time over to the left side of the equation you get

P*t = W

or in units

W hrs = J

to get Kilowatt hrs just multiply each side by 1000 to get

kW hrs = kJ


My question is does 50 kwhrs (1 car) equal 1 bar in the energy screen?

 

I'm too tired to think, but you are off by a factor of 1000. I don't flip between the screens often but IMO the SOC fluctuates too much to draw a correlation. Since bars show SOC isn't that voltage?

 

You are off by 1000 as noted above. A new traction battery can store:

6.5 amp-hours*200 volts = 1.3kwatt-hours of energy

Only about 1/2 of that is available for use as the traction battery is never fully discharged or fully charged to promote long life. So one of the eight "bars" is about 750 watt-hours of energy in a new traction battery (maybe 1/3 of that in one after 150,000 miles of use) so that's about 4 to 12 little cars.

JeffD

 

yea my bad i was thinking about my utility bill (measured in kwhrs) at the time

did you mean that all the 8 bars = 750 watt hrs of energy?

 

More info here:
Toyota Prius Battery Specs - EAA-PHEV

All bars are not created equal

Rob

 

Something struck me about this; what do you all think?

It seems that the potential regenerated energy can't amount to very much.

Under reasonably good conditions, you might be able to regenerate two car symbols [100 w-hrs] per bar, or every 5 minutes. If you do that for an hour, you've regen'ed 1200 watt hours, or 1.2 kw-hrs, or ~ 4000 btus of energy. In that hour, if you averaged 30 mph with the car, you used at least half a gallon of gas, or ~ 60,000 btus.

So what was regenerated was about 7% of the usage -- not very much, and not a signifcant factor in why we can get ~50 mpg vs. 30 with a comparable non-hybrid. [With regen alone, the 30 mpg would go up to 32.]

I had always thought the regeneration was a bigger deal than this!

 

The big deal is that the small amount of energy stored in the battery is available to help accelerate the car. This allows the use of a small, efficient ICE in a mid-sized car without sacrificing too much performance. The small engine plus the management of the ICE so that it always rums in an efficient mode accounts for much of the improvement in MPG over other cars (another factor - low wind resistance).


JeffD

 

You also get the benefit of your brakes lasting darn near forever.

 

I've got this same rundown sitting in some old threads, but here
it is again... assuming a human in fairly good shape can produce
250 watts, or about a third of a horsepower, under fairly optimal
conditions ... if you can do that for an hour, that's 250 watt
hours, and you'd be mighty tired. So to get a good feel for
what each of those green cars is worth, what you do is this:
put the car in Neutral, have someone else sit in it and steer,
and get behind it and push it around in the parking lot as fast
as you can for twelve minutes. That's 50 watt-hours, roughly.
.
_H*

 

Correct. Four green cars is about enough energy to accelerate once from 0 to 60 MPH. Most of the benefit of the battery comes not from regeneration, but from load leveling: it allows the engine to be smaller and to spend most of its time running in its optimal power and RPM range.

 

You said it right when you said t was in seconds.

A W hr is 3600 J, so 50 W hr is 180 kJ.

That's enough energy to lift 1500 kg (a Prius plus 1 fairly heavy person) a vertical distance of over 12 m (~40 ft).

As for the bars on the consumption screen, I can only guess.
But if 8 bars represents 40% of the battery capacity (IIRC no bars being 40% full and all 8 bars 80% full), each bar is 5% of the battery capacity.
If battery capacity were 1 kW hr, then one bar would be 50 kW hr.
You've probably made a good guess. Actual battery capacity is supposed to be about 1.3 kW hr. Perhaps a bar is supposed to 50 W hr, after compensating for less than 100% efficiency of the NiMH batteries in providing power to the MGs.

As I said, only a guess.

Dave M.

 

Of the Prius information displays, I find the regenerated power graph to be useless eye candy, as is the inane power flow pictograph with the crudely rotating wheels. Give me one display with four bars - Hybrid battery SOC, Hybrid Battery ammeter, instantaneous MPG and a bar telling me what position the accelerator pedal potentiometer is at, and at what point the ICE will be activated if I am driving in "EV" mode. As for numbers, other than what might be displayed under the bars, trip and overall MPG would be ideal. I wish the present power flow display would show you whether or not the ICE is running. Though the docs state it will be at least turning over at speeds of 42mph and above, it seems from the feel and behavior of the system that there may be some conditions at higher speeds where it might not be running...

 

If the instantaneous mpg reading is 99 mpg, I would assume that the gasoline engine probably is not "running", although the crankshaft will be spinning above ~42 mph.

To be sure, you would need another gauge that shows whether the fuel injectors are metering out gasoline. Or, maybe an LED could be connected to the wire harness for a fuel injector, hooked up so that it would blink as voltage pulses trigger an injector.

 

A second thought about what I wrote:

Granted, what you all responded is true, that most of the benefit of the battery comes not from regeneration, but from load leveling, etc.

But I neglected in my calculations that the motor is more efficient than the engine [perhaps 80% vs. 30%?]. Thus the energy regenerated to the motor is worth proportionally more than the same amount of energy in the raw gasoline I would otherwise have to buy.

Thus I would revise my estimate of a potential reasonably good regeneration savings to 20% [vs. 7%], and a contribution of an increase in mpg from 30 to 36.