How many turtles did you get today?

<div class='quotetop'>QUOTE(formerVWdriver @ May 28 2007, 04:18 PM) [snapback]451177[/snapback]</div>

Hey, I resemble that remark! I never thought anything would reform my leadfoot ways, but the Prius did. Just tell your family that you decided it was far better to be a law-abiding citizen and set a good example to other motorists by adhering to lawful speed limits.

 

Heh...we call 'em "turtles" too.

So far, nobody has painted a bunch on the driver's door, like wartime aviators.

 

It is so liberating for me to realize that I'm not the only one who sees turtles on the consumption screen! I think it's from reading "Yertle the Turtle" when I was little.

 

Haw! I was afraid this was going to be another roadkill thread.

I have only had my Prius three weeks, but I'm still a little fuzzy on what the turtles are about. I mean I can understand kW regenerated in principle, but haven't been able to match the appearances of the turtles and what is happening with the car up in my head.

 

Not just leafs, some Lexus / Toyoa MFD's display squares, others, little cars. Somewhere this came up before, and posted 'em for the 'unbelievers'.

 

<div class='quotetop'>QUOTE(formerVWdriver @ May 29 2007, 08:09 AM) [snapback]451411[/snapback]</div>

Actually, there is a turtle icon that shows up when the battery is extremely low and can't be used for acceleration (so you have to drive slow until the battery recharges), but that's on the dashboard somewhere.

These "turtles" (leaf-cars) represent energy recaptured from regenerative braking. So a lot of leaf-cars mean you did a lot of braking. Since this is not 100% efficient process (80%?), and using the energy from the battery also has a loss (10%), you will get lower mpg than when slowing down without braking and accelerating without using the battery. Preserving 70% of your momentum is better than throwing all the energy away however, which is what non-hybrids do.

 

<div class='quotetop'>QUOTE(Tideland Prius @ May 29 2007, 08:04 PM) [snapback]451553[/snapback]</div>

Figure I get the best mileage when the uphill/downhill ratio/duration matches the battery pack's output. 4,5 l/100 km has been achieved.


Long descents on mountain passes produce multiple turtles and no fuel consumption at all!


A future Prius with three times more battery headroom and twice the ICE power is my wildest dream. Mileage would most certainly be radically improved.


Finally: A converter box on this site that transforms MPG to l/100 km or the other way around would be very useful for all Prius chatters living on the metric areas of planet earth...

Could it be done?

 

<div class='quotetop'>QUOTE(nerfer @ May 29 2007, 10:06 AM) [snapback]451506[/snapback]</div>

You're being WAY too generous. There's no way you're getting over 50% back. I don't think you even get 25% back. My educated guess puts it somewhere between 10 and 20%.

Your reasoning is right on though, of course. The fewer turtles you get, the better your gas mileage will be (unless of course you are just coasting down hill!).

And this is a different situation in a real EV where ALL your power comes from the battery and almost all your slowing goes back into the battery (in the case of a good EV, you can recover about 50% of your energy.)

 

<div class='quotetop'>QUOTE(tiger roach @ May 29 2007, 09:33 AM) [snapback]451418[/snapback]</div>

kWs ? My Prius only says Watts regenerated. Did I get a lemon !!!

 

<div class='quotetop'>QUOTE(formerVWdriver @ May 28 2007, 06:18 PM) [snapback]451177[/snapback]</div>

I laughed out loud when I read this because when I first got Phoebe I thought the symbols were rabbits. :lol: Now, when I read this I'm thinking literally of the Hare and the Tortoise and thinking there's more than a modicum of truth buried here.

 

<div class='quotetop'>QUOTE(Rick Auricchio @ May 28 2007, 09:34 PM) [snapback]451263[/snapback]</div>

<div class='quotetop'>QUOTE(formerVWdriver @ May 29 2007, 08:09 AM) [snapback]451411[/snapback]</div>

That's a really good idea! but to avoid the roadkill misinterpretation, you could just do a leaf, instead of a leaf textured car. easier to paint too. but then I guess that could be misinterpreted as killing leaves....

 

<div class='quotetop'>QUOTE(ystasino @ May 30 2007, 09:28 AM) [snapback]452056[/snapback]</div>

Did you not get the matter/antimatter booster option?

 

<div class='quotetop'>QUOTE(darelldd @ May 30 2007, 12:51 AM) [snapback]451910[/snapback]</div>

I've heard this low efficiency for regenerative braking before but never quite understood why. A few searches here gave just dribs and drabs of information but no coherent explanation.

A post by Hobbit here:

http://priuschat.com/index.php?showtopic=1...iency&st=20

notes that braking current is limited at 100A so even moderate braking at speed may engage the hydraulic brakes.

So, I get that -- if you hit the brakes hard you exceed the regen capacity. And I understand that you have friction brakes at low speed.

Beyond that, is it the electrical heating loss from high current flow that is the limiting factor that kills the efficiency of regenerative brakes? I vaguely recall that the heat loss is proportional to the square of the current. If so, there would seem to be gains to be had from braking as slowly as reasonable.

Anyway, that's my question. Putting aside the issues of exceeding the regen limit of 100A, and the use of friction brakes at low speed, is it the heat caused by high current that kills the efficiency of regenerative braking? And if so, does that mean slow braking (aka coasting to a stop) gives higher energy recovery? If so, anybody know how much higher?

I have to believe the 10-20-30% figure that gets kicked around is an average. How do I beat the average?