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Energy wasted braking

5K views 22 replies 6 participants last post by  PStechPaul 
#1 ·
So I've always been a big fan of coasting toward red lights/stop signs, and probably do so more in an EV. I especially enjoy when I've annoyed someone to the point where they switch lanes and rev the engine to pass me just so they can sit at the red. More often than not I can approach the light as it turns green doing 30 and speed past dummy as he's doing 5 mph and I'm doing 40.

Anyways, the goal is usually to get down to 30 or 35 before I have to brake, and I'll often try to go much lower if there's no one behind me, and I was wondering how much energy is actually saved by doing this.

Assuming 1000 kg vehicle that gets 250Wh/m I get the following values:

mph: joules = energy saved (if coasting to a stop from this speed)

45: 225534 = 63 Wh
40: 178200 = 49.5
35: 136434 = 38
30: 100237 = 29
25: 69609 = 19

So this would lead me to beleive that if I were to coast from 45 mph, I could go 1/4 mile, but it seems like I should go much further than that. It feels like I'm doing at least 1/4 mile just by coasting from 45 down to 30. Why is that? What is a typical coaster distance?
 
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#5 ·
Tires, Bearings, Gearing, Wind Drag, Slight variations in the road, and an assortment of other tiny things can affect your coasting distance. Each EV would be different. There is no way to have them all the same. Do you remember Jack's cost tests with his vehicles? There is also a point of obsession and reason.

Pete :)
 
#7 ·
Yeah, I never coast unless I have a need to slow down, so no time is being wasted, unless you think the foot needs to be on either the gas or the brake at all times to 'save time'. Many people around here think they need to be going at least 5 over before they're allowed to slam the brakes for a stop sign or light.
 
#9 ·
SUV dude the other day, changes lanes 4 times in 1 block before the lineup at the light. End result, in front of me instead of behind me. 2 miles and who knows how many lane changes later before he turns left as I go straight. I had really been hoping for one of the people he cut off to clip him.
 
#10 ·
Nevada state law makes it a sin to go less than 5 over the posted.

That is why I wanna see +$5.00 a gallon. And then those idiots whine about prices like low cost is a God given right.

Back to the topic: Any changes noted using all this coasting? perhaps less time to charge, or better SOC? Was it quantifiable?
 
#13 ·
Back to the topic: Any changes noted using all this coasting? perhaps less time to charge, or better SOC? Was it quantifiable?
I'm running a JLD404 AH counter now, so I can actually measure small changes. I should try driving angry ICE style (one pedal at all times) sometime and see just how bad it is.
 
#11 ·
$5 will change nothing for the SUV, it's only the people who are already hurting that will hurt more and keep trying to change.

No real changes here, I was just trying to quantify the effects of regular behavior. The only times I could tell a noticeable difference from coasting was when I had a dying lead pack where missing a single red made a significant difference in watts to get home.

One possible application would be to look at the numbers and see if there's much difference in pulse driving vs cruising. A lithium system with ah counting would probably make it much easier, as my lead seem to each pretty much anything in charge cycle overhead.
 
#15 ·
I messed around with the brakes over the weekend, so I don't know what my average usage is now, but yesterday it was about 275 wH/m

I angry ICE'd it today and got 339 wH/m. Got pretty tired from all the pedal action and motor was pretty toasty at the end. Not something I'd care to repeat, but an interesting experiment.
 
#16 ·
I have an EV calculator on my website at http://pstech-inc.com/VehiclePower.xls, and when I used a total vehicle weight of 2500 pounds, at 50 MPH, the kinetic energy is 80 W-H. So if your vehicle normally uses 4800 watts, you waste about one minute of run time. It can be calculated using M*V^2.

In terms of cost, at $0.10/kw-h electricity, it is really insignificant. Here is a handy calculator: http://www.1728.org/energy.htm
 
#21 ·
Good points! :) And even more significant may be the energy needed to accelerate back to 50 MPH after each of those wasteful stops. :rolleyes:

For my own purposes, I want to see if it's possible to achieve a sort of "over unity" by driving my electric vehicle uphill, unloaded, and then come back down with a heavy load of firewood, and use regenerative braking to recoup what was expended and even register a net gain! :cool:
 
#23 ·
Ah, but that's not over unity. How much power did it take to grow the rice that you fed your peasants to carry the wood up that hill?
Actually it's solar and wind power, since the wind blew the seeds there and the sun provided power to make the trees grow. And I had to use a lot of power to cut the trees into logs and split them. I could possibly use the tractor's batteries for an electric chainsaw, but that would greatly skew the results. Then again I could use the wood with a steam power plant on the tractor, to avoid using fossil fuels.

Also, all sources of power on the earth are ultimately derived from solar power which in turn is nuclear fusion. And nuclear fusion in stars originally formed radioactive elements that we use in fission reactors.
 
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