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Towing a Tesla at 70 MPH replenishes battery at fast charger rates

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Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#51

Post by hourislate »

codeulike wrote: post #48
lapetitejort wrote: post #29

Earlier quoted context omitted.

That would be a neat test. Find a steep hill, preferably as straight as possible, and test how many times an electric car can traverse it before running out of batteries. Would the distance traveled exceed that on a flat road with no generation? By how much? I'm sure someone in San Fran has already tested this.

Would the distance traveled exceed that on a flat road with no generation? No. Climbing the hill the car uses extra energy (compared to a flat road) because its fighting gravity. On the way back down the hill regen will recover some of that gravity-fighting energy but nowhere near all of it.

This scenario is a little different than a car but a Swiss company is experimenting with a Komatsu Dump Truck that basically recharges its battery using regen braking on it's trip down so it has enough power for the trip up. It actually generates a surplus of an extra 10kwh because the truck is carrying a full load down.

https://phys.org/news/2017-09-e-dumper-world-largest-electri...

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#52

Post by croon »

TheSoftwareGuy wrote: post #46
seanmcdirmid wrote: post #32

Earlier quoted context omitted.

+3 miles hopefully didn’t include the energy spent going up, or the law of energy conservation would have been broken.

I think the wind at his back is key here. His car was acting like a wind turbine

I think OP meant winding and not windy, but even if not, Teslas (and any other car) are designed to be aerodynamic, not the opposite, so it's quite impossible to yield more energy than it cost in that scenario, even ignoring motor efficiency, regenerative braking efficiency, and every other real world inefficiency.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#53

Post by rektide »

Random piece of trivia i found interesting, the dash shows a watthours/mile used view while towing.

There's a good bit of variance as the video goes on, but there's a couple periods where it seems to top out at -1200 watthours/mi. 54 mi/h * 1200 w*h / mi = ~65kW watts (87 HP) charging, which is a common rate from superchargers.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#54

Post by Retric »

sokoloff wrote: post #45
Retric wrote: post #33

Earlier quoted context omitted.

It’s likely fine, 65 kW is only ~85 HP. Simply maintaining highway speeds is ~25HP, so as far as the tire is concerned it’s the equivalent of mild acceleration or breaking. The regenerative breaking system is likely designed for long mountain roads, so it might overheat but probably not.

65 kW is a little over 87 horsepower (parent previously claimed ~80 HP, now edited to 85). To get 65 kW into the battery, you have mechanical and electrical conversion losses on top of that. The tires are seeing pretty close to 100HP.

That really depends on what the 65 kW being displayed represents. If it’s the AC power from the regenerative breaks that should be extremely efficient, post AC/DC conversion things look worse etc.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#55

Post by sokoloff »

Retric wrote: post #54
sokoloff wrote: post #45

Earlier quoted context omitted.

65 kW is a little over 87 horsepower (parent previously claimed ~80 HP, now edited to 85). To get 65 kW into the battery, you have mechanical and electrical conversion losses on top of that. The tires are seeing pretty close to 100HP.

That really depends on what the 65 kW being displayed represents. If it’s the AC power from the regenerative breaks that should be extremely efficient, post AC/DC conversion things look worse etc.

The article claim is pretty clear:

> putting back electricity into the batter[y] at a rate of 65 kW

The article could be wrong, of course.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#56

Post by ols »

The most spectacular example of regenerative braking are trains that are used in Scandinavia, heavily loaded with iron ore that is transported to the coast:

"In Scandinavia the Kiruna to Narvik electrified railway carries iron ore on the steeply-graded route from the mines in Kiruna, in the north of Sweden, down to the port of Narvik in Norway to this day. The rail cars are full of thousands of tons of iron ore on the way down to Narvik, and these trains generate large amounts of electricity by regenerative braking, with a maximum recuperative braking force of 750 kN. From Riksgränsen on the national border to the Port of Narvik, the trains use only a fifth of the power they regenerate. The regenerated energy is sufficient to power the empty trains back up to the national border. Any excess energy from the railway is pumped into the power grid to supply homes and businesses in the region, and the railway is a net generator of electricity." (via https://en.wikipedia.org/wiki/Regenerative_brake#Conversion_... )

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#57

Post by rektide »

pcarolan wrote: post #15

We have trains in chicago that reach whiskers up to charging lines above them. Same as the trolley systems in San Francisco. What if every major city to city freeway stretch had these in a lane for electric vehicles?

Seems like a lot of physical infrastructure spread out over a lot of area for little gain. Little gain because it doesn't feel like charging at fixed stations is so bad, and it's not something folks need to do that often. There's other challenges too. You'd also need to build some system for billing, such that people don't start to steal power. Do we trust the cars to meter themselves? Or do we try to have the line monitor who is using how much power continuously?

Personally i more imagine something like this video, except instead of physically towing a car to run it's generator, the "tow" vehicle is merely a truck with a lot of batteries, battery-powered charger (easy), and charge plug at the end of a boom arm. Folks can summon a on-the-go charger & it follows them around for ~30 minutes & charges them.

I like the big-dream nature of your ask, how it seeks to adapt the infrastructure of the road to the new power modality. It seems dauntingly expensive, but it's certainly going to be more power-effective & material-effective than battery-charger-trucks are.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#58

Post by monkeybutton »

hourislate wrote: post #51
codeulike wrote: post #48

Earlier quoted context omitted.

Would the distance traveled exceed that on a flat road with no generation? No. Climbing the hill the car uses extra energy (compared to a flat road) because its fighting gravity. On the way back down the hill regen will recover some of that gravity-fighting energy but nowhere near all of it.

This scenario is a little different than a car but a Swiss company is experimenting with a Komatsu Dump Truck that basically recharges its battery using regen braking on it's trip down so it has enough power for the trip up. It actually generates a surplus of an extra 10kwh because the truck is carrying a full load down. https://phys.org/news/2017-09-e-dumper-world-largest-electri...

And going up it is empty. Its basically exploiting the fact that rocks at the top of a hill have higher potential energy than at the bottom. If you charged the trucks with wind/solar at peak times and used them to carry the rocks back uphill you could have yourself a very convoluted and mechanically fraught battery!

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#59

Post by unknown_error »

hourislate wrote: post #51
codeulike wrote: post #48

Earlier quoted context omitted.

Would the distance traveled exceed that on a flat road with no generation? No. Climbing the hill the car uses extra energy (compared to a flat road) because its fighting gravity. On the way back down the hill regen will recover some of that gravity-fighting energy but nowhere near all of it.

This scenario is a little different than a car but a Swiss company is experimenting with a Komatsu Dump Truck that basically recharges its battery using regen braking on it's trip down so it has enough power for the trip up. It actually generates a surplus of an extra 10kwh because the truck is carrying a full load down. https://phys.org/news/2017-09-e-dumper-world-largest-electri...

That's actually pretty cool. It's kinda like a dam... harnessing potential energy stored by geologic processes and turning that into power? I'm sure there's some fancy physics word for it that I don't know.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#60

Post by unknown_error »

seanmcdirmid wrote: post #32
unknown_error wrote: post #16

Earlier quoted context omitted.

Show HN: lapetitejort goes hiking, discovers perpetual motion

+3 miles hopefully didn’t include the energy spent going up, or the law of energy conservation would have been broken.

Maybe lapetitejort had better lawyers.
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