EV (electric vehicle) News and Discussion

Forums › Transport (cars, bikes and boats) › EV (electric vehicle) News and Discussion

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#2941140 12-Jul-2022 14:12

SaltyNZ: that's why most EVs don't have a multi-speed transmission. The benefits just don't outweigh the extra complexity and weight. Combustion engines require complex transmissions because of their narrow speed range.

MotorTrend: Where’d My Horsepower Go? Drivetrain Power Loss & The 15% "Rule"

...Strap your 298 [horse power car] to the dyno and you may be disappointed to see little more than 220 to 230 horses measured at the rear wheels. Where did that 60-plus horsepower go?...

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#2941141 12-Jul-2022 14:14

mkissin:

Batman:

ok so more kw/hp motor doesn't help. cheers

one day i'm going to compare the EV6 RWD and the Model Y RWD and do the hills at different speeds and see what happens ...

That would be super interesting if you were able to collect useful data, so I hope you do!

Interpret the data would require you having the CdA for each car, which manufacturers almost never give out. This is different to the just the Cd (drag coefficient) number, which they do often spout in marketing material, but which is largely meaningless without the A bit (the frontal area).

You'd also want the rolling resistance of the tyres, and so on and so forth. Basically, you need a wind tunnel and a dyno.

it's not that hard

on the same day on the same stretch of road for about 10kms

uphill 40, 70, 100kph what is the kwh/km

flat road 40, 70, 100kph what is the kwh/km

- maybe not so easy to do 40 on the open road so might do it in town for that bit, plenty of hills in dunedin

get in the other car, rinse repeat, same weather conditions

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#2941143 12-Jul-2022 14:19

SaltyNZ:

As a general rule, under all conditions, slower is more efficient. Drag is proportional to the cube of velocity; power is (sort of, it isn't a straight line for a real motor) proportional to current. If you want to double your speed you will need ~8x the power, so ~8x the current. But resistive loss in the power train is proportional to the square of the current so at double the speed you waste on the order of 64x as much energy due to resistance, directly impacting your range. EDIT: of course I forgot to add that you get there in half the time, so the total loss is "only" 32x as much.

Gears don't really change it that much with an electric motor which has a much wider range of speed where power is approximately linear. So as others have said - that's why most EVs don't have a multi-speed transmission. The benefits just don't outweigh the extra complexity and weight. Combustion engines require complex transmissions because of their narrow speed range.

In any case ... if you try driving at 75mph in NZ, it won't be the range of the car that crimps your style.

i don't believe for a second that they are not trying to figure out 2 speed EVs for the future.

the way the taycan can smash the aero penalty at 75mph that you have so well calculated just by changing gears, there's got to be something for people to aim for.

maybe Kia won't do it, but BMW iX, Mercedes, i'm sure will want bragging rights. if they do limited autonomous driving - if they can figure that out, a 2 speed transmission is a piece of cake.

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#2941144 12-Jul-2022 14:26

Batman:

it's not that hard

on the same day on the same stretch of road for about 10kms

uphill 40, 70, 100kph what is the kwh/km

flat road 40, 70, 100kph what is the kwh/km

- maybe not so easy to do 40 on the open road so might do it in town for that bit, plenty of hills in dunedin

get in the other car, rinse repeat, same weather conditions

Assuming the car will give you those numbers to a useful degree of accuracy, all you're comparing is an apple to an orange.

That's fine if that's what you want, but you're not going to be able to cross-compare those numbers in any meaningful way. The two cars (EV6 and MY) are just too different in every imaginable way.

At best you're just going to prove that physics works, and your kwh/km numbers are better at lower speeds.

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#2941152 12-Jul-2022 14:28

i want to travel distance across mountains.

very simple question - which car is better.

mkissin

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#2941154 12-Jul-2022 14:40

Batman:

i want to travel distance across mountains.

very simple question - which car is better.

For a longer distance? Easy. The one with the bigger battery, driven as slowly as is safe.

If you want to go fast, you'll need to minimise CdA but that's a linear saving instead of the cube of velocity.

If you want some drive train data, this is a link to a very technical review of the old Nissan Leaf inverter and motor. It'll still be relevant. Take a look at slide 11 - https://www.energy.gov/sites/prod/files/2014/03/f13/ape006_burress_2013_o.pdf

The takeaway is that the change in efficiency for both the motor and inverter are almost negligible over an incredible range of speeds.

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#2941157 12-Jul-2022 14:57

Batman:

i want to travel distance across mountains.

very simple question - which car is better.

OK, well, don't buy a Leaf, and in general more powerful motors translate to more powerful generators which means more regen / less use of mechanical brakes. Other than that I haven't really seen any detailed comparisons of mountain driving between different models.

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#2941158 12-Jul-2022 15:15

Batman:

the way the taycan can smash the aero penalty at 75mph that you have so well calculated just by changing gears, there's got to be something for people to aim for.

It smacks of VW's ability to apparently extract power without emissions. Until they were caught.

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#2941161 12-Jul-2022 15:30

Batman:
i want to travel distance across mountains.

very simple question - which car is better.

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#2941171 12-Jul-2022 15:50

jarledb:
Batman:

i want to travel distance across mountains.

very simple question - which car is better.

can the mod explain how this is relavant to comparing the Kia RWD to the Model Y RWD?

also where is the report button for mods?

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#2941183 12-Jul-2022 16:10

Batman:

can the mod explain how this is relavant to comparing the Kia RWD to the Model Y RWD?

also where is the report button for mods?

I think you were very close in this comment to the quote I posted.

If you are really interested in good suggestions to cars that would work for you, then why not ask which cars can do the range you need? And maybe also what your budget is?

BTW: If you want to report me, just contact Mauricio and he will deal with it.

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#2941325 12-Jul-2022 19:52

I've been getting a few hyundai kona ads on my Facebook feed and managed to follow the links far enough to get specs and prices.
From what I can see, to match the specs of the ($58k) BYD Atto3, you need to get the top spec Kona at 88k. Then add the subsidy to get a price difference of $38k.
This helps me retrospectively justify my BYD pre-order but I think the Konas are going to be a hard sell
I was expecting them to come in significantly below the EV6 pricing

alasta

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#2941335 12-Jul-2022 20:59

When the Kona electric launched about three years ago I was really hoping that it would be much cheaper by now. Pricing for the new generation Niro hasn't yet been announced, but it seems likely to be similar to the outgoing generation.

I think it's really disappointing that mainstream electric offerings like this haven't yet managed to get down to $60k with the government subsidy because at that point they would start to become financially viable for a lot of people. Higher interest rates are also not helping to make the financials stack up.

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#2941336 12-Jul-2022 21:03

alasta:

When the Kona electric launched about three years ago I was really hoping that it would be much cheaper by now. Pricing for the new generation Niro hasn't yet been announced, but it seems likely to be similar to the outgoing generation.

I think it's really disappointing that mainstream electric offerings like this haven't yet managed to get down to $60k with the government subsidy because at that point they would start to become financially viable for a lot of people. Higher interest rates are also not helping to make the financials stack up.

I am guessing it is more to do with supply and chip shortages etc at the moment, where cars are easily selling at high prices.

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#2941396 13-Jul-2022 09:57

forget the Ora Cat. I want the Ballet Cat

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