electric vs gas theory

[cheapcookie]

Ok so yesterday I had a discussion with a guy.

I think his point was that electric vehicles aren't comparable to gas.

He kept repeating over and over that an electric motor has max torque at 0rpm

I said that a brushless motors is usually run at high rpm, and that motor torque and mechanical torque are different.

And the important part about solving a problem with a brushless motor, is to run it at max power.



Ok so my question to endless sphere is, hows is it relevant that an electric motor has max torque at 0 rpm(in an argument against electric vehicles)???

 

[Chalo]

It is relevant, in that it's an advantage for EVs. Your friend may be oblivious to the fact that electric vehicles accelerate *much* faster than ICE vehicles with the same power output. It is their generous low-speed torque that makes most of the difference.

And, ideally you want to run an electric motor at a faster speed than what develops max power, because efficiency climbs substantially as speed rises from that point.

There's nothing left for ICE street vehicles to do better than EVs, except refuel quickly and (for the moment) cost somewhat less. If that's someone's idea of superiority, then I encourage him to take a Daisy Red Ryder into battle, because it's very cheap and its magazine holds 650 rounds.

 

[billvon]

Ok so my question to endless sphere is, hows is it relevant that an electric motor has max torque at 0 rpm(in an argument against electric vehicles)???

That's an argument _for_ electric vehicles.

In an ideal motor that has a given power output (i.e. 200hp) torque is always equal to power divided by RPM. Since nothing is ever ideal, other things limit maximum torque, like the strength of the output shaft. But the closer you can get to that ideal the faster you can accelerate at a given max power.

With electric motors you are close to that ideal. With IC engines you are pretty far from that ideal, because you need to get to pretty high RPM's to get max torque - so for much of the operating range of the engine you have to live with poor acceleration. You can get around that partially by using a transmission to keep the engine at its most powerful point, but then you start losing power to shifting.

 

[Izits]

Your guy friend is also going to point out that gasoline is just SO much more energy dense than batteries, it's ridiculous.
For example the Chevy volt is only rated to go 53 miles on it's 435 pound battery but it will go about 370 miles on just it's 9 gallon fuel tank that weighs 63 pounds.

It's easy to see why a society would be slow to give that up.

 

[billvon]

Your guy friend is also going to point out that gasoline is just SO much more energy dense than batteries, it's ridiculous.

Good comeback to that is that a Tesla can get 362HP out of a 70 lb motor; the engine in a Mustang Mach 1 can only output 305HP - and weighs 600 lbs.

 

[Izits]

Your guy friend is also going to point out that gasoline is just SO much more energy dense than batteries, it's ridiculous.

Good comeback to that is that a Tesla can get 362HP out of a 70 lb motor; the engine in a Mustang Mach 1 can only output 305HP - and weighs 600 lbs.

Excellent point. But he's probably going to reply that when you add the battery and the liquid fuel to those two weights the advantage will turn around and go the away. Unless you're just talking about driving to the end of the street.

 

[billvon]

Your guy friend is also going to point out that gasoline is just SO much more energy dense than batteries, it's ridiculous.

Good comeback to that is that a Tesla can get 362HP out of a 70 lb motor; the engine in a Mustang Mach 1 can only output 305HP - and weighs 600 lbs.

Excellent point. But he's probably going to reply that when you add the battery and the liquid fuel to those two weights the advantage will turn around and go the away.

Well, given that the P100D is currently beating almost every other car on the road in 0-60 and the 1/4 mile (events that depend on power and weight) that would be a hard argument to make . . .

 

[Izits]

Well, given that the P100D is currently beating almost every other car on the road in 0-60 and the 1/4 mile (events that depend on power and weight) that would be a hard argument to make . . .

If his guy friend is a drag racer he should be quite impressed. But if he wants to drive the car from Tours to Paris and back then 1/4 mile racing ability may not mean much to him.

 

[billvon]

If his guy friend is a drag racer he should be quite impressed. But if he wants to drive the car from Tours to Paris and back then 1/4 mile racing ability may not mean much to him.

Agreed. But in that case torque curves or relative weights don't really matter.

 

[cal3thousand]

It's very relevant. You have your max torque right out of the gate and he has to wait for his car to spin up to that. (one of the reasons Tesla Model S regularly beats the piss out of anything other than exotic race cars)

It's also clearly touted by turbo engines over normally aspirated engines, as having your torque earlier is better. Why would you want to wait??

 

[Dauntless]

So for your gas engine you need a transmission to use it efficiently so you can keep the rpm low. It has its' torque when the rpm is high, but you want to keep the rpm low to drive. So you're in a higher gear, torque is reduced from the engine and the gear ratio. I'm not sure what 'Max torque at 0 rpm' really means, seeing as how that torque at zero is---ZERO! DNE, etc. Until you get off zero. (How do you get it off 0 when there's no torque.) But you run it efficiently by keeping the rpm up. Afterall, isn't the max POWER halfway between 0 and no load speed? (Where you still have half torque.)

I think he just doesn't understand this max torque at 0. At least not any better than I do. But what IS the argument even supposed to be? Does he actually have something he's trying to say when he's going on about zero?

 

[Chalo]

I'm not sure what 'Max torque at 0 rpm' really means, seeing as how that torque at zero is---ZERO! DNE, etc. Until you get off zero. (How do you get it off 0 when there's no torque.) But you run it efficiently by keeping the rpm up. Afterall, isn't the max POWER halfway between 0 and no load speed? (Where you still have half torque.)

I think he just doesn't understand this max torque at 0. At least not any better than I do. But what IS the argument even supposed to be? Does he actually have something he's trying to say when he's going on about zero?

I think it's you who's not understanding torque. It's just force, no RPM required. Power being a function of force times velocity, or in this case torque times RPM, whenever the RPM equals zero, the power also equals zero. But the torque can be any amount.

 

[spinningmagnets]

I was recently reading some of the data on the Koenigsegg Regera hybrid. He stated that he didn't add electric motors to the drivetrain because he wanted to make a more "green" car, he did it because he wanted an all-wheel drive supercar with no performance compromises, and he added three motors in very specific places to maximize their benefits.

Gasoline motors produce poor torque at low RPMs, and in order to maximize the peak horsepower, most engines have a very peaky horsepower curve, and then try to make up for it by adding lots of transmission gears...so the engine can stay up in its best power range, regardless of the road-speed. Shifting gears in a sports can be fun. Some like it, some don't (many sports cars now come with an automatic shifting option).

The Regera occupies a middle ground in my mind, much like the electric bike. An ebike is not a pedal-only bicycle (yes, I am a cheater), but it also isn't a car (I'm not giving up my car). However, for me? An ebike is a still serious transportation vehicle and also possibly a fun week-end toy.

Back to the Regera...Instead of going the conventional route and using a long V12, he chose a fairly small 5.0L turbo V8. The engine was designed from the ground up knowing that it would have a thin axial-flux motor between the engine block and the rest of the drivetrain. That combination worked well enough in its designed purpose that it doesn't have a transmission (like the Tesla).

By making sure that it has an engine in the combination, the on-board battery could be smaller. Although the battery can be topped-off by plugging it in overnight, it can sustain legal-speed cruising using a combination of the gas engine and only drawing on the battery for acceleration. During steady cruise, the system converts the motor to a gen, and tops off the battery. It does have an "electric only" mode that can be engaged at any time. The electric mode provides redundancy, if there are ever any problems with the engine, so you can get home if you run out of gasoline.

One of the more innovative things about it is that...it does not use cams or a timing chain to open the valves on the engine. The valves are actuated by pneumatic force, similar to F1 race car engines (which are capable of running to over 18,000 RPMs IIRC), and the actuators are engaged by a computer-controlled electrical signal. This also provides 100% variable valve timing, and the engine runs very clean as far as emissions.

 

[Ianhill]

I love both types of spinning shaft equally so for me there is no bias, but it's clear any motor that needs no gears through out its rev range has to have a much more constant torque output.
Like mentioned horsepower is nothing more than torque × rpm so a high performance electric motor will beat out combustion pound for pound always.
It's the energy storage and power control devices that add the extra weight amd cost compared to combustion both motor are quite equally priced I would have thought to produce.
A tank of fuel, a fuel pump with a plastic Inlet etc is barely 100kg loaded to the brim and does a fair distance compared to a electric vehicle equivelent the power control and energy storage will be many 100's of kg more for less range so they both have their place at the moment ev make sence in city and rural if your energy is cheap and there's insentive but if you live in alaska then your stuck with pump gas and ice for now I'd say.

Turbos have alot of torque high up the revs so at low rpm there's simply no torque to pull like a train that's why drag racers use trans brakes and build boost and rpm at the line to leave at a decent torque producing rev range, most cars use smaller turbos these days to eliminate turbo lag with a turbo that spools faster and sooner to bring the torque curves peak closer to the horsepower peak for a engine that always feels lively.

The rugera is a stepping stone I think there's been many electric cars before it but the way it's been designed to use its power is lethal it's well ahead of the pack in so many ways it's build is a complete package in a new way on so many fronts ground braking jaw dropping math porn modern art of its time better than any picture or building so much time and effort truly amazing.

 

[Dauntless]

I think it's you who's not understanding torque. It's just force, no RPM required. Power being a function of force times velocity, or in this case torque times RPM, whenever the RPM equals zero, the power also equals zero. But the torque can be any amount.

That's just it, I AM understanding it. People get a little carried away, same with horsepower, neither means anything alone. Or at zero. It's a rate of change determination of how determined the change is. But NOT how capable of changing. Nor is the potential for change particularly important for much of the time you're driving. Once you have some minimal capability for it here and there, the matter is settled. Crazy Jerry's Centurion that he won the mileage event with is nearly devoid of torque, that's where his mileage came from.

So turbo doesn't really do anything for you at low rpm, a supercharger doesn't do much at high rpm. Which is better? Or do you want them both on your engine? Or does it even matter? I think I know this (Type of ) guy mentioned really well. He latched onto an expression that didn't mean anything to him but sounded impressive, so he says it over and over and pretends he's really kewl for saying it. The question is, will you be sucked in?

The Tesla beating something. The Tesla can't even beat a "Trash Car." (This is one of the sites my DSL can't seem to open lately, not sure what you'll see.)

http://insideevs.com/eric-lundgren-phoenix-ev/

 

[Chalo]

Well, an electric motor typically develops more torque at dead stall than at any other speed, with a diminishing amount of torque all the way to the motor's free speed where torque falls to zero. I guess I don't understand your statement:.

I'm not sure what 'Max torque at 0 rpm' really means, seeing as how that torque at zero is---ZERO!

Which isn't true at all. It's only true that power is zero at zero RPM. If the motor is held stationary by a brake, an obstacle, etc., then it can develop more torque-- force, not power--than if it is free to rotate.

 

[amberwolf]

That's just it, I AM understanding it. People get a little carried away, same with horsepower, neither means anything alone. Or at zero.

Motor Torque is, as noted, just a measure of static force acting on a lever (wheel, bar, etc), and does not indicate anything about movement, does not require any movement to calculate it.

Might require a teeny tiny bit of movement to measure torque because our measuring devices / techniques are not perfect, but the torque is there whether or not movement occurs.

I'm not a math guy so I won't pretend to be able to understand the formulas or how they are derived, so I can't explain it well either; maybe this can?
https://en.wikipedia.org/wiki/Torque
If not, maybe one of the references there, or some other book or site?


Motor Power, however, does require motion to exist, as it's a measure of work done; be it labeled in watts or horsepower or whatever. You might see watts expended on a locked-up wheel's battery-current measuring device, but that's doing work creating heat (and maybe melting the windings in the motor or smoking the FETs ).

 

[cheapcookie]

Lets say I hold the motor shaft still until the motor runs out of torque (0RPM)

wouldn't it fry my controller and my battery before the vehicle moves ? ( and the motor itself)

because of the insane current passing through ?

Thanks a lot for the discussion, pretty interesting view points here, and a lot to learn !

 

[amberwolf]

Lets say I hold the motor shaft still until the motor runs out of torque (0RPM)

The motor will never "run out" of torque. As long as nothing melts and power is supplied to it, it will continue producing torque.

wouldn't it fry my controller and my battery before the vehicle moves ? ( and the motor itself)

If you prevent the shaft from moving, and you have insufficient protection against a stall, then yes.

 

[Dauntless]

http://www.aquariusengines.com/

So the real issue will always be the ability to get the little electric shaft spinning and cooling in relation to how much electricity burning through it vs. the ability to move whatever amount of linkages in the liquid/vapor engine and cool them for the amount burned in it. One basic concern is just how much does all the mechanisms of the ICE weight. If it weighs less, creates less resistance to moving, there's less fuel used to create your HP/NM. I remember the past issues with the rotary, I'm not sure where's it's at today, I assume there's still long term durability problems, etc.

As you can see at this website and various news reports, there's all sorts of possibilities for improving the efficiency of gas engines, as long as you're ready for something completely different. I'm not sure that possibility exists for the electric motor, the real concern is for making battery development outpace ICE development. I wish I could here a recording of this guys' argument, but I feel sure he didn't even have one. He latched onto that expression without a clue what it meant, kept the OP from responding to something he didn't understand either, all without that expression seriously offering anything important.

And Alice runs off chasing that white rabbit. . . .

 

[Ianhill]

The way electric turns the shaft is linear but ice engines need could ter weights etc to keep the momentum going larger flywheels etc all mass that electric can get rid of there's no way electric will lose to an ice engine if it's designed well enough that's why we have diesel electric trains haulage knows the power of electric is on demand in a near instant.
It's as easy as energy in over energy out giving efficency the missing bit will be heat and noise etc this is why an electric motor is so great it has much less complexity and it wastes less energy upto 3× more efficent but as we know the density of our stored energy differs between the two, petrol is what it is but battery's will be getting denser and denser for the foreseeable future at least there's many tipping points range, charge rates cell longevity etc but the motors themself's are well evolved and if we can supply the power it will beat ice all day long, I'd like to see a super capacitor drag car prove that electric is king and will not be reckoned with.

 

[billvon]

The Tesla beating something. The Tesla can't even beat a "Trash Car." (This is one of the sites my DSL can't seem to open lately, not sure what you'll see.)

?? That's a guy who used old laptop batteries to build a 130kw battery and stick it in a junker. It beats the Tesla in range, not acceleration. (His trash car actually blew a fuse and got stranded during the test.)

As you can see at this website and various news reports, there's all sorts of possibilities for improving the efficiency of gas engines, as long as you're ready for something completely different. I'm not sure that possibility exists for the electric motor

Gas engines have been around as vehicle power for over a century; electric motors were used for a brief time around 1900 then not again until over 100 years later. We have about 10 years experience with large scale electric motor use in vehicles.

There is a lot more to learn about electric motors - not so much left to learn about ICE engines. We've had far longer to mature ICE technology.

 

[billvon]

Lets say I hold the motor shaft still until the motor runs out of torque (0RPM)

It won't run out of torque. It will just stop.

wouldn't it fry my controller and my battery before the vehicle moves ? ( and the motor itself)

Controller? No, not if it does phase current limiting (most good ones do)
Battery? No, it will just run down if you hold onto the shaft long enough.
Motor? Maybe. Most motors rely at least somewhat on air moving around and inside them. But if the phase current is kept low enough that a stationary motor can dissipate the heat, then no problem.

 

[Hillhater]

[
Gas engines have been around as vehicle power for over a century; electric motors were used for a brief time around 1900 then not again until over 100 years later. We have about 10 years experience with large scale electric motor use in vehicles.

There is a lot more to learn about electric motors - not so much left to learn about ICE engines. We've had far longer to mature ICE technology.

Electric traction motors have been in vehicles continuously over the past 100 yrs. (think ....trams , trains, light trucks, mining equipment, fork trucks, etc etc)
Not to mention their continuous use in industry as stationary drives.
I would think there is more potential for improving a <40% efficient ice engine , than there is in in improving a 95+% efficient electric motor. !

 

[cal3thousand]

I think the whole turbo engines not having torque at low rpm is a misunderstanding. They may have less torque at extremely low (near-idle) rpms where a NA-engine more torque available at at very low (again, near idle) because of higher compression ratios, but they quickly lose to the turbo engine beginning at ~1,500 rpm. So for that ~500 - 1500 rpm range, there is lag. After that, you're into boost and a (well-designed) turbo engine has 80% of it's peak torque already. In a front wheel drive car, you're feeling the torque-steer by now and the revs and subsequent HP will come on fast (if tuned right).