Hello, everyone and welcome. In this video
we're going to be talking about why electric cars have peak torque available from zero RPM or a complete standstill and
Recently I attended drive revolution where I was able to check out a bunch of different hybrid and electric vehicles and the Chevy Bolt
Actually won the Northwest green car of the year award
And I think that was well deserved. One of the cool things about electric cars
Is that you know they're doing something that you hear a lot about in marketing terms now,
So a lot of companies are saying hey
We're able to achieve peak torque at just 2000 RPM or 1500 RPM.
All these companies are trying to you know bring down when you get peak torque available in the engine range
for internal combustion engines because they know that's a more responsive, more fun to drive vehicle and
Electric cars actually do this the best because they have that peak torque available from zero RPM, So in City environments
You know where you're maintaining these low speeds. They're actually a ton of fun because you always have that peak torque available
So, how are they able to do this?
Well, basically we're going to talk about motors generators and then get into why that peak torque is available at zero RPM
So if you haven't already I have a bunch of different videos on how electric motors work
This is going to be a very generic overview
So if you want more details check out the links in the video descriptions. I have quite a few videos on this subject
But very basically how a motor works is you supply a current through a wire
Which is going to be your motor ultimately you have a magnetic field, so you've got North-to-south
Magnetic field traveling right here and so as that current travels through that wire
Within that Magnetic field it's going to generate a force to rotate
that that wire there so basically rotate the motor the armature of the motor is going to start to Spin and
This is covered by fleming's left hand rule now old convention states that current travels from positive to negative
Electrons are actually traveling in the opposite Direction
but that's the convention so using fleming's left hand rule if you line up the
field with your pointer finger your force or your current rather with your
middle finger then your thumb is going to point the direction of the force and so as you can see there
Field current Force so it's going to Force that to rotate
So the more current you applied to this copper wire the more it's going to want to Spin and will Spin faster and faster
Now a generator is basically doing this in reverse and so as a result the current is going to be in the opposite Direction
But basically you're going to be rotating the armature so spinning that copper wire
Through that magnetic field and so to use fleming's right hand rule because this is in reverse
so if you have the field coming from your pointer finger you've got
Your current with your middle finger
And then your thumb will show you the force your thumb is of course as a result of turning that Clockwise
so you're creating that Force you have the magnetic field and then you're going to
Have that current be created in that clockwise direction there so you can see that's the opposite of right here
Okay now these two are actually happening simultaneously
So when you supply that current you're going to start spinning this motor
But because you're spinning the motor you're going to have a back voltage in the opposite Direction
So it kind of goes back and forth yes, you you supply the current you spin that motor up
But once you have a spinning motor the rotation of that motor creates this back, Emf or electro-motive force
So the two are curved simultaneously and the faster you spin up this motor the more back Emf
You're going to have and so you know you've got your current here from North to South just like this
It's the exact same scenario, but basically you have to keep in mind that once this is spinning as it rotates
It's acting somewhat like a generator and as a result it has that back Emf
So your working voltage is equal to your supply voltage minus your back emf. So just a quick example
Let's say you had a working voltage of 120 outlet 120 volt outlet you plug in it starts spinning up
And you've got a back emf of 100 volts, so your working voltage is just 20 volts now this explains
Why you have peak torque available at zero RPM because
Back Emf is only occurring once this is actually rotating
So the faster you spin it up the more back emf you have so when it's not rotating at all you have no
Emf no back Emf and as a result all of the power that's going into it is creating torque
And so you know you may notice for example if you turn on a vacuum cleaner in your house
And the lights will dim very quickly, but then they'll come right back after the vacuum cleaner is spinning up
So what's happening?
There is right when you turn that vacuum cleaner on the voltage requirement the current draw from that vacuum cleaner is really high
Because you don't have any back emf. You're not spinning it up yet
So you have a huge current draw to spin up that electric motor then once the electric motor is rotating its actual
Working voltage is much lower as a result of the back Emf, and you see your lights very quickly come back to their normal levels
So you get full torque available at zero rPM. That's because you're not spinning
You don't have this generator effect of the motor which is kind of working against you in your working voltage
And so basically what happens is however much power
you supply that motor is going to find an
equilibrium
where it spins up to a certain speed where the back Emf and your
Resistance to you know moving forward in the case of a car arrow drag things like that are
Equal and so you're going to be at a certain speed at that point your back Emf plus the resistance is from you know driving
Rolling resistance things like that equal each other out, and you're at a set speed you will supply more power
You increase your speed, but ultimately when you're at zero rPM. You give it full power
There's no back Emf because it's not actually
Spinning and as a result you have peak torque and then that torque starts to taper off with rPM
So thank you guys for watching as mentioned
I have plenty more videos on you know how electric motors work
AC/DC that kind of thing if you'd like to check those out in the video description if you have any questions
Or comments feel free to leave them below. Thanks for watching