# Typical Horsepower?



## dougingraham (Jul 26, 2011)

Horsepower isn't all that important. It is torque that matters most. HP would end up determining the top speed but torque will determine how long it takes to get there. When I first drove my car I had the controller set to limit battery current and motor current to 300 amps and the voltage was that of 33 cells. On the dyno I saw just below 40 wheel HP. 300 amps * 33 cells * 3.2 volts = 31.7 kw or 41HP. The car was a bit sluggish accelerating but it stayed up with traffic easily and I was able to reach low 70mph speeds eventually. The torque at that current was probably around 50 ft-lb which was half of the original ICE motor in the car. It is much more sprightly with a 1000 amp motor limit which the dyno says is 277 ft-lb of torque.


The old adage Torque wins races but HP sells cars is true for EV's as well.


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## tomofreno (Mar 3, 2009)

Actually both torque and power determine acceleration. Power is the product of motor shaft torque and shaft angular velocity. An electric motor can apply peak torque as long as the motor controller can keep increasing voltage to drive max current through the motor as back emf increases with motor rpm. Beyond that current starts decreasing with increasing rpm and motor shaft torque decreases. Max continuous motor power is determined by cooling. 

Torque determines acceleration (tractive effort is wheel torque divided by dynamic tire radius), so acceleration decreases as current decreases. So for example, the Spark EV has high torque and acceleration below about 40 mph, but acceleration tails off above that. Time for 0 to 60 mph is determined by peak torque and to what rpm the motor and controller can supply it - power. Shifting a transmission will of course decrease motor rpm maintaining peak torque, but torque multiplication to the wheels is decreased. You need high wheel torque out to high rpm for fast 0 to 60 mph time. Many times this is limited by the motor controller or the battery pack for ev's. Also DC motors typically have a max rpm of around 5500, so you need a motor with enough torque to use a high enough gear ratio and still have high wheel torque to the desired vehicle speed (see John Metric's thread in this section). Tesla uses a high torque AC motor that will deliver peak torque out to high rpm (but of course it too tails off at higher rpms).


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## Duncan (Dec 8, 2008)

Hi Bubble

As far as horsepower is concerned there are two numbers to think about,

Continuous power
It's surprising how little power you need to maintain speed - for a normal sized car 30 or 40 hp is enough
Bit more if you have any long hills

Burst power
For acceleration - the more the merrier
For reasonable performance an extra 50hp is fine - you cant use it continuously because your speed rises and you have to back-off

This is where the DC motors score - most of them will let you use about four times their continuous rating 

Example - I have a Forklift motor in my car,
At 48v in the forklift it is rated at 10Kw - 15Hp - at ~ 1000rpm

at 150v and 3000rpm it should be able to produce 30+Kw all day (the higher speed means that its cooling is actually better)

My controller can punch 75Kw through it - 100hp
But If I had a bigger controller that could be doubled or trebled

When comparing to an IC car remember that 150hp is at 6,000rpm - at more normal revs you actually have a lot less available - 80hp at 3,000rpm, 40hp at 2,000rpm

When the Tesla roadster was being compared to the Lotus it was developed from the Lotus had 20% more power and 20% less weight

In the hands of an expert the Lotus was faster - with most drivers the Tesla walked away
If you were in exactly the correct gear the Lotus was a bit faster
In the Tesla you simply press the pedal - no gear-changes, no power-bands - just go


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## tomofreno (Mar 3, 2009)

Duncan, I don’t think it much matters whether AC or DC. Most motors are designed close to maximum specific electric and magnetic loadings (armature current density and field flux density) so AC or DC of a given size are capable of putting out about the same power. How long they can do it is mainly determined by cooling. The HPEVS AC motors are vented and have an internal fan similar to series DC motors. Adding a blower permits either one to put out more power for longer time (total energy dissipation). Maybe you are thinking of TENV AC motors (totally enclosed non-vented).


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## Duncan (Dec 8, 2008)

tomofreno said:


> Duncan, I don’t think it much matters whether AC or DC. Most motors are designed close to maximum specific electric and magnetic loadings (armature current density and field flux density) so AC or DC of a given size are capable of putting out about the same power. How long they can do it is mainly determined by cooling. The HPEVS AC motors are vented and have an internal fan similar to series DC motors. Adding a blower permits either one to put out more power for longer time (total energy dissipation). Maybe you are thinking of TENV AC motors (totally enclosed non-vented).


Hi Tom
It's probably the AC controllers that are the limiting factor 

Because DC controllers are dollar for dollar much more powerful most will allow you to produce much more power compared to the continuous rating of the motors,
A Soliton can give 300Kw (until your motor melts)
The only AC controllers that are anywhere near that powerful are $20K +


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## tomofreno (Mar 3, 2009)

Yes, that's true too.


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## dragonsgate (May 19, 2012)

This is a paraphrase from another quote I read. Horsepower is how fast you are going when you hit the wall. Torque is how far you move the wall.


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## McRat (Jul 10, 2012)

Torque is your enemy.

RPM is your friend.

Horsepower is your Daddy.

It's simple. Would you rather have a 15,000 rpm, 100hp driveline that weighs 200lb, or a 1,500 rpm, 100hp driveline that weighs 2000lb.

Torque can be altered, while the HP remains the same.

Given a 7000lb vehicle, you will need 1000HP to run a 10 second ET. It doesn't matter if it's a diesel with 2000ftlb or a motorcycle engine with 400ftlb. It has to have that 1000HP to get it done. But the motorcycle driveline can be made far lighter. Without huge torque, you can make much lighter components.

Look at trucks. You can get a 400HP gas engine, or a 400HP diesel engine. However, the diesel engine, trans, and rear axle assy weigh almost twice as much. In fact, it almost exactly correlates to the difference in peak HP rpm. The diesel is 3000rpm, the gas is 5500rpm. The diesel engine is 900lb, the gas is 500lb. 400 trans, 250 trans. 600 axle, 400 axle.

If you want a lightweight EV, you need to aim at high RPM, not high torque at the motor.


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