Electric VS Gas Horsepower?

SquidBonez

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We all know the benefits of electric motors and how they deliver their power. Electric motors can put out their max torque at zero RPM, while gas engines' ratings are their max at a specific RPM, yada, yada, yada. But I've heard the saying that 1 electric horsepower is *rougly* equivalent to anywhere from 2 to 5 gas horsepower because of how they deliver their power. I'm curious if that's really true.

I am currently building a 440cc Duromax powered off road go kart/buggy that is producing around 20 horsepower and 30 ft-lbs of torque. I plan on eventually converting it to electric, but I want to have at least identical (ideally better) performance than this 20 horsepower engine. The system I have planned is a 72V, 200A max setup. This translates to 14.4KW, or about 19.3HP. That's only about a 3.5% less power than the gas engine if my math adds up, but would it technically outperform the gas engine because of the electric motor's power delivery?

My guess is that it would not just because of the power delivery but also due to less drivetrain loss (no CVT belt slip to account for). What do you think?
 
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Functional Artist

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"UNDERSTANDING THE DIFFERENCES IN HORSEPOWER​

THERE IS A WORLD OF DIFFERENCE AMONG HORSEPOWER RATINGS, WHICH CAN CAUSE CONFUSION WHEN REPLACING ENGINES AND MOTORS.

Engineers like to say that if the results do not match the math, then go back and check the math, because the sum cannot be less or more than the total of the parts. This brings us to the subject of horsepower and all the different types found on the farm.

There is engine, PTO, drawbar, electric, hydraulic, and wheel horsepower. It is important to understand how horsepower is determined for each power source. For example, you may have a 5-hp. gas engine you want to replace with an electric motor. What would be the gas engine horsepower equivalent in watts?

MECHANICAL HORSEPOWER​

When it comes to internal combustion engines (of any fuel), the horsepower it generates is based on the amount of work it does over a period of time. The faster the engine can perform the same amount of work (load), the more horsepower it has.

Horsepower in an internal combustion engine is calculated from its torque production working against a load that is called a brake (either water-based or electrical) via an eddy current. Though we refer to horsepower, the true metric of an engine’s power is its torque.

Mechanical horsepower (determined on a dynamometer) is determined by multiplying torque by engine rpm and then dividing that sum by 5,252. Though this equation stays the same, there are different test protocols that control the inlet air, coolant, and water temperatures; barometric pressure; humidity; rate of acceleration; and how quickly the load is applied to the engine.

In North America, engines are rated using the Society of Automotive Engineers (SAE) standard. Yet, there are multiple SAE standards. The difference among standards is found in the barometric air pressure, humidity, and ambient temperature values. These are called correction factors. So when considering an internal combustion engine, it’s important to determine which standard and correction factors were used to rate it.

ELECTRIC MOTOR HORSEPOWER​

To determine the horsepower of an electric motor, you need to know the voltage input, current draw in amps, and the rated efficiency of the motor. Also remember that 746 watts equals 1 hp. The input voltage and current draw in amps is from Ohm’s Law, which states that volts × amps = watts.

To calculate the horsepower of an electric motor, use this formula: volts × amps × rated efficiency ÷ 746 watts.

Let’s take, as an example, an electric motor rated at 480 volts, 50 amps that has a 92% rated efficiency. Thus, the horsepower of this motor is 480 volts × 50 amps × a 92% rated efficiency ÷ 746, which = 29.59 hp.

Now, some electric motors such as those used on shop air compressors will have their power stated as peak horsepower. This represents the power the motor has just as it starts, which sometimes can be five to seven times the rated continuous horsepower. This bump in horsepower is caused by the motor’s start windings being engaged.

It’s also important to know that an electric motor has full torque output at 0 rpm. This compares with an internal combustion engine that requires a certain operating speed to achieve peak torque.

Be mindful of the efficiency rating of replacement electric motors. One that has a higher rating will be more powerful, run cooler, and cost less to operate than a less-efficient motor."
https://www.agriculture.com/news/business/understanding-the-differences-in-horsepower

 

Functional Artist

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Ok Kool! :thumbsup:
...but, what does all of that mean?

Well, I'll try :cheers2:

First keep in mind that we're talkin' about (2) very different "critters" (like cats & dogs)

They both have similar characteristics (both have 4 legs, a mouth & ears etc.)
...but, they are also, very different too (bark, meow etc.)

Electric motors have all of their torque available right from "go"
...but, that torque doesn't increase with the RPM's

Whereas gas engines don't have much torque available at low RPM's
...but, that torque increases as the RPM's increase

So, gas engines usually have an overall speed advantage, due to the necessity & use of a transmission
...& by increasing the gear ratio, as the engine's torque is increasing, which increases speed

Whereas an electric motor would not usually benefit from a transmission
...because increasing the gear ratio but, not the torque, severely increases the load but, not the speed (so much)
...so, to go faster ya gotta use a higher voltage motor (for more RPM's)

Did that make sense? :huh:

So, to kinda answer the SquidBonez question, "it depends" on the kart (over all weight, tire size, gear ratio, use etc.)
...but, I'd say a 2:1 ratio, is a good place to start, for comparing the two (like ~3HP elec. = ~6HP gas)

Also, keep in mind that "your" choice of batt pack literally "tips the scale" on an electric kart
...& so, is a big factor "in" its performance (or lack thereof) ;)
 

Terry 57

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Rather than have a single motor,
Is it possible to put 4 electric hub motors each 5000 watts and deliver similar performance.
It would distribute the weight on the rear axle from 2 wheels to 4 and illuminate issues with the drive (motor) to the driven (rear axle cog)
You can add reverse to the controller and choose speed settings. I'm curious if anyone has done a hub wheel motor build ?
 

redflash

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All that tech stuff accepted.......but......My experience says......the electrical way is COOL,,,,,,but it will cost 3 times as much as the gas engine, and 6 times more tinkering to get to perform correctly.
If you are a certified geek and love long nights in the garage, and have endless amounts of Cash.....Go electric.
However If you want to enjoy this ride a lot sooner, with way less expense,,,,,,,,, then just get a 420 and be done with it !

I'm NOT looking to start a controversy ,,,,,, just my opinion

Da redflash
 

Functional Artist

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Rather than have a single motor,
Is it possible to put 4 electric hub motors each 5000 watts and deliver similar performance.
It would distribute the weight on the rear axle from 2 wheels to 4 and illuminate issues with the drive (motor) to the driven (rear axle cog)
You can add reverse to the controller and choose speed settings. I'm curious if anyone has done a hub wheel motor build ?
Check out Grimsel
...it's Bad Azz :2guns:
...a world record holder :thumbsup:
...& has (4) electric hub motors :cheers2:

Here's a virtual assembly video
&
Technical tour
 

redflash

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No offense but to me a geek is an electronics genius. and I am a mechanical genius........but electricity ..not so much !
 
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ezcome-ezgo

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Check out Grimsel
...it's Bad Azz :2guns:
...a world record holder :thumbsup:
...& has (4) electric hub motors :cheers2:

Here's a virtual assembly video
&
Technical tour
That's cool really. But I have a question I am too lazy to research myself: Has anyone actually made the wheel itself into the rotating (rotor?) assembly of a motor? The concept is sort of the opposite of the conventional electric motor, the center being static and the outer assembly rotating. I figured a "Geek" would know.
 

panchothedog

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I don't have a dog in this fight. And I know it's not a fight. I am into RC model
boats. Fast ones. Have been for 35 years. The electric brushless motors available today are almost beyond belief. A motor 1&1/2" in diameter by 2" long
that weighs 10 oz. can put out close to 2 hp and motors the size of a coke can
is capable of 8 to 9 hp. Electric boats can tear up Nitro and gas powered stuff.
I have boats that run 70 mph, and am in no way a Big Gun. BUT I have absolutely no interest in a battery kart. Just seems to complicated. Not right.
Gas engine are so much easier. Maybe I am just too old and been around internal combustion engines for too many decades. Just my 2 cents worth.
 

madprofessor

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There are some visceral bonuses to gas as well............. Nothing like the throaty sound of a hotrodded and well-tuned gas engine, and that buzzing little vibration you can feel every time you goose the throttle just isn't there on nice and quiet electric karts. For long distance from home or help, a quart or half gallon sealed container of gas can be attached to a kart, a portable powerplant for recharging is nothing I've ever seen.
 

Functional Artist

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There are some visceral bonuses to gas as well............. Nothing like the throaty sound of a hotrodded and well-tuned gas engine, and that buzzing little vibration you can feel every time you goose the throttle just isn't there on nice and quiet electric karts. For long distance from home or help, a quart or half gallon sealed container of gas can be attached to a kart, a portable powerplant for recharging is nothing I've ever seen.
Hey Mad,
Have ya ever had that instant torque "pin ya to the seat" feeling? :sifone:

Some electric karts have that mechanical/gear "whirring" kinda sound like an Indy car :auto:

Um... a portable power plant, for recharging is called :cheers2:
...wait for it :innocent:
...Solar Panels :devil2:
 

nobled2

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Hey Mad,
Have ya ever had that instant torque "pin ya to the seat" feeling? :sifone:

Some electric karts have that mechanical/gear "whirring" kinda sound like an Indy car :auto:

Um... a portable power plant, for recharging is called :cheers2:
...wait for it :innocent:
...Solar Panels :devil2:
Something solar powered sounds interesting....
 

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