# Realistic?



## demolay rules (Feb 28, 2008)

also obviously thats not how they got the 1000 watt info.


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## elevatorguy (Jul 26, 2007)

I figure it to be just under 5 hp. 36x100=3600 3600/746(1hp) = 4.8hp
what is unknown is the rpm of the motor, so figuring speed is a problem.
88 feet per min is 1 mph, so you would need tire diameter, motor speed and gear ratio to figure this. Also would need to derate the motor rpm for load by a little bit, I usually guess about 10-20%
Jerry

http://www.austinev.org/evalbum/preview.php?vid=1174


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## mattW (Sep 14, 2007)

At cruising speed it would be the same power as a 5hp motor at peak rpm, for acceleration you would leave a 5hp behind since you are getting close to that peak rpm across the entire RPM range dropping off towards the end. So you can think of it as a 5hp motor with an efficient CVT to keep it at the redline no matter what speed you were at.


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## Mastiff (Jan 11, 2008)

Electric motors are rated by their Continuous power.
Thus this motor is a 1000-Watt continuous motor, it can take 36 volts and 27.7 Amps essentially forever.

1 Horsepower is equal to 754.6 watts, so if you take the 36 volts times the 100 amps for 3600 watts and divide that by 754 you get 4.83 Horsepower.

As MattW said, this electric motor will perform better than a 5 HP gasoline motor.
Electric motors have low RPM Torque which will give you good acceleration.


Now as for speed, that's a bit more complex as Elevatorguy explained, but you should be able to get a speed of 25-30 MPH.


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## DVR (Apr 10, 2008)

Find out the max RPM of the motor, the tire size and feed them into this calculator

http://www.diygokarts.com/speed-calculator.html

It'll give you a theoretical top speed. It worked out pretty accurate for me ICE go kart


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## ngrimm (Oct 19, 2007)

Thanks for the link to the calculator. My grandson is bugging me to get started on his electric go kart which we are building from riding lawn mower parts. That calculator would have helped me when I built my horseless carriage. I was too lazy to use the formulas so I guessed and now it's geared a little too slow. Norm


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## Wirecutter (Jul 26, 2007)

elevatorguy said:


> I figure it to be just under 5 hp. 36x100=3600 3600/746(1hp) = 4.8hp





Mastiff said:


> 1 Horsepower is equal to 754.6 watts, so if you take the 36 volts times the 100 amps for 3600 watts and divide that by 754 you get 4.83 Horsepower.


 This has always bugged me a little. I see a lot of different numbers used to calculate between watts and horsepower. When I calculate horses from watts, I use the more conservative number of 765w/HP. I know I could use a more optimistic figure, but I rationalize it because I know the system I use is not 100% efficient.

One school of though is that the conversion is lossy, like exchanging currency at those rip-off kiosks at the airport. So perhaps you can _make_ one horsepower worth of mechanical energy with 765+ watts, but with one horsepower turning a generator, you'll only get 746 watts.

Of course, a more reliable way to figure it out is to use a dyno, but I don't have access (or spare cash to rent) a dyno.

-Mark


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## kixGas (May 2, 2008)

demolay rules said:


> I am looking at this kit for a go kart: http://www.beepscom.com/product_p/kit-sc-36.htm
> The problem is I want to know how fast it would go/how many horsepower it would have at 36v, 100a, and 4 to 1 ratio. I contacted cloudev, and they said you can find peak hp on a motor by multiplying volts*amps converted into hp. I have never heard of this method and wanted to know if it will really perform like a 5 hp motor.



I built my son a 36V gokart with a small 1000 watt motor like similar to the one you have pitcured in your post. It is geared at 5.8:1. Here is a video of him driving it. It doesn't have excellent acceleration but it is good for a 6 year old. Hopefully that will give you an idea of the performance you would be looking at. If I were to do it all over again I would get a larger motor (Etek or similar) and a programmable controller and dial down the speed until he was old enough to go faster.


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## lazzer408 (May 18, 2008)

Holy cow. I just had this all figured out and crashed...  Here we go again... 

36v*100a=3600 (input watts)
3600*.80=2882 (output watts assuming 80% motor efficiency)
2880/746=3.86hp

5hp Briggs has 7.29lbs-ft torque. (hp=torque*rpm/5252)

3.86hp*5252/7.29lbs=2780rpm (rpm=hp*5252/torque) (same torque as 5hp briggs less 820rpm)
or...
3.86hp*5252/3600=5.63lbs (torque=hp*5252/rpm) (same rpm as 5hp briggs less 1.66lbs torque)

Bottom line.

A 5hp briggs will stomp you silly.


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