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DIY go-kart


Furd's Avatar
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08-24-14, 12:15 PM   #41  
I think that "farm duty" just means the motor is more tolerant of voltage drop without overheating. If you have a three-phase generator I would strongly suggest three-phase motors as they will have the highest starting torque. You could use a variable frequency drive to give better control and still use a single-phase generator with three-phase motors. With out the drive you will be unable to control the speed except by varying the speed of the engine driving the generator and THAT would be a rather poor method on this size of rig.

 
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Justin Smith's Avatar
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08-24-14, 09:56 PM   #42  
I guess that you are referring to electric motors. If they are both inboard from the wheels, they will have to rotate in opposite directions, but I guess you knew that and have a plan.
Yep, I'm referring to electric ones. I looked up online yesterday before I posted if I could reverse the motors and it looks easy.

I think that "farm duty" just means the motor is more tolerant of voltage drop without overheating. If you have a three-phase generator I would strongly suggest three-phase motors as they will have the highest starting torque. You could use a variable frequency drive to give better control and still use a single-phase generator with three-phase motors. With out the drive you will be unable to control the speed except by varying the speed of the engine driving the generator and THAT would be a rather poor method on this size of rig.

They can take more electrical abuse and have a higher starting torque. I only have single phase right now but I have up to 30A 240V. Judging by golf cart design, I'm going to need at least 4hp of motor, but looking on craigslist 3 phase motors are cheap. I'll have to check on VFD prices.

 
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08-26-14, 07:58 AM   #43  
Do you guys think a 3HP motor would work? It's on Craiglslist for $100. The guy also has a 7.5HP but I don't think my generator would start it.

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08-26-14, 09:02 AM   #44  
Be sure you do your rating from the SFA (service factor amps). Note motor is stamped with SF 1.15.
This is a way for a manufacturer to rate at less hp. for the work ability of a motor. This was used excessively in pump industry. (ie. my pump is a 1/2 hp. but will pump as much as brandX 3/4 hp. [yes, I have a service factor of 1.5])
Multiply SF times rated hp. to get true hp.

FWIW

RR

 
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08-26-14, 09:14 AM   #45  
Rough Rooster
Be sure you do your rating from the SFA (service factor amps). Note motor is stamped with SF 1.15.
This is a way for a manufacturer to rate at less hp. for the work ability of a motor. This was used excessively in pump industry. (ie. my pump is a 1/2 hp. but will pump as much as brandX 3/4 hp. [yes, I have a service factor of 1.5])
Multiply SF times rated hp. to get true hp.

FWIW

RR

I got 3.75HP, that should be enough considering the farm's electric is 4hp and has 6 deep cycle batteries in it.

 
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08-26-14, 08:42 PM   #46  
Well I called the guy and he said it sold, so it's back to the drawing board. Of course, I think I am going to use electric drive as it's more in my field of knowledge. Plus there's no transmission and clutch to buy.

 
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08-27-14, 04:27 AM   #47  
Be sure you do your rating from the SFA (service factor amps). Note motor is stamped with SF 1.15.
This is a way for a manufacturer to rate at less hp. for the work ability of a motor. This was used excessively in pump industry. (ie. my pump is a 1/2 hp. but will pump as much as brandX 3/4 hp. [yes, I have a service factor of 1.5])
Multiply SF times rated hp. to get true hp.
Sorry RR but that is not the way it works. Service factor is a TEMPORARY overload factor and NOT the true horsepower. Motors with a SF over 100% are often used on pumps and compressors to allow for temporary loads that exceed the nominal horsepower of the motor. Operating in the service factor for long periods of time WILL decrease the life of the motor.

I have seen motors burn up on a regular basis when they are run into the service factor for long periods of time.

 
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08-27-14, 06:48 AM   #48  
I have seen motors burn up on a regular basis when they are run into the service factor for long periods of time.
My point, EXACTLY!

(not wrong, just misunderstood)

RR

 
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08-27-14, 09:43 PM   #49  
Sorry RR but that is not the way it works. Service factor is a TEMPORARY overload factor and NOT the true horsepower. Motors with a SF over 100% are often used on pumps and compressors to allow for temporary loads that exceed the nominal horsepower of the motor. Operating in the service factor for long periods of time WILL decrease the life of the motor.

I have seen motors burn up on a regular basis when they are run into the service factor for long periods of time.

I would think in theory that using anything near the service factor for my setup would only be to get the cart going and if I'm going up a real steep hill with a really heavy load, which will rarely happen.

 
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