how do i decide what power motor i should use?

[pinkguy13]

I'm really interested in building a go-kart but i cannot figure out where to start. I decided to start with the motor because i do want to build an electric go-kart but i cannot figure out how to decide on the power of the motor i should purchase.

Also i don't understand how to calculate weight and speed to the motor power.

If someone could just point me in the right direction i would really appreciate it.

 

[landuse]

Welcome to the forum. Have a look in the electric section of the forum and read all the sticky threads available. They will start you off.

Next, you have to decide on the type of terrain you are going to ride on. Do you know?

 

[pinkguy13]

thanks for the help.

I was planning on just using it in flat areas like a street or like a dirt track at the most. Most likely in a parking lot or street.

 

[HelloYOU]

Depends on a lot of factors, but I usually like to start off at 1500 watts as my starting point for a go kart build with final drive ratios of 6:1 for this power level. Good quality motors at these power ranges tend to be a bit expensive, but if you look at the surplus sites, then you can get some decent quality motors at surplus prices.

Like just recently I bought one of these motors: http://www.surpluscenter.com/Electrical/DC-Motors/DC-Motors-Face-Mount/2-5-HP-2000-RPM-36-VDC-MOTOR-IMPERIAL-ELECTRIC-P66SR274-10-2357.axd that are rated for about 1800 watts at 2000 RPM with 36 volts applied with current draw of 65 amps at full load, and the price is very low compared to if you bought new stock of this motor.

Next, you need to decide on motor controller that is compatible with motor type you use. In this case it is a DC brushed motor, so we need a controller for this type of motor. A good choice is the AXE4834 controller that works up to 48 volts input with current draws up to 300 amps. This controller can be programmed to limit current, speed, and accel and decel profiles.

The final step is getting some good batteries. Use sealed lead acid batteries only. Never use car batteries. Good choices are those glass mat batteries such as the Optima Yellow tops or Odyssey extreme batteries. There is also places that sell batteries out of hybrid cars at deep discounts that will work perfectly too.

I assume you already built gas go karts, so should already know all the other details that I did not cover.

 

[ChromeRhino]

Depends on a lot of factors, but I usually like to start off at 1500 watts as my starting point for a go kart build with final drive ratios of 6:1 for this power level. Good quality motors at these power ranges tend to be a bit expensive, but if you look at the surplus sites, then you can get some decent quality motors at surplus prices.

Like just recently I bought one of these motors: http://www.surpluscenter.com/Electrical/DC-Motors/DC-Motors-Face-Mount/2-5-HP-2000-RPM-36-VDC-MOTOR-IMPERIAL-ELECTRIC-P66SR274-10-2357.axd that are rated for about 1800 watts at 2000 RPM with 36 volts applied with current draw of 65 amps at full load, and the price is very low compared to if you bought new stock of this motor.

Next, you need to decide on motor controller that is compatible with motor type you use. In this case it is a DC brushed motor, so we need a controller for this type of motor. A good choice is the AXE4834 controller that works up to 48 volts input with current draws up to 300 amps. This controller can be programmed to limit current, speed, and accel and decel profiles.

The final step is getting some good batteries. Use sealed lead acid batteries only. Never use car batteries. Good choices are those glass mat batteries such as the Optima Yellow tops or Odyssey extreme batteries. There is also places that sell batteries out of hybrid cars at deep discounts that will work perfectly too.

I assume you already built gas go karts, so should already know all the other details that I did not cover.

Great info. I like the specific parts list you gave as a start. Well done

---------- Post added at 07:50 PM ---------- Previous post was at 07:28 PM ----------

I think knowing your expectations and how much you are wilking to spend would be pretty helpful. Also, its important to note that electric motors and internal combustion engines produce power in different ways. A gas engine starts off idling with very little hp or tq but as the engine builds momentum it builds tq and hp, the higher the rpm the more hp and tq until you reach the current limitations of the engine and then efficiency drops back off. An electric motor is at rest until it recieves energy. An electric motor basically makes 100% of its tq and hp as soon as it starts to turn and slowely looses power from there with rpm (basically due to friction and heat making it less and less efficient). So a 2hp gas engine might be ok for a light gokart, light load in a small yard a 2hp electric motor will be enough for a large kart with a large payload to accelerate so hard it will rip your face off. So that's one thing to keep in mind. You can use an online watt to hp calculator to help out.

Depending on your expected performance and amount you want to spend will determine what combination of go-fast goodies you should get.

 

[HelloYOU]

Great info. I like the specific parts list you gave as a start. Well done

---------- Post added at 07:50 PM ---------- Previous post was at 07:28 PM ----------

I think knowing your expectations and how much you are wilking to spend would be pretty helpful. Also, its important to note that electric motors and internal combustion engines produce power in different ways. A gas engine starts off idling with very little hp or tq but as the engine builds momentum it builds tq and hp, the higher the rpm the more hp and tq until you reach the current limitations of the engine and then efficiency drops back off. An electric motor is at rest until it recieves energy. An electric motor basically makes 100% of its tq and hp as soon as it starts to turn and slowely looses power from there with rpm (basically due to friction and heat making it less and less efficient). So a 2hp gas engine might be ok for a light gokart, light load in a small yard a 2hp electric motor will be enough for a large kart with a large payload to accelerate so hard it will rip your face off. So that's one thing to keep in mind. You can use an online watt to hp calculator to help out.

Depending on your expected performance and amount you want to spend will determine what combination of go-fast goodies you should get.

My go kart with 72 volts and 300 amp current limit did not make me feel like I was getting my face ripped off because I set a ramp up rate to gradually increase power to the motor instead of instantaneous in the motor controller settings. A DC motor will exhibit behavior based on how its being controlled by the controller. Obviously if you allow lots of current into the motor and the current ramp up rate is set to full value, then it would be a very quick acceleration.

The AXE series controllers allow a lot of flexibility when you want to fine tune a DC motor to perform a specific way. Hence, why I recommend it. I could make my go kart act like a gas go kart in take off if I wanted to by simply adjusting the settings in the controller.

 

[ChromeRhino]

My go kart with 72 volts and 300 amp current limit did not make me feel like I was getting my face ripped off because I set a ramp up rate to gradually increase power to the motor instead of instantaneous in the motor controller settings. A DC motor will exhibit behavior based on how its being controlled by the controller. Obviously if you allow lots of current into the motor and the current ramp up rate is set to full value, then it would be a very quick acceleration.

The AXE series controllers allow a lot of flexibility when you want to fine tune a DC motor to perform a specific way. Hence, why I recommend it. I could make my go kart act like a gas go kart in take off if I wanted to by simply adjusting the settings in the controller.

I understand. Well said. But I was trying to give the OP an idea of the differences between a gas engine and dc motor hp ratings against actual seat of the pants performance possibilities of each one with the same hp rating.

 

[ChromeRhino]

My go kart with 72 volts and 300 amp current limit did not make me feel like I was getting my face ripped off because I set a ramp up rate to gradually increase power to the motor instead of instantaneous in the motor controller settings. A DC motor will exhibit behavior based on how its being controlled by the controller. Obviously if you allow lots of current into the motor and the current ramp up rate is set to full value, then it would be a very quick acceleration.

The AXE series controllers allow a lot of flexibility when you want to fine tune a DC motor to perform a specific way. Hence, why I recommend it. I could make my go kart act like a gas go kart in take off if I wanted to by simply adjusting the settings in the controller.

It never fails to amaze me just how argumentative people are and how much people try to belittle others to make themselves look and feel smarter than others. It seems like this forum has no shortage of those people

The OP wanted some direction on how to determine what motor to get by pwer rating to which I informed him how dc motors work differently than ICE's and let him know that a 2hp dc motor is much more powerful than a 2hp ICE by using the metaphor that a 2hp gaser would struggle on a small kart while a 2hp dc motor would feel like its would rip your face of on a big kart in comparison.

Are you trying to say the hp rating of a dc motor is comparable to those of Inteenal combustion engines and so they would be similar performance?

I don't get why you are arguung with me that your current set up doesn't rip your face off like it is somehow proving that something I said was wrong and then turn around and admit that you have it programmed so it won't rip your face off but if you reprogrammed it then it would. And to top it off you failed to mention the hp rating of your motor. Then you finish talking about which controller you recommend and why? He was wondering how to determine how powerful of a motor to get. Stsy on topic.

My point would be that your dc motor would outperforme the same hp ICE so much so that it would be like your getting your face ripped off from the speed and acceleration in comparison to the ICE of the same rating on your kart.

Why even try to argue a moot , off topic point that you turned around and admited it was because you programned it to do so??

 

[ezcome-ezgo]

Chrome, I read and re-read Hello's post and I am not sensing the "argument". The guy is sharing his knowledge in a pretty straightforward way, just like you did. No need to get all bristled up about it. Thanks for the interesting comparison regarding the motors, BTW, I never thought about it like that before.

 

[ChromeRhino]

Chrome, I read and re-read Hello's post and I am not sensing the "argument". The guy is sharing his knowledge in a pretty straightforward way, just like you did. No need to get all bristled up about it. Thanks for the interesting comparison regarding the motors, BTW, I never thought about it like that before.

Thank you for your opinion and input. Its quite possible (and probable) that I misunderstood the reasoning for his reply to me. I was up late working with little sleep and have been having to defend myself on another topic a lot lately and I couldn't figure out with my fatigued mind why he was replying to me with that information and what he was trying to get across to me.

With my mind in better condition I can recognize that he may have been thinking that I thought a 2hp dc motor wouldn't be able to be controlled and would only rip your face off, and he was under the impression that I thought a 2hp dc motor was too much??

Whatever the reason its more clear to me that it wasn't an attact towards whether I was right or wrong, but more like information to help me to understand something a point I don't recognize and I took it wrong. I apologize, Hello, for being so defensive. I was wrong for doing so and recognize my mistake.

Now I'm wanting to delete my reply to Hello lol I feel bad I was so defensive.
Thanks again, ezcome-ezgo for pointing that out to me and giving me your take on the matter.

 

[ezcome-ezgo]

It's all good, as the young people say. Glad to have your knowledge and insight here, that's what makes this forum great.

 

[ChromeRhino]

It's all good, as the young people say. Glad to have your knowledge and insight here, that's what makes this forum great.

Thanks I'm not sure how much knowledge and insight I bring but I appreciate the sentiment I'm not sure if I will post too much more, I am starting to doubt my way of thinking isn't much appreciated around here and I'm not really one to just repeat the same conditioned responses and tend to think a little outside the box. Oh well, I can still continue my builds without posting on this forum. We will see how it goes though.

 

[landuse]

Thanks I'm not really one to just repeat the same conditioned responses .

That is the nature of a forum though . New people come around with the same questions all the time. I sometimes too find it a little tiring giving the same advice over and over, but the cool thing is that sticking around here i am still learning a lot, even though i am probably one of the longest standing members. Sheesh....i now feel old

 

[chancer]

Thanks I'm not sure how much knowledge and insight I bring but I appreciate the sentiment I'm not sure if I will post too much more, I am starting to doubt my way of thinking isn't much appreciated around here and I'm not really one to just repeat the same conditioned responses and tend to think a little outside the box. Oh well, I can still continue my builds without posting on this forum. We will see how it goes though.

Please give it some time. We are not as bad as it seems.
Thinking outside the box is good. Otherwise nothing ever gets better.
People are just skeptical at first when they see a Newbie giving advice to a newbie. Even if you are an old wise Newbie.
Thanks

 

[Jrgunn5150]

I like to buy the most power motor I can afford, I have no logic or reasoning, I just go big.

 

[ChromeRhino]

I like to buy the most power motor I can afford, I have no logic or reasoning, I just go big.

That's usually been my thoughts too. I was planning an electric kart build and found out my old neighbor owned a shop that would repair and refurbish DC motors, controllers and all kinds of stuff. I told him I wanted the biggest motor he had lying around. Bad idea, you needed a forklift to move it around. It was for a really big electric forklift. lol I said, "ok, we can step it down several hundred pounds. Let's try to keep it below the need for a two man team lift... for now." Unfortunately the bulk of his business was the huge motors for forklifts and stuff. I did think about powering a small pickup truck with one though.
He said a motor that runs the hydraulic pump on one of them should work well though. He moved shortly after that and I didn't catch the name or address of where his shop was.