Electric Cooler-Kart

[dmittermeier]

I have embarked on a project that is a little more complicated than I intended (like most are). I designed and fabricated a "go-kart" frame that fits a 50L cooler on it with room for 2 people to sit on. After doing some preliminary research, I purchased a 1000W 36V motor and (3) AMG 12V 35ah batteries wired in series. I realize I am on the heavier side of things (about 450 lbs fully loaded), but thought this set-up would get me by. I have seen people use similar set ups on seemingly larger vehicles. Boy was I wrong. The motor spins up real nice when suspended in air, but when the tires hit the ground, it barely moves. Even unloaded with just the weight of the frame and myself standing on it (about 295 lbs), I have to, very slowly, twist the throttle to get it moving or else the motor stalls out (makes noise but doesn't spin). The set up has a decent top speed on flat ground, once moving, but ANY type of incline kills it and heats up the controller and motor. This is my first electric build, so I am 100% lost with all of this, which is why I am here. So, to my question, am I missing something with this motor/battery set up, or is it just simply underpowered? Feel free to ask any clarifying question if more information is needed. I am about to purchase a 3000W 72V motor and 72V lithium Ion battery pack, thinking my set-up is just underpowered, but didn't want to waste my money if I was missing something. I am not looking for anything to take me 40 mph (though I am not opposed to it) but some acceleration would be nice, and to not die on the slightest of inclines. Any suggestions or advice would be much appreciated.

Thanks!

 

[Balmorhea]

It sounds like you have the wrong wire assignments for your motor. There's a "false positive" combination where the motor turns too fast, without much torque, and uses a lot of current. That might be what's going on. Basically it's the motor and controller fighting with each other.

Chances are your motor is also too fast for the vehicle's operating envelope, but even if so, it should still get things moving nicely.

 

[dmittermeier]

It sounds like you have the wrong wire assignments for your motor. There's a "false positive" combination where the motor turns too fast, without much torque, and uses a lot of current. That might be what's going on. Basically it's the motor and controller fighting with each other.

Chances are your motor is also too fast for the vehicle's operating envelope, but even if so, it should still get things moving nicely.

I appreciate the response and information. I had never heard of the "false Positive" issue until now, but my symptoms appear like it could be my issue. I have now done a little research into it, but I am still not sure where these wires are. My throttle is a 5 pin that the controller was set up for. I did have to reverse the polarity on the motor to get it to rotate the intended direct. The motor is advertised with the ability to do this. There are only two wires going into the motor. Is the phase-hall on the throttle side or the motor side? I have bought two similar controller (different brands), both having the same issue and even seemingly burnt one out after one, very short, run (it shut itself off and now puts resistance on the motor without even being plugged into a power source).

Thanks!

 

[SlowCo]

What motor exactly? Mid drive or hub? If mid drive your gearing is too tall probably. If hub motor: in what diameter wheel is it laced? Again probably geared too tall. I.e smaller wheel needed.

 

[dmittermeier]

What motor exactly? Mid drive or hub? If mid drive your gearing is too tall probably. If hub motor: in what diameter wheel is it laced? Again probably geared too tall. I.e smaller wheel needed.

Its a mid drive, chain driven. Model number: MY1020 - 36V 1000W. I have an 11 tooth sprocket on the motor and 42 tooth sprocket on the axle. So, if gearing is too tall, then I am overloading the setup. Sounds like I need to go bigger on the motor and power supply to be able to pull the gearing.

 

[dmittermeier]

What motor exactly? Mid drive or hub? If mid drive your gearing is too tall probably. If hub motor: in what diameter wheel is it laced? Again probably geared too tall. I.e smaller wheel needed.

Oh, I forgot to mention, It only has 12.5" rear tires.

Thanks!

 

[Balmorhea]

I did have to reverse the polarity on the motor to get it to rotate the intended direct. The motor is advertised with the ability to do this. There are only two wires going into the motor.

Oh... you have a brushed DC motor. So you don't have phase and Hall wires, just motor + and -.

In that case, I think you have a 1000W motor but a much less powerful controller. Or maybe your batteries can't come up with the juice your motor craves. Anyway, it's a much different problem than I was guessing earlier.

And yes, your gearing is too tall. When I used a Unite MY-something motor on my first e-bike, I used a 12t motor sprocket and a 144t wheel sprocket. The wheel was about 27 inches, but even accounting for that I had a much greater reduction ratio. That bike cruised at about 18mph with a gross weight over 400 pounds, which is probably faster than an ice chest should go on a regular basis.

 

[dmittermeier]

I did have to reverse the polarity on the motor to get it to rotate the intended direct. The motor is advertised with the ability to do this. There are only two wires going into the motor.

Oh... you have a brushed DC motor. So you don't have phase and Hall wires, just motor + and -.

In that case, I think you have a 1000W motor but a much less powerful controller. Or maybe your batteries can't come up with the juice your motor craves. Anyway, it's a much different problem than I was guessing earlier.

And yes, your gearing is too tall. When I used a Unite MY-something motor on my first e-bike, I used a 12t motor sprocket and a 144t wheel sprocket. The wheel was about 27 inches, but even accounting for that I had a much greater reduction ratio. That bike cruised at about 18mph with a gross weight over 400 pounds, which is probably faster than an ice chest should go on a regular basis.

Ok, this makes sense. I really appreciate all the help. You can only do so much research, it is nice to talk to people with actual experience. I know I am new to this type of build (my mechanical background is internal combustion), but I could not figure out where the, non existent, hall and phase wires were.

As I do not have enough ground clearance for a much larger axel sprocket, do you think a 3000W 72V motor will get this thing to accelerate? Or do I need to look for something much bigger? I am not afraid of speed because I can always not twist the throttle as much, but I would definitely like some acceleration.

 

[Balmorhea]

You don't want more voltage; you want more amps. Amps are torque, volts are rpm. So you'd be better off using 36V or even 24V, but a controller and battery that can supply lots of amps. Your motor should be good for 40A at least.

And you need to be careful not to cook your motor, with lots of current and gearing that's somewhat too tall.

 

[dmittermeier]

You don't want more voltage; you want more amps. Amps are torque, volts are rpm. So you'd be better off using 36V or even 24V, but a controller and battery that can supply lots of amps. Your motor should be good for 40A at least.

And you need to be careful not to cook your motor, with lots of current and gearing that's somewhat too tall.

Ok, understood, purposely buying a motor that is higher in the voltage is a waste of time and money. My motor says its rated current is 35.6 amps. So the idea would be to buy a controller and a battery that can supply that amount of current to the motor and hope to not cook it, correct?

 

[SlowCo]

What controller do you have now? Do you have a photo (of the label) or link to it?

 

[dmittermeier]

What controller do you have now? Do you have a photo (of the label) or link to it?

It is the one at the link below. 31 amp max. Came with the throttle I bought.

https://www.ebay.com/i/222964459702?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=222964459702&targetid=935083617507&device=c&mktype=pla&googleloc=9031539&poi=&campaignid=10876471603&mkgroupid=107964302620&rlsatarget=pla-935083617507&abcId=9300401&merchantid=113788810&gclid=CjwKCAjw_NX7BRA1EiwA2dpg0iNO9RpF7l8qRiqi6VGzgfmaGfkzWe9vEe_97nH_PZp_XMelDC-ChRoCLiAQAvD_BwE

Thanks!

 

[SlowCo]

So your controller is matched to your motor, that's good. Then it is indeed the gearing that is too tall. You wrote you have not enough ground clearance for a larger wheel sprocket. So you'll need a jackshaft (two stage) reduction. Or buy a geared brushed motor.

 

[dmittermeier]

So your controller is matched to your motor, that's good. Then it is indeed the gearing that is too tall. You wrote you have not enough ground clearance for a larger wheel sprocket. So you'll need a jackshaft (two stage) reduction. Or buy a geared brushed motor.

I appreciate the help! I will look around for something geared.
If I were to buy a more powerful motor, how much power do you think I would need, in order pull the gearing I have currently? Do you think that Is that feasible?
I have been told that I need more amps to get more torque. There is a 3000W 60V motor that puts out about 50A which is a little more than 20 amps over what I currently have.

 

[SlowCo]

It depends on how fast you want to go with the Cooler-Kart. A rough estimate would be that your "36V 1000W" motor and controller should be able to get up to 15mph with that weight if geared correctly. So you can still use those if you make a jackshaft (two stage) reduction.