
For increases in supply voltage to the motor the noload motor speed will vary by the same percentage (n%) as the increase in supply voltage. The maximum output power is (n%) X 4. So for a 24 Volt 2500 RPM motor running at 36 Volts the RPM changes to 3750 RPM, and the Wattage changes to 1000 Watts. (For a 50% Voltage increase the math is 50%x4=200%, 500Wx200%=1000W)
To realize the power that the 24 Volt motor has running on 36 Volts, a more powerful 1000 Watt speed controller would need to be used in conjunction with it. Running a 1000 Watt motor on a 500 Watt speed controller will only provide half the power that the motor has the potential to produce.
Also to achieve the full power that a 36 Volt 3750 RPM motor has, it would need to run near its top RPM speed range. So having a proper gear ratio is very important in order to get full power out of the motor.
Installing a larger sprocket on the motor will increase the gear ratio which I would not recommend until testing the setup with its current gear ratio. If the motor does not lug under load with the current gear ratio then I would feel safe going ahead and increasing the gear ratio to gain more top speed.
However if the motor lugs and does not run near it top RPM under load then I recommend installing a larger sprocket on the rear wheel or axle. This would decrease the gear ratio which would provide more mechanical advantage to the motor and also allow it to operate at a higher RPM so it will produce more torque and power.
Here is a drawing showing different motor to wheel gear ratios depending upon wheel and motor sprocket sizes. The drawing assumes that the motor is powerful enough for the load it is under. If the motor is not powerful enough for its load then using a higher gear ratio could reduce the vehicles top speed by making the motor run at a lower RPM than it should which lowers its output power, and could also result in overheating the motor.
Thank you. I now understand why the controller is the limiting factor. It’s because overvolting a 24V 500W motor by a factor of 1.5 essentially turns it into a 36V 1125W (500x1.5x1.5) motor.
I need a 36V controller that can output at least 1000W. Which one would you recommend? I found the SPD361000 (http://www.electricscooterparts.com/hookup/CT660B9.htm) and the Blue Sky 1200W controller (link removed).
As an experiment, I hooked up my 36V 500W controller to the original Razor (24V 250W) motor and I did NOT see an increase in top speed when running at 36V. Any idea why that is? The controller should not be a limiting factor in this case.
Regarding larger sprockets for the motor, can you please let me know which ones will fit? How about SPR2514A, SPR2515A and SPR2516?
Thanks.
Please let me know if you have any questions.
Please let me know if you have any questions.
Thanks for all your help.
Space is limited in the Razor Dune Buggy so I went with the SPDCT660B9 controller. Unfortunately, I’m not seeing much improvement in top speed. It’s around 10mph (up from 9 or so), not 13mph as I was expecting. Would the SPD361000 really make a difference? You would think that the 40 amps (1400 watts @36V) that the SPDCT660B9 puts out would be enough to take full advantage of the 24V 500W motor. It certainly has awesome torque, even for an adult.
The good news is that I figured out why I couldn’t reach top speed (13mph) with the 24V 250W motor from Razor running at 36V. It turns out that the motor’s wires were crossed and that I was actually running in reverse mode (I’m using the SPD36500R). I switched it to forward and now it goes at 13mph instead of 9mph!
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I am sure that the SPDCT660B9 and MOT24500X2500B would be able to propel the go kart faster than 10mph with the right gear ratio. Since the motor now runs at a top speed of 3750 rpm it needs to rev at a fairly high speed to produce the power that it has the potential to make.
To take the guesswork out of this I would like to determine the gear ratio of the power transmission system and the wheel size so we can see what speed the cart is geared for right now. I assume that the cart has its original 32 tooth rear axle sprocket, please correct me if I am wrong or if you have another sprocket size installed on the axle.
I will use the following data for the calculation: 8" wheels, 32 tooth wheel sprocket, 11 tooth motor sprocket, 3750 RPM motor. The calculation for this data indicates a top speed of 30.78 MPH as shown below.
It looks to me like the current gear ratio is the problem. At 10 MPH the motor is running at 1237 RPM. The motor/controller combination does not have enough power to propel the go kart to 31 MPH. It propels it to 10 MPH and then at 1237 RPM the motor can not produce enough power to go any faster. I recommend installing a larger sprocket on the axle to increase the gear ratio so the motor can rotate at a higher RPM and produce more power. Here is the same gear ratio/speed calculation using a 65 tooth axle sprocket:
The calculator indicates that the top speed is 15.13 MPH with a 65 tooth sprocket on the axle. The motor will rotate at 3750 RPM at 15.13 MPH so it can produce the full amount of power that it has the potential to. I recommend replacing the axle sprocket with a larger one to allow the motor to run at a higher RPM.
We have the gear ratio and MPH calculators that I used to make these computations available for anyone to use on this page: http://www.electricscooterparts.com/motorwheelgearratio.html
Please let me know if you have any questions.
The actual tire height is 7.5” and the gear ratio is 8.47:1. That’s because there’s a jackshaft so the gear ratio is 32/11 x 32/11 = 8.47.
At 3,750 RPM, that’s a speed of 9.88 MPH which is what I’m getting. That makes sense now.
That’s actually a good setup because the enormous torque is really fun and the top speed is good enough. I’ve come to the conclusion that anything faster could be dangerous for the kids.
I’m still puzzled by the speed of the standard Razor Buggy. The top speed is advertised as being 9mph but that would imply that the motor is running at 3400 RPM, which seems high. I did see 9 mph when I tested it right after I bought it but now it’s closer to 7mph, no idea why. 7mph corresponds to a motor RPM of 2650, which seems more reasonable. Do you know the official RPM of the Razor Dune Buggy motor? Thanks.
I agree that 3400 RPM seems high for a factory rating on one of these type of motors. The highest RPM that I have ever seen on an electric scooter/bike/go kart motor is 3000 RPM.
Good to hear that the top speed and gear ratio is working out good for you. 9.88 MPH is a good top speed for a kids go kart. Also good to hear that the motor is revving up to its top speed so it can produce all of the power that it has the potential to make.
Hi ESP  I have all original equipment on a razor dune buggy. I'm looking to increase top speed and need some advice. From the post above, if I add an additional 12v (replace the 2 w/ 3 112v 9amp), then I'll need a 1000w controller to increase the speed  correct?
So, given 36v and 1000w controller, how much speed should I gain?
If I added a 36v motor to the mix, how much speed would that add?
Any parts recommendations would help. I'm just trying to figure out what efforts will gain what type of results.
Thanks!
To start the modification all you need to do is add an additional battery. The original motor is 350 Watts so if you overVolt it by 12 Volts it should output around 700 Watts and have an increased RPM which should increase the top speed a lot.
You may or may not see more speed gain by switching to a 36V 1000W controller. A 36V 1000W controller will definitely be more reliable and run cooler than the original controller running at 36V though,
If you add a 36V motor it will run at a lower RPM than an overVolted 24V motor so the cart will run slower.
I would start with adding a third battery and a 36 Volt battery charger and taking it from there. If you are satisfied with the results then you should think about replacing the original two batteries with the same brand as the third battery, as mixing and matching battery brands is not recommended and can damage the batteries over time due to their different chemistries.
Keep an eye on the temperature of the motor and controller during the first few times the modified go kart is being used. If either part is running too hot then you may want to consider upgrading that part to something with higher ratings so it runs cooler and does not burn out.
Fantastic! I was thinking I'd go ahead and put in three 9amp batteries to increase ride time.
If you could recommend a battery, I'll go ahead and get 3 of them ordered. Thanks again!
I believe that Laurent (the person who started this forum topic) added an extra battery that was the same size as the original batteries. However I am not sure where or how he mounted the extra battery. Laurent, if you are reading this maybe you can explain to James or attach a photo showing where to mount the the third battery.
1 I do not know if the stock controller can handle running at 48 Volts because I have never tried that before. It may or may not be able to handle it. I do know that a 48 Volt controller would work perfectly with a 48 Volt battery pack. I recommend going with a 48 Volt 750 Watt or 1000 Watt controller because overVolting the motor causes it to draw a lot more Watts than running it at standard Voltage.
2 I just did the calculations for running a 24V 450W DC motor at 48 Volts and got a result of 1800 Watts just like you did, so that appears to be the right number. We have a 48V 1500W brushed motor controller that comes very close to the 1800 Watts that the motor will have the potential to produce at 48 Volts. In fact you might be better off limiting the Wattage to 1500 Watts or less so the motor does not overheat.
3 Installing a smaller sprocket on the motor will decrease the gear ratio and give the scooter a slower top speed and more torque for better hill climbing. If you are looking to increase the top speed then having a smaller sprocket on the motor would not be beneficial.
4 A 36V charger will not work with a 48V battery pack. You will need a 48V battery charger to use with a 48V battery pack.
Riding on flat ground tends to keep motors cool so you may be alright under those conditions. Overheating is what makes electric motors fail, so as long as the motor is not overheating then it will not be prone to failing. The temperature of the motor can be checked by placing your hand on it after a ride to determine if it is overheating. Of course if the motor has overheated this could burn your hand so I recommend to start by touching with your finger for a fraction of a second before committing to actually placing your hand on it. Also if the motor is overheating it will have a burning electronics smell when you are near it which is a sure sign that it has been overheated.
Thanks for letting me know about the out of stock items. If you could please let me know which items you were looking for that are out of stock I can give priority to getting them back in stock again.
Please let me know if you have any further questions.
Laurent
If that's not going to work, my other options are:
1) Keep the 24V 500W motor but go back to a 24V battery and controller and change the motor sprocket to increase top speed. Do you know where I can find bigger sprockets that will fit the motor shaft? What about SPR2514A, SPR2515A and SPR2516 sold at electricscooterparts.com?
2) Use the original Razor 24V motor and controller but run them at 36V by adding a third 12v battery. I've done a quick test on my other buggy and that yields at least a 25% increase in top speed (although I was expecting 50%).
Thanks for your help.
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