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Volts vs. Wattage, Speed vs. Torque

I have a Razor Ground Force that is currently 24v, 250w. I am going to upgrade it for more torque and higher top speed. I am trying to understand how changing the voltage (upgrade to 36v or 48v) compares with upgrading the motor wattage (500w, 750w, or 1000w). I understand the basic of voltage times amperage equals watts. But how does this affect a scooter or go kart?


What if you replace a 250w 24v (running at 24v) system with a 250w 48v (running at 48v) system? Will a higher voltage motor with the same wattage have more torque? Longer battery life?


What if you replace a 250w 24v (running at 24v) system with a 500w 24v (running at 24v) system? Will a higher wattage motor with the same voltage have more torque? Longer battery life?


So I am trying to decide if I should upgrade the big three (battery, controller, motor) to 36 or 48v. I don't plan on over-volting but rather use gearing to do it right. I am also trying to decide if I should upgrade the motor to a higher wattage? But I don't know how these factors interact. 

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If the motor is being ran at its factory rated Voltage then the motor's Watts rating determines the amount of torque and horsepower that it will have the potential to produce when used in conjunction with a controller that has the same Watts rating as the motor. A controller with the same Voltage rating and a higher Watts rating than the motor can be used and the power that the motor will have the potential to produce will then be increased, however, the motor will then be more prone to overheating because more current can be supplied to it than it was designed to continuously handle. It is best to match the Watt ratings of the motor and controller for the highest reliability.


If the motor is not being overvolted then the Voltage of the system does not effect the amount of power that the motor can produce, and only the Watts rating of the motor and controller will effect the motor's potential to produce power. A 24 Volt, 36 Volt, and 48 Volt 250 Watt motor will all have the same amount of torque and horsepower, and a 24 Volt, 36 Volt, and 48 Volt 500 Watt motor will all have the same amount of torque and horsepower.


The battery capacity is determined by the Voltage of the pack and the Ah rating of the batteries in the pack. For example a 24 Volt battery pack made with two 12V 10Ah batteries will have half the run time as a 48 Volt battery pack made with four 12V 10Ah batteries if both battery packs are running a controller and motor with the same Watts rating.


Since you are not planning to overvolt the motor then the Voltage of the system will not effect the power of the motor and any Voltage can be used without a change in power. Other factors can effect the decision for which Voltage to use though such as the size and number of batteries and how they will fit on the vehicle. For example two 22Ah batteries for a 24 Volt pack might not fit well onto the cart, while three 15Ah batteries for a 36 Volt pack might fit good onto the cart, making the 36 Volt pack a better choice for the build in that case.


Upgrading the motor to a higher Wattage would be the only reason I can think of to modify the cart, as installing a new motor with the same Wattage would not improve the performance of the cart.

That is fantastic. Thank you for the explanation. So that means....

 

Torque is a function of the wattage of the motor. Higher wattage of motor = more torque output.

 

Speed is the result of correctly gearing the motor. A motor with more torque can be geared for more speed. (Ignoring overvolting motor to make it spin faster and decrease life)

 

Run time is a function of how fast the battery is being discharged. For the same wattage motor a battery setup will deplete faster at a lower voltage because higher amps are being consumed. The more amps a battery pack is putting out the faster it will discharge, ie less run time.


I upgrade to a 500w motor (with appropriate controller for voltage). and run 4 12v 10Ah batteries.

At 24v it needs 20.8 amps. 2 parallel sets of 2 batteries in series (20 Ah total). 

At 48v it needs 10.4 amps. 4 batteries wired in series (10 Ah total). 


It seems to me even through the 48v setup uses half the amps, the battery pack has only half the Ah verse 24v setup so it balances out. I would think the 48v setup would last a little longer run time because it is drawing a lower amperage but maybe by only a couple minutes, especially if there is a lot of full amperage usage. Is this correct?

You are absolutely correct, the lower the Amp draw on a lead acid battery the more capacity it will provide. The difference in battery capacity between a high and medium Amp draw is fairly small though so I usually do not mention this behavior when explaining the fundamentals of lead acid battery packs, however, it is something that will effect ride time and a good thing to consider when designing a battery pack.
So if u was to use 3battryes 36v but then use a 4th but run that in parallel . So 3 running to make 36v and the 4th as back up would that work . Put it on a switch . Could that be done . That way u r uping the ah time and running time I think . It looks like it would work . I am doing 36v scooter . And have one battey could they work . I think with yours Brett you would be better doing the gearing I reacon u get more mph . But as this lot are gods when it comes to this stuff . A more bigger motor as I believe will give u more power up hills is they right

Similar question as above but I AM overvolting the motor. 36v battery system with a 36v 1000w controller and a 24v 350w motor right now. If I purchased your 24v 750w currie motor I don't believe the top speed would change at all (they're both 2600 rpm 24v motors overvolted to 36v). Would the torque be the difference? 

A battery pack made with four 12 Volt batteries with a switch that changes it output from 3 batteries (36V) to 4 batteries (48V) can be made as long as the three 12 Volt batteries used for the 36 Volt side, and the single 12 Volt battery used for the 48 Volt side are charged with separate 36 Volt and 12 Volt battery chargers.

When upgrading from a 24V 350W motor to a 24V 750W motor that is being overvolted to 36 Volts I would expect an increase in torque with the overvolted 750W motor compared to the overvolted 350W motor.

Ok thank you. I guess where I'm confused then is how does the difference in the motor wattage tell the controller to output a different current? Isn't the controller really the brains behind everything? 

The controller is sometimes called a brain box however it is only about as smart as a water faucet. It will control the speed of the motor from 0-100% and output up to the maximum amount of current that it was designed to. That is the limit of its intelligence.

The controller will output up to the maximum current that it is rated for if the motor demands that much current. The electrical power demand of the motor is controlled by the amount of mechanical power that it is asked to produce by its mechanical load.


For example if a motor has a 1/4 horsepower load on it and demands 10 Amps, and the controller is rated for 30 Amps, then the controller will supply the full amount of current that the motor demands. However if the motor has a 1 horsepower load on it and demands 40 Amps, and the controller is rated for 30 Amps, then the motor will only be supplied with 30 Amps and will only output 3/4 horsepower.

Very clearly explained. Thank you again. There's a reason everyone recommends ESP!

I don't understand something, sometimes the controller's rating is regarded to volts and the motor's to watts, but sometimes the controller's rating is regarded to watts and the motor's to volts ( or amps), i.e they switch around. Is this interchangeable so you only need to convert watts to volts so you can have the volt rating  for the 2? Sorry if I didn't make much sense I'm really new to this.

And also regarding battery life, will a 24V 20Ah (2x 12V 20Ah) battery have the same battery time as a 48V 10Ah (4 x 12V 10Ah)if the motors are the same rating

Controllers and motors both have Volts, Watts, and Amp ratings although manufacturers do not always list these specifications on the identification label. The Watts and Amps specifications can not be compared to each other because on most controllers and motors Watts is a continuous rating and Amps is a momentary or peak rating. The Voltage rating is more straight forward though. Usually the Amps rating will be around 50% higher than the Watts rating so for example a 24 Volt 500 Watt controller will be a good match for a 24 Volt 30 Amp motor, and visa versa.


A 24V 20Ah battery pack and a 48V 10Ah battery pack both have the exact same amount of capacity and will provide the same amount of ride time if used with controllers and motors that were the same Voltage as the battery pack and had the same Watts ratings.

What's the difference between let's say a 1000W motor and a 5000W motor? Both can be run at the same voltage and amperage yes? But the 1000W motor is more prone to overheating if a high voltage is used? Or is the higher watt motor capable of producing more torque at same voltage and amperage than the 1000W motor since less energy is converted into heat? Does the 5000W motor use more energy than a 1000W motor at the same voltage and amperage? I.e takes more amps

So Volts times Amps equals Watts. V x A = W


In your example the larger wattage motor will produce more torque and require more energy than the lower wattage motor.


A 1000w motor is going to produce the same amount of torque regardless if it is 12v or 48v. The difference is how many amps it will take to produce the torque. You run a higher voltage to have less amps. Run lower amperage is easier on electronic components and battery life. You will get more run time running a battery on a lower amp load then a high amp load. 


You increase motor wattage to get more torque. The scooter will accelerate faster with a higher wattage motor. You then change gear ratios if you want to go faster. 


You increase volts to keep your amps down. Most common configuration seems to be 24v up to 500w, 36v up to 750w, 48v up to 1000w for scooters. Puts you at about 20-21 amps at full throttle. Choose wire size, fuses, and switches to handle 25 amps.


Some people overvolt motors. Adding more voltage to a motor then what it is rated for causes it to spin faster. The scooter goes faster but you kill the motor in the process. The right way to do it is to buy a larger motor and change the gear ratio to get the speed you want.  


My example. I put a 24v 500w setup on my Razor gokart. It was fun, my 10 year old loved it, but I smoked the motor because it couldn't handle my 200lbs. So then I went 1000w 48v and oh holy hell it is awesome. The torque rips you off the line. These little karts should come with 1000w 48v from the factory! I still have the same top speed (I don't want it faster for my son to get hurt) but it launches off the line and burns those little tires if you want to. As he gets old I will change the gearing to get slower acceleration but higher top speed. But for right now it is good. 

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