Usually if you run higher voltage on a low voltage DC motor then it will draw more current as it is not wound for the higher voltage. HOWEVER, nearly all good quality DC speed controllers like AXE, Curtis, Sevcon, Evnetics, and Zilla, all have what is called ACTIVE motor current limiting.
The way this works is that the current is monitored by some electronics by means of a shunt resistor or some other means of measuring motor current. When the current gets above a value set by the software, the active switching elements (Mosfets or IGBT's) will switch off and the current will fall, then they will switch on when current falls below the set value until it goes above the set value, then its off again. This happens many thousands of times per second! The result is the current to the motor is regulated from not going above the set value you programmed into the controller.
So what you do you for if you want to run a motor that is 36 volt rated, at 72 volts, but you want double the power? Easy, find what the continuous rated power and current draw is for the lower voltage. I will use the ES-22-2 motor as an example as I have used this motor very successfully in my builds. This motor is rated at 3600 Watts output at 130 amps draw and turns at 2100 RPM on 36 volts.
At 72 volts at 130 amps you will get about 7200 Watts output and the motor will spin at 4200 RPM. To keep the current draw at 130 amps, just go into your controller setting and set motor current limit to 130 amps. On my AXE7234 controller I like to run my current limit at 300 amps, but I gear down my kart with 6:1 ratio since I go more for acceleration than top speed. At lower gear ratios like 4:1 you may want to set current limit closer or at the continuous rating of the motor. I have successfully run this motor on 5:1 ratios before with no issues, but acceleration just was not enough for me. I like to be thrown back very hard in my seat.
One caution I must state is that higher voltage will cause more arcing on the brush/commutator interface. I do not recommend over volting more than twice the voltage rating of a GOOD quality motor. For interpole motors you can go even higher, but you won't see interpoled DC motors until you get into the larger frame sizes like a Warp 11 HV, which has interpoles in them.
The way this works is that the current is monitored by some electronics by means of a shunt resistor or some other means of measuring motor current. When the current gets above a value set by the software, the active switching elements (Mosfets or IGBT's) will switch off and the current will fall, then they will switch on when current falls below the set value until it goes above the set value, then its off again. This happens many thousands of times per second! The result is the current to the motor is regulated from not going above the set value you programmed into the controller.
So what you do you for if you want to run a motor that is 36 volt rated, at 72 volts, but you want double the power? Easy, find what the continuous rated power and current draw is for the lower voltage. I will use the ES-22-2 motor as an example as I have used this motor very successfully in my builds. This motor is rated at 3600 Watts output at 130 amps draw and turns at 2100 RPM on 36 volts.
At 72 volts at 130 amps you will get about 7200 Watts output and the motor will spin at 4200 RPM. To keep the current draw at 130 amps, just go into your controller setting and set motor current limit to 130 amps. On my AXE7234 controller I like to run my current limit at 300 amps, but I gear down my kart with 6:1 ratio since I go more for acceleration than top speed. At lower gear ratios like 4:1 you may want to set current limit closer or at the continuous rating of the motor. I have successfully run this motor on 5:1 ratios before with no issues, but acceleration just was not enough for me. I like to be thrown back very hard in my seat.
One caution I must state is that higher voltage will cause more arcing on the brush/commutator interface. I do not recommend over volting more than twice the voltage rating of a GOOD quality motor. For interpole motors you can go even higher, but you won't see interpoled DC motors until you get into the larger frame sizes like a Warp 11 HV, which has interpoles in them.
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