# 48V v/s 120V



## PStechPaul (May 1, 2012)

I'll reply the same as in my PM:

Well, the motor is designed for 48VDC and that's what the chart shows:
http://hpevs.com/Site/images/jpeg/power-charts/pdf/ac20_48v_650a_imperial.pdf


I assume this is an AC induction motor and it should be possible to overclock it to 3x at 6000 RPM with 144V where it should draw the same current and provide the same torque but 3x the HP. However There will probably be more losses and less efficiency, and their controller is apparently not designed for the higher voltage. It seems that it provides a peak output of 25 HP at 2000 RPM at about 650 amps and 45 volts, which is 29.2 kW or 39 HP, indicating a rather poor efficiency of 64%. 

I did not find data on the AC-20 at 120V.


The motor is designed for motorcycles and golf carts and not for full size passenger EVs, much less executive sedans. It is only a 60 pound motor, after all. That's about the weight of a standard 5 to 10 HP induction motor. You will either have to work with a motor manufacturer to get the specifications you really need, or invest in a motor designer who might be able to do better for less, or rewire a standard motor for a power boost. But you're not going top do much better than the AC-50, which is rated at 73 HP and is only 115 lb:
http://hpevs.com/catalog-ac-50.htm


That's probably about half of what you want for an executive sedan or limousine. You might start with a high efficiency 40 HP standard ACIM and boost it to 120 HP, and it will be about 300-400 pounds.


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## major (Apr 4, 2008)

kishor5466 said:


> As torque *rpm =power if the motor can give greater rpm and torque at 48V then how is that it gives only 25 HP of power??


That system has a limit of roughly 500A and 45V. That is 22.5 kW input power. 



> Or is it as below i have explained
> 
> The power speaks of how faster the motor can give energy to the systems .Hence though the torque at 48 V is greater and the peak rpm is equal to that of 120V , the motor can't give 50Hp of power at 48 V because the time taken by the motor to reach the required RPM at given torque is more , hence the power is lesser since power is energy by time...
> 
> ...


These motor performance specs are given at steady state conditions. So the time it takes to reach speed does not enter into it.

This is an AC induction motor. It has a base frequency (which relates a base speed). The maximum torque from the motor is available only at and below base frequency. Above base frequency the maximum power is reduced because the maximum torque is lower.

Base frequency is proportional to the maximum voltage. So at higher voltage, the motor can produce the maximum torque up to a higher RPM, hence higher power.

Good data for all possible combinations of applications for motors and controllers is difficult to obtain from most dealers or makers. And the data or charts which are provided often have inconsistencies or errors.


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## kishor5466 (May 15, 2012)

major said:


> Base frequency is proportional to the maximum voltage. So at higher voltage, the motor can produce the maximum torque up to a higher RPM, hence higher power.


Does that mean any motor when operated at higher voltage will give a wider constant torque region though the speed will be increasing , so that the power is also increased??


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## major (Apr 4, 2008)

kishor5466 said:


> Does that mean *any* motor when operated at higher voltage will give a wider *constant torque* region though the speed will be increasing , so that the power is also increased??


Even though "constant torque" is a term used in the literature often, I don't like it. The motor output torque is determined by the load primarily and then the motor characteristic via the source (battery and controller). My comments apply to the context to which I was addressing. Those may well apply to other motor/system applications but I am not prepared to say they are universal for "any" motor.


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## Dennis (Feb 25, 2008)

kishor5466 said:


> Does that mean any motor when operated at higher voltage will give a wider constant torque region though the speed will be increasing , so that the power is also increased??



Electric motor torque curves are derived from the motor's fundamental characteristics in where the motor is hooked up to a power supply instead of some motor controller. The constant torque is not a characteristic of any motor, but is a control characteristic from a motor controller.

Constant torque occurs when current is held constant. In DC motor controllers current limit is what limits current to a fixed value. When a motor controller is held at 100% in throttle position and a motor is connected to this controller that is accelerating a mass, whether it is linear or rotational, then the current will be limited by the controller in which turn the torque will be constant when the motor is accelerating a mass. 

The motor eventually produces enough opposing voltage as it spins faster and faster against the motor controller's output voltage that will then cause motor current to fall below current limit of the motor controller and thus the current draw becomes dependent upon the voltage difference of the motor controller output and the motor's opposing voltage across the electrical resistance of the motor.


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