# Over powering AC



## onegreenev (May 18, 2012)

AC motors are usually coupled with a controller matched to the motor. Let's take the AC 50. Depending on the controller purchased you can run 96, just under 120 and now the 144 vt all on the same motor. I would not run like 250v through them. They were designed as low voltage motors with some but in leeway. Stay within a reasonable parameter and you should be fine. You always want to cool your motors and controllers.


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## major (Apr 4, 2008)

Dustin_mud said:


> Is it *safe *to *over power* a ac motor in short burst or is there no good way to keep it cooled?


Overpower  You mean overload? Sure you can. And you can run AC machines faster to increase power output. And you must manage it thermally. Is it safe  You ask strange questions. What do you mean "safe"? Maybe; maybe not  Just depends if you know what you're doing and how far you push it. And there are more cooling options with AC machines due to the absence of the commutator.


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## Dustin_mud (May 22, 2012)

Forgive my questions as I am a converting gear head, "safe" as in not to burn my rig down to the ground. lol


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## sergiu tofanel (Jan 13, 2014)

Of course you can "overpower" an AC motor. The only issues that come to mind are current overload (which can overheat and consequently burn out the motor) and over revving (hard to do with an AC) which may cause mechanical damage. I would guess that you will burn out the controller before you burn out the motor.


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## Red Neck (Feb 1, 2013)

With the motor, overheating is the issue you should think of, but a solid motor also has a thermal diode in it and will go offline if it reaches unsafe temps. 

The other thing is the kind of bearings used. To which RPM.
AC motors can really spin well, but it is better if you check
what the bearings are rated at. You can still go a few
thousand RPM over that, but for long term use, it is
best if appropriate bearings are used.


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## subcooledheatpump (Mar 5, 2012)

To be clear, with a higher available battery voltage, the AC motor can achieve higher frequencies while maintaining constant current. 

This means with a higher voltage, you can achieve higher motor speed while maintaining torque. 

If the voltage falls, you may still be able to reach high speeds, but only with reduced torque. 

Overcurrent in an AC motor is also possible, to achieve greater torque. Although with greater current, you also produce much more heat as Power = Current squared x resistance.


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## PStechPaul (May 1, 2012)

AC induction motors are subject to the limitations of breakdown torque and locked rotor torque, which are typically 2x to 4x nominal. Thus at rated frequency you might only get three times rated power (and three times rated current). But losses go up by the square of current, so a 96% efficient motor (4% losses) would have 4*4%=16% losses at 2x (for 84% efficiency), and 9*4%=36% losses at 3x (for 64% efficiency). These losses create heat in the stator and rotor, and will cause the temperature to exceed the insulation rating in a short time (several seconds to a minute or so), and can result in breakdown and catastrophic failure. But it is common practice to include a thermostat in the windings to shut down the motor before it burns up. An induction motor is very reliable if run conservatively and properly protected, and the only items that might need occasional replacement are the bearings.


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