# Nominal rpm x Peak rpm on a electric motor



## major (Apr 4, 2008)

DiasAida said:


> I am currently projecting an electric motor to run in a electric car and I came with a question that I can not answer with my knowledge:
> The car that i am projecting have 76 rated torque with 3200 rpm nominal speed. But with these variables it is not possible for it to reach the 60 km/h needed on the project. I need to increase the speed up to 4500 rpm (still within the speed range of 6000 rpm) but I do not know if this is going to shorten the motor life and if it is possible to maintain that rotation for long periods of time (like 4-5 minutes). Can somebody help me with this?
> 
> Thanks
> ...


Hi Marcos,

I think you are confused about motor "rating" or as I call it---the nameplate game. At face value, your post seems confusing and one would just tell you to choose the appropriate gear ratio to run the motor at your desired RPM for the required vehicle speed (km/h). So I hope I am addressing your question.

Electric motors are rated for a specific condition, meaning at a particular RPM, torque, voltage for a specified time with certain ambient conditions and thermal management (cooling). The makers of the motors then can assure that their products conform and users will know what to expect, exactly. This information often times gets abbreviated and stamped on the nameplate. These figures are often called "nominal".

Electric motors routinely are capable of operation beyond these nominal ratings. For instance RPM can be higher, in your case 6000 max. This means that this motor can operate without damage and give acceptable life operating at 6000 RPM or below. However, this does not imply that the other "ratings" such as torque will apply when operated at other than nominal RPM (3200).

The same logic often applies to nominal torque. Motors can operate at "overload" torque which is greater than nominal torque, but for reduced time periods before rated temperature is reached.

In your case, the motor is rated at 76 Nm (or lb.ft.---you don't say which units) at 3200 RPM. It is likely that it will operate perfectly well at 4500 RPM, but will not be able to put out 76 Nm for long without overheating. An increase from 3200 to 4500 RPM at the same torque would be 40% increase in power output. So at 4500 RPM, your motor may be able to run for long periods without overheating if the load torque is lower. A reasonable guess would be 40% lower torque so the power is the same. But----it is not a sure bet----check with the motor manufacturer to be sure.

I hope this addresses your question.

major


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## DiasAida (Aug 10, 2011)

Thank you so much for the information. It helped me a lot!


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