Engineering Question: Please explain "peak rating" for an E motor

Marketing people often play games with peak ratings. In the old days audio amplifiers were advertised with ridiculous power ratings, based on peak figures. The same thing happens with motors and engines.

Generally industry standards eventually rein in this sort of behavior. NEMA has rating standards for motors, but not everyone uses them. I have no idea what G.M. is using for its Volt rating.

Tom

 

NEMA defines peak power as the speed and torque where a motor generates the highest power. All motors following the NEMA standard are rated for continuous operation unless there is a time rating.

Tom

 

I don't know if it is a standard definition, but peak is generally the maximum that can be delivered without regard to how long that maximum can be maintained. As Tom said, marketing people love to use it, but it is close to worthless with regard to comparing two different motors (or whatever).

 

Continuous means 24/7.

Tom

 

There are too many standards. Companies often make up their own to show their product in the best light. GM is probably doing that, but I haven't looked at the details.

Tom

 

Both are useful numbers. Continuous is, well it's continuous.

Peak isn't defined unless they define it but I think it's reasonable to assume it's available for short bursts like 0-60 acceleration or maybe as long as passing another car. The definition of how long you can use peak probably includes factoring in temperature at the start of peak usage and ambient or cooling system temperature.

 

This sort of discussion isn't limited to electric motors, but also applies to internal combustion engines. For example, the diesel engine in my sailboat is rated at 10 hp, but it is a 500 pound engine. It can do 10 hp for the rest of your life, as long as you add fuel and oil once in a while.

Most small marine diesel engines are rated with some sort of peak rating that they can do for only a few minutes without damage. It's really a useless rating.

Tom

 

To me the really important number is MTBF. Not even the marketing folks bother with this.