# DC motor efficiency at overloads...?



## CroDriver (Jan 8, 2009)

As far as I know a DC motor is 80%-90% efficient at normal (rated) loads. What can we expect when we overload the motor with 5X the rated current? 

Let's say we have a Kostov 11" (a totally imagined situation  ) that is rated for 40kW (192V/250A). 










What efficiency could it have when we push 1000 Amp trough it? 

50%? 60%?


----------



## DavidDymaxion (Dec 1, 2008)

This was done via math and estimation, but in the past I estimated John Wayland's old 11 inch Kostov was down to about 60% average efficiency running the 1/4 mile. He had an old Zilla controller that would do max about 1200 battery Amps and 1800 motor Amps, but IIRC he was down to about 1/2 that by the end of the run due to battery sag and back EMF.


CroDriver said:


> As far as I know a DC motor is 80%-90% efficient at normal (rated) loads. What can we expect when we overload the motor with 5X the rated current?
> 
> Let's say we have a Kostov 11" (a totally imagined situation  ) that is rated for 40kW (192V/250A).
> 
> ...


----------



## major (Apr 4, 2008)

CroDriver said:


> As far as I know a DC motor is 80%-90% efficient at normal (rated) loads. What can we expect when we overload the motor with 5X the rated current?
> 
> What efficiency could it have when we push 1000 Amp trough it?
> 
> 50%? 60%?


Hi Cro,

The efficiency at 1000 amps depends on the condition (speed). At 1000 amps and zero RPM, efficiency is zero %. As the speed and voltage rise, the efficiency raises also. At full battery voltage to the motor, the efficiency is likely in the 60 to 70 % range for the particular motor you describe at 1000A. But that is just a guess. You'd have to know more about the motor to calculate it, or get the figure from Palem.

Regards,

major


----------

