Ques. How is brake horse power calculated?
Ans. From the following formula:
| B. H. P. = | 2 π L N W |
| 33,000 |
in which
| B. H. P. | = brake horse power; |
| L | = lever arm, in feet; |
| N | = number of revolutions per minute; |
| W | = force in pounds at end of lever arm as measured by scales. |
Example—In making a brake test on a motor, the lever arm of the brake is 3 ft., and the reading of the scales is 30 lbs. When the motor is running 1,000 revolutions per minute, what is the brake horse power?
Substituting the given values in the formula,
| B. H. P. = | 2 π x 3 x 1,000 x 30 | = 17.1 |
| 33,000 |
Now, if the voltmeter and ammeter readings be 220 and 65 respectively, what is the efficiency of the motor at this load?
The amount of power absorbed by the motor, or in other words, the input is