Resistors in parallel question

[redman]

Hi,

Can anyone help me with this question?

When I try to work it out, I always end up with a different answer to the book.

To vary the speed of a d.c. series motor it is usual to connect a diverter resistor in parallel with the field winding.

The field of a series motor has a resistance of 0.6ohms and the diverter resistor has three steps, of 5ohms, 4ohms and 2ohms.

Assuming that the total current is fixed at 28A, find out how much current flows through the field winding at each step of the diverter.

These are the answers from the book : 25A, 24.4A, 21.6A.

Thanks

 

[msb2003]

The current is splitting proportionally, inversly to the relationship between the field winding and the diverter resistor

 

[NozSpark]

It's just inverse ratios

(28/(5+0.6))*5=25

(28/(4+0.6))*4=24.4

(28/(2+0.6))*2=21.6

HTH

 

[redman]

Thanks for that,

Seems simple now. Think I was just making it more complicated than it actualy is when working it out.