# DC Machines

1. Aug 24, 2008

### Vagrant

1. The problem statement, all variables and given/known data
A dc machine(6W, 120V,1500rpm) is separately excited and delivers rated current at rated terminal voltage.Field winding is connected to 120V supply. Rfw=100$$\Omega$$.
a) Determine the value of field current
b) Determine the value of Rfc required.

2. Relevant equations
Vf= IfRf

3. The attempt at a solution
In the question the value of Vf is given, while both If and Rf are variables. So I need another relation to find out both the values. Is there another relation that I'm missing?

2. Aug 24, 2008

### montoyas7940

Unless I misunderstand the problem, you can get everything you need from the power equations P=IE and P=I^2*R.