# Battery charging Problem

1. Oct 19, 2009

### phys-unit

1. The problem statement, all variables and given/known data

A cordless drill battery charger is rated at 30.0 W but requires only 13.5 V. It contains a transformer that converts 120 V household voltage.

(b) What is the current in the secondary coil while the battery is charging?

(c) What is the current in the primary coil while the battery is charging?

(d) The battery is rated at 3150 mA·h life and generates 12.0 V. This means, for instance,that it could supply 100 mA of current at 12.0 V for 31.5 hours. How much energy does the battery store?
4 J

(e) What is the minimum time required for the 30.0 W charger to fully charge the battery? While such a time is possible in principle, in practice charging times are much longer.

2. Relevant equations
Vs/Vp = Ns/Np (I think this is what I should be using)

3. The attempt at a solution
I just don't get how to set any of it up.

EDIT! ALRIGHT, I got A and B A is 2.222 and B is .25

If someone could show me how to do it I'd be really happy :\

Last edited: Oct 19, 2009