Electronic – Need a Loud Electrical Component for Magnetic Lock

You're on the right track in two regards; your calculations headed in the right direction, and the Radio Shack guy doesn't know what he's talking about. A general good start in thinking about electrics is to consider vague magnitude. You have a project dealing with 40W here. Does 1/8 of a Watt sound like the right sort of answer?

The bit of calculation you need here is the power dissipation in the resistor. A series resistance circut (when resistors are connected end to end, "in series") is pretty simple. In this case, we know that the current flowing in the circuit is 0.335A or so. We also know that the resistor you are using is 100 Ohms.

The power dissipation in a component is Volts X Amps. Combining this with Ohms Law, we can show that this power is also Amps squared X the resistance in Ohms.

This gives us 0.335 X 0.335 X 100. Which gives an answer of 10.77 Watts.

So the vague magnitude speculation actually gave you a pretty good answer, calculating it we find a 20W rated resistor will comfortably handle this load. And not to trust the guy in Radio Shack.

edit Oh poo, I didn't realise you have two parallel strings. And now I'm typing this retraction I can't see your picture. BRB.

edit 2.

Okay, we now have 50 lamps across 120V. The total resistance of all the lamps is V*V/P, which is 120*120/20, or 120*6, which is 720 Ohms. Divide that by 50 to get the resistance of 1 lamp, which is 14.4 Ohms.

Now the resistor needs to be the same resistance as 27 lamps, so it's 27*14.4 which is about 388.8 Ohms. So that's our resistor.

The current flowing is I/R, which is 120/720, about 0.166 Amps. And the power dissipated by the resistor is 0.166*0.166*388. Which comes back to 10.77 Watts again; which it ought to because we're dissipating about (rule of thumb) 1/4 of the entire string's rated power as useless heat in the resistor.

With the given information and discussion, I think the motor will operate with the following connection. The capacitor may not be needed. It the current in the start coil can be measured during start and it is relatively low with a capacitance value used for similar Hp motors, it might make sense to try a direct connection from the switch to the power line. There would be a risk of burning out the winding fairly quickly if it is designed for use with a capacitor.

Various electrical diagrams for washing machine are available on the internet. Some show motors that use a start winding with no capacitor and some show a capacitor. The extra centrifugal switch is shown on some as switching a function external to the motor. The extra contact on the starting centrifugal switch is shown as feeding power to an external function when the motor is up to speed.