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Old 10-10-2012, 03:37 PM   #7
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Originally Posted by whynotthinkwhynot View Post
Here's a thread on how someone bypassed (actually bridged) the low speed circuit. Ignore the comments about how current (amps) will be increased. It won't. I have 2 master electrician licenses, so I know electricity. The fans will pull the same current on low or high speed, voltage is reduced (and thereby fan speed) but current will remain the same. It would stand to reason that you wouldn't be pulling more than you would on high speed since the fans have only one winding. It would be nice if Ford were to give us multiple winding fan motors instead of resistive circuits, but that would be much more expensive, and larger.

Solution to cooling fan resister failure???
Thinking I missed something I took pause and looked at the Bosch motor used in the radiator cooling fan assembly. The motor is just a basic DC (direct current) motor - it has brushes and coils of wire with a set resistance. Yes - nothing is transformed. There is no inverter and no AC (alternating current).

Aside from practical knowledge or theory - let's look at the obvious. FORD Uses a '50 amp' fuse in the high speed circuit and a '30 amp' fuse in the low speed circuit. That alone should tell us that MORE current is used for HIGH speed fans and LESS current is used for LOW speed fans.

And WHAT is the difference between the HIGH speed Circuit and the LOW speed circuit you ask - THE COOLING FAN RESISTOR - that's it. You can accurately conclude here that jumpering the resistor WILL increase the current in that branch of the circuit.

I think what is being misunderstood here is: CURRENT is the same, in a series DC circuit, through all components in that SERIES circuit for a total value of RESISTANCE. When you remove (short out) a component in that series branch your total resistance DECREASES and INCREASES your current, applied voltage stays the same for the branch. You can use the voltage divider formula to calculate voltage dropped across each component.

Look at ohms law: E=I*R, or I=E/R. When resistance goes down, current goes up (It's a denominator (R) vs. numerator (I) thing, on opposite sides of the = sign).

Or just look at what FORD did when they designed the circuit branch:
circuit diagram here: Solution to cooling fan resister failure???

HIGH speed fans got 50amps.
LOW speed fans got 30amps, nearly a 70% difference in the fuse current ratings.

This is first year circuit theory in any Associate or Bachelors Degree program. Ignore all you want, But then it is YOUR car......

Maybe we are confusing another aspect of ohms law, POWER. P=I*E or P=(I^2)*R or P=(E^2)/R and total power in the circuits.
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