Most of you probably know about Ohms Law or have heard it mentioned at some seminar, how often do you use it in your diagnostic procedures? Some of you may laugh at the mention of it, or may not even know what it means. It can be a powerful tool, and help you in electrical diagnostics.
One Volt of electrical pressure will push one Ampere of electrical Current through one Ohm of electrical Resistance.
You have probably seen the circle divided three ways with the symbols "I" for current, "V" for volts, and "R" for resistance, I will not confuse you with that here, just tell you the formulas.
If you know two of any of the three values, the third can be found with simple math:
If you have amps and ohms, multiply amps times ohms to get voltage. (E = I X R)
If you have volts and ohms, divide volts by ohms to get amps. (I = E / R)
If you have volts and amps, divide volts by amps to get ohms. (R = E / R)
"I" stands for Intensity or electrical current. flow
"E" stands for volts or EMF. (ElectroMotiveForce) pressure
"R" stands for Resistance or ohms. resistance
All this was discovered by a German scientist named Gustav Kirchhoff, who found that, the sum of the voltage drops across all resistances in a circuit must equal the voltage of the source. Also that, the sum of the currents flowing into any point in a circuit equals the sum of the currents flowing out of the same point.
Some of you may find this a bit confusing, others may understand it perfectly well, lets put it to practical use.
To find the motor resistance in this case study, divide volts by amps, 12.6Volts/20.43Amps=0.61 Ohms or six tenths of an ohm. The new motor pulled 10.95Amps, so 12.6Volts/10.95Amps=1.15 Ohms