Starter Voltage Drop

In-Time Electrical Training — An explanation of the starter voltage drop test, with a real shop example. www.brighterideas.com

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[kdoubleish]

In your voltage drop test for the starter, why does the meter reflect both voltage at the battery and voltage drop at the starter. It seems between the battery terminals your measuring source voltage where as between the solenoid positive and starter ground your measuring what is missing? Does the meter always reflect only the differences in voltage between two points? Does the meter ever become part of the circuit and alter the readings? Or is the meter always an "objective" observer?

[bivideo7]

@kdoubleish The voltmeter always measure the difference between the positive and the negative terminals, whatever and wherever. By reading the loaded battery voltage and subtracting the starter voltage drop, you're adding up the individual voltage drops in the cables in reverse. The voltmeter doesn't affect the reading, and it can't lie to you.

[greco37]

in the first example (10v,10v) you said that the starter is using all of the voltage. Don't you mean none of the voltage?

[bivideo7]

@greco37 No - if the starter wasn't using any of the voltage, the drop would be 0.0V. A voltage drop measurement is kind of an "energy consumption" reading. The load should use as much of the energy as possible. When you put the leads on either side of the motor you're measuring what voltage the motor is consuming. If the number is the same to source voltage, there isn't any missing energy - it's all accounted for. If the reading was low, something else would be using something, which is wrong.

[andres220]

Ground cable? I thought starters were grounded through the engine?

[bivideo7]

@andres220 I work mostly with large frame engines, which have ground cables. If you're working on a car, you need to place the ground probe on the starter frame attached to the engine.

[Amopower]

I bought the FET book as well as the LoadPRO and want to diagnose a starter circuit. (good book). Does the LoadPRO change any of the steps in this video? I *think* the LoadPRO eliminates the need to crank the starter since it puts juice in the circuit itself, but I was not positive (no pun intended).

[yungmatt009]

ITT xD

[bivideo7]

@Amopower ------ Yes. If you put the leads on the terminals you'll miss the problem.

[Amopower]

Why posts and not terminals, is that to rule out a possible cable connection issue?