Starter Motor On Car Testing

4 May 2011

These tests were completed on a starter motor on an engine set up outside of a vehicle.
Before carrying out any tests however, the ignition or fuel injection system must be deactivated (which we did by removing the fuse), the battery to be checked for serviceability (after removing surface charge, checking voltage - result 100% - 12.7v), the right range has been selected on the digital meter (20DC volts) and that the vehicle is in neutral, which in this case does not apply.
The avaliable voltage across the battery while cranking needed to be checked, which is specified 9.5v minimum. The result was 11v which is plenty.
We then had to perform a voltage drop test (while cranking) between battery positive and solenoid starter input, across solenod main input and output, and between battery negative and starter motor body. The specifications of these were all very low. The first was specified less than 0.2v, however the result was 0.4v (well over and therefore failed). The second was specified less than 0.1v, and the result was 0.17 which is not too much over but still a fail. The third was specified less than 0.2v and the result was 0.91v which again is too high and failed. The maximum allowable voltage drop across the component is 0.5v and the total turned out to be 1.48v, almost 3 times that value.
The starter motor current draw to be tested using a clamp meter. The specified current draw is 125-150 amps. The test result was 133A which is a pass.

REPORT:

The voltage drop showed increased figures than specified which means there is resistance within the circuitfrom the battery to the starter motor and within the solenoid. Amps however were within specified range. The resistance source needs to be minimised for starter motor efficiency.
Starter circuit test failed.