To test a starter motor for faults while it is attached to the engine there are steps you need to take to insure that the testing you do is right and accurate. Firstly you must determine whether the car is equipped with any device that requires a power source for its memory, and if it is, you must make sure no memory is lost before disconnecting the battery, to do this you can do either one of two things, firstly you can attach a 9v battery to the cigarette lighter of the car or attach a memory minder device to the cigarette lighter. This will protect any memory within the car i.e radio stations or keycodes you may need to operate the radio.
The preliminary check before carrying out a starter circuit voltage drop test-
- · Has the ignition or fuel injection system been deactivated?
- · Has the battery been checked for serviceability?
- · Have you selected the right range on your meter?
- · Is the vehicles transmission in neutral?
The OVC (open circuit voltage) of the battery must be checked, this is to insure that you will be able to test the starter with sufficient battery power. The OVC of the battery should be between 12.4v-12.6v this converts into between 50% and 100% charge. To do the OVC you attach your meter Positive Probe to Positive battery terminal and Negative meter probe to the negative of the battery terminal and wait for your reading. If you get a reading of over 12.6v this is known as surface charge, this can be drained by turning the lights or fan on for a few seconds or until you get a meter reading between 12.4v and 12.6v
Once you have established the OVC of the battery you must check the available voltage drop across the battery terminal while cranking. To do this you again attach positive to positive and negative to negative and crank the engine for a few seconds, the reading on your meter should go down and be less than your OVC of the battery but must be above 9.5v which is the universal Cranking voltage specification (spec) if the cranking voltage fails the battery must be retested to determine its condition before continuing with the test.
The next part of the test is to check the starter circuit for voltage drop. First check the loss between the battery positive post and the solenoid starter input stud while cranking. The spec for this test is less than 0.20volts, anymore and it is a fail. Next you check the loss across the solenoid main input and output terminal studs while cranking, the specs for this is less than 0.10volts, anything more is a fail. Lastly you check the loss between the battery negative and the starter motor body while cranking, the spec for this test is 0.20volts, again anything more is a fail. Now you add the voltage drops together to find the maximum voltage drop. The maximum allowed is 0.50volts, anything higher is a fail and there is something wrong with the starter wiring or magnetic fields.
The last test you have to do is checking the starter motor current draw, the starter current draw specifications is anything between 125 and 175amps. To check the current draw you need to use an inductive ammeter (clamp meter) which is designed to take up to 400amps. To use this clamp meter you must set it on 400 amps DC and push the zero button to zero the meter, once the meter is zeroed clamp it around the positive battery lead anywhere between the positive terminal and the ‘B’ terminal of the solenoid. To get a reading it is easier if you have someone crank the engine for you as it is cranking push the hold button, as this will retain your reading so you do not lose it.
No comments:
Post a Comment