Weekly Waveform #2 - Voltage Drop testing the starting circuit

This is the Second in a series of labscope activity exercises to help us pick up that labscope for a few minute a week and perform a test with it. This will be a skill building series to help new and experienced technicians become familiar with labscope operation and waveform acquisition. If you want to follow along with the series make sure to subscribe and join the FB group. https://www.facebook.com/groups/automotiveweeklywaveforms Voltage drop testing the starting system. If you have a multichannel scope now is the perfect time to build a skill and use that second or third channel. This test can be performed just fine with a single channel scope but requires taking multiple captures. I had Scope ground connected to battery negative Channel 1 connected to battery positive 20 V scale Channel 2 connected to engine ground (alternator bracket) 2 V scale Channel 3 connected to starter B+ terminal 20 V scale My sweep time was 200ms In order to get out voltage drop on the positive cable we have to do some math and subtract channel 3 from channel 1 (channel 1 voltage - channel 3 voltage = voltage drop). We also need to make sure the cable is under load so make sure to take measurements during the time the engine is cranking over on the waveform. Once comfortable with this test, assuming the starter isn't hidden under the intake, you should be able to perform this test in less than 5 minutes. If only checking the battery voltage and voltage drop on the negative cable this is about a 2 minute test with tons of information. Here is my screenshot from the test. https://altusdrive.com/Home#/Gallery/Details/10104C4F947344A19172424AB9D0A9FA