VAT-40 Amperage scale

When I did the alternator test on the Subaru with the help of other students, I suddenly realized that I had been reading the wrong amperage scale on the VAT-40 for the entire time in the class!! There is a red and blue amperage scale. The VAT-40 has a rotary switch to set it to different modes. In "Starting" mode, the correct amperage scale is the red scale (0-500A). In "Charging" mode, the blue scale (0-100A) is the correct one. I had been doing the alternator test with the VAT-40 set to the "starting" mode and reading the blue scale. So when I thought the amperage was 20A, the alternator was really putting out 100A. I should have set the mode to charging and read the more detailed blue scale.

I think the Mazda's alternator is probably ok. I'll remeasure it next week.

The Subaru alternator put out about 80A at 14V and 2500 rpm. Spec was 65A or more at 14.1V. The front mounted alternator allows easy access to the thick B+ cable, so I clipped the current probe onto that cable.



Other completed tasks:

Tire rotation
CV boots inspection

I noticed some tissue stuffed into the exhaust pipe near the junction of the left and right exhaust manifolds. I took a picture of it and will ask the dealer mechanics about it.

Measured specific gravity of battery cells. The results seem to vary depending on how much electrolyte was drawn into the hydrometer.