Amperage question

[Jean-Marc Dugas]

I had 2 new bearings installed in the alternator along with new brushes & springs and rectifiers. The engine bay is now a little quieter.

I did an amperage test today to see how everything works. What i did was to throttle the engine to 2,000 RPMs and turned all the electrical things I could on and tested how many amps at the battery and at the alternator.

At the alternator I had 83.2 amps


And at the battery I had -6.2 amps


The images are upside down!

Is this normal to have negative amps?

 

[Jean-Marc Dugas]

MAybe I took the negative reading from the negative side of the battery...mmmm....will have to test that again tomorrow.

 

[Paul Steinberg]

Yes, you can get a negative reading if you draw more amps from the battery than the alternator can supply. Happens all the time with my 1962 Chevrolet when I use the siren. My present alternator is a 42-amp model, and one of these days I will install the one that came with the car, which is a 65-amp alternator. I had the original serviced, and used the 42 in its place, and never got around to switching it back.

 

[Jean-Marc Dugas]

The alternator is a 145 Amp unit, so it should not draw from the battery at a load of 83 Amp since it still has 62 Amps available. That is my understanding of how this works, the alternator should supply the load until it is maxed out and then the battery comes in with the additional amps.

 

[Jean-Marc Dugas]

Tje positive or negative reading depends on the way the clamp faces. Learned something new today.