Under the Hood: Your Car's Alternator

Well, that was an odd sound. I had gone out to my truck and instead of a nice crank...I got a lousy chattering sound from under the hood. Yep...Something wrong with the charging system.

I popped the hood and considered the problem for a few minutes. The ignition switch works because the starter tried to engage. The starter worked when I turned the ignition switch so it must be okay too. That leaves the battery and the charging system as the likely culprits.

I brought out the battery charger and clipped the leads onto the battery posts and switched the charger to on. I watched the ammeter on the charger to see how high it would go under load and it went all the way to ten. A ten amp draw indicated a very drained battery. Well, it had been a few days since I had tried to start the old truck. Could be there was a bad connection and a slow drain on the battery from somewhere.

A few hours later the draw was down to a two and I unclipped the leads from the battery and the engine started right up. Well, this actually fixed nothing as I had charged the battery from the charger. I still needed to determine why the battery had gone dead. Taking a volt meter I selected the DC setting and placed the leads from the meter across the terminals of the battery. They showed twelve volts with the engine running. Twelve volts was not the reading I was hoping to get. A healthy charging system should have showed thirteen to fourteen volts. Something in the charging system was not working well. And that something, was probably the alternator.

The auto parts store wasn't all that far away and I took the chance to drive over there. They offer a free charging system analysis and that test would tell me for certain what was actually wrong.