Faulty Ignition? Is it the Battery or Alternator?


I’m not very mechanically inclined when it comes to automobiles, but I did learn a nifty little trick the other day… This subject deals with common ignition problems, as in the often confused vehicular ailment; do you have a faulty alternator or battery?

The automobile's electrical powerhouse - Alternator...

The automobile's electrical powerhouse - Alternator...

A lot of my car problems that have occurred within my driving history, for the most part, have been related to the ignition system. I’ve had a few starter solenoids installed, an alternator and numerous amounts of batteries that needed replaced (mostly due to booming sound systems) down through the years.

When having faulty ignition problems, many people are often quick to blame the battery, terminal cables, or the starter solenoid…but what about the alternator?

The alternator, when it involves auto-mechanics, is basically a rotating machine that transforms mechanical energy to electrical charge in the form of alternating current – by definition, an electric generator for producing alternating current. The alternator, when working correctly, maintains an electrical charge for your vehicle’s system, hence keeping your battery charged in the process.

A couple days ago, I learned some advice from an ol’ southern “shade tree mechanic,” as they say. Personally, I call it good, useful knowledge through working experience.

Well, anyway, my girlfriend’s car has been having trouble starting lately, electrical gadgets not operating correctly, and just overall acting zapped & drained of power.

I first thought it was the alternator, due to an intuitive hunch, but how in the hell do I know for sure? I checked the battery, and yes, it was dead. I looked at the battery post terminals, and yes, they were corroded & funky looking. I knew it wasn’t the starter solenoid, since the car would start after charging the battery. I changed out the terminals, but yet, this damn thing would keep dieing out – even after a full battery charge.

Okay, it is either the alternator or the battery cells are shot and I need to replace the battery.

Instead of taking a chance (I’ve did this before) and go out and buy a new battery, she asked her step-dad about it. He had, as he stated, an ol’ mechanic trick that would determine if it was the alternator or not.

He said to fully charge the battery, connect the cables, and start the car. …And from there, after the car has been running a couple seconds, remove the negative cable from the battery. After removing the negative cable, If the car shuts off, it is your alternator…and if it keeps running, it is your battery or some other electrical issue. I followed this advice, and as soon as I removed the negative cable from her car, it shut off. So, by this form of testing, it is definitely the alternator – and he touted this sly, old-school method, to have a 99% chance for accuracy.

I didn’t know that! Just to make sure, I went over to my car that is currently functioning properly (for now; fingers crossed) and started it and removed the negative battery cable after a couple seconds…and it never missed a lick. I thought, “okay, this is some damn good advice.”

From there, we ordered the part for her car, changed the alternator, and it is now running smoothly. So this proved, that this little bit of knowledge that I learned a few days ago, to be true. Many people would have run out and bought a new battery, before considering it to be the alternator.

Bottom line: If you’re unsure if it is the battery or the alternator, try this simple testing method first; it may save you the expense of a new battery – that you didn’t even have to buy.

Also, take heed to the advice from another mechanic about this subject:  

“Good trick, but just be careful not to do it on many of the newer model cars, or you will have more things to reset in the car than you would want.

There is also the risk of blowing a diode in the alternator.

I just look for output at the alternator with a milli volt meter.

Most alternators when they break down only need one or two small components replaced to be good as new. If you are handy, you can do this yourself providing you know where to purchase these bits. We have electronics shops here that sell the parts for a couple of dollars. I always sort my own alternators.”

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