Car Repair & Diagnostics : How to Test a Car's Alternator

When testing an alternator on a car, it's important to first check to see if a battery has enough voltage. Use a test light on a car's alternator with help from an auto mechanic in this free video on car repair and diagnostics.

Expert: Tom Brintzenhofe
Bio: Tom Brintzenhofe has been a mechanic for the past 17 years.
Filmmaker: Reel Media LLC

Category:

Autos & Vehicles

Tags:

• auto repair
• car repair
• auto maintenance
• auto service
• car maintenance
• car care
• car service
• automobile
• car engines
• diagnostics

[lakayna]

thanks that straight to the point

[idae209]

I have a fan on the intercooler of my car which takes a good amount of volts runs about 13.5. runs fine on during the day but at night when i have the fan and the lights on the voltage drops to about 12.5 and fluctuates to about 13volts back n forth. I have a meter installed in the car and while im driving the alternator doesnt seem to regenerate more volts but only maintains or drops about 0.5volts. Main question is, is it normal that it does that or should i get a stronger alternator?

[casper123]

The best ehow video i've seen, very informative.

[valleystylez1]

Is it a problem when an alternator is overcharging! I thought they only come into play when they detect the battery needs them.

[Nalleflaca]

@cmaldonado8 you probably have an alternator contaminated with oil or dirt that is causing the inductor's brushes to not make good contact to give a constant field so the armature is giving you a higher transient output voltage. If this is the case, just by cleaning the alternator should be enough and of course eliminating the cause of contamination.

[nightrain766]

1.2volt per cell...6 cells in a battery...static voltage should be 12.6 volts. Yours was 12.58 so that's close. Also it's normal for newer cars to charge over 14 volts, people shouldn't be scared of this. To get a true test of integrity one should be also looking at Amperage, that's the really killer in the charging game. [licenced mechanic, with 3 years at auto electric shop]

[jeff35209]

Thanks for the video, it helped a lot

[taiwoo]

THE MAN IS A GENIUS! :D iv watched all these i can say.

[JohnsAutoParts]

Good information. Test before replacing. You can save yourself some unnecessary work.

[cmaldonado8]

what if the voltage is going all the way up? will I'm driving the needle to the battery gauge goes all the way to the right and my red light warning to the battery turns on. can anyone help me?

[Jackcc5]

well it makes cents because a 12 volt battery puts out 12 volts of power then the alternator puts in 13 volts or 13 and a half volts so it gives it more then it needs.

If it doesn't then it means the alternator is fucked