How to Test Alternator Voltage Output (AutoUpkeep.com)

After watching this video, you will be able to safety test alternator voltage output. This test can be completed using a basic multimeter (~$25). Multimeters are also known as VOMs (Volt-Ohm-Meters) or DMMs (Digital Multimeters). The surface voltage of a fully charged battery when a vehicle is not running should be between 12.5 to 12.8 volts. Most automotive batteries are lead acid 12-volt DC (Direct Current). Each of the six cells in a 12-volt DC battery produces 2 to 2.1 volts. When the engine is running, the alternator will typically put out between 13.8 to 14.8 volts. Cautions: Park the vehicle outside or connect the vehicle's exhaust to an evacuation system. Carbon monoxide is deadly. For more car care information, visit AutoUpkeep.com.

Category:

Autos & Vehicles

Tags:

• auto
• suv
• automotive
• automobile
• car
• truck
• alternator
• testing
• multimeter
• voltage
• volts
• volt
• how to
• upkeep
• vom
• DC
• Direct Current
• battery
• charging system problems

[WlSEGUY]

I just bought a brand new fully charged battery but it drains completely within hours of running the engine. I recharged the battery again and got the same problem... does this sound like altinator issues? Thanks for your time.

[AutoUpkeep]

@WlSEGUY Hi, It sounds like the alternator isn't charging. You need to test the charging system (use the video for guidance) or take it to a shop to have it tested.

[classicrock4ev3r]

question i tested my battery with a dvom and it displayed 12.3 volts the alternator charge was about 14.5 i think my battery needs to be charged?

[AutoUpkeep]

@classicrock4ev3r

Your alternator recharges the battery... at 14.5 volts it is sending sufficient voltage to the battery. A fully charged battery has 12.6 volts (2.1 volts per cell...your battery has 6 cells). Your battery may have a weak cell or low electrolyte. If your battery has removable vents caps (some are sealed), you could check the electrolyte level and specific gravity (with a battery hydrometer) of each cell. Each cell should have a specific gravity rating between 1.254 - 1.280.

[AutoUpkeep]

@classicrock4ev3r

...one more thing...if the electrolyte is low, add only distilled water. Wear safety goggles and chemical resistant gloves. Please Note: Battery electrolyte will eat through clothing. If you do get electrolyte on your skin, clean promptly with soap and water. Do not allow flames or sparks near battery gases. Battery gases can explode.

[ronbros]

my new AGM battery says minimum voltage with engine runnin should be at least 14.4 -14.8 volts. WHY??

[AutoUpkeep]

@ronbros

AGM (Absorbent Glass Mat) battery, a type of valve-regulated lead-acid battery still needs to be recharged like other batteries. You need electrical pressure (Voltage) to recharge the battery. The greater the electrical difference (you have about 12.6 volts at your battery and 14.6 volts from the alternator) the greater the flow between them. The AGM manufacturer must have identified that on average it needs about a 2 volt "pressure difference" to adequately keep the battery charged.

[Poogoblin18]

What a great demonstration! An easy, safety minded illustration. You're hired!

[sw1000xg]

AWESOME VID! Just bought a multimeter and wanted to know how to do this cheers...

[haegrie]

Great clear vid. Pro work!

[ArMeNWiGGeR]

Yo, I Have Opitima Battery And New Alternator In One Year Ago But Why Would I Have -12.9 Voltage? how can I fix the voltage increases?

[stylicho]

@mostcanwait Make sure the connections on the battery are good.

[TheEsevee]

@mostcanwait might be the started I would check the gRound 1st

[mostcanwait]

what if the battery is reading 13.03 but won't crank the engine?

[10Secondcopper]

What do you do when the vehical in question has two batteries and both batteries are charged by the alternator at the same time?

[MrRaiders6769]

@AutoUpkeep Great video. I did the same check myself. running was 13.99 constant. Running with lights and radio it held at 13.97. I turned on the A.C. full blast and the DC dropped to 12.5 then returned and struggled between 13.55 13.75 and once the engine was at normal operating temp it staid steady at 13.25

[jeffmacon33]

i've been looking for a technique like this forever, feel dumb i didn't think of it earlier cuz it's so simple. message comin atcha..thanks!!