For an alternator what is the normal voltage supposed to be on a gauge on my dashboard?

Question

I replaced my alternator and replaced the corroded battery terminals, it still only shows 11-12 volts on my voltmeter on the instrument panel - I am assuming this means the jeep is only running on the battery - I guess on accessory, the volt meter says 10-12 as well - so if the alternator kicks in, the volts should go up to 14-14.5 right? I am just trying to rule out that its a low voltage battery -

Thanks for all the good answers - I am charging the battery now - just to be sure - it starts, but doesnt quite go to 13 - better than before - my question is then if the car is running, but the battery is low - would the voltage be a full 14.5 or be the 12 i am seeing - could it be my battery rather than the alternator not doing its job?

Answer 1

A new, fully charged lead/acid battery produces 2.1 volts per cell which means a new, fully charged battery should show voltage of 12.6 volts at the terminals with nothing on. An alternator is NOT designed to recharge a dead or discharged battery. If an alternator is allowed to produce this much current for a long period of time, it starts to blow the diodes to protect the windings in the rotor and stator. An alternator is designed to keep a charged battery charged and this includes producing enough current to run any accessories that may be running on the vehicle, as well, such as the lights, A/C, radio, etc. An alternator should produce approximately 13.8 to 14.2 volts and it can run as high as 14.5 volts, depending on the type of battery that came OEM in your vehicle. GM charging systems use a set voltage of around 14.4 volts in their systems since they use a maintenance free type of battery as OEM and this type of battery will accept higher charging rates than other batteries. If you have a low battery to start with, your alternator will show low voltage. All test manuals state "insure that the battery is good (holds a load equal to one half of the Cold Cranking Amps stated on the battery without going below 9.5 volts with load applied) and fully charged before diagnosing charging system problems." I'd suggest you should have replaced the battery cables, not just the ends since corrosion builds up in the actual cable over time which causes very high resistance in the battery cables, themselves. The bolt-on ends are frankly great for emergencies but lousy as replacements for bad battery cables since they tend to loosen with underhood heat and since you're dealing with DC current, loose connections mean voltage drops in the charging or starting system. Check the battery for state of charge (if discharged - charge using a battery charger) and ability to hold a load (described above) if the battery checks out then suspect the alternator (probably has an internal voltage regulator). Also, make sure fan belt is tight and in good condition as this will have some effect on the alternators output, too! Good luck!

Answer 2

If you are close to an Autozone, they will test your battery/alternator for free. As for the volts, the general rule is the needle should be in the middle on your dash gauge. I don't think the volts increase on the gauge when the alternator kicks in - 20 years of driving and I've never noticed it. If there was a problem with either, your battery light should be on as long as the car isn't really old.

Answer 3

the guage will give a reading of 12 volts take the reading at the battery with the engine running it should read 12 volts but increase to 14.5 to 15.5 as you rev the engine you should not discount a poor battery any autoshop that sells batteries can test your battery by putting amp meter on it under load this will make sure your battery is fully functional the regulator in your alternator is unlikely to be faulty. a good way to test this as you rev up your battery light should go out if by any chance it gets brighter then the regulator pack is suspect

Answer 4

Getting bad alternators is a common problem, most parts stores don't confirm if they work or not, they just give you the box and say good luck, Your voltage should be around 14-15 v as long as you don't have a bunch of accessories and stereo equipment. I would try another alt, and ask the store to confirm it works before you leave.

Answer 5

Good thinking. That doesn't mean a battery problem, though; more likely your voltage regulator is not connecting your new alternator to you battery, which it should if you are drawing the battery down.. Check that voltage regulator, or replace it if its not integral to the alternator (many now are on newer models).

Answer 6

14-14.5 is right. If the charging system was entirely shot I'd expect to see way less than 11-12v and a big drop when you add load like the rear demister, headlights and 'cigar lighter'.

A charged batter not on load should give 13.8v, not the 12v that some are saying, a lead-acid cell gives 2.3v and there are 6 in a '12v' battery.

Answer 7

normal voltage is between 13.5 to 14.5. check it with a hand held voltmeter on the battery with the moter running and you will know the true voltage. this should have been done before changing the alt.. also the voltage regulater wires should be checked for a live input

Answer 8

10 - 12 V is correct