Testing alternator voltage

[UGotSmkd]

This is for a 2000 Silverado. I used a voltmeter and touched the red on positive and black on negative on my new battery. My reading with the engine at idle is ~14.5v with high beams, radio, etc. on. I did not apply any load. With the engine off, it was showing ~12.5v. Both of these readings were consistent each time I tried.

IDK, but I stilll have a feeling I am not getting a true reading by measuring the voltage through the battery terminals. I just wanted to know if there is another way to test it or is this method accurate enough?

[UGotSmkd]

Nobody has tested an alternator?

[G8GT721]

sounds right to me. autozone/advanced auto can usually test them if your trust them.

whats the problem your having, that you checking the altenator?

[GRRRR8]

Thats the correct way to do it. Your readings are good.

[UGotSmkd]

sounds right to me. autozone/advanced auto can usually test them if your trust them.

whats the problem your having, that you checking the altenator?

Well, the battery I just replaced was bad and thought it may have affected the alternator. On top of that Charlie replaced the belt tensioners and idler pulley. It really quited down the noise in the engine compartment. The only thing unchanged has been the alternator, and it seems like I hear alternator whine, but maybe it's just the way these Chevy trucks are.

[UGotSmkd]

Thats the correct way to do it. Your readings are good.

Cool, BUT I didn't put any load on it, and from time to time the voltage needle will drop , but never below 14v.

[GRRRR8]

Cool, BUT I didn't put any load on it, and from time to time the voltage needle will drop , but never below 14v.

If you had radio, hi-beams etc on, that is a load. :)

[UGotSmkd]

If you had radio, hi-beams etc on, that is a load. :)

Lol, true. What the hell was I thinking? I guess I meant to say I did not rev the engine while I was testing the voltage.

[Tjay74]

If you want load it down then turn everything on you can while taking readings.

Headlights, high beams, AC, seat heaters, wipers, stereo at moderate volume and hazards.

[todds87ss]

fan on high might be the greatest load, and a good test for the alternator.

[UGotSmkd]

fan on high might be the greatest load, and a good test for the alternator.

Yeah, I didn't have the fan running. I will retest with the fan on this time.

[95_9C1]

i had some interesting readings, recently

normally, my voltage reads around 14.7, but on a recent trip i observed it dip down to as low as 12.9 and hover at 13.1 then rise to 13.9 over consistent highway driving

it has since returned to 14.7

is this normal ?

could my alternator be faulty ?

any ideas ?

[-Ray-]

I'm not sure what it means, but my voltage moves up and down too. I'm on the stock battery also.

[Struggle]

Alternator is not going to put out any more voltage than neccassry to keep the system charged. The older systems would charge at a slightly higher voltage. The closer the voltage is to system voltage while maintianing battery charge is ideal as the less the alternator has to work the better your fuel mileage will be on newer vehicles. Also newer vehicles rely heavily on the battery so some fluactions is to be expected.

[95_9C1]

i am on the stock battery, too

under engineering mode, during these low alternator outputs, the battery charge was indicating an 84-85% reading - this is much higher than any previous battery charge reading (usually 64-72%)

yesterday, the car was back to a 14.7 running voltage with a battery charge reading of 80%

perhaps, 85% is the peak of my stock battery's ability to hold a charge as read through the variable of engineering mode

what do you think?

[TomPierce]

If the battery is charged, it does not need the alternator to do anything. Hence the low output levels.

If you had high battery charge and high alternator output you'd eventually damage the battery.

Now, normal is 80%.

[-Ray-]

i am on the stock battery, too

under engineering mode, during these low alternator outputs, the battery charge was indicating an 84-85% reading - this is much higher than any previous battery charge reading (usually 64-72%)

yesterday, the car was back to a 14.7 running voltage with a battery charge reading of 80%

perhaps, 85% is the peak of my stock battery's ability to hold a charge as read through the variable of engineering mode

what do you think?

The state of charge will vary depending on conditions. Temperature will change the state of charge,

[95_9C1]

so, today it's 14.5 volts with a 70.1 % battery charge ... which is effectively "normal" or what i have been used to seeing since owning the car ...

so, basically, all is well

thanks for the input, guys