How much is "enough" alternator/battery voltage??

[GT500Steve]

Since the weather has warmed up I am getting a little concerned about the alternator on my 2007. Driving it today in 90 degree weather the voltage started out at 13.9-14.1 with the AC on while at cruising speeds. After driving an hour or so it was down around 13.3-13.5 and never really fell below that. While at a red light however, I turned the AC on max, headlights and rear defrost on and it dropped to 12.2. It held there and didn't go any lower, but didn't jump up hardly any when I revved the engine. The stock alternator took a dump a couple of years ago, and I replaced with a quality aftermarket stock replacement... Didn't upgrade to a PA performance, and it has the factory size alternator pulley.

So, I can't exactly say the alternator is "failing", but I'm not comfortable with the output. Usually it used to hover around 14.0 volts and never go much lower even under a lot of load. Do any of you watch the battery voltage on the Aeroforce gauges and what are you seeing?

 

[fullboogie]

That's not right. mine holds 13.9-14.2 no matter the rpm or load. Your alternator may be on the way out.

 

[Imatk]

I've gone through two stock alternators on my car... I'm not a huge fan of them.

I just installed the PA Performance/Shelby alternator and I'm hoping it will hold up better.

 

[ShiftyThePirate]

Since the weather has warmed up I am getting a little concerned about the alternator on my 2007. Driving it today in 90 degree weather the voltage started out at 13.9-14.1 with the AC on while at cruising speeds. After driving an hour or so it was down around 13.3-13.5 and never really fell below that. While at a red light however, I turned the AC on max, headlights and rear defrost on and it dropped to 12.2. It held there and didn't go any lower, but didn't jump up hardly any when I revved the engine. The stock alternator took a dump a couple of years ago, and I replaced with a quality aftermarket stock replacement... Didn't upgrade to a PA performance, and it has the factory size alternator pulley.



So, I can't exactly say the alternator is "failing", but I'm not comfortable with the output. Usually it used to hover around 14.0 volts and never go much lower even under a lot of load. Do any of you watch the battery voltage on the Aeroforce gauges and what are you seeing?

12.2 is severely low, I only hit that low when I pushed my 1000w amp in my Challenger (1000w RMS, peak 1300) fully and the lights would dim and all. You need at LEAST 12.4v to start a V-8 in my experience, when my battery in my 6.1l HEMI died we had to wait until it was up to 12.8 to start it. If you arean't running a serious aftermarket sound system (700-800+ amps for the subs, and more for the speakers) That is really low and no need for it to be draining so much. Sitting for 2-3 days in the cold that car wouldn't start I can almost promise. If you DO change out the alternator I recommend (just for warranty and hassle-free sakes) getting an AGM battery.

 

[19COBRA93]

I had a momentary issue with mine recently and it started fine and ran fine on 11.6 volts. But, I did get a "Check charging system" warning instantly, and the battery light was on.

I'll have to watch mine when all that stuff is on full. But I don't think it drops that low normally. It seems like low 13's is as low as it gets when everything is on.

 

[ShiftyThePirate]

I had a momentary issue with mine recently and it started fine and ran fine on 11.6 volts. But, I did get a "Check charging system" warning instantly, and the battery light was on.

I'll have to watch mine when all that stuff is on full. But I don't think it drops that low normally. It seems like low 13's is as low as it gets when everything is on.

Oh driving you are fine even going down to 11.2v, it's just, if you shut off the car...you are in trouble, it is not going to crank the motor. The ONLY serious drain Mustangs have stock is XENON if you have them, as they use 2x the power HIDS do but warm up in the blink of an eye. But to START an average V-8 you need about 12v, the bigger the v-8, the more voltage. Once you are moving you really can't fully drain it as the alt is constantly recharging.....

If you want to change alternators (though only crazy audiophiles do this) you could go with a mean green. http://www.mean-green.com/ stock though, no reason for that crazy of power dips.

When your battery DOES go below it's normal voltage and has to be jumped though, you need to start looking for a replacement, once drained past normal it will never fully regenerate\hold it's charge. AGM batteries have a 5 year warranty due to how built they are vs standard batteries AGM have kinda a deep cycle built into them which allows them to discharge fully and achieve full recharge. I had my 300$ 1000 cold cranking one go bad 1.8 years later and batteries plus just put in a new one. They stopped selling Optima, Optima used to be the "best" and now they are total crap.

 

[scotsam]

Before you dump the alternator I'd check the battery. I've had a few batteries with internal problems (short?) that would draw the voltage down and they would drive you nuts thinking it's an alt.. Especially since they would work ok but you would end up with charge lights and low voltage.

 

[ShiftyThePirate]

Before you dump the alternator I'd check the battery. I've had a few batteries with internal problems (short?) that would draw the voltage down and they would drive you nuts thinking it's an alt.. Especially since they would work ok but you would end up with charge lights and low voltage.

+1 to this. Even buying the highest end batteries I've had issues with them going out WAYYY early, thank god for warranty. Some shops would actually say "it was your alternator" (esp on my FJ Cruiser, a effin' Toyota") It clearly was NOT the alt, so don't let them b.s. you. Alternators going out under 75k unless you are stressing them with a high powered audio system (amps and all) is bull-crap.

 

[scotsam]

I own a shop and I see what some places can/will do. I like taking people's money I just don't like stealing it! Speaking of high end batteries I've had a few optima red tops do that exact thing to me.

 

[GT500Steve]

Thanks for the input guys. That is a good idea to check the battery before I go to the hassle of changing out alternators. I will take it to work tomorrow and load test it before I proceed with anything else. I just kind of assumed it was the alternator due to how much I beat the crap out of my car at the track.... I've always heard that rpms kill the alternators on these cars, and I twist the guts out of mine lol.

 

[scotsam]

I could still be. But when an alternator reaches it's charging limit amps will increase as volts decrease. If a plate shifted in the battery and is shorting that may well be the case. I'm lucky that I have batteries to test with because sometimes you can load test a battery and it will read ok.

 

[ShelbyGT5HUN]

Three years is all I expect out of a stock battery.

Correct me if I'm wrong, but the stocker is around 590CCA? That's LAUGHABLE!!! Miatas come with 550CCA. Add in all the electronics, and electric fans on the GT500, and you should have at least 800CCA. Combine it with the fact that we don't drive our Shelbys alot, and you get a prime candidate for sulfation. This car deserves a way better battery than it comes with stock!

 

[GT500Steve]

Thought I would update, and I have a couple additional question.....

I went ahead and installed the PA Performance 200amp alternator this past week, as well as the upgraded wiring kit as well. Also, to be safe I went ahead and did a new battery as well. While at cruising speeds the battery voltage on the Aerforce gauge holds at 14.2-14.3 volts, which made me feel more comfortable. However, at idle it will drop down into the mid 13s if I am sitting at a red light with the brakes and AC on, and with the headlights on it will dip into the high 12s. However, tap the gas and it shoots right back up to 14 volts again. When I got the alternator from PA Performance it already had a larger pulley on the alternator to slow the rpms down while at the track (which is probably what killed my stock alt), and I know this can effect charging at idle. Any guys that have done the larger alternator pulley swap have similar issues?

 

[19COBRA93]

I'm just running a stock alternator, but with a BPS underdrive (larger) pulley. I experience the same range in volts. Cruising I see low 14's. But at idle with a/c and headlights on it drops into the high 11's. A tap of the throttle and it ramps back up. If I were stuck in traffic on a hot night, I think it would become a problem.

 

[Heddde]

My car was warning for trac control off then the ABS warning come up and the the dashlightning went off then the headlamps and then the car died a minute after.
Just to get away from the street i used another used batterie and i drove home 15minutes and then that batterie also was done...Alternator ? i think soo

 

[GT500Steve]

I'm just running a stock alternator, but with a BPS underdrive (larger) pulley. I experience the same range in volts. Cruising I see low 14's. But at idle with a/c and headlights on it drops into the high 11's. A tap of the throttle and it ramps back up. If I were stuck in traffic on a hot night, I think it would become a problem.

Thanks. I was pretty sure it was the larger pulley causing the low voltage at idle, it's just always nice to have a second opinion.