b09676

2012 base Vette in Phoenix, about 112 degrees out, and I noticed at idle, with ac on, volts dropped to below 13, probably about 12 and then picks back up to slightly over 13 when I proceed from a stoplight. Car not overheating at all but just wondering if the drop in voltage is OK/normal.

JacksAO

I'm on the other side of the valley and mine does nearly the same. At 1st start up I'll see 14/14.3 on the DIC and as the car comes up to temp in this weather I'll see 13.2/13.6 at traffic lights. Its done this ever since I bought it almost 8 years ago and I've only had to put 2 batteries in.

Bsull

I live in Mesa and have had a recent battery change. The old battery was a Duralast Gold 2 years old (based on the date on the battery) and it tested OK at Autozone. I had a couple of issues documented in a different thread and decided to change the battery anyway. New battery, stayed with Duralast Gold, shows the same as JacksAO. I know some folks here recommend swapping the stock alternator for one made by Mechman, but even their website says that the alternator might not keep up with demand at idle, so why spend $500 or more and not see improvement.

dpigguy

mikeCsix

I'm in Surprise, flew down to inspect my home after the windstorm, glad it wasn't too hot to get on the roof this afternoon.

With the compressor running and the fans running on high plus your radiator fans running (draws a LOT of current), and the engine at low rpms, your system is responding normally. If there was an issue, the voltage would not kick back up when you increase engine rpms. Changing batteries won't make any difference. If you were to scour the internet looking for a charging curve for these alternators you could see they can't produce much at low rpms, Remember too, it takes horsepower (and more heat) to create charging current, If you were to make the drive pulley smaller(for the alternator) it will increase your low end charging current because the alternator is spinning faster, but you may run into trouble with the alternator (over spinning it) as you approach red line.

Just a side note, make sure your engine fan connectors are good, clean, and tight. Many stories of how these connectors have melted. With clean and tight connections, less current will be needed to drive the fans which is easier on your charging system.

NY09C6

Seeing voltage down to 12.6-12.8 at idle on brief occasions is not a concern at those temps as long as it is mostly above 13 or so.

b09676

Thank you guys for the quick responses, I appreciate it.

JacksAO

Just a side note here: After owning the car for 8 years I finally bought a Cetk battery maintainer last week. Hooked everything up and to my suprise it stayed on "charging" for 2 days before getting a green light.

Bruze

Is the battery also 8 years old?

Don't assume that just because it shows "Charged" that the battery still has full cranking capacity. If it's 8 years old it most assuredly doesn't.

JacksAO

Is the battery also 8 years old? No. The car is on its 2nd battery under my ownership. When I bought the car the dealer replaced the OEM one with another Delco that lasted just over 3 years and when that one died I replaced it with a Autozone Duralast Gold which is still in it. I've had the best luck with the Duralast batteries in all of my cars since I've lived in Phoenix the past 40 years.

farmington

mikeCsix

Actually pretty normal. Those small maintainers don't put out a lot of power so it takes awhile. My daughter lost her alternator and she drove her Blazer home. By the time she got there, the battery was really low. I connected my Deltran Battery Tender to it and 4 days later it finally went green. Vehicle fired right up too.

The Battery Tender brand (the smallest one) puts out maybe 750mA, that is less than an amp. The beauty of it is it will charge the battery to 14.2 v and let it drift back down to about 13.2 and then hold it there. Your battery can go a very long time at that voltage without losing much water.

ruxvette

I heard the haboobs were pretty nasty.

Bruze

But if a battery gets discharged too much or too often, it will never take a full charge again no matter what kind of charger you put on it (slowest charge is always best, but it still won't bring a damaged battery back to full life).

It may work fine here or there, but if the weather gets really cold and the vehicle doesn't fire as it should, or you make a lot of short trips it may fail you.

Dano523

Not true on some alternator not making more than the needed amperage output on idle.

Hence the OEM 3 pole 145 amp Valeo alternator only puts out about 14 amps at idle, while the billet 6 pole alternators put out 45 amps or more at idle instead.

So when your at the stop light, and the A/C and engine heat spinning the raditor fan to draw air through those heat exchanger coils, the raditator fan is drawing close to 16 amps itself, the OEM alternator can not keep up with the demand of the car (why you have the drop in voltage). When you start to drive and the RPMs increase, then the OEM alternator can put out up to 140 amps (depending on the RPMS), and it recharges the battery back up. Hence the more that the battery is discharged and charged back up, the faster you wear out the battery.

mikeCsix

They were! Several homes in my neighborhood sustained roof damage. I flew down Friday morning after neighbors reported concrete shingles in our driveway, I got on the roof and found 3 had dislodged in one section and may have impacted the roof in two places to cause more damage. Waiting for the roofer to show up today.

mikeCsix

Dano, your gift for detail never ceases to amaze! Thanks for making my previous point regarding the drop in output of the OEM alternator at idle, coupled with the high AC fans in cabin plus the high current radiator fans overwhelming the alternators ability to keep up. Imagine if it were a dark and rainy night too, while you're sitting at a stop light with your custom stereo and amplifiers booming.

Not knowing what the output charging curve looks like on the OEM alternator, granted it is low as most are except for custom applications and low rpm diesel engines, options are few. One could install a smaller pulley on the alternator increase output at idle but risk overspinning the alternator at 6500 rpm's, go to a higher output alternator like the Billet and give up a few ponies, or just realize you'll be changing batteries more often. Plus there are those folks that like to us underdrive pulleys to eke out all of the HP they can get.

Through the charge/discharge cycles, sulfur buildup on the lead plates in a lead-acid battery gradually reduces battery capacity as the sulfur inhibits electron flow. Sulfation can be broken down with sophisticated battery chargers that can recondition batteries, you would have to remove the battery from the car due to the higher charging voltages/with low current flow (16.2vds approx at 2 - 3 % current if memory serves) plus temperature
monitoring to reduce current flow should the battery begin to overheat. Those types of chargers are pretty expensive plus require expert knowledge to operate them, it's easier to just replace the battery as capacity falls below usable levels. My previous points regarding the length of time to charge an automotive lead-acid battery using small battery maintainers is valid, granted starting batteries are designed for short high current applications and a quick recharge as the charging algorithms in modern cars use. The higher voltages we see today help stave off plate sulfation but can't reverse it.

The other nemisis of the traditional lead-acid battery is plates sloughing. Lead build-up at the bottom of the plates will eventually short out the cell. You can charge a battery up using a basic battery charger and immediately test it and it will look good as all of the good cells have enough power to compensate. But overnight, that shorted cell will pull down the voltage so it is best after fully charging your battery to let it sit idle for 24 hours disconnected before testing for capacity and voltage retention.

Dano523

Over spinning the Oem valeo altnator at idle to get it to produce more amperage there, does not end well at RPM red line instead.
Does not matter if you change out at the HB to over drive the entire drive line, or just the alternator pulley size to spin it faster at idle alone, since it really over spins the alternator at redline isntead.

Hence when you over spin the Valeo alternators, they end up cracking the armature plastic winding coils cages, taking the alternator completely out instead.
Hell, on the LS7 redlining to 7K, its surprising that OEM Valeo alternator last as long as it does to start with. The 125 amps had a major problem with coil cages cracking, but it as never really solved on the 145amps either.

Skip to 12;40 to see where the coil cages crack on the amateur from the alternator being over spun.

mikeCsix

Hi Dano, I actually watched the entire segment. Pretty interesting actually.

You can calculate the alternator rpm's by knowing the pulley sizes and coming up with a ratio. So if the ratio is 2.5:1, that 7,000 redline is pushing the alternator to 17,500 rpm's and those little bearings inside are going to cook!

Back in the day with V-belt technology, there was a limit to how much current you could generate, and of course the difference between small frame and large frame alternators. 125 amps was about max out of a small frame.

Dano523

Yep, and although the new 3 phase alternator are a touch more efficient to increase the max amp outputs, the really game changer is the amount of phases/poles to the alternators to increase the amperage output at lower RPMS instead. .