So I knew my old Delco battery didn't have long for the world... Today it finally decided it had had enough. Being around 6-7 years old, I figured it was time to replace it.

I bought a new Optima Red Top and installed it tonight after work. When I first installed it, the DIC said 14.1V. After driving a while with the A/C on and stereo on, I decided to look again at the DIC. It was at 13.2V-13.6V.... Went into eat some dinner at the local Chilis and of course it was dark outside... Now I needed to add headlights to the A/C and stereo... Looking at the DIC I see a pretty much constant 13.5V

The strange thing is when I turn on a accessory like the rear defrost or go from headlights off to on... I see the volts drop to 12.3 or so for a split second, then return to about 13.5V.

It seems the alternator is kicking the voltage up when demand is there. BUT,,, where did the 14.1V go that I started out with? I don't see the lights dim or anything like that... I do have a cammed engine and it does lope at idle... also a 25% underdrive crank pulley and 6000k HID low beams.

Considering the mods I listed does this all seem normal or should I be thinking about replacing the alternator to accompany the new battery? I believe its the original unit and it had 87,110 miles on it.

Battery is now at 12.7V with the engine off. Same voltage at the D pin on the alternator and the large red alternator feed wire.

TIA

 

I am by no means an expert on this but I have been tracking basically the same exact issue for about 2 weeks now. You can check out the thread here http://forums.corvetteforum.com/c5-t...lp-please.html. IF your car is an A4 you might be experiencing what I think I have narrowed my issue down to which is that the decoupler or "clutch" on the alternator might be getting weak. Many threads I have read indicate that the stock 110 amp alternator is borderline and a little slow to respond when keeping up with the electrical demands at best which you see when you ask more from it. The decoupler seems to "bite" a little better when cold and get more "slippage" in it after it warms up. Other than that your numbers sound pretty normal. You can pull the belt off and give the pulley a couple of spins back and forth while holding it tight and see how much "lag" you feel on the internals to verify this. If it is already weak, when you demand more from it the resistance increases and the clutch will "slip" more.

Not at all telling you that this is definitely the answer but it is a good place to look with the info you posted. Hope you get it worked out. I've spent quite a few hours tracking this down.

 

FYI - a fully charged battery will read 12.6-12.8V at rest. That's 2.1V/cell.
If the battery is fully charged and in good shape, the charging system does not have to put out 14+V, 13.5V is fine to keep the battery charged.
It sounds to me like your charging system is working as it's supposed to. Just keep an eye on it, and as long as the car starts every day and the battery voltage stays in the range that you are seeing, don't start replacing parts that aren't broken for no particular reason or get yourself worked up about a problem that may not exist.

 

FYI - The DIC is not always accurate. My '01 Z is off by almost 1v when compared with my multimeter.

 

Yes. It is.

More driving and less worrying.

 

Mine is exactly the same... 1Volt difference. So its around 14.1 with accessories on at the battery and engine running of course.

 

The DIC digital voltage reading and analog volt meter read the voltage AFTER the ignition switch.

The switch contacts (depending on their condition and how carboned they are) will dictate the voltage loss through the switch. Ive see losses as bad as 4 VDC.

If you want an accurate alternator / battery charging reading, read the voltage directly on the battery OR on the CIGAR LIGHTER circuit as it is connected to the HOT AT ALL TIMES bus.

If you have a 97 - 03 you can also read full battery/charging voltage on the aux power connector wires in the passenger foot well hot at all times wire.

BC

Bill

 

We recommend typical alternator output to be in the range of about 13.7-14.7 volts, but I would agree with Bill and tacman in questioning the accuracy of your DIC reading. Keep in mind you are running an underdrive pulley, which may prevent your alternator from supplying the electricity your vehicle is demanding, especially if you are running high-draw accessories, like air conditioning. You can replace your alternator, but if you still run an underdrive pulley, you may continue to have the same issues.

Jim McIlvaine
eCare Manager, OPTIMA Batteries, Inc.
www.pinterest.com/optimabatteries

 

Thanks everyone... I have established that with the DIC being 1 volt (lower) difference from what the reading is at the battery, that there is no issue. Im getting 14.0 to 14.3 at the battery while engine is on and accessories are on. At rest without the battery tender, the battery reads 12.7-12.8 which AFAIK, is a fully charged battery. The old battery was in fact DOA....Just due to age as far as I can see.