raptorc5

Hi guys,

I have an issue with my voltage dropping down to 11.5-12.0 while at idle (2003 Vette). When I give it a little gas or start to move it will jump back to 12.8-13.7.

This voltage drop is causing my auto start alarm to shut down and then restart several times (it senses the low voltage). My dealer says that this is normal in the C5's during summer temps while using the air. I'm not an electrical engineer, but this doesn't sound right to me. I just installed a new Optima red top, but it didn't change anything. Any ideas?

lucky131969

Where are you reading this voltage drop?

raptorc5

On the dash, both voltage gauges.

lucky131969

The voltage needs to be read at the battery, not the DIC....for troubleshooting. That way you can see if you have an issue with the charging system, the ignition switch, etc. All the common sense stuff applies here, i.e. inspection of battery cables for corrosion/security, starter connections, etc.

Trios

I am an electrical engineer, and it doesn't sound right to me either. Temperature won't change the output of the alternator by any significant amount. The a/c might as it will lower your RPMs slightly, but again it wouldn't just be a summer thing.

I am 100% with lucky on this one. Check wires, grounds, connections, etc.

You said you just replaced the battery; one thing I will say is that I have seen on numerous occasions (not with C5's, but other cars), where a bad battery has worn an alternator to death, trying to charge it all the time and failing. Get a quality multimeter and check the output of your alt at idle; if its under 13 volts, it's bad/going bad/slipping on the belt.

bigvx5

i was gonna recommend checking the belt to make sure its not loose or slipping...

dgrant3830

As lucky mentioned the battery, cable connections and so on, his suggestion with the starter cable is particular important as that is where the battery, starter and alternator all come together. Do not forget that its electrically hot down there unless you first remove the battery's negative cable from the battery itself. If all of those connections are clean, tight and no evidence of burned/overheated wire insulation, then pull the alternator and have it load tested. The normal voltage level is 13.8 to 14.1 for these cars while the engine is running.

j84buick

Do a search for "the big three". It may help you and is a weak point in most cars. I did mine and I run 14.3-14.5 at idle. Up from 13.8 or so.

corvettebob1

"the big three".
Did a search and nothing turned up, please explain.

Randyman2002

OK... I give up!

j84buick

Basically it involves upgrading three cables in your car. For me I used 4 gauge wire.

- Alternator to Battery
- Chassis to Battery Ground
- Engine to Chassis

Here are a couple links to help. I also recommend YouTube. They have a ton of videos on there.
http://forums.corvetteforum.com/audi...ig-3-pics.html

http://forums.corvetteforum.com/audi...-for-a-c5.html

allenwaddle

I am also new to this but can you expalin why going from alternator to battery and then new motor to ground would not do the same. I do not get the point of moter to chassis wire?
Thanks,
Allen

lucky131969

Guess I'm missing the point. The claim by these audio installers, is the increasing the diameter of the wire (ground and voltage) will precipitate maximum current flow. I really don't see how that applies to the OP's situation. Besides, if there was a current demand on the factory wiring, that the existing wiring was not capable of handling, fuses would blow....and in the absence of fuses, things would melt.

I'm sure having a O gauge power wire looks really cool in a Scion, with a 1000 watt stereo system.

Bill Curlee

Grounds on our C5's are MINIMUM requirements for proper electrical component / module operation. When you mix in corrosion, loose connections and age, things start to work poorly. Anything that you do to provide a good ground for the car, will help. Do you need O cables. NO. I add a 10 ga wire from my alternatorr to G-101 and it seemed to help with my frequent CHARGING SYSTEM FAULT message at start up..

The alternator BATT connection on the back of the alternator is the OUTPUT, connects to the starter solenoid main terminal and then goes up to the battery. That is prime real estate for poor connections and should be checked for proper connections.

Reading the system operating voltage from the DIC or IPC gage is NOT a very good representation of over all system voltage. Take your reading directly at the battery cables on the battery. Then,,compare that to the DIC / IPC voltage.

If there's are large difference between Battery voltage at the terminal and the DIC/IPC voltage,,,your Ignition switch is most likely at fault and needs to be rebuilt or replaced.

BC

j84buick

OP is experiancing low voltage. My personal experiance after upgrading the big three was a .5 voltage increase. I never claimed it would solve his exact problem. I stated "upgrading the big three may help". I will let the OP decide whether or not my information was relevant.

Not much to add to what Bill said who is real expert in this conversation... but if you need further evidence that the stock system is not as efficient as it could be take a look under your battery and see the puny 10 guage wire that connects your battery to the chassis. Consider the big three upgrade like the HID upgrade. Sure the stock lights work fine but they are MINIMUM requirements... but they could work so much better. Is it worth it? That's for the owner to decide.

lucky131969

I know Bill is the only expert in this thread, but there are two wires from the negative battery terminal...one is a 4 gauge, and the other is 8 gauge. The 8 gauge is connected at G104, and the 4 gauge is connected at G106.

So you change out the cables, and you get a .5 volt increase. Issue.... probably bad connections. And what exactly do you gain by changing the 4 gauge wire to 0 gauge...let's see.

The O gauge wire has a resistance value of ~ 0.000098 Ohms per foot.

The 4 gauge wire has a resistance value of ~ 0.000292 Ohms per foot.

The 8 gauge wire has a resistance value of ~ 0.000628 Ohms per foot.

I have a hard time believing IASCA would recommend O gauge wire for such a short distance, especially considering the current draw for said length.

....but heck....I'm no expert......

Bill Curlee

Wow.... all that extra resistance,,,shucks,,,,,,,changing the wires to O gage,,,is worth at least 20 HP. The looks alone is worth 5 more HP

Oh,,,I forgot,,, The extra weight of the wire, -25 HP.

BC

lucky131969

True, but at least your C5 electrical system will be capable of delivering 250 amps.......