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Old 01-04-2010, 08:11 PM   #1
mcgilles
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Default Charging system running at 15V+...what to do

the C5 has been sitting for a while but on a battery charger (CTEK) due to the weather. Its very cold out but the roads are finally in decent shape so I drove it to work today. temps were between -5 and 5 just about all day. I don't think that would cause this problem.

I've seen very healthy voltages from this car before, usually running at 14.0-14.6V. even slightly higher than the normal 14.4

well today I found while on the way to work I noticed it was running at 14.9-15V which seems way too high to me. on the way home it just barely hit 15.1 and 15.2 for a few seconds. Looks like the voltage regulator is not working right.

the stock voltmeter shows the red band as voltages below 8.5 or higher than 17.5. somehow I think that I would be having major problem well before 17.5V

the voltage was elevated through the entire day, which was about an hour of total drive time. just as I got back to my house it dropped back to 14.2-14.4, right where its supposed to be. I don't know if it was a fluke, or if the regulator is on its way out.

should I get the alternator replaced right away? what's a good alternator and how much am I looking? Or is it fine and nothing to worry about? some people use 16V batteries for race applications without alternators...seems like any 12V accessory should be fine at that voltage. but I don't like it running that high when its not supposed to. is there any protection circuit in the car anywhere that would protect the car's electronics in the event of a serious over voltage condition?

also, in the 3 years I've owned this car I've gotten charging system fault messages right after startup, about 3-4 times total. each time I cleared the message and checked the voltage. it was running at 14-14.6 like it usually did and everything was fine. I don't recall what code it was throwing, it hasn't happened in a long time. no fault messages today even running at 15+ volts. I certainly don't want to endanger my car's electronics.
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Old 01-04-2010, 08:14 PM   #2
mcgilles
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oh and it was doing this with an SLP underdrive on it...isn't that like a 20-25% under drive? Do I have a really good alternator on the car or is this a big problem waiting to happen...
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Old 01-05-2010, 12:08 PM   #3
The Wrench
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Interesting. I noticed the other day it was kinda cold here in Texas (about 30 F) and my '08 Caddy was charging at around 15 V.
Usually it runs around 13.8-14.4.
We know that the cooler the temp, the poorer the electrical conductivity of any wire, connection, or battery internals (or semiconductor in the regulator for that matter) so maybe that's the issue. Never really noticed it in the Vette in cold weather, but we don't get too much cold down here.

One issue I did have with the Vette however; the wiring connection on the starter loosened up, and the charge voltage went over 15 sporadically. This was due to the intermittant increased resistance of the loose connection causing the regulator to pump up the voltage.

So, based on that, the first quick check might be to tighten the battery/starter/alternator connections and be sure they are good and clean. Also might check the battery voltage with the engine off after sitting awhile; that would be a good indicator of battery condition.
Should be 11.5 to 12.5 if the battery is decent.

Always look for the most likely culprit; in this case the battery (in super cold conditions like you have).

Let's see what the other guys say; can't recall reading any specific threads about cold weather and charging voltage.

DG
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Old 01-05-2010, 12:22 PM   #4
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It sounds pretty well normal to me. If I'm not mistaken, more voltage is required to charge a cold battery. The colder the battery, the higher the charge voltage. At that temperature, 15 volts sounds about right.
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Old 01-05-2010, 12:47 PM   #5
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I see higher voltages in my 2000 when its been on a battery maintainer than when I leave it off for summer months.
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Old 01-05-2010, 01:22 PM   #6
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Quote:
Originally Posted by The Wrench View Post
We know that the cooler the temp, the poorer the electrical conductivity of any wire, connection,
No "we" don't know this....

Conductivity and resistivity have an inverse relationship. Electrical resistance increases with temperature; therefore, conductivity decreases. So when temperature decreases, resistance goes down, conductivity increases.
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Old 01-05-2010, 02:32 PM   #7
chaase
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Quote:
Originally Posted by lucky131969 View Post
No "we" don't know this....

Conductivity and resistivity have an inverse relationship. Electrical resistance increases with temperature; therefore, conductivity decreases. So when temperature decreases, resistance goes down, conductivity increases.


At laest for wires, we won't go into semiconductors. 15v sounds like a reasonable range. If the charge gauge does not show as read until 17v then you are definitely okay.

Last edited by chaase; 01-05-2010 at 04:08 PM.
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Old 01-05-2010, 04:02 PM   #8
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Go bigger on your stereo/amps and she'll come back down.
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Old 01-05-2010, 09:56 PM   #9
mcgilles
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thanks for the input! I'm just going to keep an eye on it. as long as 15 is safe the electronics will run better on it anyway!

I looked up the charging system in the manual and in the sections to evaluate the system it seems to indicate that 13.5-15 or 13.5-16V is a perfectly acceptable range (it says normal is 13.5-15.0; but doesn't indicate that there is anything wrong until it sustains over 16V...strange) it also says that there is a DIC message for high voltage or low voltage, if low voltage (less than 9.5 for 10+ seconds) is detected it will raise the idle to try to get more alternator output, if high voltage is detected (18V+ for 5+ seconds) the PCM shuts down most of its outputs to protect the car's electronics. doesn't sound like the engine will shut down, but the PCM goes into minimal function mode. never knew that. I wish it would just kill the engine if the voltage were that high! that would damage things.
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Old 01-06-2010, 05:38 PM   #10
The Wrench
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Oops; senior moment. Of course electrical resistance through a wire increases with temp.
In semiconductors (and in my brain apparantly) it's generally the other way around.

Oh, drove the new Caddy quite a ways today in 45 degree temp, and the voltmeter sat on 15.1 most of the way. So, it's probably a normal GM thing (or maybe my battery is already getting old).

DG
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Old 01-06-2010, 07:23 PM   #11
Bill Curlee
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Anytime you have an issue with the alternator/charging system,,,,ALWAYS,,,,, check the connection between the BATTERY AND ALTERNATOR first thing!

If the alternator senses a LOW voltage, it will boost output. If the connection between the POSITIVE battery terminal and the BATTERY connection on the back of the alternator for a good solid connection.

You can try to connect a wire from the POS terminal on the battery to the BATT terminal on the back of the alternator. If the voltage returns to normal, the connection between the POSITIVE battery terminal and the BATTERY connection on the back of the alternator is compromised. Most likely at the starter solenoid.

Click the image to open in full size.

Read the charging voltage directly at the battery terminals and see if it is different than the DIC voltage or IPC gage voltage.

Please let me know if you make any head way on this issue.

Last edited by Bill Curlee; 01-06-2010 at 07:30 PM.
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Old 01-06-2010, 07:52 PM   #12
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max charging should be 14.8 violts , no matter what the temp
Did you check it with a good meter or did you go by the DIC ?
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Old 01-06-2010, 09:48 PM   #13
mcgilles
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I did check this with a digital multi-meter, but by the time I had a chance to check it I was home and as described earlier the volts dropped to 14.4 just as I pulled into the driveway. however when I checked if the DIC digital readout was spot on with what I saw on the battery terminals. I did not have a chance to check it when it was running high however.
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Old 01-06-2010, 09:51 PM   #14
mcgilles
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Quote:
Originally Posted by Bill Curlee View Post
Anytime you have an issue with the alternator/charging system,,,,ALWAYS,,,,, check the connection between the BATTERY AND ALTERNATOR first thing!

If the alternator senses a LOW voltage, it will boost output. If the connection between the POSITIVE battery terminal and the BATTERY connection on the back of the alternator for a good solid connection.

You can try to connect a wire from the POS terminal on the battery to the BATT terminal on the back of the alternator. If the voltage returns to normal, the connection between the POSITIVE battery terminal and the BATTERY connection on the back of the alternator is compromised. Most likely at the starter solenoid.

Click the image to open in full size.

Read the charging voltage directly at the battery terminals and see if it is different than the DIC voltage or IPC gage voltage.

Please let me know if you make any head way on this issue.
Thanks Bill! I was hoping I'd hear from you on this. I'll see what I can find out.
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Old 01-06-2010, 09:51 PM
 
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