Voltage While Running
Thread Starter
Intermediate
Joined: Apr 2006
Posts: 37
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From: Gilbert AZ
Voltage While Running
I was wondering what the typical voltage should be when running on my 87. Most of my other cars have relatively high voltage 13-14+ while its running, however, on my Vette it runs anywhere from 11.2-12.0. The battery just died the other day, so this voltage is measured with a brand new battery, on the fabulous 80's digital dash.
Thanks.
Thanks.
Drifting
Joined: Sep 2005
Posts: 1,867
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From: Pasadena Maryland
You have a problem in the charging circuit. A fully charged battery should be over 12 volts. While charging you should see 13 to 15 volts. You need to have it checked, or if you have a meter check it yourself?
Team Owner
Joined: Jun 2005
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From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
And kal is close to saying, you may in fact have a problem with your alternator. You are absolutely right about 13-14+. Mine usually runs about 14.3 when I'm running.
Just remember this: when a battery goes, it starts to tax the charging system, namely the alternator. It is possible that the alternator is going out as a result of that.
Altho all alternators are going to go anyway, eventually, it is probably safe to say that if you were to catch a dying battery before it got too bad, you'd probably extend the useful life of your alternator, while only replacing a dying (but not fully dead) battery. Long sentence. I think I know what I meant to say.
Just remember this: when a battery goes, it starts to tax the charging system, namely the alternator. It is possible that the alternator is going out as a result of that.
Altho all alternators are going to go anyway, eventually, it is probably safe to say that if you were to catch a dying battery before it got too bad, you'd probably extend the useful life of your alternator, while only replacing a dying (but not fully dead) battery. Long sentence. I think I know what I meant to say.
Le Mans Master
Joined: Jun 2006
Posts: 5,642
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From: One day you're a Comet...the next day you're dust... Arkansas
I would take your alternator off and have it tested. Most Autozones have a tester and will do it free. They also have a very good NEW alternator called Duralast Gold for about $120 exchange.
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
I've found that between the alternator and the digidash there is usually between a 0.1 and 0.3 volt droppage. Your readings sound far too low. I would also for the sake of doing it measure at alternator what it is putting out for voltage.
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
Originally Posted by trailblz
Is there any way to test the output of the alternator while it is still on the car?
p.s.
Check it at the Alt and at the Battery to rule out corrossion of the wire between them.
Drifting
Joined: Sep 2005
Posts: 1,867
Likes: 3
From: Pasadena Maryland
You need to check all connections before you spend a dime! Clean your battery terminals, disconnect and clean the wire from battery positive to the alternator, "at the back of the alternator". If you have a meter check battery voltage with car off, you should see 12.5? then start the car and check the votage at the battery, you should see 13 to 15. You can measure the voltage at the back of the alternator to check the quality of the connection. Ground out the meter black lead and then measure the battery positive post, now measure the wire at the back of the alternator. You should see the same voltage "Within a couple tenths of a volt"
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Thread Starter
Intermediate
Joined: Apr 2006
Posts: 37
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From: Gilbert AZ
I checked/cleaned all of the connections then took it to AutoZone for a test, and they said it tested fine. The voltage they read was 12.5 to 13.5 while running.
I wonder if there is a bad wire to the voltage sending unit or a bad voltage sending unit. One of the wires coming off the alternator had a splice in it to some sort of sensor on the block. Is that the voltage sending unit?
I wonder if there is a bad wire to the voltage sending unit or a bad voltage sending unit. One of the wires coming off the alternator had a splice in it to some sort of sensor on the block. Is that the voltage sending unit?
Instructor
Joined: Oct 2002
Posts: 121
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From: Hanover Ontario
I had the same problem....usually runs between 13.8-14.4V. Started to dip into 12V range then the battery died. Replaced the battery, then the alternator went.So I guess I'm trying to say replace the alternator but don't get screwed like I did. When it first happened I bought a remanufactured Delco unit (I was told it was perfect and would last as long as a new one). It died within a year. Replaced with a brand new Delco unit and it works perfectly after a few years.
Moral of the story: NEVER buy a remanufactured alternator!
Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
There is no splice in the alternator output wire, it goes directly to the jump start terminal behind the battery and it has a fusible link in it. Also, your alternator output voltage is low, even the Autozone measurement is low. Normal alternator voltage is 14.7 volts cold which drops to 13.7 volts hot. You should have seen the red battery symbol light come on on the dash because your voltmeter readings if correct show that the alternator was not charging your battery. At 11 to 12 volts, you are running only on the battery and the battery is considered discharged at 12.0 volts. Scorp is correct in that there is a 0.3 volt drop in the ignition switch contacts and the dash voltmeter reads the voltage after the ignition switch. Also, keep in mind that with the alternator not charging the battery, the dash voltmeter reads low and is inaccurate. Compare the battery terminal voltage with the dash voltmeter and believe your voltmeter. Alternator voltage below 13.2 volts is a defective alternator !!!!
Thread Starter
Intermediate
Joined: Apr 2006
Posts: 37
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From: Gilbert AZ
Originally Posted by BADDUCK
Are you saying that your dash voltmeter is still reading less than 12v as before?
Yes, the dash reading is different than the reading on the Autozone machine.
Thread Starter
Intermediate
Joined: Apr 2006
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From: Gilbert AZ
Originally Posted by jfb
There is no splice in the alternator output wire, it goes directly to the jump start terminal behind the battery and it has a fusible link in it. Also, your alternator output voltage is low, even the Autozone measurement is low. Normal alternator voltage is 14.7 volts cold which drops to 13.7 volts hot. You should have seen the red battery symbol light come on on the dash because your voltmeter readings if correct show that the alternator was not charging your battery. At 11 to 12 volts, you are running only on the battery and the battery is considered discharged at 12.0 volts. Scorp is correct in that there is a 0.3 volt drop in the ignition switch contacts and the dash voltmeter reads the voltage after the ignition switch. Also, keep in mind that with the alternator not charging the battery, the dash voltmeter reads low and is inaccurate. Compare the battery terminal voltage with the dash voltmeter and believe your voltmeter. Alternator voltage below 13.2 volts is a defective alternator !!!!
No dash light has illuminated at this point. The splice that I saw is a 18 or 20 guage wire, not the output wire for the alternator. I'll try and get a picture.
Would a bad alternator charge at all? I have been monitoring the voltage on the dash while driving and the voltage will increase as I accelerate. Even with the A/C and headlights on. This to me would signify that it is working...at least partially?? right?