charging voltage at idle (1 Viewer)

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You guys with Ultragauge, Scangauge, etc, what voltage do you see at idle? I used to think I would see over 13v, but today I was only seeing 12.2-12.5v at idle. Seems a little low to me, I know that these old alternators are not rated very high, and I do have a 20gph water pump and fan running all the time.

I am at 154,500 miles and original alternator, just wondering if it is getting tired. I need to get everything pretty much 100% in the next 2-3 months.
 
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My charging voltage at idle according to my Scangauge II is 14.7 volts most of the time. Hope that helps!
 
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Hmm so yeah doesn't sound good for my alternator. Unless it is still good and I have just added too much crap. Lol
 

LFD2037

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Some say it's an 80amp & some say 100amp. I'm still not sure which it is 100% for sure! Anyways, where/how are you reading it? From the back of the alt., @ the battery, using a meter or SG or?
 

LFD2037

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Hmmm. That'll show you what the ECM is receiving. Maybe try a meter & see if for some reason there's a difference. My battery is @ 12.7V after sitting for 24+ hours not running.
 
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I have an ultragauge. I had been reading 13.5v at all times, until my alternator decided to stop working on the way to work. I ended up getting one from oreillys because I could get it the same day. Now I'm reading 14.3-14.5v all the time. I had the original alt tested and it turns out the voltage regulator had gone bad. I'm currently sourcing replacement parts for the stock alt now.

If you're only reading 12.5v then your alt is most likely done for.
 

Dave 2000

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The 80 tends to come with an 80 amp alternator, at the age they are now it may have been replaced in the past with something different? Either way, it is not spinning fast enough to produce the goods to suit your present amp draw, I assume if you hold the revolutions at say 2000 the volts start to rise? If not then the alt belt/s are loose or the alt may be toast, try pulling the fan/water pump fuses and see if the volts come up to snuff. Another point, if you get stuck in traffic on a very hot day you will find your engine may overheat after awhile, the reason is the battery voltage is being pulled down to the point where the fan/pump is not spinning fast enough and a worse case scenario the engine will cut as the ECU will not see the correct volts. Get some readings with the A/C on/off, add in the stereo and see what is happening, obviously check the idle speed, there should be some correction when the fan/water pump come on, if not they may be dragging the idle down compounding the problem. You need 13 plus volts to charge the battery, a fully charged battery in good condition after standing will be around 12.6 remember it is a nominal 12v but in reality nearer 12.7, your battery (12.2 - 12.5) is effectively being slowly discharged at idle.

regards

Dave
 
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Good info, it looks to be temp related. In the mornings when it is cool it shows 14v at idle when it is 95-100 it shows high 12's. Load on the alternator should be the same, does heat effect alt power output?
 

LFD2037

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Heat kills batteries but it usually happens in winter when it finally dies because its harder on the battery to start when cold.
 
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You really need to measure the voltage right at the battery since what is going into the battery is really what counts.

Also verify at either side of the FL MAIN2 since the alternator output goes through the fusible link to arrive at the battery.

cheers,
george.
 
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Ok this is almost exactly what I am seeing when it is hot. Cold start in the morning I am seeing higher I idle charging. I am not having any problems so I am not going to IH8MUD it. Lol

Last night I saw 12.7-13.1 at idle with the lights on and the A/C on full. Driving in the same conditions is 13.8-14.5V or so.
 

1973Guppie

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you should be seeing 14+ at idle, easy to put a multimeter on the batt when running. I usually compare the running # to the non running batt charge #. non running 12+ and running 14+
 

LFD2037

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At idle with lights on and AC on I see 14.1V. Same scenario driving I see 14.4-14.7V. With no load on battery, while idling, you should see 14-14.7. Not running, at the battery, you should see 12.5-12.8 right after killing the motor. If your seeing less in either of these situations then
A. You have a load
B. your alternator is weak/bad
C. Your battery is weak/bad

If I ever saw 12.7-13 while its running I'd be concerned.
 

maxamillion2345

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At idle with lights on and AC on I see 14.1V. Same scenario driving I see 14.4-14.7V. With no load on battery, while idling, you should see 14-14.7. Not running, at the battery, you should see 12.5-12.8 right after killing the motor. If your seeing less in either of these situations then
A. You have a load
B. your alternator is weak/bad
C. Your battery is weak/bad

If I ever saw 12.7-13 while its running I'd be concerned.

Agreed.
 
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if you have a 20 year old original alternator that needs to be reliable for the next few months, why risk it? put a set of brushes in. my stock voltmeter got a little erratic last year, at the same mileage as yours. I threw in some brushes and she's been great since. old brushes were quite worn as to be expected
 
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This was measured at the scan gauge and I haven't put a multimeter on it. Its got 168K on the stock alternator so perhaps a set of brushes in order?
 

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