Alternator voltage

I show 13.7 when going down the road.

 

Not exactly correct. Nothing on a well operating charging system says it should show above 14.0v (even w/lights and accy's on). It may be over 14v, or it may be 13.0 to 13.9 . If the battery set's state of charge is high, and it's capacity (amps x volts) is high, and provided the load (drain on batteries) isn't excessive, it may only "require"... say,, 13.1v to 13.5v and be charging perfectly adequately. Since each cell of a battery is 2v and the total of 6 cells =12v (approx), then anything over 12.5v is in a "charging condition". Naturally if the electrical load exceeds the "storage capacity" of the battery(ies), only then will it be needed to charge with a higher voltage rate (which is also dependent on the amp output of the alternator).

Are you saying my earlier post about charging voltage rates being temperature affected, are baseless or not true??
If you understand electrical & charging systems, then you'd have an idea why you had the same reading. There are 2 valid reasons, but either reason doesn't diminish from the fact that temp certainly does affect the voltage output. I'll let you tell me them.

 

Here goes a simple answer. 13.9 to 14.0 is normal, higher its overcharging, lower is undercharging.

If you smell rotten eggs, your batteries need to be replaced. It is always best to replace them all at the same time to prevent a weaker battery from taking out a good battery.

All connections need to be cleaned tight and sealed. Grounds are just as important as the positive connections.

 

Powder,
Is your 13.9 to 14.0 a typo? If not, you are saying only within a range of 1/10 of a volt is normal. Pretty tight "criteria" for a normal system.

 

That's getting a bit too low for normal charging. I didn't mean to venture too technical in my prior posts, but it led that way to explain some things.
#1. Make sure you're using an accurate meter for voltage. Many dash gauges are not that accurate, at times. Borrow or buy a good multimeter. They are pretty inexpensive to purchase. Then also compare the reading to your dash gauge.
#2. Curious what your battery(s) voltage is after a longer (several hours) drive? And their age/condition? It would be good to check, then charge them overnight, and after disconnecting charger check the voltage again. (Best to allow several hours to overnight, after disconnecting charger, for the "surface charge" to dissipate to get a truer reading).
#3. If your 12.9v (running voltage) is accurate, sounds like you may have a bad diode in the alternator (if you already eliminated any bad connections/cables).
#4. If the batteries are not "maintenance-free", you can best check the condition of each cell with a battery hydrometer (cheap, found at any auto parts store). Batteries with internal shorts or dead cells will affect proper charging (and thus inaccurate voltage reading) as well as alternators not putting out correctly. Bottom line,, both have to be good. They affect each other.

Flightline is correct, btw. But fresh/hot charged battery may show over 12.5v (static, not running/charging). That's why it's best if you can allow time after charging for "surface" charge to dissipate. Example: Immediately after charging battery(s) they may show 12.9v, but once they cool/stabilize, they will show, say, 12.5v or thereabouts (normal), which is their stable accurate reading.

 

my truck puts out 14.4 during the day. 14.2 at night with the lights on. so you all are saying i'm overcharging.

my 2012 chev and my 97 chev both put out 14.7. i've had my 97 for 6 years now and yet to replace the battery.

back in the old day. temp made a difference. but i don't think it plays out so much with todays technology.

and you need a minimum of 13.1 volts with all accessories running. a fully charged battery is 12.6 plus 1/2 volt making 13.1. and that's at an idle. todays alternators are considered weak at 13.5. considering they put out much higher amperage then what they used to.

course, i flunked the ASE exam and never went to delco remy training.

test the output of the alternator and compare to final reading at the battery. there will always be voltage drop from point A to B.

 

So on an alternator on a 94 3406e it should be at least 13.5? Mine seems hover around that mark too often for my tastes. I recently had the belts off and spun the pully by hand and noticed something strange. When spun counter clockwise it has significant drag and when clockwise the drag would stop after a few turns in that direction. Doesn't seem right.