Charging voltage dropping off

Hi All.
Have been experiencing an issue with the charging voltage dropping off in my old girl, starts off at 14.3 and then drops to as low as 13.1 according to the ECU Talk on the dash. I thought it may have been a battery issue as the thing was 4 years old so I changed it. It made no difference so I thought it may be the alternator so I changed it with no change to issue. . . . . it seem as though the voltage drops off when the engine warms up so now I am thinking it may be the belt tensioner (which was replaced around 12 months ago. Has anyone else had similar issues and if so what was the cause. . . . after shelling out a total of $700 for a new battery and alternator I guess another couple of hundred for the belt tensioner will be no drama, just hoping it's nothing more serious.
Cheers
A.J

How old is the car ?
Could it have one of those smart alternators that drop down a notch if battery is charged and/or there is no load on it ?

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Originally Posted by Hodge

How old is the car ?
Could it have one of those smart alternators that drop down a notch if battery is charged and/or there is no load on it ?

Sent from my SM-G920I using Tapatalk

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2003 3lt grenade Hodge, had a new alternator about 18 months ago so was a bit skeptical about changing it. I have even disconnected the auxiliary battery to see if that was the issue but made no difference, once the engine is at operating temps it drops off to between 14.1 and 13.1. The issue with it dropping below 13.3 is it stops charging the auxiliary as the Redarc senses the voltage drop and shuts off.

We've got a 2002 grenade and have replaced tensioner twice but never noticed a voltage drop, replaced alternator because the clutch was seizing up , I was told the wires to alternator do get dickie .

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Originally Posted by Wetty

Hi All.
Have been experiencing an issue with the charging voltage dropping off in my old girl, starts off at 14.3 and then drops to as low as 13.1 according to the ECU Talk on the dash. I thought it may have been a battery issue as the thing was 4 years old so I changed it. It made no difference so I thought it may be the alternator so I changed it with no change to issue. . . . . it seem as though the voltage drops off when the engine warms up so now I am thinking it may be the belt tensioner (which was replaced around 12 months ago. Has anyone else had similar issues and if so what was the cause. . . . after shelling out a total of $700 for a new battery and alternator I guess another couple of hundred for the belt tensioner will be no drama, just hoping it's nothing more serious.
Cheers
A.J

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When the voltage drops to 13.1v, open up the bonnet & check the voltage at the battery & alternator B+ output on the alternator.
Use a known accurate multimeter, and see that reading is consistent with the ECUtalk reading.

What issues are you having other than voltage showing too low?

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Originally Posted by dom14

When the voltage drops to 13.1v, open up the bonnet & check the voltage at the battery & alternator B+ output on the alternator.
Use a known accurate multimeter, and see that reading is consistent with the ECUtalk reading.

What issues are you having other than voltage showing too low?

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Have done that Dom, and the voltage fluctuates on the meter as well. I checked the wires on the plug that connects the alternator to the wiring loom and one of the wires was corroded so I cut it off and soldered it back together. This made no difference, however I did start the car without the plug connected and it was reading 15.9 volts on the ECU Talk and meter. . . . . needless to say I shut the engine off quick smart. It appears as though there is a voltage regulator somewhere in the wiring loom that my be the issue. It's off to the mechanic tomorrow for a yearly fluid drop so they might be able to diagnose the problem.

Quote:

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Originally Posted by Wetty

Have done that Dom, and the voltage fluctuates on the meter as well. I checked the wires on the plug that connects the alternator to the wiring loom and one of the wires was corroded so I cut it off and soldered it back together. This made no difference, however I did start the car without the plug connected and it was reading 15.9 volts on the ECU Talk and meter. . . . . needless to say I shut the engine off quick smart. It appears as though there is a voltage regulator somewhere in the wiring loom that my be the issue. It's off to the mechanic tomorrow for a yearly fluid drop so they might be able to diagnose the problem.

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Auto sparkie has a better chance isolating any issues of this kind.
You've got dual batteries, so there might be some extra wiring that may be causing this issue.
The voltage regulator is usually inside the alternator, not outside.

I really don't know the answer for you. This is assuming you do not have flat battery problems.
A battery when discharged will be recharged at a higher voltage and when it is charged the voltage will drop to a float voltage.
My auxiliary battery on an in car DC-DC system drops to a float voltage of 13.2 volts as does my workshop C-Tek 240 volt charger.
When the engine is turned off after the voltage has dropped to the 13.1 volts have the battery tested, if its fully charged all is sweet.
Well I think it is!
Good luck.