Is my alternator on the way out?

[1hdtman]

Hi all,
I have an early 1hdt 80 series with dual battery setup up. I have a fridge with kings dc to dc charger.
I also have a turbo timer which displays the battery current voltage when the car is running.
My voltage fluctuates between 11.8 to 13.6.
If the second battery charging, the voltage drops to 12v on average.
The first question, is this normal or is my alternator isn’t functioning as it should?
I did not fit the system myself, but I know everything about it.
Your help will be greatly appreciated!

 

[1hdtman]

 

[jpoole]

Check voltage at the alt and other points in the system using a multi-meter. Unless the batteries are pretty deeply discharged and being brought back up or the system is otherwise supporting a heavy load your resting voltage should be around 14.1 most of the time. Some alts, or further points from the alt in the system, will rest at different voltages but they typically get there relatively quickly and spend most of their time in a consistent range based on current load.

Brushes aren't too hard to pull/check/replace on these if that ends up being relevant.

 

[Marco Lau]

one of your batteries might be on its way out. What is the current voltage for both batteries when sitting? early 80s come with either an 80 or 90 amp alternator, which is not adequate for charging all the accessories you currently have on the rig. I have upgraded my alternator to 150amp and i am running dual electric fans setup with a fan controller, a dual zone fridge and i get about 13.6 -14.2v, With my 80 amp alternator setup, it would dip down to range between 11.6 -12.3....

 

[1hdtman]

one of your batteries might be on its way out. What is the current voltage for both batteries when sitting? early 80s come with either an 80 or 90 amp alternator, which is not adequate for charging all the accessories you currently have on the rig. I have upgraded my alternator to 150amp and i am running dual electric fans setup with a fan controller, a dual zone fridge and i get about 13.6 -14.2v, With my 80 amp alternator setup, it would dip down to range between 11.6 -12.3....

is it normal for the rpm to drop to 0?, know the car is running

 

[robnicko]

I 2nd Marco's comment however what chemistry is your 2nd battery, AGM, WetCell, Lithium?
also grounding points for your 2nd battery?

I run my 2nd batt (wet cell deep cycle) under the bonnet and its voltage pretty much mirrors the start battery when the engine is running using a Pirahna DBE180sx, 14.6v initially then down to 14.0-14.1
When I 1st installed dual batts many moons ago the Earth on the 2nd batt wasnt good enough and it would only get about 13.5v when the starter batt was at 14.6. I made up new earth cables (1 to the motor & 1 to the frame) and ever since the voltage is equal on both

 

[TheBussman]

perform battery and alternator tests before guessing. Is your second battery at a low state of charge when your voltage is low? if you have a 60 amp alternator you may just be using up all your system's capacity charging it up. I've seen some fluctuating alternators with bad rectifier.

 

[1hdtman]

I 2nd Marco's comment however what chemistry is your 2nd battery, AGM, WetCell, Lithium?
also grounding points for your 2nd battery?

I run my 2nd batt (wet cell deep cycle) under the bonnet and its voltage pretty much mirrors the start battery when the engine is running using a Pirahna DBE180sx, 14.6v initially then down to 14.0-14.1
When I 1st installed dual batts many moons ago the Earth on the 2nd batt wasnt good enough and it would only get about 13.5v when the starter batt was at 14.6. I made up new earth cables (1 to the motor & 1 to the frame) and ever since the voltage is equal on both

Sorry for the late reply,
Under the bonnet, not sure
At the back of the car 2x 120ah lithium ion.