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Curtis B.
Curtis B., Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 26045
Experience:  Technician turned service manager on multiple lines of trucks and engines, used in industry.
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My alternator was charging 13.6 sometimes 13.8 at idle, but

Customer Question

Hi there, my alternator was charging 13.6 sometimes 13.8 at idle, but when at high rpm always when to 13.2 or lower, I changed the alternator and still doing the same, now don't go higher than 13.4 at idle and 12.9 when driving, batteries are 1month old and I am using the alternator we replaced, 140 amp.
Submitted: 12 days ago.
Category: Medium and Heavy Trucks
Expert:  oldnewenglandmarine replied 12 days ago.

Hi Luis, my name is Jason.

Are you measuring the voltage directly at the battery with a hand held volt meter, or are you relying on the gauge in the boats dashboard?

Expert:  oldnewenglandmarine replied 12 days ago.

Are you still with me?

Customer: replied 12 days ago.
Just what it show on the dashboatd
Expert:  oldnewenglandmarine replied 12 days ago.

Voltage needs to be double checked at the batteries, you could simply have a bad gauge or a bad electrical connection at the gauge. That is the starting point, did you have any further questions for me on the issue?

Customer: replied 12 days ago.
RI got now it'seems jumping get between 13.3 and 13.5
Expert:  oldnewenglandmarine replied 12 days ago.

Voltage needs to be double checked at the batteries, you could simply have a bad gauge or a bad electrical connection at the gauge. That is the starting point, did you have any further questions for me on the issue?

Customer: replied 12 days ago.
Dont have a voltmeter with me
Expert:  oldnewenglandmarine replied 12 days ago.

Okay. You did pay the website 26 dollars to speak with me, and they did charge you the 26. How is It I can help you?

Customer: replied 12 days ago.
Will have to go to a Volvo truck shop next week
Customer: replied 12 days ago.
Just want to know why it's charging somewhat good at idle but not at high rpm?
Customer: replied 12 days ago.
The pulley is good fast
Customer: replied 12 days ago.
For the last couple of days don't want to go higher than 13.5-13.6 even at idle, it just to go all the way to 13.8, 13.9.
Customer: replied 12 days ago.
Batteries are new and already change alternator
Expert:  oldnewenglandmarine replied 12 days ago.

You are in the boat category, is this engine in a boat or some kind of commercial truck? (D13 engines are used in both)

Customer: replied 12 days ago.
Volvo 780 commercial truck
Expert:  oldnewenglandmarine replied 12 days ago.

Okay this is the wrong category. I will opt out.

Customer: replied 12 days ago.
Ok
Expert:  Curtis B. replied 11 days ago.

What is your concern? Are the batteries going dead, or too low to start the truck? The alternator will not charge more than is needed. With new batteries , it is not unusual for alternator to not charge over 13.5 volts. have one on a GMC that will drop down to 10 olts, then when battery gets a little low, I will look over and its charging 15 volts. It always keeps batteries up , and has caused no problems. I batteries go dead, and truck won't start, then it is a problem that needs to be looked at further!

Expert:  Curtis B. replied 8 days ago.

I see question is still open, did you see my response?

Customer: replied 8 days ago.
truck still doing the same, only charging at idle, batteries almost empty.
Expert:  Curtis B. replied 8 days ago.

I see no indication that voltage drops below 13 volts. Are you measuring voltage at the batteries ? A battery with 13 volts should have plenty of voltage to start the engine. Are batteries lower than 13 volts? What does the battery voltage drop to when trying to crank? You may have too much amperage being drawn by the starter!

Customer: replied 8 days ago.
Batts are now ok because I let the truck running 70 hours at idle after someone Jumpstart me.
Customer: replied 8 days ago.
At idle charge goes up very slowly, begin jumping from 12.8, 13.1 to 60 hours later 13.9 . 14.1
Customer: replied 8 days ago.
Running it maintains around 13.2, dropping to 12.9 at night with lights on.
Expert:  Curtis B. replied 8 days ago.

I really don't see that you have a charging problem. But alternator will not charge more than it sees from battery, I would recommend you take it to a good electrical shop and have them check it

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