Voltage indicator fluctuating

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bertola

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Joined
Feb 27, 2010
Posts
44
I went out to to motorhome today to start it up and run the systems.  It is a winnebago vectra with a cummins engine. Everything wen well except that on initial start up I notice the buzzer for the low air pressure was changing tones.  So on further inspection I notice the the voltage indicator was fluctuating between  about 12.8 and 13.8 volts.  It did this for maybe 5 minutes then settled down to the normal range and stayed there for about the hour drive that I made.  Is this something I should have looked at prior to hitting the road tomorrow?  Is this an indication of a failing alternator or maybe voltage regulator? - (I'm not even sure if diesel engines have them).  Maybe the batteries? Any ideas would be appreciated.

Thanks,
Craig McKeand
 

John From Detroit

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Joined
Apr 12, 2005
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25,117
Location
Davison Michigan
His is theory..  IN fact it is two theories.

1:There are  many different isolator systems, Some are "Intellegent" and bi-directionsl (mine is) on some of these systems they monitor voltage.

If the battery voltage on both sides is say, less than 13, it assumes the engine is NOT running and you are NOT plugged into shore power.

If the voltage on one side rises above 13, it assumes that EITHER the engine is running and charging the battery or the house charger is operating and doing the same and connects the two so they both charge.

IF the house batteries are low enough, they then draw the system voltage back down till the isolator drops out.

After several cycles.. The house batteries have some charge, and the isolator hangs in there.

Theory 2:

Self-resetting thermal circuit breaker in the house line sees way too much current flowing to the very hungry batteries and says "Time out" again after several cycles, the house batteries have some charge and it hangs in there.
 

donn

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Joined
Nov 8, 2009
Posts
4,709
Sounds normal, my Dodge Cummins does the same thing until the battery gets fully recharged.
 

bertola

Active member
Joined
Feb 27, 2010
Posts
44
Thanks everyone for the input.  Just got back from a 1200 mile trip with no problems.  I guess it was happening normally and I just hadn't noticed.

Craig McKeand
 

Neal

Well-known member
Joined
May 13, 2009
Posts
538
Location
East Texas
bertola said:
voltage indicator was fluctuating between  about 12.8 and 13.8 volts.

My 08 has done similar, when on a cold startup, since new. When warm it goes straight to about 14 volts
 

Kamper Dave

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Joined
Feb 3, 2011
Posts
195
Location
Wisconsin
The Cummins intake Grid Heaters are programmed to cycle for the first several minutes. They draw an incredible amount of current and will indeed dim the lights until they quit cycling.
 

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