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Old 01-19-2022, 01:35 AM   #1
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Alternator Overcharging

Hello all. A brief background about this situation. My alternator is putting out 19.3v at startup and is overcharging the battery to the point that within seconds of starting acid is starting to boil out from under the caps.
Well here is an update to the situation. I removed the new alternator and took it in for testing after crawling around underneath the rig looking for loose and frayed wires. It passed with flying colors,14.3v! This then begs the question, why is it overcharging?! Well a call to RVworld and a description of what is happening along with year make and model. I was told that there is a secondary voltage regulator somewhere in the engine. Apparently in the 90’s this was a common practice. Relieved that is is not something major, I just have to find it! If anyone knows where the possible location of an external voltage regulator in a 96 Dolphin Rv I would appreciate it. Dealing with people getting sick so I don’t have a lot of time.
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Old 01-19-2022, 09:40 AM   #2
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Sorry that I can't help with your question. But I have to wonder, how does the voltage increase to 19 if the alternator is only putting out 14.3 volts?
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Old 01-19-2022, 09:55 AM   #3
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With more information on the alternator and your battery isolator, we will be of more assistance.


If this is a DUVAC alternator and the SENSE wire has any resistance, it is feeding the alternator false info and causing it to output at higher voltage.


So, if a DUVAC, read voltage between the sense terminal and ground. Should be exactly the same as between the positive and negative terminals of the chassis battery. If it reads lower, THAT will cause the overcharging.
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Old 01-19-2022, 10:06 AM   #4
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A few thoughts to share that may help. Usually if there is an external regulator then it is usually mounted on the firewall along the side of the engine with the alternator. Many times it is a shiny thin module (~5"x3") with a single connection plug connection with 3 wires in it. You should be able to follow the wiring from either direction, alt to regulator or regulator to alternator if you find something similar to what I am describing.

On the other hand, if the alternator you have now has an internal regulator, then it may be easier and provide better results to wire the alternator so that the external regulator is no longer used. Generally this could be as simple as unplugging the regulator and\or may require you run a positive wire back to the alternator where the regulator was plugged in, which likely the power cable is already there.

Which alternator does yours have installed? ~CA
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Old 01-19-2022, 10:37 AM   #5
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Sounds like you have a voltage regulator that is malfunctioning. If the regulator is external, replace it. If it is internal to the alternator, you will need to replace the alternator.

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Old 01-19-2022, 11:21 AM   #6
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Is this gas or DP ? First off is same alternator when this all started. Did you do any other work on or around batteries or positive power connections before it started. Plus one on issue with sense wire issue with Dulvac alternator used in DP. Look for corroded wire bad crimp connectors. I haven't read of external regulator in coach of that era. if so it wouldn't increase voltage of working internal regulator.
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Originally Posted by wolfe10 View Post
With more information on the alternator and your battery isolator, we will be of more assistance.
I believe you can just change a Leese Neville internal voltage regulator module if you can get right the one.


If this is a DUVAC alternator and the SENSE wire has any resistance, it is feeding the alternator false info and causing it to output at higher voltage.


So, if a DUVAC, read voltage between the sense terminal and ground. Should be exactly the same as between the positive and negative terminals of the chassis battery. If it reads lower, THAT will cause the overcharging.
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Old 01-20-2022, 12:41 AM   #7
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Which chassis do you have Ford or Chevrolet? You would be better served posting in the correct chassis forum. Ask the Moderators to move your post.
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Old 01-20-2022, 10:57 AM   #8
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Find this and check for clean and shiiy connections on every end of wire, large and small.

They are not all the exact but look like it.Click image for larger version

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Old 01-20-2022, 11:05 AM   #9
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Even check it's ground wire.
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