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Alternator Charge Fault Light


Billhump
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We have a 2006 Diplomat - 400 ISL Cummins engine with an original LEECE NEVILLE #LBP 2180 160 Amp alternator.  The original alternator was just replaced with a new LEECE NEVILLE # LNLB 2180 GH at a Cummins repair center.  Now the ALT/Charge fail light will not go off.  I told the Cummins Service manager that this light was controlled by the 6V terminal on the back of the alternator which goes to a 6V relay in the front bay under the driver's seat.  After being at the Cummins Repair Center for more than a month, I have now picked up the coach and will troubleshoot the problem myself.  I have talked to a Leece Neville service tech and was informed that all 3 terminals on the back of the alternator have 7.5V.  I have tested the 6V relay socket for this circuit and have no power at terminal 86 with the engine on,  and terminal 85 is the ground.  This was confirmed by both a multi meter and the labels on the wires to the socket.  The alternator is producing a 13.7V charge to the batteries. The horn, lights, wipers, and dash instruments all work. My first question would be: Is there a fuse between the alternator terminal and the 86 port on the relay socket? 2. Do all 3 terminal in the back of the alternator produce 7.5V?  HELP!!

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If you have no voltage on pin 85 (pin 86 and pin 30 go to ground) then I would check the inline 5 Amp fuse.  Are you checking AC or DC voltage at pin 85?  You can check the relay by simply removing it....and the ALT FAIL Light should go out.  

It is not clear which "all 3 terminals" of the total of 8 or 9 terminals you are referring to.  There are two large terminals, which are ground and +12VDC main output.  There are 3 field (stator) connectors.  Then there is the Ignition Terminal and the DUVAC Terminal.  I'm hoping that the alternator is wired correctly.  Maybe you could confirm which wires are on which terminals.  I have helped dozens when replacing their alternator, and over 90% of the problems were incorrect wiring.  

Are you sure you got the correct Alternator?  I don't show the 2100 Series as DUVAC Alternators.  

 

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Thank you Rick N. The alternator installed on the coach at the factory was a Leece Neville #LBP 2180, Cummins service center replaced that alternator with a Leece Neville #LNLB 2180 GH. When I called Leece Neville today, they told me that the two alternators were the same. I believe this alternator has 3 field (stator) connections, the two large terminals which are ground and a 12 VDC main. There are no terminals for ignition or DUVAC terminal. Tomorrow I will check the wiring that I have and look for the 5 AMP fuse. Thanks again

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19 hours ago, Billhump said:

 The alternator is producing a 13.7V charge to the batteries. 

I just though about this last night.  The output should be regulated at 14.1-14.4 volts.  Your 13.7 is low - more like a float voltage from a smart charger, which the alternator is not.  This could be due to the DUVAC terminal not being connected correctly.  Or it could be you have other battery related problems.  Lastly, it could be the alternator is defective, not putting out the full charge voltage, which would also trigger the ALT FAIL circuit.  I suggest you re-check the wiring of the alternator, specifically the DUVAC terminal (if there is one - as per the drawing) and troubleshoot the low alternator output first.  Once that is corrected, you may also correct the ALT-FAIL indicator.

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Update:  I just pulled the Prestolite data sheet for the alternator number you provided.  It does NOT have DUVAC (as the drawing for 2006 Diplomat shows it).  Given that, and since I have no drawing to determine how it was originally wired, I'll provide some educated thoughts.  First, since there is no DUVAC or any other means for external input of battery condition, and the regulator is internal (built into the alternator) I conclude that the voltage sensing is based on the main 12 Volt battery voltage.  There is no ability to compensate for voltage drop between the alternator and the battery.  This is only a real problem when there is some sort of Isolator used between the alternator output and the actual batteries.  Again, based upon the 2006 Diplomat Wiring Diagrams I have, you don't have an Isolator (solid state device) but rather some implementation of a Big Boy Relay. 

That said, I recommend that you check the output at the alternator, not at the battery (yes they SHOULD be the same) and confirm it is not at the Prestolite Specification of 14.2 (14.1-14.4) volts.  If the output of the alternator is not at the correct voltage, check you batteries and cables, though this is unlikely the cause.  More likely the voltage regulator in the alternator is defective, or possibly some other internal (diode) is bad.  In any case, I suspect, if your reading are correct, that you have a defective alternator.  Before troubleshooting a bad ALT-FAIL signal, first make sure the alternator is good....it may be telling you that indeed your alternator is defective. 

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Rick, when Cummins checked this alternator, they indicate on the bill that they had 13.8 VDC on the battery studs of the chassis batteries. The chassis batteries are isolated from the house batteries with an isolation relay located in the main fuse box under the driver’s seat. The 2 chassis batteries are new and maybe 3 months old. I will check the VDC at the alternator this afternoon. I am presently going through the electrical system and have found the auxiliary lights, docking lights and mirror adjustments are not working now, but worked before alternator change out. My led daytime running lights are now pulsating when the engine is running. Thanks for your troubleshooting knowledge. It’s very helpful.

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32 minutes ago, Billhump said:

Rick, when Cummins checked this alternator, they indicate on the bill that they had 13.8 VDC on the battery studs of the chassis batteries. The chassis batteries are isolated from the house batteries with an isolation relay located in the main fuse box under the driver’s seat. The 2 chassis batteries are new and maybe 3 months old. I will check the VDC at the alternator this afternoon. I am presently going through the electrical system and have found the auxiliary lights, docking lights and mirror adjustments are not working now, but worked before alternator change out. My led daytime running lights are now pulsating when the engine is running. Thanks for your troubleshooting knowledge. It’s very helpful.

I would start at the alternator.  That is where/when the problem occurred.  I think that the 13.8 VDC is low - maybe low enough to cause problems.  I agree that since you have the isolation relay, and hopefully short (less than 5-ft or so) battery cables, that the DUVAC system is not needed....I'm surprised that is what the drawings call out.  What else happend/was touched when the alternator was replaced.  It's quite odd that several systems are not working if that is all that was done.

 

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 I would have guessed it was a Duvac system and then the 06 Diplomat drawings show Duvac.

Perhaps the replaced alternator was not the proper one, unless the OP knows for sure.  It could have been replaced before with the wrong one

This is why this forum has recommended for a along time to get the alternator rebuilt.   The complications that can follow replacing it can be hard to rectify.                      Especially after the old alternator is gone.

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Problem Solved- This 2006 Diplomat has a LEECE Neville alternator, which is different from the DUVAC alternator used in the Monaco models above the Diplomat. After some research and help from this forum, I began checking the Electrical Systems in the coach: Here is what I found. Alternator VDC output at the positive and negative terminals (engine running) 14.15 DC, the 3 auxiliary field (stator) terminals output 7.2 VCD each. When I rewire the alternator per 2006 Monaco diplomat wiring diagram, the alt/charge fail light and annunciator now work as they should.  Special thanks to WATERSKIER-1 and all who provided help to me on this problem. 

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