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03-07-2014, 08:42 AM
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#1
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Junior Member
Join Date: Apr 2013
Posts: 19
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Voltage gauge fluctuates high/Low
2000 HR with Cummins Engine, new/rebuilt alternator. When the batteries are low and the alternator appears to be putting out. The battery indicator on the dash lights up and the gauge above the dash indicates 14.2 but drops down to around 12.3 then jumps back to 14.2. this happens every 10/15 seconds. Voltage going into the isolator from the alternator reads around 15.3. on the other side of the isolator going into both battery banks voltage is 14.2. I have not checked the voltage from the alternator to the isolator to see if it is also fluctuating but I will next time Im at the MH. Any ideas what could cause this fluctuation?
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03-07-2014, 08:56 AM
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#2
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Registered User
Monaco Owners Club
Join Date: Oct 2009
Location: Varies Depending on The Weather
Posts: 8,517
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Are you sure the shop that did the rebuild was a reputable one and the alternator was rebuilt correctly?
That's the first place I would check since it wasn't doing it prior to the rebuild.
Dr4Film ----- Richard
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03-07-2014, 09:29 AM
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#3
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Senior Member
Country Coach Owners Club
Join Date: Jan 2006
Location: Northern California
Posts: 5,868
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If the voltage at the batteries are a steady 14.2 with the engine running but the dash gauge is fluctuating then the connection to the dash gauge would be suspect.
At least, you are then getting the correct charging effect from the alternator to the batteries.
__________________
Dean
1995 38' CC Magna #5280 **** Sold after 21 years of enjoyment.
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03-07-2014, 09:44 AM
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#4
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Senior Member
Gulf Streamers Club
Join Date: Jan 2012
Location: Cincinnati
Posts: 19,925
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I think before blaming the alternator or rebuilder it would be prudent to clip another meter to the circuit and VERIFY that it is a REAL voltage fluctuation and not a loose connection to the dashboard gauges or a bad ground. You might also remove, inspect, and clean all battery connections.
__________________
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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03-07-2014, 09:56 AM
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#5
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Senior Member
Join Date: May 2013
Posts: 962
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Another vote on Alternator, or it's connection to the battery bank. A bad connection to the gauges wouldn't coincidentally read 12.3V (the battery voltage), it would likely drop to zero. Have fun chasing!
Chris
__________________
------------------------------------
American Revolution 40L CAT C9
Samsung 197, TireMinder, Ready Brute Elite with Wrangler
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03-07-2014, 10:32 AM
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#6
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Junior Member
Join Date: Apr 2013
Posts: 19
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Thanks for your input, I will do as you suggest and check the connections. Is there a chance there is a bad solenoid somewhere is the circuit? Would a bad diode in the alternator act like this?
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03-07-2014, 10:47 AM
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#7
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Senior Member
National RV Owners Club
Join Date: Feb 2012
Location: Spokane Valley, Wa
Posts: 1,987
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Keep in mind that the voltage drop thru the isolator is about a 1/2 volt.
Does your system use a out board regulator if so that might be your problem.
__________________
Art
1999 Trade Winds 7371 Cat 3126B w/current upgrades
1990 D 250 Dodge Ram Cummins Turbo
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03-07-2014, 11:13 AM
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#8
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Junior Member
Join Date: Apr 2013
Posts: 19
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Not sure what a out board regulator is. I have a Big Boy ( or at least I think I do) attched to the isolator and that controles the boost between the two banks
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03-07-2014, 11:29 AM
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#9
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Senior Member
National RV Owners Club
Join Date: Feb 2012
Location: Spokane Valley, Wa
Posts: 1,987
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You either have a internal regulator a part of the alternator or you have a alternator
that uses a out board regulator.
You say you have a isolator and that allows two or more batteries to be charged with
neither battery or banks of batteries being effected by the other ie the reason it is called a isolator.
You need to find out if the alternator has either a internal or external regulator.
A flaky regulator will cause the problems you indicate as will several of the items
others have posted.
__________________
Art
1999 Trade Winds 7371 Cat 3126B w/current upgrades
1990 D 250 Dodge Ram Cummins Turbo
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03-07-2014, 12:23 PM
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#10
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Junior Member
Join Date: Apr 2013
Posts: 19
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Again, thanks eveyone, I will run the test you suggest and see what I get. I do have an internal regulator so am am leaning toward a bad alternator.
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03-07-2014, 12:48 PM
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#11
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Senior Member
Join Date: Apr 2012
Posts: 1,414
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Quote:
Originally Posted by Rehbergl
Thanks for your input, I will do as you suggest and check the connections. Is there a chance there is a bad solenoid somewhere is the circuit? Would a bad diode in the alternator act like this?
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Could be a solinoid but I hope one is not installed. I too think a regulator problem may be there. Do you have a fl chassis? If so my voltmeter went to 0 and turned out to be the vdc. Look up vdc on rv2. A bad diode would cause your alternator to scream while charging as the load is no longer the same throughout the revs.
__________________
Dave and Laura & two cats
02 Discovery with Accord toad
retired auto rv tech and teacher, wife rt nurse
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03-07-2014, 04:12 PM
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#12
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Senior Member
Tiffin Owners Club Freightliner Owners Club
Join Date: Apr 2012
Posts: 2,079
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if I understand correctly you have a isolator that allows the regulator to charge both battery banks. The very easy check to make is to disconnect the isolator from the charging system. Start the engine with only the chassis batteries in circuit. See if the problem still exists. If not your alternator is ok and the problem is with the isolator or the coach batteries.
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03-07-2014, 05:47 PM
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#13
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Senior Member
Winnebago Owners Club Freightliner Owners Club
Join Date: Dec 2010
Location: DW Driver - Englewood FL
Posts: 1,448
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what is the temperature where you are at
I recall going through this same problem, possibly on another forum, but the same engine and year. It was determined that, If it is below 50 degrees the voltage will change as the preheater comes on and off.
after a few minutes it should stabilize. my meter does the same thing. 14 plus then it drops then it goes up then it drop - eventually it stays at 14
__________________
La Dagobago
99 36 FL Winne Chieftain 5.9 ISB Turbo Cummins DP, 24' box with HD Sporty Hobby of 1970's Suzuki dirt bike restoration. Visit my blog.
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03-07-2014, 08:28 PM
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#14
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Member
Join Date: May 2012
Location: Mineola, TX
Posts: 84
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Same for me. During cold weather, this happens for about 2 minutes, engine warms up then stabilizes. I had it checked out this past December and it was the preheater doing it.
Quote:
Originally Posted by ladagobago
I recall going through this same problem, possibly on another forum, but the same engine and year. It was determined that, If it is below 50 degrees the voltage will change as the preheater comes on and off.
after a few minutes it should stabilize. my meter does the same thing. 14 plus then it drops then it goes up then it drop - eventually it stays at 14
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__________________
2011 Thor Astoria, 40ft - 2012 Ford Fusion Hybrid, 2017 Jeep Wrangler
Blue Ox - Baseplate, Towbar and Brake
Retired USAF
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