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Topic: Engine Light, Alarm and Low Voltage (Read 631 times) previous topic - next topic

Engine Light, Alarm and Low Voltage

After driving about 30 miles yesterday, engine light and alarm came on. Silverleaf indicated alternator low voltage.  11.7 volts.  Pulled off road and inspected.  Belts OK and no apparent loose connections.

Started generator and put battery switch in Boost mode.

Sat on the side of road, called nearest Cummins and 2 Freightliner dealers to see if they could help.  No help available.  Called FOT and left message for call back.  Decided to continue driving while waiting for call back.

After driving for about an hour, noticed voltage slowly increase to 12.4v and then engine light and alarm went off.  Voltage continued to increase to 12.9v.  Cycle repeated 2 more times before return call from FOT.  Ronnie suggested that it could be the battery isolator and instructed me to measure voltage at all three posts.

With everything off and not connected to shore power measured 2 volts at center post (alternator) and 12 volts at both battery posts.  Was not able to connect with Ronnie with my findings but assume that this may be normal.

Today I decided to do some further checks.

No shore power, Engine off, Boost on.  Battery Isolator:  House battery 12.6 v, Alt 4.5v, Chassis 4.5v.
No shore power, Engine off, Boost off.  Battery Isolator:  House battery 12.6v, Alt 1.6v, Chassis 4.5v.

No shore power, Engine on, Boost on.  Battery Isolator:  House Battery 12.5v, Alt 10.5v, Chassis 4.5v.
No shore power, Engine on, Boost off.  Battery Isolator:  House Battery 12.5v, Alt 10.5v, Chassis 3.7v.

Other observations:  The inverter charges a maximum of 10 amps.  When it is charging and with Boost switch on even of a charge is sensed to turn off alarm and engine light.  When the inverter senses that the house batteries are fully charged it stops charging, chassis battery slowly drops below 11.7v and alarm and engine light come back on.

I am puzzled by the low chassis battery reading at isolator.  The chassis batteries spin the Cummins effortlessly.

It seems like, if I had to, I could continue an my trip.  Over the next couple of weeks I will be driving 2 1/2 days before returning home.

Thoughts?  Tips?

Thanks for your help!!

Don
Don & Sue
2009 NImbus 38
2020 Jeep Grand Cherokee toad

Re: Engine Light, Alarm and Low Voltage

Reply #1 –
When reading voltage across any of these components you should never see more than a volt of resistance. So alternator to isolator should've minimal. Across isolator the same. Center of battery post to cable, should also be the same. If you show voltage or your test light illuminates you have a problem right there. Yes you can run with boost selected. Probably have a chance of having a failed sense wire also. Tells alternator what to charge to.
Scott

Re: Engine Light, Alarm and Low Voltage

Reply #2 –
Reply in SOLID LETTER CAPS:

No shore power, Engine off, Boost on.  Battery Isolator:  House battery 12.6 v, Alt 4.5v, Chassis 4.5v. BOOST SOLENOID MAY OR MAY NOT BE BAD.  IF IT GETS ITS "CONNECT SIGNAL" FROM THE CHASSIS BATTERY, IT WILL NOT/WAS NOT DESIGNED TO WORK WITH VOLTAGE THAT LOW.

FIRST THING I WOULD DO IS FULLY CHARGE THE CHASSIS BATTERY USING A SEPARATE CHARGER.  A "STUPID" CHARGER FROM ANY PARTS HOUSE OR WALMART IS WHAT YOU WANT. THEN CHECK ALL CONNECTIONS AT ALTERNATOR, ISOLATOR AND BATTERY BANKS.  THIS INCLUDES THE SMALL SENSE WIRE TO THE ALTERNATOR.

TROUBLE SHOOTING ANY ELECTRICAL SYSTEM WITH A BATTERY THAT LOW CAN LEAD YOU IN CIRCLES.

THEN, TROUBLESHOOT AT THE BATTERY ISOLATOR WITH ENGINE RUNNING AT 1,100 RPM OR SO. WHEN YOU DO IT, LEAVE THE BOOST SWITCH OFF.

THERE ARE SOME SIMPLE "WORK AROUNDS" ONCE WE KNOW WHAT IS WRONG.  BUT A CHASSIS BATTERY WITH A BAD CELL IS KIND OF TUFF TO "RESURRECT".

Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Engine Light, Alarm and Low Voltage

Reply #3 –
Isolate everything prior to troubleshooting

Re: Engine Light, Alarm and Low Voltage

Reply #4 –
We like others have driven for over a week with a failed alternator by driving with boost on generator running to power battery charger. Never get towed with failed alternator as log as generator & battery charger are working.

Seems like alternator has failed and chassis battery is way too low for a good lifespan. And maybe boost is not working.

Re: Engine Light, Alarm and Low Voltage

Reply #5 –
Quote from: wolfe10 –
Reply in SOLID LETTER CAPS:

No shore power, Engine off, Boost on.  Battery Isolator:  House battery 12.6 v, Alt 4.5v, Chassis 4.5v. BOOST SOLENOID MAY OR MAY NOT BE BAD.  IF IT GETS ITS "CONNECT SIGNAL" FROM THE CHASSIS BATTERY, IT WILL NOT/WAS NOT DESIGNED TO WORK WITH VOLTAGE THAT LOW.

FIRST THING I WOULD DO IS FULLY CHARGE THE CHASSIS BATTERY USING A SEPARATE CHARGER.  A "STUPID" CHARGER FROM ANY PARTS HOUSE OR WALMART IS WHAT YOU WANT. THEN CHECK ALL CONNECTIONS AT ALTERNATOR, ISOLATOR AND BATTERY BANKS.  THIS INCLUDES THE SMALL SENSE WIRE TO THE ALTERNATOR.

TROUBLE SHOOTING ANY ELECTRICAL SYSTEM WITH A BATTERY THAT LOW CAN LEAD YOU IN CIRCLES.

THEN, TROUBLESHOOT AT THE BATTERY ISOLATOR WITH ENGINE RUNNING AT 1,100 RPM OR SO. WHEN YOU DO IT, LEAVE THE BOOST SWITCH OFF.

THERE ARE SOME SIMPLE "WORK AROUNDS" ONCE WE KNOW WHAT IS WRONG.  BUT A CHASSIS BATTERY WITH A BAD CELL IS KIND OF TUFF TO "RESURRECT".


Chassis batteries are 10 years old.  While I am not surprised that 1 or both could fail, I am puzzled that it has never failed to start and even now spins the Cummins easily.  I actually suspected that my meter or my method was faulty because it read 12 volts last night.  I put a battery charger on the coach batteries.  The charger says that it is capable of 30 amps but is only charging at 15 amps.

Will do further checks tomorrow.

IT'S A HOBBY!!

Don
Don & Sue
2009 NImbus 38
2020 Jeep Grand Cherokee toad

Re: Engine Light, Alarm and Low Voltage

Reply #6 –
Another possibility could be the resettable fuse in the 12v line to alternator.  My symptoms were similar and the fuse had come apart.  There are three fuses, one 30 amp and two 15 amp.  Check schematic for which one.  I think it was the center one in the attached photo from my coach.  I replaced all three because of age.  They are available from Foretravel or NAPA also has them.  Panel is located next to isolator on my coach.
Bill and Joyce, The House2 and Dashboard Pig III
2000 U320 4210 CAI (The House2)
Build # 5733
2019 F150 King Ranch FX4

Re: Engine Light, Alarm and Low Voltage

Reply #7 –
All of this back and forth is making me think "Bad Connection."

Second is bad alternator.

My third thought is to remind everyone that a modern high impedance volt-meter has a gotcha built in, and using a 12V light bulb to load down the circuit under measurement may shed more light on the subject than taking a voltage reading with no load.  Id est, those Alternator 4.5V and 1.6V reading may become "0" with as little load as that from a wet fingertip because the high impedance voltmeter is measuring the back leakage through the battery isolator diode be stopped by the rectifier diodes in the alternator creating a pool of higher EMF electrons between the isolator and the alternator.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Engine Light, Alarm and Low Voltage

Reply #8 –
My go to tools for these types of problems are my Digital Fluke meter, incandescent test light. Load cell battery tester, old school battery charger.
Determine the state of the batteries.
            Charge as required
            Check capacity of batteries isolated individually
              Change defective batteries and verified fully charged state
                Verify condition of leads and voltage drop again with load cell
                  Clean and resolve any power cable or ground issues
At this point you now can now start actually checking voltage output of chargers and alternators and actually see the real issues not being masked by all the regular multipliers that generally were the original problem. And if it is a actual charging issue all these steps will generally cost you nothing. But if you replace the alternator you may find yourself going back threw the steps anyway.
Nice thing about a load cell all voltages are no longer masked by resistance issues. They are easily isolated with a corresponding voltage drop at fault.
Scott

Re: Engine Light, Alarm and Low Voltage

Reply #9 –
The engine wont start with a true 4 volts.  The cable /reading/method are suspect.IMHO.
 

Re: Engine Light, Alarm and Low Voltage

Reply #10 –
I thought that I would give everybody an update.

Since the chassis batteries were 10 years old, I decided to replace them knowing that it likely was not my problem.  It turned out that 1 of them was bad. 

I decided to continue the trip, driving with the generator on and the boost switch on.  With the new batteries at least the dash alarm didn't come on.

Alternator replaced yesterday.

All is well.  Thanks everybody for your help!

Don
Don & Sue
2009 NImbus 38
2020 Jeep Grand Cherokee toad