Forum Discussion

First5Farm's avatar
First5Farm
Explorer
Oct 02, 2015

Possible alternator problem

My latest (additional) problem is with my charging system.
When we left Wednesday night for last weekends trip, I started the coach and it kicked into high idle. The little Freightliner screen showed low voltage. The gauge read just below 13 volts. Our trip was only about an hour and a half away and one I did not want to miss. I took a gamble that maybe the batteries were a tad low and that they would come back up under way so went for it. The gauge stayed at about 13 volts or a little under and about half way there, the check engine light came on. Once there, we checked the batteries with a load test and they were fine. They are less than two months old so I was hoping they weren't the problem. We checked the alternator while it was idling and it read between 12.9 and 13.3 volts. I was told it should be putting out 14 volts. We decided to go for it Sunday afternoon and headed home. Not knowing if it would help or not we ran the generator most of the way home. No check eng light this time but the gauge still read just below 13v. The cables are all nice and clean. Am I correct in thinking it is the alternator or maybe the regulator?
Thanks,
Billy
Class A
  • Kayteg1's avatar
    Kayteg1
    Explorer II
    Oct 03, 2015
    The brushes are build into Voltage Regulator.
    They last long time on modern alternators and it is the run hr or mileage that counts not the time.
    The proper charging should be > 13.5V while < 12.5V would indicate the coach running on battery power.
    13V is tricky. That would indicate some charge, but only putting a load would give definite answer.
    Easy test is to turn all headlights, blower, rear defroster if you have it and then see how the voltage changes.
    For CEL you need to scan the code.
    You can buy scanner for $35 those days, or $20 for computer plug, so not much excuse to not own one.
  • lawrosa's avatar
    lawrosa
    Explorer
    Oct 03, 2015
    wildmanbaker wrote:
    When the brushes get warn or glazed, the alternator can act this way. Rather than just replacing parts, some trouble shooting should be done, as Brent has suggested. Just changing the alternator may end up with it still not working correctly.


    Brushes?? where are there brushes??? If there are then I better change mine after 20 years...LOLOLOLOL
  • wildmanbaker's avatar
    wildmanbaker
    Explorer
    Oct 02, 2015
    When the brushes get warn or glazed, the alternator can act this way. Rather than just replacing parts, some trouble shooting should be done, as Brent has suggested. Just changing the alternator may end up with it still not working correctly.
  • Jamboree89's avatar
    Jamboree89
    Explorer
    Oct 02, 2015
    Agree with Wolf10 I had similar symptoms last year, it was the battery isolator and not the alternator.
  • Kidoo's avatar
    Kidoo
    Explorer
    Oct 02, 2015
    Below 13 is not normal. Mine rarelly reads 14, unless the batteries would be very low. Maybe you should check with a voltmeter directly and compare to your gauge.

    I would have it tested by a reputable shop that rebuilt alternators. I had mine cleaned and they replaced the bearings for less than $100.00, the brush did not need replacement.
  • wolfe10's avatar
    wolfe10
    Explorer
    Oct 02, 2015
    Several different "styles" of alternators used on motorhomes.

    I would start by checking wiring from alternator to battery isolator, battery isolator itself and wiring from isolator to batteries. If a remote sense wire, check it carefully, it is small gauge (generally from chassis battery terminal of a diode-based battery isolator to alternator sense terminal.

    Then check voltage at the B+ terminal of the alternator, battery isolator and batteries at high idle.
  • RoyB's avatar
    RoyB
    Explorer II
    Oct 02, 2015
    My truck alternator does about the same as my converter/charger unit does... It always starts out with 14.4VDC and then starts falling back depending on the battery charge demand.. I can see 14.4 - 13.6 - and then 13.2. Then as I drive it down the road it will jump between 13.2 and 13.6...

    13.2 is about the lowest DC VOLTAGE I see on my setup...

    Roy Ken
  • lawrosa's avatar
    lawrosa
    Explorer
    Oct 02, 2015
    sounds like the alt yes. The regulator is built into all the alts today AFAIK.

    And yes the alt should put out over 14 v....

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