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USMC46's avatar
USMC46
Explorer
May 18, 2013

Alternator Failure

We're currently sitting at Rocky Mountain Cummins in Albuquerque. Had to be towed in night before last. We were coming up I-25 and all my guages started actiing up, especially my voltage guage. I literally watched it drop all the way until it reached bottom at 9 volts. I managed to coast in to a rest stop, got parked, and literally could not move another inch as the transmission would not work. I guess I had no idea that without power, the trusty Allison is helpless. My alternator gave very little warning. Coachnet had me towed in to Rocky Mountain Cummins and they have a nice place to park with hook ups. The alternator was bad...real bad. It's replaced and we're headed out in the morning. A word of caution to others who may not really understand the conection between battery power and the Allison. Get your alternator checked out if you suspect it is not putting out the voltage you need. Had mine failed on me between Lincoln and Socorro on NM 380, we would have been in a real fix ! By the way, Coachnet had me towed by Interstate towing here in Albuquerque and I have nothing but good things to say about Coachnet and Interstate. I asked what the tow bill would have been had I had to pay it out of my pocket, and was told it would have been over $1000. That makes the $120 annual fee for Coachnet road service seem like a real bargain !
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    May 19, 2013
    In your coach, starting the generator while you still have more than 11.5 volts will work, and keep the house and engine battery charged while driving.
    wa8yxm wrote:
    The Allison transmission, and most modern engines as well, are all computer controlled.. Computers eat elecricity, that's the battery's problem, when the battery goes down the computer crashes and... Well, you know what happens next.

    Question: (WIth implied suggestion)

    My coach has a bi-direcitonal isolator, this means if the house converter is operational the chassis is charged as well as the house. (Likewise the house is charged by the engine)

    In your coach, starting the generator while you still have more than 11.5 volts will work, and keep the house and engine battery charged while driving.

    I also carry jumper cables and other means to jumper if needed.

    If you have a Bi-directional isolator skip the next sentence and go the the all caps line.

    Why not jumper the house and chassis batteries together and...

    START THE GENERATOR to provide for battery charge?

    In the case of the person posting, he did not notice that the voltage was low, until it was well below 11 volts, and it would not start the generator at that point. So to late to save himself from a expensive tow - even if it was the insurance company paying for that towing job.

    If he had noticed the voltage at 12.0 or 11.8, he still could have started the generator, at at least kept much of the 12 volt load off his coach battery, and also save the engine battery a lot of power. But running at night, with over 40 amps going to the lights, you can run down all the batteries fairly quickly once the alternator went out.

  • YC_1's avatar
    YC_1
    Nomad
    May 18, 2013
    One note on using the Generator, particularly on a diesel. Some have a cutout circuit to block the house charging system from supplying power to the engine batteries when the ignition switch is on. In this case you need to keep the aux/emergency start button depressed. So just starting the generator may not do the trick by itself.

    Since the op's generator would not start he could have used one jumper cable to combine his batteries long enough to start the gen. Not the safest thing to do because at that stage there probably would have been a good spark and that is not good. Turning off the battery disconnect switches would probably suffice while connecting the cables.

    So if you notice something like this get the generator fired up early on.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    May 18, 2013
    The Allison transmission, and most modern engines as well, are all computer controlled.. Computers eat elecricity, that's the battery's problem, when the battery goes down the computer crashes and... Well, you know what happens next.

    Question: (WIth implied suggestion)

    My coach has a bi-direcitonal isolator, this means if the house converter is operational the chassis is charged as well as the house. (Likewise the house is charged by the engine)

    I also carry jumper cables and other means to jumper if needed.

    If you have a Bi-directional isolator skip the next sentence and go the the all caps line.

    Why not jumper the house and chassis batteries together and...

    START THE GENERATOR to provide for battery charge?
  • HiTech's avatar
    HiTech
    Explorer
    May 18, 2013
    X2 at the first sign of an alternator outage issue I start the genset as well. In coaches that do not share the charge with the chassis battery you can flip the override switch to connect them, or even jumper the systems together to continue until you can get to a place for repairs.

    Does not work for all coaches but well worth a try.

    Jim
  • MrWizard's avatar
    MrWizard
    Moderator
    May 18, 2013
    i did the generator charger trick when driving a gasser with multiple belts
    won't work IF you break a 'serpenine' single belt, on a dp , even some gassers are single belt
    have to be aware of the belt and 'over heating' issues
  • USMC46's avatar
    USMC46
    Explorer
    May 18, 2013
    Fred: Thanks for the input. By the way, at the rest stop, my generator also would not start. I guess it starts off the chassis batteries ? Although I appreciate the other technical advice, it was way over my head. I'm not sure what all Cummins did here, but the coach has been plugged in to shore power and all the batteries seem to be back up and functioning. I may run the generator some this morning as we leave Cummins headed north to Colorado. Thanks again. I'll look into the advice.
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    May 18, 2013
    Hi,

    Most RV's you can start the generator, and the normal system will connect the coach battery output to the engine starting battery. When My alternator went out, I was in Yellowstone, and started the generator right away. (belt broke, the alternator was actually fine). I turned on the charger, and drove to Flag Ranch, stayed a few days, drove into town for a new belt, was fixed in a short time by me.

    I could have driven farther if needed, because the power steering was on another belt, and the water pump and cooling fan is served by both belts on my 97 F-53 Ford motorhome with a 460" engine.

    Good to know that a small power failure will stop most of the things from running. The engine will not get a signal to run, the fuel pump will also stop. You where lucky to find a rest area.

    Now I hope that you recharged all the batteries before starting the engine. It takes a lot of amperage to recharge the battery, and this can overheat the diodes inside, causing the new alternator to have a very short life.

    If you have a inverter, my suggestion is to not run the battery low, and to use the generator to recharge the coach battery if you have been dry camping more than two nights. You probably have a 440 amp hour coach battery bank, and that can put a large load on the alternator. The cost to run the generator is insignifcant, and will take a lot of strain off the alternator and it's belt.

    Another thing that the Cummins dealer probably already checked is for a loose conection. Disconnecting a alternator from it's battery is a sure way to melt the diodes inside it. This can happen if the alternator output wire is loose, and does not conduct power to the battery. I have also seen it happen to two people who have electronic battery isolator, where one of the connections melted, and the alternator output was not going to either of the batteries.

    I would recommend if you have a electronic type battery isolator to install a mechanical solinoid isolator. Grainger.com has a relay made for forklift contactor, rated at 125 amps max, and has silver allow contacts. 6C017 if I recall right. Albuquerque has a Grainger branch, the Cummins dealer should be able to buy the part, they normally keep one on the shelf.

    What I would do to correct the wiring is remove the electronic isolator, and wire the alternator output directly to the engine starting battery, then install the isolator to the coach battery with #4 or #2 wire. Turn on the isolator with a wire that is powered when the key is on or in ACC position, such as the +12 wire that turns on the radio while driving.

    Fred.

    Fred.

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