Forum Discussion

pweekly's avatar
pweekly
Explorer
Aug 25, 2018

Generator draining chassis batteries

Hi all:
We have a 2005 Mandalay 400HP Cummins and don't use it a whole lot. (although have been better this summer). We take it yearly to a football game weekend and use the generator. Sevel times, while running the generator from a Friday to Sunday morning, the chassis will be dead. I am thinking that the generator is running off the chassis so rather than charging it up, it is slowly draining it. the house batteries are fine. I started the generator and if I switch the chassis batteries to the disconnect, it kills the generator (leading me to think what I do about them working together for more than just powering up the penny).

So, given that we are going next weekend on a football weekend, would attaching a battery minder like the Noco Genius to the chassis batteries solve my problem (if only temporarily).? Any other ideas you can think of? Thanks so much.
Trish
Class A
  • copeland343's avatar
    copeland343
    Explorer
    Aug 25, 2018
    Our Onan generator does not charge the battery. It uses the battery to run the 12 volt items on the generator ( fuel pump etc). If 12 volts is disconnected the generator shut down. The Inverter/battery charger in the RV charges the battery when running off the generator or shore power. Your might be the same check fuses. Until you find problem you can connect a 110 volt battery charger to battery to keep battery charged. We have done that when our inverter burned a circuit board.
  • John_Wayne's avatar
    John_Wayne
    Explorer II
    Aug 25, 2018
    You mite look into a Trick-L-Start, or for this week-end just get two large alligator clips and some heavy wire and hook the pos house battery to the pos starting battery when the generator is running and take it off when it isn't running
  • dougrainer's avatar
    dougrainer
    Nomad
    Aug 25, 2018
    Your Mandalay should have a built in system(bi directional charger system) to charge the Chassis batteries when on Genset or Shore Power. That way the Genset will not drain the chassis batteries and then kill the genset. As you mentioned, you can install a standalone charger to the chassis batteries to fix the problem or get the original problem diagnosed and fixed. Another way to accomplish charging the chassis on Genset is to use a toothpick to keep the Battery BOOST switch engaged. THAT will tie both battery banks together to stop your problem. Doug
  • pweekly's avatar
    pweekly
    Explorer
    Aug 25, 2018
    Interesting. I have had it looked at and nobody can find the problem. (very frustrating). It seems to charge ok when on shore power but won't charge when on generator (like it is draining it, not just not charging it). The toothpick thing is interesting. Hmm. I have a standalone to get me through the weekend and hope that works and have checked most of the fuses. The genset fuses were fine and the bank of fuses in the bay of the inverter were fine. Any other ideas of where other fuses could be? I feel like an incompetent Sherlock Holmes.
  • Isaac-1's avatar
    Isaac-1
    Explorer
    Aug 25, 2018
    2005 may be a year or two early for a bi-directional charging relay, vs a conventional battery (relay or diode type) isolator, though it does vary with brand.
  • tropical36's avatar
    tropical36
    Explorer
    Aug 25, 2018
    pweekly wrote:
    Hi all:
    We have a 2005 Mandalay 400HP Cummins and don't use it a whole lot. (although have been better this summer). We take it yearly to a football game weekend and use the generator. Sevel times, while running the generator from a Friday to Sunday morning, the chassis will be dead. I am thinking that the generator is running off the chassis so rather than charging it up, it is slowly draining it. the house batteries are fine. I started the generator and if I switch the chassis batteries to the disconnect, it kills the generator (leading me to think what I do about them working together for more than just powering up the penny).

    So, given that we are going next weekend on a football weekend, would attaching a battery minder like the Noco Genius to the chassis batteries solve my problem (if only temporarily).? Any other ideas you can think of? Thanks so much.
    Trish

    First thoughts are that something else is on and draining the chassis batteries.
    The Genset doesn't run off of them, except for maybe providing excitation and control voltage.
    So, I'd say that the Big Boy Relay or other, isn't closing, as it should and thereby is incapable of charging the chassis batteries.
    Do you have a voltmeter handy and what are the readings for the both the house and chassis batteries? Also what change in voltage is there, with no outside power and with the genset running?
    Does it stay charged with shore power?
  • pweekly's avatar
    pweekly
    Explorer
    Aug 26, 2018
    tropical36 wrote:

    First thoughts are that something else is on and draining the chassis batteries.
    The Genset doesn't run off of them, except for maybe providing excitation and control voltage.
    So, I'd say that the Big Boy Relay or other, isn't closing, as it should and thereby is incapable of charging the chassis batteries.
    Do you have a voltmeter handy and what are the readings for the both the house and chassis batteries? Also what change in voltage is there, with no outside power and with the genset running?
    Does it stay charged with shore power?

    It seems to stay charged without issue when connected to shore power. I don't have a voltmeter but have a battery charger that has a tester button. I am not very handy here. BUT, I did find these little boxes next to each solenoid in the battery bay tonight. Thinking maybe they are breakers? I think (and I wish I was more sure, but was just sort of feeling around each one) the one connected to the solenoid by the chassis batteries clicked. So maybe it is a breaker? (anyone?) Would that be something that would explain my issue? Sorry so technically inept. My husband isn't well so it kind of got thrown on me.
  • dougrainer's avatar
    dougrainer
    Nomad
    Aug 26, 2018
    It WILL stay charged on Shore Power, because NOTHING is drawing 12 volt power from them. The Genset IS drawing power when running and the chassis are the batteries for starting the Genset. Genset's do NOT have a battery charger, so while the genset is running the Genset is drawing 12 volt power to stay running and after running for hours drains the Chassis batteries and then they are dead and the Genset dies. We sold and serviced Mandalay from your year model and NEVER had that complaint from my customers and I will admit it has been more than 10 years since I have worked on a Mandalay. Doug

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