12V system disconnects when I try to start the generator using batteries.

[gkunst]

Coach batteries test to be fully charged.  Push generator start button and the 12V system goes down.  Start the RV and with the motor running, the generator will start.  Also the 12V system comes back on line and continues to work after the generator is shut down. I?ve been researching the battery disconnect switch and the battery isolation system but have not heard of a similar problem. Any ideas? This is on a 2014 Forest River Sunseeker.
George

 

[mel s]

Coach batteries test to be fully charged.  Push generator start button and the 12V system goes down.  Start the RV and with the motor running, the generator will start.  Also the 12V system comes back on line and continues to work after the generator is shut down. I?ve been researching the battery disconnect switch and the battery isolation system but have not heard of a similar problem. Any ideas? This is on a 2014 Forest River Sunseeker.
George

A corroded or loose battery connection, or a corroded or loose ground cable connection, can cause that.

 

[Gary RV_Wizard]

The system voltage is falling too far when the genset cranks. The most common reasons for that are those mel cited, with the addition of a weak battery. A battery can show full charge (reaches 12.6v) but still unable to deliver a lot of amps on demand. One weak cell is enough.

With the engine alternator running, the system voltage stays up and the genset starts ok.

Some questions:

1. Does the coach have an isolation switching relay or the diode type isolator module? 

2. How did you determine the chassis battery is fully charged? The genset starts from the chassis battery.

3. Is there a chassis battery disconnect? Many RVs no longer have those, but I don't know about yours. The house battery disconnect doesn't play in this scenario.

 

[gkunst]

With regard to question No. 1, Gary, I don?t know. I have some pictures of the Battery Isolation Manager if that would help.  If not how would I tell between the switching relay or the diode type isolator? When the 12 V shuts down there is a sound like a switch is tripping.
No. 2. Used a volt meter.  Chassis battery is brand new and connections looked very good. No problems at all starting up the RV. Coach batteries are also less that a year old.  I believe they are Lifeline gel.
No. 3 It?s probably not what your asking but the RV storage place put a disconnect switch on the chassis battery for when the RV is in storage. Otherwise there is a disconnect switch above the battery isolation manager panel that I assumed disconnected all power to the RV.

So are you saying that when the generator is started, the house battery is not used and the power comes from the chassis battery?  Is there some type of switch or solenoid that would shut down the power and then reset when either the generator comes on or the RV is hooked up to shore power?
I just returned from the RV storage and used a volt meter on the chassis battery (12.6) and the RV batteries (12.4). Its been in storage a little over a week.  I have a 12V plug in meter that I plugged into the 12 volt outlet for the front TV which read 10.4 but the 12V lights appeared strong when I turned them on.

 

[Mark_K5LXP]

the chassis battery (12.6) and the RV batteries (12.4).
...
12 volt outlet for the front TV which read 10.4

That's a pretty strong clue.  2V is a huge drop and could explain your starting issues.  Start at the battery terminals and follow the circuit along. 

Mark B.
Albuquerque, NM