"Accessory" position connects engine and coach batteries

[Eric6A]

I have 2005 24SS Greyhawk. When I switch the ignition key to the "Accessory" position, I can hear a relay in the engine compartment "click". After that, the coach battery is connected to the engine battery. Is that normal?

I don't think my previous Class C motorhome did that (it had a 1997 E350 chassis). It's probably not a problem, as I don't have any need for the accessory position. The dash radio and Sirius XM receiver run off the coach battery, so the ignition switch in "Off" when we are parked.

[LkptRvPilot]

Hi Eric,

How do you know that the coach is being connected to the chassis battery?

The coach(house) and chassis battery should be isolated from each other via a battery isolator. This isolator allows the alternator to charge both the coach and chassis, but one battery should not have direct connection with the other. There should be a "power assist" button that energizes a relay to connect both but only to be used in emergency situations.

If you believe that the batteries are somehow connected, either your isolator failed or the assist relay has failed closed.

I believe the "click" you hear is the accessory power relay (i.e cigarette lighters, ect).

[Eric6A]

Originally Posted by LkptRvPilot

How do you know that the coach is being connected to the chassis battery?

I noticed the battery monitor for the coach battery showed a voltage reduction when I switched the ignition switch to the "Accessory" position, and it showed it was supplying several amps of current (probably charging the engine battery, which is 1 volt lower than the coach battery, due to the solar panel charging on the coach battery).

After reading your comment, I put a meter on the isolator relay coils. The coil is definitely powered on when the key is in the Accessory. The power assist button to help start the engine does seem to work properly for that function.

So, it appears Jayco intended this to happen, but I don't know why. Perhaps it was to protect the engine battery from being discharged if someone wanted to listen to the radio while the engine was off? Or maybe give you an easy way to charge the engine battery when you sit for weeks at a campground or boondocking?

[Grumpy]

Not sure if JAYCO added them to the "Class C", but on the SENECA's they have it set that the converter charges the chassis battery while connected to shore power.

[LkptRvPilot]

Out of curiosity, is the isolator relay powered in the "ON" position (but not yet started), and does the button work at that point?

I have to admit, you have me stumped.