Hi All..I think I know the answer but I'm open to feedback/suggestions... So I was doing some testing to my Minnie and come to find out the engine is not charging my house batteries. If I depress the AUX start button I hear an audible click, so I believe the relay works in that regard. I tested the house battery solenoid with the engine running and I do have ~14.5 volts on the chassis side of the solenoid and then just 12.8ish volts on the house side - the same amount that was there with the engine off. The generator/shore power will charge the house battery.Before I swap the solenoid out is there anything else I should check? I hear there should/could be a fuse somewhere for this solenoid, would it be in the chassis fuse panel?Thanks

Just be cause it clicks doesn't mean it is making contact.Appears you need new relay. NAPA stocks them. Make sure you get a continuous duty!

I believe motor home battery charging is prioritized such that the chassis battery will get charged first, then switches over to the house batteries. If your chassis battery needs to be charged, then you will get the measurements you are seeing.If you have a battery charger, I would charge the chassis battery that way to assure it is fully charged. Then start and idle the engine for a few minutes, then measure again. You are trying to get the electrical system to switch over to the house batteries. If you can't make it happen, then with the engine running, hook up your battery charger to the chassis battery and measure again.

ron.dittmer wrote:I believe motor home battery charging is prioritized such that the chassis battery will get charged first, then switches over to the house batteries. If your chassis battery needs to be charged, then you will get the measurements you are seeing.I was curious about that.. My father had an isolator in his pickup for his truck camper that worked as you described... but I believe on my system it should pass the charge through to both batteries anytime the engine is running. I forgot where I heard/read this....

Biggyniner wrote:ron.dittmer wrote:I believe motor home battery charging is prioritized such that the chassis battery will get charged first, then switches over to the house batteries. If your chassis battery needs to be charged, then you will get the measurements you are seeing.I was curious about that.. My father had an isolator in his pickup for his truck camper that worked as you described... but I believe on my system it should pass the charge through to both batteries anytime the engine is running. I forgot where I heard/read this....I never heard of shared charging, but I am no expert on this subject matter.

I believe that there are 2 different relays/solenoids. One for the boost feature that connects the house batteries to the chassis battery and a second that allows the house batteries to be charged from the chassis ken

Auxillary Start/battery solenoid | Good Sam Community

19 Replies

Harvey51
Explorer
Jul 30, 2015
Just curious - on engines that only pass current to the house when the engine battery is fully charged, how does the engine tell when the battery is fully charged? This technology would be great for measuring the state of charge of the house batteries.

Our 2004 E350 uses the built in Ford relay in the fuse box to connect the "auxiliary" line to engine power whenever the engine is running.
enblethen
Nomad
Jul 30, 2015
Location of the relays vary by manufacturer and year. The OP has located the relay in question and needs to check it out for voltage to coil.
4x4van
Explorer III
Jul 29, 2015
On my '88 Jamboree, there are separate solenoids for the emergency start and the charge, both located under the hood. The emergency start solenoid is located on the firewall right next to the brake booster and has large battery cables, but the charge solenoid is mounted behind the driver side headlight. It has smaller (#8AWG?) wires. As soon as I turn the ignition on, the charge solenoid is energized and connects the house batteries to the chassis alternator to charge both chassis and house.
tenbear
Explorer
Jul 29, 2015
The only way you can be sure the solenoid is energized is to measure the voltage on the small terminal(s). It really doesn't matter if the energizing coil is open or if the contacts are worn out. If you don't have continuity between the 2 large terminals when there is 12v applied to the small terminal(s) - the solenoid is bad. If you don't have 12v on the small terminal(s), you have a different problem.
enblethen
Nomad
Jul 29, 2015
You can also have a helper operate the system, and feel for the relay to energize.

Three post relay

Installation/information
Biggyniner
Explorer
Jul 29, 2015
enblethen wrote:
Does the relay with 14 volts on one side and 12.8 on other, have 12 colts across small terminals or single terminal to ground?

I have not tested the small 'hot' terminal, I was going to do that next.. It only has the one small 'hot' terminal, the ground goes to the body mounting screw of the solenoid.
enblethen
Nomad
Jul 29, 2015
Does the relay with 14 volts on one side and 12.8 on other, have 12 colts across small terminals or single terminal to ground?
Biggyniner
Explorer
Jul 29, 2015
JaxDad wrote:
Beverley&Ken wrote:
I believe that there are 2 different relays/solenoids. One for the boost feature that connects the house batteries to the chassis battery and a second that allows the house batteries to be charged from the chassis

ken

X2

There is one relay in the engine compartment (the charge controller) and one in the battery bay (the aux. start relay).

I believe you will find the one under the hood is shot. It's a relatively easy swap despite the cramped quarters.

Are you sure it is the one under the hood? I was inclined to believe it was the solenoid in Aux battery bay because I am getting 14 volts to one side of it, but 12.8 on the other (house) side of the solenoid.
fourthclassC
Explorer
Jul 29, 2015
Howdy,

Went through this recently 2003 Winnie Mini. The isolation solenoid clicked real goo when I checked it with a battery. BUT no continuity change. Very common failure mode. electromagnet ok but contacts worn out / failed. Get a continuous duty Napa solenoid. Beware, if it is located in the same place as mine was, it is very difficult to disconnect/replace
JaxDad
Explorer III
Jul 29, 2015
Beverley&Ken wrote:
I believe that there are 2 different relays/solenoids. One for the boost feature that connects the house batteries to the chassis battery and a second that allows the house batteries to be charged from the chassis

ken

X2

There is one relay in the engine compartment (the charge controller) and one in the battery bay (the aux. start relay).

I believe you will find the one under the hood is shot. It's a relatively easy swap despite the cramped quarters.