After 2 nights at Yellowstone my coach battery went dead. Checked for voltage from the starting battery with the engine running and the volt meter connected to the positive lead of the coach battery (after disconnecting it from the coach battery and did not get any reading at all... 0 volts). That tells me that there is no charge line from the starting battery to the coach battery when I'm driving. My other fifth wheels etc. all had a charge line in the 7 pin connectors. Obviously this small motorhome has nothing like that :( So.. is there anyone out there who has added a charge line from the starting battery to the coach battery... and if there is.. can you tell me what size wiring I should use, what size fuse I should place in the line and whether it is worth it to put in a diode to prevent current from feeding back into the starting battery when I am connected to shore power?? I will also add a switch so that I can isolate the starting battery from the coach circuits (so I don't have to bother my fellow campers to get a boost start every time I use too much power)!! Short version.. charge line from starting battery positive post to coach battery positive terminal with switch and fuse and maybe a diode.. Thanks for any info. I am currently 6 days into a 30 day trip and need to correct this issue soon!! Thanks again!!

I am surprised that your rig does not have this function.Check your owner's manual for electrical operation.Does it have a genset?

There is all the wiring and even the extra 30 amp receptacle for a genset but it was never installed. I think they were going to have that, then changed their mind and didn't get around to adding a charge line. Maybe the coach builders also didn't want to put in a line with the idea that someone would inadvertently drain the starting battery???

Locate your battery control center. You may need to operate the battery disconnects and listen for it's location. That is if rig has battery disconnects.If you have battery disconnects, look to see if there is another large relay in the same area. It would have two large posts and one or two small posts. One side of it would go to chassis battery and one side would go to the coach battery. Trace out the wire that is on the small post(s) One should get power when the rig is running the other should connect to ground.

Thanks enblethen. I do have a battery disconnect next to the back door.. opposite side of the power panel but it is completely separate from the Power Panel. I will have to check the fuses under the dash and under the hood to-morrow morning (it's dark here in Idaho right now). There are a couple of terminal posts behind the power panel (under a couple of drawers) but I haven't seen a relay anywhere.

Hi,Make, model and chassis of motorhome may help us help you.My E-450 had a sixty amp fuse that blew quite regularly. The OEM isolation relay lasted only about 1 year. I replaced the fuse with an auto reset circuit breaker and the relay with one that had much higher amperage capacity.

Adding a battery charge line... | Good Sam Community

MEXICOWANDERER
Explorer
Oct 07, 2015
Memory vulnerable is the main negative point to that kind of setup. I have a bin full of cast aluminum 50 -amp switches and they have number eight brass screws threaded into copper tangs. Finding number eight terminals for six gauge wire might be a challenge.
RJsfishin
Explorer
Oct 07, 2015
My charging circuit quit working, but rather than chasing it down to a bad solenoid or etc, I just brought the positives from both battery banks (house and chassis) to the dash on a 50 amp off/on switch Now I have manual control over it. I used #8 wire, no fuse,...all works fine.
MEXICOWANDERER
Explorer
Oct 07, 2015
0.0 volts with or without the engine running? That just does not sound right. Even a worthless cadaver of a battery retains a volt or so. You measured 0.0 volts sticking meter probes directly into the lead posts of the battery, right?

If you are planning to stay with a single battery SIX GAUGE wire connected to the alternator terminal then to a SIXTY AMP rated fuse is fine. I prefer the totally automatic battery combiner products that allow full current to flow to the house battery. Like Blue Seas or Sure Power. They are much easier to connect than a solenoid.

I sheath wire that passes under the rig inside old garden hose and I keep it away from exhaust pipes. NAPA stores usually have wire and terminals. Where you are ALL BATTERY SALES on the internet can get stuff UPS to you in a day or so. Don't forget the 60 amp breakrr or fuse.
RoyB
Explorer II
Oct 07, 2015
I was like WESTEND with my standard 2010 FORD truck purchase. There was an unmarked envelope in the glove box that had a fuse and relay in it. No literature or anything for it was for...

After looking in the manual I noticed it showed a relay and a fuse for 'trailer charge'. The actual slots were blank so I added the FUSE and RELAY from the envelope and that gave me TRAILER CHARGE voltages when the ignition key was turned on...

I think most of the other truck manf do the same thing...

Roy Ken
westend
Explorer
Oct 07, 2015
You may have to install a fuse or relay into a 12V distribution box on the chassis. In a Ford Pickup truck the box is located in the engine compartment. I don't know where it's located on a van chassis. Your owner's manual should have information about this.
You_can_t_take_
Explorer
Oct 07, 2015
Hi Pianotuna.. It is a 2006 Ford E350 Chassis with the 5.4 litre V8. I see in the manual that I may have a 60A Auxiliary battery relay at location 20 in my fuse panel.. will check to-morrow!!
pianotuna
Nomad III
Oct 07, 2015
Hi,

Make, model and chassis of motorhome may help us help you.

My E-450 had a sixty amp fuse that blew quite regularly. The OEM isolation relay lasted only about 1 year. I replaced the fuse with an auto reset circuit breaker and the relay with one that had much higher amperage capacity.
You_can_t_take_
Explorer
Oct 07, 2015
Thanks enblethen. I do have a battery disconnect next to the back door.. opposite side of the power panel but it is completely separate from the Power Panel. I will have to check the fuses under the dash and under the hood to-morrow morning (it's dark here in Idaho right now). There are a couple of terminal posts behind the power panel (under a couple of drawers) but I haven't seen a relay anywhere.
enblethen
Nomad
Oct 07, 2015
Locate your battery control center. You may need to operate the battery disconnects and listen for it's location. That is if rig has battery disconnects.
If you have battery disconnects, look to see if there is another large relay in the same area. It would have two large posts and one or two small posts. One side of it would go to chassis battery and one side would go to the coach battery. Trace out the wire that is on the small post(s) One should get power when the rig is running the other should connect to ground.
You_can_t_take_
Explorer
Oct 07, 2015
There is all the wiring and even the extra 30 amp receptacle for a genset but it was never installed. I think they were going to have that, then changed their mind and didn't get around to adding a charge line. Maybe the coach builders also didn't want to put in a line with the idea that someone would inadvertently drain the starting battery???