Coach Battery

I would replace your RV's battery charging solenoid with what ron.dittmer showed in his upper photo - but a much better version.

This approach will eliminate any voltage drop from "diode type" interconnect devices, such as is shown (I think) in ron.dittmer's lower photo. You always want the full alternator output voltage being applied to your battery terminals - not anything less. Here's a better version of the stock solenoid that comes in so many RVs. It even has a silver alloy contact option to stop corrosion of it's contacts ... and it's what I installed in our MH after the stock solenoid failed in a couple of years such that my coach batteries were not getting charged from the alternator:

http://shopping.murcal.com/Catalog/Bear-DC-Contactor-Family/114-1211-020;jsessionid=0a010c471f43e3c1a11ecc744d4b88c1f3921dcee21e.e3eSch4MaN4Re34Pa38Ta38Naxf0

Thank you. It works..

Cruisineasy wrote:
ron.dittmer
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you may have a b.i.r.d. device that un-isolates both batts whenever 1) shore or genset are charging, or 2) when the alternator is charging. it may have failed or maybe one of its 5 or so connectors came loose.

ron.dittmer
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Hi,

Generally the diode type ought to be avoided as they have a voltage drop of 0.7.

I used a relay type.

I agree that the issue is likely the isolator. They look like one of these.

This is the cheaper mechanical type most commonly installed because they cost around $15-$20


This type is more reliable but not very common because of the cost around $50.


Unfortunately they can be mounted most anywhere in the rig, but the popular location is under the hood near the alternator.

Our first motor home had a Toyota chassis and the cheaper mechanical isolator which burned up and almost damaged an adjacent wire harness, just melting the black wire jacket alone. I replaced it with the better type which never gave me trouble over 15 years and I sold the rig with it working. You can see the better blue one in this picture in the lower-right area.

Hi,

The oem Ford relay lives underneath the chassis battery in my E-450. The contacts burned so I upgraded when I replaced it. I also replaced the 60 amp fuse with a 50 amp auto resetting circuit breaker.

On mine, it is in an electrical compartment at the back of the storage bay right behind the entry steps.

Yours may be anywhere. Follow the hot wire from the coach battery, it will go fairly directly to that relay.

The isolator can be mounted most anywhere that Jayco thought was appropriate. As an example, on my Coachmen (which, of course, could be entirely different), the isolator solenoid is mounted next to the coach battery under the entry steps, along with the main coach battery fuse and a little bus bar with connections for the converter, the main DC distribution panel (via the battery disconnect switch), etc.

I gather that not infrequently the isolator is mounted somewhere under the hood.

If you have an emergency start switch, pressing it causes the isolator system to temporarily un-isolate the two batteries. If you have someone press and release it you might be able to locate the isolator by listening for a relay/solenoid clicking on and off.