This is a topic that has caused me much thought and work.
When we purchased our Thor Hurricane 31H, I went to pick it up and it had a dead battery. The dealer (Camping World in Sacramento) replaced the battery and sent me on my way. Only 5 miles down the Interstate, the instrument lights started to flicker followed by the engine shutting off. When the instrument lights started to flicker, luckily, I got into the right-hand lane as a precaution and when the engine quit, I was able to coast off the Interstate without much of an incident except the Highway Patrol stopped and informed me that I can’t camp on the side of the road.
I called Camping world, and to their credit, a technician quickly came out and was knowledgeable enough to realize what was going on.
The end result was the Chassis disconnect relay had failed (probably a long time ago) and the chassis battery was not charging. The weird thing is that in this system, the engine electronics are connected to the battery side of the disconnect so the alternator will not run the engine electronics. They probably do this to protect the electronics from voltage spikes since the battery acts as a buffer. The problem is that once the battery voltage gets too low, the engine quits and leaves you with no power steering and rapidly deaccelerating.
On this coach, all the disconnects are located in a centralized Battery Control Center (BCC) and the fix was to move the Top right wire from the alternator (see photo below) over to the Top left lug (to the Chassis battery) effectively bypassing the Chassis disconnect relay. Later, after reading other posts about this, I put the wires back to where they should be and installed a jumper wire. Of course I insulated it after the photo was taken.
After replacing the defective solenoid, I later installed a manual switch on that same jumper wire effectively making a manual bypass for that disconnect relay (peace of mind for me).
Since then, I have modified this system numerous times. Here are the solenoids in question. The top left is the interconnect (emergency start) relay (see photo below). It is a typical RV type relay designed for continuous use. Unlike a Ford start relay, it has two small terminals for the controlling switch. The Ford start relay has only one small terminal and is grounded through the car frame. The Ford relay is also NOT rated for continuous use. The RV specific ones are rated for continuous use. It requires power to hold this relay closed.
The other two relays are the “Latching” type which means they require power to change from open to closed and vice versa but don’t require power to hold them in either state. This requires a double throw momentary switch to control them rather than a single throw momentary switch like the interconnect relay. The latching solenoid types are better for continuous use since the latching coil doesn’t heat up with time like the simpler interconnect relay will.
Anyway, I decided that relying on a relay for my safety while driving down the highway is not a good feeling, I decided to change things a little. To make a long story endless…I installed manual bypass switches on both disconnect relays and another manual switch on the coach battery for storage purposes (*but still left a provision for charging the coach battery while in storage*).
Here’s my schematic of the new system.
I would suggest for everyone to install bypass switches for both disconnect switches. If everything works correctly, you will never use them. But if a disconnect fails, a bypass will at least save your trip and possibly save your life if one fails, like mine, while on an Interstate highway during commute traffic.
This switch or one like it and a couple short battery cables from the auto store doesn't cost much. If you can find a red cable, it is better.
Part of my pre-trip checklist is to close the manual bypass switch to ensure my alternator is charging the chassis battery. After the trip (or if we are parked for a while) I open the switch and let the solenoid do it's job. It may be overkill but having my coach quit while driving on an Interstate is a scary thing! I also made a battery control panel for the cockpit where I can monitor and control my batteries and the disconnect relays. No sense in waiting until you stop to check the batteries. I monitor them while I'm driving and the engine is on.
Linear Mode
