Were all the problems I've had my own damned fault??

[jymbee]

Seems like every trip we're had some kind of issue with keeping the tow vehicle charged. Issues ranging from corroded pins to connectors melting, to a very expensive incident trying to figure out why the brake lights and cruise stopped working. That last one involved multiple back & forth with Ford techs before finally finding a blown fuse that was only accessible by removing a portion of the structure under the dash.

Numerous other factors but briefly when we connect I go through the usual sequences of steps, shift through the gears slowly, end up in neutral, switch key to ACC, shut the engine off and hook up the connecting cables and Patriot brake. Upon arrival, first thing I do is to shift gear to park, and hopefully start the car. I say hopefully as at times the battery would be too weak to start the car.

When driving I see the "L" warning flashing on the display in the coach indicating low battery and if caught in time I've resorted to disconnecting the battery to prevent it from discharging. Numerous issues there of course...

Flash forward to a month ago when we had to replace the battery in our tow vehicle. At it's life end given its age and the fact that it had been drained to zero repeatedly due to it not being charged while traveling. Beyond the shock at what they get for new batteries these days, somethi8ng else the mechanic said got me to thinking. He checked the cable that connects the coach to the car and said that was fine but to be sure to disconnect the cable before starting the car as failing to do so could send a charge back through the coach and cause damage (or words to that effect).

As I always did the opposite, start the car while connected then disconnected all, I'm now thinking that my ignorance may have been responsible for some of these expense issues we've had over the years? Needless to say, going forward, whether true or not, I'll always disconnect before starting the car.

 

[Lou Schneider]

There's too much voltage loss through the long, thin wire from the motorhome's front engine to keep the tow vehicle's battery charged. It may be able to deliver a trickle charge if nothing is drawing power from the battery but since voltage loss is proportional to the current, any power draw reduces the voltage delivered by the wire below the battery voltage so the tow vehicle's battery gets drained first.

A DC to DC converter in line with the charging wire from the motorhome will solve this. Mount it close to the tow vehicle's battery. When it sees voltage coming from the charging wire it will boost it to 13.8 volts to keep the tow vehicle's battery charged, even if the current causes the incoming voltage to drop as low as 8 volts.

Damaging anything in the motorhome by running the tow vehicle's engine while connected is extremely unlikely, but the DC to DC converter also blocks any reverse current going back into the motorhome.

Here's one that should work.

DC/DC 8V-40V Step Up Step Down to 13.8V 10A 138W, Boost Converter​

 

[jymbee]

There's too much voltage loss through the long, thin wire from the motorhome's front engine to keep the tow vehicle's battery charged. It may be able to deliver a trickle charge if nothing is drawing power from the battery but since voltage loss is proportional to the current, any power draw reduces the voltage delivered by the wire below the battery voltage so the tow vehicle's battery gets drained first.

It's my understanding that the function of one of the "pins" in the curly cable that connects the coach to the car is used to supply a trickle charge to the car's battery. For a number of years that worked well, even after very long drives of 8 hours or more.

A DC to DC converter in line with the charging wire from the motorhome will solve this. Mount it close to the tow vehicle's battery.

That's interesting since at one point when we were having an issue and it was determined that the cable itself was likely at fault, when doing some rewiring and setting up a new cable the tech at a BlueOx service shop installed some kind of device and I was told it would provide an extra boost (my term) to keep the battery charged. Don't know the technical details but quite likely something similar to what you posted.

 

[Kirk]

When driving I see the "L" warning flashing on the display in the coach

What display, the one for your aux. brake?

Numerous issues there of course...

That all depends on the vehicle you tow. I did that for many years, until I added a wire to charge the battery. Some cars used to have the removal of a fuse in the towing instructions to prevent discharge.

I was told it would provide an extra boost (my term) to keep the battery charged.

That was most likely a DC to DC converter as Lou has suggested. It may be that it was working but has failed.

 

[jymbee]

What display, the one for your aux. brake?

Yes, on the display in the coach

That all depends on the vehicle you tow. I did that for many years, until I added a wire to charge the battery. Some cars used to have the removal of a fuse in the towing instructions to prevent discharge.

The cable connecting the coach to the tow keeps the battery charged while the tow is in AUX. Worked great with no issues for the first several years.

Happy to report that things seem to back to normal given no issues with the last few weeks of our current trip.

One thing I noticed was that cable on both ends connected but didn't seem to be real snug so I "clamped" it in with a couple of zip ties to make sure the connection held tight.

 

[RayIN]

Having to use a zip-tie usually means both plug ends are worn-out.
You can use the center pin of the 7-way Bargman connector to run a#10 charge wire from your MH battery to the towed battery, just remember to unplug the towed when the MH engine is not running or the battery may not start the MH.

 

[jymbee]

Having to use a zip-tie usually means both plug ends are worn-out.
You can use the center pin of the 7-way Bargman connector to run a#10 charge wire from your MH battery to the towed battery, just remember to unplug the towed when the MH engine is not running or the battery may not start the MH.

Thanks for the input.

Makes sense but in this case both connections, car & coach, have been replaced in the last year. The cable itself is also new but is a newer BlueOx then the original that came with the kit originally. The cable itself is probably superior but I notice that when I disconnect, even after all the lights & charging has been working for hours, they seem to unplug more easily that I would think.

There's a little nub on the car connection but this new cable doesn't seem to clamp down down on that very well. Coach end does close down over the nub at that end but given some very rough roads wondered what it would take to work free.

Thus my "can't hurt" decision to snug them both down with zip ties and just snip them off when arriving at our next stop.

My main question in all this remains, when after arriving at our destination if I start the car first without disconnecting the coach to car cable, could this chase a problem. Last repair shop claimed it could send a charge back to the coach (my words) resulting in an issue of some kind.

 

[RayIN]

"Last repair shop claimed it could send a charge back to the coach (my words) resulting in an issue of some kind."
Put a diode in the charge line prior to the MH plug, possible problem solved. Diodes allow electricity to flow 1 direction, that's why most LED's only work when plugged-in correctly.