Two days ago Jeff and Kathy’s Fleetwood Bounder developed a problem with its 12 VDC house electrical system.  From the symptoms Jeff described it appeared that the AC-to-DC converter may have developed a problem.  Several people stopped by to help so I backed out of the situation.  Too many cooks, etc.

We were gone all day yesterday so I did not have a chance to check with Jeff to see if anything got resolved.  He stopped by our coach this morning to see if I could come down and have a look, so that answered my unasked question.  There is a RV technician who services many of the rigs in the park.  He stopped by briefly yesterday and said he would be back, but had not made it back yet.

The Bounder is equipped with conventional RV appliances for heating, air-conditioning, and refrigeration as well as low voltage DC lighting.  Some appliances operate on propane, some on 120 VAC, and some on both (selectable).  What they have in common is that they all require 12 VDC to operate their control circuits.  If the DC house voltage is not high enough none of these appliances will work.

Failing house batteries would be one possible cause of a DC house voltage problem.  A failed AC-to-DC converter would be another.  A main function of the converter is to maintain the charge on the house batteries which act like a large capacitor in the system and can supply 12 VDC power (for a while) when then rig is not plugged in to shore power and the auxiliary powerplant is not running.  Without the charger function the energy stored in the battery bank will be used by the various appliances.  As the state of charge drops so does the voltage.  Eventually the voltage drops low enough that the appliances will not work.

Jeff had already disconnected the ground cable from the chassis/starting battery, removing it as a load on the converter output.  We turned off the shore power and then disconnected the ground cable from the house battery bank, which consists of two 6 VDC deep cycle batteries in series.  I checked the voltage of both the chassis battery and the house battery bank; both measured 11.5 VDC.  A fully charged “12V” battery with no load and no surface charge measures 12.6 VDC.

I had Jeff turn the shore power back on and measured the voltage across the two house batter cables (with the ground cable still disconnected).  It measured 4.5 volts.  That was obviously not going to charge the battery bank or operate the appliances, but it was odd and not what I expected.  I thought it would be zero, indicating a total failure of the converter.

We left the ground cables off of both the chassis battery and house battery bank.  We connected Jeff’s small battery charger (6 A) to the engine battery and borrowed John’s 20 A charger to charge the house battery bank.  After a couple of hours the house battery bank was up to 12.4 VDC; not fully charged but apparently accepting charge.  Ditto for the chassis battery.  The refrigerator, however, had lost most of its cold and we needed to get it turned back in.

We decided to leave the shore power to the rig turned off so the converter would not be energized, plug the refrigerator AC power cords directly in to the shore power pedestal, and reconnect the house battery bank ground cable to supply 12 VDC to the refrigerator control module.  This allowed the refrigerator to run on 120 VAC and the 20 A battery charger to act like a converter and continue to charge the house battery bank while we figured out what to do next.

This makeshift arrangement worked but was intended to be temporary.  What I really wanted to do was get the converter disconnected so we could restore 120 VAC shore power to the motorhome and not have a faulty converter causing problems.  Up to this point, however, we had not been able to physically locate the converter.  The AC breaker panel did not even have a circuit breaker labeled for the power supply to the converter.

I examined the point of entry for the shore power cord and decided the converter had to be somewhere in the driver side rear of the rig.  The bedroom is located in the rear of the motorhome and that corner of the interior is the shower.  Just forward of the shower is a built in dresser.  The toe kick had a grill that I originally took to be a heat register for the furnace.  It seemed likely, however, that the converter might be under there as this area is directly above the bay where the auxiliary power plant is installed and both the DC and AC distribution panels are close by.

We figured out how to remove the two large lower drawers and there it was, along with the AC power transfer switch.  The converter was a WFCO-8865 rated at 65 A. It was plugged into an AC outlet box on the floor of the cabinet and had two large DC output cables and a chassis ground wire.

I unplugged it, disconnected the DC output ground cable, and taped the exposed conductor to prevent a short circuit.  Jeff restored the shore power and we figured out which circuit the outlet box was on; a 20 A circuit breaker marked “small appliance.”  I plugged it back in and measured the voltage at the converter DC output terminals.  13.5 VDC.  Again, not what I expected to see.  It turns out that I think the reason I was seeing 13.5 VDC may have been that I was looking at the battery voltage.  The case of the converter is bonded to the chassis and so is the  negative terminal of the house battery bank.  Apparently the DC negative connection on the converter is also bonded to the case.

While I was disconnecting the DC negative cable from the converter I discovered that the end of the red (DC positive) cable was not secured properly at the converter and could easily be pulled out.  Yikes!  That could account for the 4.5 VDC we saw earlier at the battery end of the cables.

In order to make their rig as usable as possible I unplugged the converter, plugged the refrigerator 120 VAC cords back in to their outlets, and left the 20 A charger connected to the house battery bank to act as a temporary converter.  With any luck  they were able to use any of their AC or DC devices through the evening and overnight hours.