Ground Problem - no power on battery, power on Gen. and shore.

[Vince Warde]

I have a 1978 Tiffen Allegro - As noted above it has no power on the battery - but 12v works fine on shore and Generator.  I expected that the was a problem on the positive side - but it turns out that it's on the negative side.  I have power all the way out to the fixtures - but no battery ground.

 

To make things even stranger, the skin of the RV is grounded to the battery - and the generator starts of this battery, so I can't figure out at this point where the grounding problem is.  Anyone have any ideas?  Am I right in assuming that the ground does not go through the "electrical center" where the power convertor and relay is located?

 

The next time I go to work on it I am going to take a look in the generator compartment in case the coach ground comes from there.  Positive side problem are SO MUCH EASIER!

 

Thanks!

[John "T" Nordhoff]

Okay, when plugged into shore power or the genny is running its the Converter/Charger that supplies 12 volt loads and since they then work you know the Converter/Charger is indeed "Grounded" But if no 12 VDC from the coach battery (and assuming you say the + end is okay and the battery is okay????) the - from the coach battery must NOT be bonded to the same ground point that the Converter/Charger is. Id run a direct jumper wire from - off the battery to where the big main - is at the Converter/Charger THAT WAY THE - OF THE BATTERY HAS TO WORK AND FEED LOADS SAME AS THE - OF THE CONVERTER/CHARGER. In theory if the battery - is bonded to the coaches frame that should serve as a connection for 12 VDC loads that use the frame as ground (like maybe the genny) buttttttttttttt if coach loads like lights and fans etc etc are fed from the Converter/Charger and the battery - isnt bonded to the - out of the Converter/Charger 12 VDC LOADS WONT WORK OFF THE BATTERY NOR WILL THE BATTERY GET CHARGED. Again, you MUST have a good connection from the Converter/Charger - to the battery - and that must be missing although the genny could still start if its connected to + of Converter/Charger and frame ground (assuming battery is okay with a frame ground, just misisng a bond from there to - of Converter/Charger)

OR ELSE JUST RUN A HEAVY CABLE FROM - OF CHARGER/CONVERTER TO FRAME GROUND should do it since starting the genny tells me the battery alreadt has at least a good frame ground...............

Let us know what you find

Ol John T in Indiana long retired Electrical Engineer

[Vince Warde]

Thank you for the prompt reply.  You understood the situation clearly and I understand your suggestion.  The missing piece of information for me was that the charger/convertor could be providing 12v-.  It will be very easy to connect it to battery ground for a test.  If that works I can do something permanent.

 

I will let you know how it turns out.

 

Thanks again,

 

Vince

[Vince Warde]

OK, weird outcome.  It turned out that the connection to ground was not the problem.  I connected it to ground - no go.  In fact the charger/convertor is chassis HOT - yep 12+

 

I turned out that the 12+ from that Battery was very resistive - lights would barely glow.  We ran a new 12ga feed and all the lights, plus the stove hood fan work fine, but......

 

Water pump and furnace still have resistive connections.  Corrosion???  How common is it to have to rewire older units?  I am usually good at 12v wiring, but I would prefer to do as little work as possible to get it working reliably.

 

Water pump is leaking, so that will have to be replaced too.....

[John "T" Nordhoff]

While its true, corrosion can affect older units, its just as common loose connections can do the same. If there are any screw down terminations I always remove the wire and clean (oxidation, rust etc) it then replace and retorque. I dont usually see any problems whatsoever where the wire itslef is routed, its at the terminals and connection points and splices etc where age and temperature fluctuations and vibration cause problems. Another thing thats common in furnaces and water heaters and fridge etc. that use a printed circuit electronic control board is where the flat ribbon cable attaches to the circuit board oxidation occurs. On those I carefull remove/unplug the ribbon cable connector then use a pencil eraser to polish n shine up the copper where the plug mates.

If the water pump needs replaced I hope it NOT a Ford engine grrrrrrrrrrrrr those dern pumps have a dozen or so bolts that all connect up or go through power steering pumps and AC compressors and air pumps etc etc and are a major bear to change out.....BTDT and got the T Shirt more then once..

John T

[Vince Warde]

Thankfully the pump that needs to be replaced is the fresh water pump.  It is also one of the circuits with a resistive connection.  The interesting thing about the furnace is that it works on 110v.  Are there any RV furnaces that run directly on 110v and 12v?

 

I can understand the water pump not working, but It am at a loss to explain why the furnace works on 110v but not on 12v - since the output from the convertor/charger should be the same 12v irregardless if the 12v is coming from the convertor or the battery, right?

 

Inside the charger/convertor everything is spade connectors - not screw terminals.  Are they more prone to corrosion?

 

Thanks!

[John "T" Nordhoff]

YOU STATE
"I can understand the water pump not working, but It am at a loss to explain YOU why the furnace works on 110v but not on 12v - since the output from the convertor/charger should be the same 12v irregardless if the 12v is coming from the convertor or the battery, right?"

NOT EXACTLY If the RV battery is good and its fully charged, its voltage will be around 12.6 volts HOWEVER a good converter/charger will raise that to the 13 to 14 and over voltage when its plugged in, connected and working.

Those circuit board controlled devices ARE VERY SENSITIVE TO LOW VOLTAGE AND WILL SIMPLY NOT WORK IF THE VOLTAGE IS MUCH BELOW 12. Thats where good tight corrosion free conenctions are A MUST. I had a fridge that refused to ignite on a good coach battery (12.6 volts) but would if the converter was plugged in (13.8 volts) and after I serviced all the connections and terminals and used a pencil eraser to shine up the copper where the ribbon connector attached THEN SHE WORKED


YOU STATE: Inside the charger/convertor everything is spade connectors - not screw terminals. Are they more prone to corrosion?
I dont think so but if they seem loose n wiggly I remove them and use pliers to squeeze them down just a tad and wire brush the surfaces and then re attach usually fixes any loose or resistive connections.

If devices work when the converter/charger is operating but NOT otherwise the battery is weak or theres too much resistance and resulting voltage drop in wirews or connections or terminals. 12 volts total at a device isnt very forgiving but 13 is.

CHECK AND CLEAN AND POLISH AND TIGHTEN EVERY POSSIBLE SPLICE AND TERMINAL AND CONNECTION AND BE SURE THE BATTERY IS GOOD then take two aspirins n call me Monday at the office

John T

[Vince Warde]

Good thought about the battery putting out less than the convertor.  I will put my voltmeter on it next chance I get.  I do have a solar array connected, and a switch that DCs the load when in storage, so I don't think that the issue.  Still need to check though.

 

As for a resistive connection in the convertor/charger I think you may have nailed it.  I am going to check and clean ALL the connections.

 

Thanks again!