Battery trouble - 7.4 volts to house batteries...

If I ran the generator then I would get full voltage to the house batteries but in order to start the generator I had to start the RV.

Curious, doesn't the generator just supply 120 V to the converter just as the shore power does? Why the difference on the DC side then? If you are measuring the voltage at the batteries with the engine running, maybe the voltage is provided by the engine alternator, not the generator/converter. You could find out by starting the generator, then shutting off the engine and measuring the DC voltage at the batteries.

The difference in voltage at the cutoff switch vs at the batteries could be explained by the switch being open or broken open.

I know it is all very confusing with wires all over the place and no way to tell which is which. It would be nice if the wires were labelled so one could get hold of the engine supply wire at the batteries, disconnect it and measure just it's voltage. A DC clamp current meter is very helpful for seeing how much current (charge per second) is flowing through which wire.

Anyhow, understanding will come from isolating each source of DC so it can be checked independently.

Ok, after wasting a bunch of time trouble shooting the problem seems to have resolved. In summary, my house batteries were not getting any kind of charge. The confusing thing was if I disconnected from shore power and disconnected the cables to the house batteries there was approximately 6 volts on those lines. If I disconnected the chassis battery then there was no voltage to the house batteries. If I ran the generator then I would get full voltage to the house batteries but in order to start the generator I had to start the RV. Anyway, I needed to get the slide back in so I hooked everything back up and ran the generator for a little while. When I was done I rechecked the house batteries and they were now receiving a charge??? The only thing I can think of is when I originally disconnected the chassis battery to replace the terminal ends that maybe what ever controls all the charging/switching got all screwed up from lack of power? I'll check again tomorrow to verify that everything is still working. Very odd.

Is this a class A or C? Do you have a solid state battery isolator? When you were replacing cables is it possible that you loosened a cable connector to something? You probably have a transfer switch if you have a built-in generator. Do all of your 120V devices operate on either shore power or generator?

The strange thing is that if you have 11.4 V at the battery terminals (dead battery, BTW), you should have that same voltage throughout your 12V system. It should not go down to 6V unless you have a shorted cell.

Why would there be 14 volts at the converter and only at the switch.

Answer 1: Bad connection.. Very bad connection
Answer 2: Bad hunk of cable (Wire) NOTE I have seen both with my very own eyes on the rig I'm sitting in... only it was on a load, not on the charger line.

Had my chest freezer die on me.. A quick check showed no voltage to the unit. Had good voltage at the distribution panel when I unhooked everything but when i went from a volt meter to a test light,,, Not good at all.

Traced it to the wire that feeds the beast.. Found the bad spot (Stood out like a broken bone) and did a bit of surgery.. All was good.

later a splice (Different one) went bad.. Performed same surgery there (Cut out the bad section, spliced and SOLDERED the wires, and sealed them against chemical and/or water intrusion) And it happened again (Another connector)

At least I know how to fix em.

A 50 amp plug has two 120 volt hot legs, a neutral and a ground. A 30 amp plug has one hot leg, a neutral and a ground. Since your RV appears to have a 50 amp cord, is it possible that your 50 amp to 30 amp adapter is only wired to feed one of the two hot legs in the 50 amp cord?

I disconnected the shore power and house batteries and still record 6 volts through the house battery cables and at the junction block for the slide/hydraulic jack and generator. It appears that somehow the starting battery is suppling the 6 volts because when I disconnect it, there is no voltage at the sites mentioned. The starting battery itself has over 12 volts. Not really sure what is happening. Possibly a fuse at the dash???

Ok, I've confirmed that approx 14 volts are leaving the converter but only ~6 is showing up at the batteries (cables disconnected and measurement is through these cables). If I run the generator (in order to do this I have to start the coach) then the terminals receive the full ~14 volts. I checked the cables at the generator and hydraulic slide pump and they are getting the same ~ 6 volts when plugged into shore power and the battery disconnected. I'm a bit perplexed as to where this voltage drop would come from or what to check next...

Sounds like the converter is not charging as you indicated but it may be the batteries are so discharged with a bad cell or shorted and the converter cannot keep up. I would remove the batteries and put a volt meter directly to the battery cables and get a reading. If you are seeing 13.8-14 + volts it is the batteries not the converter. Good luck.

Did some more checking. sorry for my confusing information. I realized earlier that I incorrectly measured my batteries. Since they are in parallel I did it wrong. Having said that, I have confirmed a voltage at the batteries of 11.4 wether I'm plugged into shore power or not. If I start the generator then I do get 14 volts and can open the slide out. So it appears that the converter may not be sending out a charge??? I'll go do some prodding around on that.

flapbreaker wrote:
Thanks for the feedback. Clearly I do not fully understand how my RV house batteries are wired or charged. I did a little more testing. I can start the generator after starting the RV. When I test the voltage at the batteries with the gen running I get the 14 volts I expected but on 30 amp shore power I only get 7amps. My circuit breaker is a 50 amp model so I'm using a 30amp shore power adapter. Is it possible that what ever charges my batteries is only delivering 1/2 the power due to only using on 120v line when using 30 amp power? This would be very disappointing if the house batteries do not charge fully on 30 amp service.

No 1/2 output is not possible by using a 30 amp 120v supply. You posted that you are seeing "7 amps" at the battery when your RV is powered by shore power. I'm going to assume that you meant 7 volts. If you are using a meter and seeing 7 volts measuring across battery terminals, you have a battery problem.

It may be that you had a charging problem previously, and that caused the battery to fail with a shorted cell.