12V Electrical Issues - It's Complicated

Normally, we don't do eight hour trips, but had the occasion this past weekend. Normally, the Inverter is on during our trips and we run a laptop and the Mifi's, as we did this time. Sometime late in the trip, I noticed the mifi's had died, like they were not getting power, although there was not indication on the power panel monitor that anything was wrong.

I fired up the generator enroute and left it running, but it was showing a 14 amp load which I am not sure I could explain since the only thing on was the refrigerator. The mifi's came back to life, and twenty minutes later I shut down the generator.

Then we had the problem again, so I tried to start the generator and it would not do anything. We go to the campground, and I am thinking maybe I discharged the batteries, and we plugged up, me hoping the batteries would charge up if they were down, but I did not test them at that point.

The 12v lights are dimming and brightening, the generator will not fire, and the batteries all seem to have a charge. When I tried to fire up the A/C on shore power, it stopped and started like the controller was losing power (if I correctly understand that the controllers are 12v).

I need to do some serious troubleshooting for this mess and would appreciate some help on isolating the issue in a methodical way. What baffles me is why the generator has lost the ability to fire in all of this, unless it needs the 12v part of the house batteries.

I can run my multimeter but after that I need some detailed help!

The starter motor of the generator is powered from the house batteries in many motor homes. In many cases, you can use the Aux, MOM or whatever the switch is called in your MH, to jump start the generator just as you would do the engine if the chassis battery needed it. Might be a good idea to have the engine running while you try that, just for that  bit of a kick from the engine alternator. From the other symptoms I would say your house batteries were not well charged at that point. And remember, charging low batteries is NOT a 2 hour affair, it takes many hours to fully charge them.

The fridge was not the only thing powered up under the conditions you described. If you had left it on "Auto" it would have been  cooling using 120V as well, a possible 5 amp draw right there. The converter would  also  be on if 120V was produced by the generator and it was probably charging the house batteries.  If you left the water heater switch on, it may have been powered up too. (Hope there was water in it, if so.)

One way to quickly check if the House batteries are being charged by the converter while on shore or generator power is to measure the Voltage across the battery posts. If you  see 13.5V or more they are being charged. If not you will have to check further for a C/B for 120V converter power, possible fuses on the converter output etc.

Stu is correct. Just recharge your batteries and all will be ok.

The house batteries are at 6.33 volts sitting, and a little over 7 when charging using the Xantrex 456. We are currently on shore power, and the engine was running when I was trying to start the generator. We turn the electric water off when traveling.

I can try the Aux Switch for the generator but I think I have to be disconnected from shore power for it to work.

p.s. I think I was testing the 6v side of the batteries being charged. When I located what I thought was the 12v series side, I got 13.22 volts charging. The batteries were recently watered and terminals cleaned, and I think I will recheck all of that.

Are we thinking the generator is smart enough to require a certain voltage before it will even attempt to spin?

I assume you have a battery bank consisting of 2 6V in series and perhaps two more?

I cannot find anything on a Xantrex 456, Is it an INverter? there is an Inverter Prosine model 458 with a 12V charger...  But in any event, it looks like they are charging.

skyking4ar2 said:

Are we thinking the generator is smart enough to require a certain voltage before it will even attempt to spin?

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Yep, if there isn't enough voltage and amperage the gen won't spin.

Are we thinking the generator is smart enough to require a certain voltage before it will even attempt to spin?

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Not really intellegence, but yes.  You need enough voltage for the electromagnet in the solenoid to overcome the spring tension and pull the contacts together before the starter will get power.

Magnetic flux reduces in intensity in proportion to the distance from the magnet, so once the contacts are engaged and touching each other, they will stay engaged until the voltage drops to a much lower value and spring tension is able to overpower the magnetic attraction and pull them apart.

Alfa38User said:

I assume you have a battery bank consisting of 2 6V in series and perhaps two more?

I cannot find anything on a Xantrex 456,

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Yes, I have four Interstate U2000 Deep Cycle 6V batteries.

It's a Xantrex Freedom 458 with a charger. .(happy fingers..)

You might, at one point, want to separate the batteries and measure each one individually to be sure that all are good (i.e. measure 5.7-6v) and none have a bad cell and thus will take a full charge.

Were you eventually able to start the Genny using the Aux switch??

Later last night, after having the charger running all day, I did not have the problems with the lights, and the A/C controller did not have any issues starting and running the A/C's without kicking out.

It is raining today, but tomorrow, I will pull and check each battery, clean terminals again, and make sure I don't have a problem. I will also try the generator test with the Aux switch. Today, it would not attempt to start, but I am not sure I don't have more than one problem yet.

You have to have some problems to get the experience to troubleshoot.

If the batteries are up, check connection to the starter and generator frame. My onan just clicked till I cleaned up the terminal at the starter.

I still think the batteries are not fully charged or there is a wire loose. The generator won't even light the switch.

Tomorrow, when the tornadoes quit, I will have to drag all the batteries out and test them individually. They seem to have a lot of weeping on the tops that was not there before.

Kim,

The weeping may be because the batteries were very low and had to charge rapidly after just having been topped off. I'd monitor until the charging voltage settles out at about 13.6 and they stop bubbling (yes they will bubble from the heat of charging if the rate is real high). They also may be hot to the touch. You might want to check the specifications on the converter to make sure it is a quality three stage model.

Note that high charge current is often the result of a dead cell in one of the batteries since this effectively lowers the resistance of that pair of batteries. In that event I'd expect the bubbling to be from one pair of batteries (assuming only one bad cell).

The initial problem was almost certainly just DEAD batteries, but a bad cell is certainly possible.

Once you are certain that the batteries are fully charged (will probably take 8-10 hours), check the voltage at the generator solenoid (or just listen for it to click when the start button is pressed) if it still won't start and then go  from there.

Ernie

(yes they will bubble from the heat of charging if the rate is real high)

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Heat doesn't create the the bubbles - it's electrolysis, the splitting of water into it's component atoms of hydrogen and oxygen.

It's the same principle used in commercial hydrogen production - pass an electric current through water and hydrogen atoms gather around the negative electrode, oxygen atoms around the positive electrode.  When the battery is charging, these combine with the plates to reform them to their charged state.

The gasses are created whenever current passes through the electrolyte.  You see more bubbling towards the end of the charging cycle because less is being absorbed by the plates themselves.

That's why batteries have to be vented properly - the bubbles aren't water vapor, they're potentially explosive hydrogen and oxygen gasses.

Update:

Today, the batteries measure 6.92/13.8 charging, 6.76/13.46 static. I did use a hydrometer to check the one battery that I could easily get into, and it registered at the top of the scale. Tomorrow, I hope to be able to disconnect the other three, use the hydrometer, and then measure the voltage on each one disconnected.

Is the hydrometer the sure test of the dead cell, or do I need to also put a load tester on the batteries? I still have a bit of the light flickering, but want to be sure all the batteries and terminals are clean and well connected.

I also believe I am going to have to find a location to test the Onan generator solenoid and see that it has full power to it. Could there be a fuse somewhere since I still do not see the generator switch light up? (at least I thought I remembered it lit up when pressed to start).

A dead cell will most obvious from the battery's overall voltage. It will be closer to 5 volts as opposed to 6 if good.

A load test should be performed on any suspiciously low  battery

A good hydrometer test is the best. If the cells are all even and in the good range, that battery is not the problem. Move on to other batteries, all connections.
I do feel your pain, I need to check connections between my batts and the main panel. I am missing some voltage along the way.

In the "what the h@ll???" department, last night I was switching on lights in the bedroom, and heard some clicking. I realized that the lights were no longer dimming, and they all were fully illuminated. I had heard the clicking before from the front of the coach when I tried to light the generator but could not isolate it.

The clicking had come from an area where the control board is located that controls the power between shore power and generator power. (I know there's a name for that board but I forget.) I had a relay on that board stick last year and keep the shore power from being routed into the coach until a technician located it, by hearing a clicking, and tapped it to clear the problem. I would be able to power up on the generator but not the shore power. I have never had that issue again.

So maybe there's a relay on that board that also routes 12v power? Anyway, today, I will attempt to light the generator again, and walk down that path. It would appear I am closing in on a solution.

The name you are  seeking may be ATS - Automatic Transfer Switch. It switches 120V power from shore power to Generator power when required. They also have a certain reputation for sticking/burned contacts that are normally caused by arcing while switching under load. All loads should be off when starting up or shutting down a generator to avoid/minimize this problem. The RV tech tapping on the relay box may have caused the sticking contacts to release but there is a message there... The problem is NOT fixed!!!

In the DC world, you may have a similar arrangement for coupling the engine battery to the coach batteries to permit charging while underway and for emergency start functions should you kill the engine battery or to permit starting the generator if the house batteries are too low. For the emergency functions this arrangement is controlled by a switch on the dash labelled MOM or Aux or something similar. Operating the switch and following the click will help isolate the actual relay responsible.

It's a Transfer switch and its basically a sensor to detect the presence of shore power and control a large relay that switches between shore power and the generator. If it hangs, you'll be stuck on one or the other. This is one reason that you should always remove large loads before plugging in, removing the plug, or starting or stopping the generator. The arc created can burn the contacts or cause them to fuse together.

Clicking here could also be caused by a bad (loose) connection in the shore power cable. This is consistent with your winding up with a dead battery. That would be because the contacts were open and your coach was running off the inverter.

If you're comfortable with it, open the transfer switch (shut off all power to the coach first) and check the relay and the connections to it. You might also want to ohm out the cable from those connections to the plug while Christy wiggles the cable to make sure there is'nt an intermittent fault.

Hope this helps,

Ernie

Note that Hydrogen is not a liquid at room temp. (and therefore not seen on battery caps) although it might cause the acid/water mix liquid to bubble out, but well filled batteries may, and often do, overflow when they are heated by rapid charging.