Does alternater charge coach battery?

[Prescott]

I have a 1992 Winnebago Warrior. I bought it used. It has a solar panel on the roof, and the coach battery is pretty much always fully charged. I'm confused about the engine charging the coach battery. The owner's manual does not specifically say that the engine alternator charges the coach battery. The only reference is, under maintenance,--"As soon as energy is removed from the battery, it should be replaced by the alternator or the converter system." Not exactly clear. So, does the alternator charge the coach battery? I suppose I could get at the coach battery and see if the voltage rises when the engine is running, but I figure somebody out there knows.

[wyocamper]

"As soon as energy is removed from the battery, it should be replaced by the alternator or the converter system."

To me that sounds like the battery will be charged by either the alternator if the engine is running, or the converter if plugged in to shore power.

On my 2015 the alternator charges both house and chassis batteries, and the same for the converter. I realize that has nothing to do with your 2002, but it sounds like it works the same.

[Morich]

For some reason the drawings for the 92 Warrior are not posted but in checking 91 and 93, the system seems to be much the same as still used on many Winnebagos and it is pretty simple to spot.

I did this snip of the 93 thirty foot as an example and you might be able to spot the same parts on your RV?

There is a big shiny solenoid which does a couple really good things for the RV. It might look very much like this if you find one:
https://www.amazon.com/May-Continuou...964099&sr=8-15

Looking at this snip of the drawing, try clicking on it to get it larger and better to read, perhaps?

The "mode solenoid" is just a set of contacts which are controlled by a wire from the dash/front area. This wire is labeled LR and gets power at two different times. When the engine runs power comes from a hot ignition circuit, down to the solenoid, goes the through the solenoid coil of making an electro-magnet move the contacts closed and passes on to ground through the body of the coil, using the mounting screws to make that contact.

When the contacts close power from the start battery, shown on the left is connect to the big lug on the right side where the coach batteries are connected. So the short answer is YES, they should connect when the engine runs and they both get charged from the alternator!

But there is a second use that we should be aware of as it may be handy. Somewhere on/near the driver, there may be a switch, maybe labeled "AUX for the second battery or "boost" as when we push the momentary switch it connect both together and gives the start battery a "boost" if it is weak!! Jump start without having to get out the jumper cables!!

[ogre]

I have no aux switch, & no power going to solenoid from alternator.

[ogre]

Wonder where the top post wire is supposed to be getting 12v?

[eyecando]

The only way to know for sure the system is working is to measure the voltage on the coach battery or the charging current to it. The voltage should increase to somewhere around 13.5v or higher with the engine running and should approximately match the voltage on the chassis battery.

Once you know it is working correctly, you can try to figure out how it is done. The most likely way is with a solenoid, but sometimes they fail and have to be replaced. If you find a bad solenoid do not purchase a standard automotive solenoid since they are not rated for continuous duty and will fail. I believe this would be the correct solenoid if you need one https://www.amazon.com/Cole-Hersee-2...dp/B0064MX7US/

[eyecando]

I learned recently that the voltage on a lithium iron phosphate battery will not rise much immediately with the engine running.

For instance, charging my 200AH lithium iron phosphate battery at 60 amps only caused a voltage rise in about a hundredth of a volt due to the low impedance.

[Morich]

Originally Posted by ogre

Wonder where the top post wire is supposed to be getting 12v?

I missed seeing this at the time but we are missing some of the vital info togive the best answer as we don't know which RV and there are lots of differences in older/newer/bigger/smaller, etc. so I do like to get down to which one rather than trying to make a guess fit all the different ways it is done.

In general, without knowing which RV, there are two places where the control wire gets the 12 Volts to operate the solenoid. And then there are also at least two different solenoids, if not solid state items to make it happen.
The three post solenoid as talked here has the LR wire bring 12V down and runs through the solenoid coil to connect to ground internally, but the common four post has both battery on LR and ground on another wire (FM?) that may be connected to the coil. Sometimes the ground is as simple as the mounting screw for the solenoid, so that a dirty solenoid can stop working just becasue the screw is dirty!

One is if we push the AUX or BOOST switch on the dash, like when we want to tie the two batteries together as a way to "jump start" a weak start battery, it sends the 12Volts.

But the other use of the mode solenoid is when we want to let the engine alternator send some of it's excess voltage/current to the coach batteries as we drive. It is not a quick process and don't be fooled into thinking a couple hours driving gets a low battery fully charged, but it does "some" charge when the engine runs.
For this there is a second connection the the LR which comes off a part of the ignition wiring which is hot while the engine runs. That does the mode solenoid operation without us having to do anything like push a button.

As mentioned, one quick way without having to dig around to find the solenoid is to check the batteries voltage. If you find the coach batteries are down like 11 volts and you start the engine and that voltage suddenly pops up to more than 12, you know you are no longer reading the battery voltage but the much higher charge voltage from the engine alternator.

A note that is often missed is that good, high voltage DOES NOT mean the battery has found magic and is fully charged, as when you shut the engine off, the voltage will likely drop back down to almost where it started!

Don't let a simple battery trick you!

If the RV is starting correctly as that shows the alternator is working, the most common reason to not find the alternator current at the solenoid is dirty cables! Basic idea of what is being said is that the battery is getting charged but that voltage is not getting from the battery to the solenoid, so a dirty /corroded cable is about the only thing to chase.