Alternator and house batteries

[WearyTraveler]

While we’re sitting here watching the world go by...

Yesterday, I posed (and you folks answered perfectly) the question about the inverter. So - we drove for about 8 hours with the inverter on and the fridge powered. We were smiling as we cruised down the highway...

When we stopped last night and I checked the batteries before firing up the gen, the gauge (lights, actually) showed that the batteries were only half charged.

I was assuming that the V’s alternator would charge the house batteries on the fly.

Did we screw up by doing this? Or doesn’t the alternator keep up with battery power depletion?

[Bob Denman]

Question: What were those indicator lights showing for a state of charge: when you first started?
The V-10's alternator has a primary job: to keep the chassis battery up to snuff.
I don't know what it's excess capacity is; but (depending upon power usage): you could have been throwing more at it, than it could handle.

[Laco]

If its setup correctly, when running your engine, you should be charging all batteries on-board. I know mine does, as I can see the voltage increase in the inverter display when the engine is running. If you have an inverter, just check the voltage display with the engine off and again when its running.

[16ACE27]

The engine will charge the house batteries if:
The USE/STORE switch is in USE (batteries not disconnected from the DC buss) and;
The Battery Isolation Manager (BIM) or other method of cross-connecting the house and chassis batteries for charging and isolating them when discharging, is working correctly.

[Bob Denman]

Originally Posted by 16ACE27

The engine will charge the house batteries if:
The USE/STORE switch is in USE (batteries not disconnected from the DC buss) and;
The Battery Isolation Manager (BIM) or other method of cross-connecting the house and chassis batteries for charging and isolating them when discharging, is working correctly.

...Provided that the chassis engine is running long enough to do so...

[tanman32225]

Not everything is at it seems..

We purchased our used MH a couple of years ago. I asked about the house batteries and were told they only charge when the genset is running or plugged into shore power. What a pita always on trips and worrying about my house batteries going dead and having to hurry to shore power.

A few months ago I began doing some research and found out most MH have the engine alternator charge the house batteries...

I was in CW out west and saw a tech so I asked him his thoughts.. He went to my coach and started checking it then came to me stating mine did not have a fuse spot. He said mine was not equipped for alternator charging.. Hmmm... I later looked at the fuse holder and the tech was holding the cover up side down.. duhhh.. I did have a fuse in the slot.

A couple of days later I was looking under my dash for a loose camera connection. I saw another fuse panel with a fuse that had a red led light next to it illuminated. I knew that was an indicator the fuse is bad. I replaced the fifty-cent fuse not knowing what it went to. Viola other things started working and my alternator began charging my batteries. Now when I travel my house batteries stay charged.

The moral is just because others tell you it will not work find out on your own through investigating the problem.

3 CW, and independent dealer and Thor steered me wrong. I small fuse and had I not had the ignition key on trying to find the loose camera connection I would never have seen the red light on.

Keep plugging until you find the problem and good luck

[Beau388]

Originally Posted by WearyTraveler

While we’re sitting here watching the world go by...

Yesterday, I posed (and you folks answered perfectly) the question about the inverter. So - we drove for about 8 hours with the inverter on and the fridge powered. We were smiling as we cruised down the highway...

When we stopped last night and I checked the batteries before firing up the gen, the gauge (lights, actually) showed that the batteries were only half charged.

I was assuming that the V’s alternator would charge the house batteries on the fly.

Did we screw up by doing this? Or doesn’t the alternator keep up with battery power depletion?

Your 175 amp alternator has about 1,700 watts @ 2,400 engine RPM (500 watts @ idle rpm) usable output, so all is fine to run the fridge IF you are not using other things in the coach. The problem is dash A/C draws about 500 watts, headlights 120 watts, TV 65 watts, fridge 350 watts unless your door heaters are on then 660 watts. If the fridge in defrost mode then 1400 watts. Your MSW inverter is about 60% efficient when powering electric motors, so 635 watts of alternator power to power the fridge through the alternator.


You are going to have to learn about battery management if you are going to dry camp. Flooded batteries start to loose some of their ability to accept a full charge the day they are filled with acid. The deeper you discharge them the more life you take out of them. The typical life of a flooded battery discharged to 50% 60 days a year is usually 2 years. They don't fail; they just don't recharge to anything like full capacity. Any flooded battery will age rapidity if left 24 hours or longer in a partially discharged state. A new battery discharged to near zero a couple times will likely never recover.
The best check of the house batteries is when there is no power charging the batteries (engine off, generator off and not on shore power). Turning the inverter on will show actual battery voltage - 12.8 volts fully charged; 12.2 volts 50% charged; 12.1 volts 25% charge and 11.9 volts 0% charged. More info @ <https://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html>