Using a Vehicle Alternator as Backup Power for RV Batteries

[DutchmenSport]

I watched a YouTube video that gave me something to think about. The video discussed how to charge batteries in a stick-n-brick house to use as an alternative power source instead of conventional generators or a solar system. Actually was something I never considered before.

How do you power the house for a much cheaper cost than investing in a house generator system, something that almost everyone already owns or has access too.

Imagine having a bank of batteries in your stick-n-brick house that provide power to an inverter that will run the basic electronics in your house, like lights, refrigerator, computers, televisions. How do you keep the batteries charged if you don't don't have a generator or solar system. (Or simply do not want to invest in the cost?)

The solution recommended in the video was to use the alternator in your vehicle, as every vehicle has an alternator, (unless it's an all electric vehicle). Attach an inverter directly to the battery of the automobile, start the engine, and let the alternator on your automobile charge and top-off the battery bank.

But then, the automobile is already producing 12 volt DC, and the batteries in the house will be 12 volt DC, so an intermediatory converter/inverter between the automobile and the battery bank is not needed. Just hookup the automobile directly to the battery bank ... like ... jump the car when it has a dead battery... battery to battery.

On the other side of the battery bank (output), is an inverter, inverting DC power to AC power for household appliances.

The idea is phenomenal, as long as one has fuel for the automobile.

So, I've had time to ponder over this concept a bit and wonder, why wouldn't this work for charging house batteries in an RV (camper). I know most trucks are equipped with a trickle charge that keeps the trailer batteries charging when driving on the road. But, why not an actual connection, similar to jumper cables.

Another thing that can be done is to use a beefed-up inverter connected directly to the battery in the vehicle. As long as the vehicle is running, the alternator is keeping the vehicle battery charging. One might have enough power from the vehicle to actually power an air conditioner in the camper.

Thoughts for discussion. I have a 400 watt inverter in my truck I use for specific small appliances, but haven't used it in years. It connects into the cigarette lighter socket. I know that one is very limited in what it can do. But if a beefier one were connected to the vehicle battery and the engine running? Well???? share your thoughts?

(assumption: The vehicle is in excellent running condition).

 

[LeftOverParts]

Fun question! FWIW, here's what Google AI shows with the assumptions given. You could try an assumption like, car with 400 watt output.

(Without looking at our electricity bill, I think the shore power cost is pretty close. Not sure about the rest of the calculations. (Reg gas locally is about $5.50/gal). The answers usually have a disclaimer like, AI generated answers can be wrong and should be checked).

 

[mlh]

I have an inverter in my F150 it’s called a Power Boost, 7500 watts. It will run my house, not all at once. It will run the heat pump and stove but not at the same time. We have run the house probably three weeks with it, and it gets 22.5 MPG. Not bad for 430 HP. The engine cuts itself on and off as needed.
As to your question. I’ve seen this on utube. I wonder how much you can run off of 75 amps 12 volts and how much gas is it going to use. And how many amps does it put out at a 1000 or so RPMs. How long will your alternator last running continuously at near full power?
I don’t know but I’ll stick to an inverter generator until I know.
Lynwood

 

[DutchmenSport]

Good comments. Maybe a bit more for clarification: As a "power back-up" in the event of power outages, not as a primary energy source instead of public utilities. And, (except for the battery bank), as an alternative to a home generator or a portable "conventional" generator (Honda, Cummins, Westinghouse... etc.), would this be a feasible alternative?

Lynwood, I find it interesting that you have actually done this with your truck. I think it's a fascinating idea, even if I do already own 4 "conventional" portable generators." I suppose with 3 vehicles sitting in the drive way, this gives me 3 more "generators!" Often times I drag one of my Cummins Onan P4500i generators with me when I'm doing some type of construction work where there is no electricity available and hauling the thing around is a chore. This is an interesting possibility. I just never thought of this, until just recently. I think I'll experiment (at home) and see what it's capable of doing.

Maybe the next time I need to use my skill saw, I won't have to drag along the P4500, a much smaller 1000 watt inverter would do the same thing.

So, actually, if one had a battery bank large enough to power an entire house, the alternator in a vehicle (would) indeed work to keep batteries charged. Interesting, most interesting!

 

[mlh]

I get 40% of my miles from the battery. That sounds like a lot but most of that is going down an incline or when I let off the gas but still 430 HP and I drive like I stole it, like the old man I am. If I go somewhere and need power I’ve got it. I have read Ford will have the Power Boost option on the Super Duty truck next year???? Don’t believe everything you read! Wouldn’t that be nice. You will be able to power your camper anywhere even traveling.
This system was a $1900 option but I got a $1900 rebate so it was free.
Lynwood

 

[Mark77]

I talked to the consultant that advised me on my current Victron setup about running shore power from the truck mounted inverter (OEM) and having smaller lithium charger keep my battery bank topped off while I was driving during a typical 400 mile travel day.

They advised me to go the DC / DC route for much faster, more efficient charging. That is what I did and I typically see about 25 amp charging going through the Victron Orion, depending on the load in the RV at any given time.

 

[Daryles]

I installed a DC-DC charger as a backup to hauling a generator for short trips. We have 1000w of solar, 552Ah of lithium batteries and a 3000W PSW inverter.

It has come in handy when you have many days of cloudy skys OR tall shady trees OR when wired into an ATS, starting/running your AC 30 minutes before arriving to cool down your rig in the summer.
Also handy when camping in Canada Providencial parks. Very strick generator hours.

DC to DC charger

I just finished installing a Renogy 60A DC-DC charger in my 5th wheel. The purpose of this is to be able to charge your RV batteries from your truck "safely" whether parked or driving. The 7 way cable from the truck to the RV does provide some charging. The most I have measured is about 7A. It...

www.montanaowners.com

 

[MandK]

I also went the dc/dc route with our Montana. I had no solar and the dc/dc would allow us to Harvest host multiple nights in a row when traveling without using a generator. Our current rig has 600 watts on the roof which will recharge the battery when there is full sun but that’s never the case it seems, so I reinstalled the dc/dc that I kept when I traded in.
FWIW, if anyone is considering a dc/dc set up but doesn’t want to deal with fishing heavy cables through the overhang, I’ll post some pictures of what I did. It wasn’t much of a problem getting them through on the Montana, but there was no way I was ever going to get them through on our rig now. It’s a simple “jumper cable” set up that I only use when needed.

 

[Mark77]

I also went the dc/dc route with our Montana. I had no solar and the dc/dc would allow us to Harvest host multiple nights in a row when traveling without using a generator. Our current rig has 600 watts on the roof which will recharge the battery when there is full sun but that’s never the case it seems, so I reinstalled the dc/dc that I kept when I traded in.
FWIW, if anyone is considering a dc/dc set up but doesn’t want to deal with fishing heavy cables through the overhang, I’ll post some pictures of what I did. It wasn’t much of a problem getting them through on the Montana, but there was no way I was ever going to get them through on our rig now. It’s a simple “jumper cable” set up that I only use when needed.
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I did the same thing on my Montana. Not sure what I will do with the newer 5er. I would like to string it through to the hitch, but haven't experimented with that possibility yet.

I used about 5 adhesive backed pads for tying cable with zip ties to hold the jumper up over the endgate. When I wanted to remove it I just cut the zip ties and left the pads to use another day.

You can kind of see it here... Back at home and not yet washed up!

 

[nickens]

I also went the dc/dc route with our Montana. I had no solar and the dc/dc would allow us to Harvest host multiple nights in a row when traveling without using a generator. Our current rig has 600 watts on the roof which will recharge the battery when there is full sun but that’s never the case it seems, so I reinstalled the dc/dc that I kept when I traded in.
FWIW, if anyone is considering a dc/dc set up but doesn’t want to deal with fishing heavy cables through the overhang, I’ll post some pictures of what I did. It wasn’t much of a problem getting them through on the Montana, but there was no way I was ever going to get them through on our rig now. It’s a simple “jumper cable” set up that I only use when needed.
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Might consider running the cabling under the skin between hitch and battery compartment just like the 7-way is cabled. less chance of catching on things and looks cleaner

 

[MandK]

Might consider running the cabling under the skin between hitch and battery compartment just like the 7-way is cabled. less chance of catching on things and looks cleaner

That’s what I did with my Montana it was fairly easy to fish it through but I can’t get it through on my current rig. Too much steel and the skin is tight to the framing. I’m not going to take the front of the rig apart to do it. It has plenty of clearance as it is.

 

[MandK]

I did the same thing on my Montana. Not sure what I will do with the newer 5er. I would like to string it through to the hitch, but haven't experimented with that possibility yet.

I used about 5 adhesive backed pads for tying cable with zip ties to hold the jumper up over the endgate. When I wanted to remove it I just cut the zip ties and left the pads to use another day.

It wasn’t too hard to do on the Montana, I was able to pretty easily get a fish tape from the pin box back to the front compartment with a little help from a 4’ ruler after removing a few screws.

Maybe an alternative to the zip ties, on my current rig, I put a tie down anchor where the front bay door holding fixture is and attach the carabiner on the cable there. But you could put it anywhere under there. I attached another one near the plug. It’s easy to unclip and store it. I only use it when leaving someplace and going to the next place with no power and not enough sun to recharge the battery. The rest of the time the cable is in the storage bay, not needed.

 

[Mark77]

It wasn’t too hard to do on the Montana, I was able to pretty easily get a fish tape from the pin box back to the front compartment with a little help from a 4’ ruler after removing a few screws.




Maybe an alternative to the zip ties, on my current rig, I put a tie down anchor where the front bay door holding fixture is and attach the carabiner on the cable there. But you could put it anywhere under there. I attached another one near the plug. It’s easy to unclip and store it. I only use it when leaving someplace and going to the next place with no power and not enough sun to recharge the battery. The rest of the time the cable is in the storage bay, not needed.

Thats the nice thing about those Anderson plugs. I only plug mine in if I have a long travel day and something using the power in the rig. Otherwise, like you the cord is coiled up in the front bay.

 

[DutchmenSport]

So, IT really is doable, as some of you are already "doing it!". Sweet! Thanks for all the input. It's always a good thing to have alternatives, a plan A, and plan B.....

 

[Capt Mac]

I also went the dc/dc route with our Montana. I had no solar and the dc/dc would allow us to Harvest host multiple nights in a row when traveling without using a generator. Our current rig has 600 watts on the roof which will recharge the battery when there is full sun but that’s never the case it seems, so I reinstalled the dc/dc that I kept when I traded in.
FWIW, if anyone is considering a dc/dc set up but doesn’t want to deal with fishing heavy cables through the overhang, I’ll post some pictures of what I did. It wasn’t much of a problem getting them through on the Montana, but there was no way I was ever going to get them through on our rig now. It’s a simple “jumper cable” set up that I only use when needed.

So my Monty has the wiring for this (installed by previous owner), but my truck does not. What does it take to add the source dc to my truck (2018 Chevy 2500HD Duramax)?

 

[scottz]

So my Monty has the wiring for this (installed by previous owner), but my truck does not. What does it take to add the source dc to my truck (2018 Chevy 2500HD Duramax)?

Does your Montana have DC-DC converter(s) installed? You need cabling from your truck battery (with a breaker at the battery) to the DC-DC converter(s). My converters are installed in the 5th wheel battery compartment. I used an Anderson plug in the bed of the truck and the mating wiring/plug run along with the 5th wheel's 7-way cord. I would not use anything smaller than #4 wire in order to carry enough current; two wires; pos & neg. The OEM wire GM installed that provides a 12V source in the seven way plug is not even close to big enough. Photos here

 

[Capt Mac]

It will be a couple weeks, but I'll get together some photos of the previous guy had done. He was fully into boondocking and it is mostly a clean professional installation. Monty is a 2017, so some of the tech may need be some updating. Thanks!
BTW, you're work is outstanding. I really appreciated the wiring diagram. That will come in handy when I try to explain how all this is supposed to work to kids.