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Is a transfer switch needed to use shore power to charge a battery bank when you remove an inverter/charger and replace it with only an inverter?

Greenshereen

Greenshereen

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Oct 15, 2021
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I was told that if I replace my existing inverter/charger with just an inverter that I will lose the ability to charge my battery bank with shore power, my diesel generator, and my alternator. Also, that if I wanted these options to charge my battery bank I would have to install new wires and use a transfer switch since the one built into my existing inverter/charger would be eliminated. That my solar power system would take between 16-24 hours of labor with two people and several days to two weeks for an RV repair shop to schedule in. I’m a complete novice when it comes to RV electrical systems and installation. But, it doesn’t make sense to me that I would have to install brand new wires unless you factor in the upgrade from lead acid to lithium iron phosphate…? Do they require thicker wires?
 
It's hard to tell you anything when you don't specify what exactly you have, and what it would be replaced with? I'm assuming your original inverter/charger has died and you need to replace it? What's the brand? Why can't you just replace it with another inverter/charger? I know that both my inverters have a built-in charger, and both have grid transfer switches, but they are 24V and 48V respectively. I'm assuming you want this to be 12V?

What exactly is the bottleneck? Are they no longer making an inverter that comes with a charger and a grid connection? Sounds to me like what the dealer wants to do is install what he has instead of what you need?

With a similar charging profile, and similar AC loads, the wire gauge should stay the same. Does the wire appear to be suffering from any corrosion, like road salt damage? If the wiring is old they may want to replace it just to be safe, but this sounds to me like trying to rack up charges.

For me, swapping out a new inverter to replace an old one would just be a couple of hours of work for myself.
 
First of all, thank you for responding! i am following Will’s plans for an eventual 4,000 watt capacity, 24V solar power system with a 3,000 watt inverter, two 40 amp solar charge controllers, and a 24V to 12V converter. I have a 1500 watt Xantrex Combi that is hooked up to 4 new lithium iron phosphate batteries (12V, 100 amp from Battle Born). I can afford only two 200-watt solar panels, but would like to use some emergency money to purchase two more soon if I can manage the install without outlaying any more cash. I am driving a 2003 36’ class A motorhome with a Diesel engine and generator.

I purchased it from a private owner as-is with the intention to have it inspected as soon as possible. I waited seven weeks for an appointment with an RV repair shop that burned through my budget for the post-purchase PDI by cleaning out my battery compartment and hooking up my new batteries and charging me just under $1400. There were just too many other incidents before that which put my family into severe financial hardship that we need to boondock full-time.
 
OK, a couple of things to start out with. Glad you want a 24V system, because I already have in place what I think you are talking about. I have this 24V inverter for my workshop, which has a built in AC to DC charger, and a transfer switch for grid connection.

Schneider Electric Conext SW4024-120/240 Inverter/Charger - RES Supply

Free Shipping! Schneider Electric Conext SW4024-120/240 Inverter/Charger, 4000W, 120/240VAC, 50/60Hz, 30A Transfer, 24VDC, 90A Charger, RNW8654024
ressupply.com ressupply.com
When you say you want "4000 watt capacity", are you saying you want 4000Wh of power, because obviously a 3000W inverter can't provide you with 4000W.

Panels are the single cheapest component these days, so please don't say you can only afford two 200W panels. Most likely, you can't afford more than 400W of RETAIL panels. Instead shop on Craigslist, with local pickup. My last purchase was just last year, and I got 245W panels for 55$each. I ended up buying both for myself and also for several neighbors. Cash and carry. Shipping is baked into the price of new panels that get mailed to you, so don't do that.

Why do you want two 40A charge controllers? Why not one 80A. BTW, with only 400W of solar that works out to be 400W/25Vcharging = 16A. Assuming you only get 85%, that's ~14A. If laying flat on the roof of the RV, then expect only 75%, or 12A. So, even with 800W of panels you'd only be pushing 32A max, and more likely 24A in the real-world.

Where is your battery compartment? Is it external and exposed to the weather, or inside the RV. IF Li batteries are charged when below freezing, they'll get destroyed. If you have 200Ah at 24V and you want to charge at 1/4C you'd need 200Ah X 0.25C X 25V X 1.33fudgefactor = 1662W of panels, more than double what your eventual plan is. Remember, laying flat, any panel will never make anything close to their rated power output.
 
Oh, I thought Will worked out the solar panel wattage to the inverter size… guess I’m gonna have to upgrade when I can get more panels. I just clicked on the link on his website that said get these two 40 amp charge controllers. I started reading about the 80 amp controller but just started with the two to not get mixed up. For now I’m sweating so many other critical expenses that I really shouldn’t even be buying anything more for this system. My father and I use very little power out of necessity, so we want the choice of being frugal if we can’t be just comfortable. I wanted a system I could grow into. We pulled out lump sums of money from our lifeline investments thinking we could contain the situation, but kept running into dishonest people along the way. We never expected to have our project delayed this long which burned through our installation money on Air BnB fees and delayed my ability to work on my income stream.

The battery compartment is curbside behind the rear dual tires. Next to it is the inverter compartment.

I will do just about anything to avoid extreme cold!!! I’m from Hawaii!!! Same with extreme heat. I figured that boondocking would ensure I’d get many hours of sun during the day. Would the panels offer a measure of cooling by the shade they provide or do they actually act as a thermal conductor?

I weighed the cost of a Victron Multiplus with the cost of the solar panels and potentially the install fee and decided that it would be more sustainable to have the independence of solar charging my battery over using shore power at an RV park. I’ve had a couple of offers to park at private residences fall through, so I don’t want to depend on shore power. Im not precluding shore power or even my generator as sources of power in the future— I just have to table them until I can establish a steady income stream.

My father also complicates the situation when I leave him alone for extended periods of time. I am a Hawaii-state licensed acupuncturist with over 21 years of study and practical experience. I am the only member of my family that can work with him on improving his cognitive functioning. Still, the challenges he presents require me to work from home so I can keep tabs on him and our pets.
 
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You can always charge the battery direct..
the issue is often the charging system could be wired to get power from the onboard system and the inverter ends up powering the charger creating a power loop that drains the battery.
Not a huge deal to adjust for this issue.

Having said that..... the inverter charger probably has a transfer switch and you may need to buy one separate to avoid multiple 120v sources feeding power at the same time. The switch is not a big deal either.

personally I like separate components over the all in one stuff. Might be a bit more effort but when something goes wrong it easier to diagnose and replace. Especially on the road.
 
Just so I’m on the same page, are you saying there is a way to plug the battery bank directly into shore power? Or, I could get a separate transfer switch which would mediate between the shore power, inverter, and battery bank? The latter is a better set up? Okay, that’s what I was thinking, too. I watched a video Will did on installing an ATS in his RV which helped me understand it’s role in mediating between the different power sources and the battery bank. I seem to recall reading that my Ambassador has a transfer switch installed already, but I’m not sure if that’s what you’re referring to. Any specs I should look for when shopping around for a transfer switch?

I don’t know what the condition of my extended wiring looks like, but the repair guys were assuming it would have to be replaced due to the age of my RV. Luckily, my RV was parked most of its life with the three previous owners (only 40,000 miles at the time of purchase in July of this year). I pushed it the hardest so far when I drove it across the country.
 
Since the RV has a generator there will be a transfer switch to select between utility power and the generator.
Need a similar switch for the inverter power. Probably a 50 amp switch.

Power for the battery charger needs to be connected before the second switch to get power from the utility cord or generator but not the inverter.
 
okay so my RV already has the ability to switch between shore power and the generator, but not between those two sources and the inverter? Would I then want to install the second switch in the inverter compartment next to the new inverter or do I have to find where that first switch is and work from that location?

The battery charger is a separate device that I need to buy or is it already in my system? The power comes from the first switch and then connects to the second switch before running to the battery bank?
 
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Where the switch is mounted will depend on how the inverter power will connect to the existing system. Generally this will become obvious once the wires are being connected.

All RVs have a battery charger. Some have a converter and many larger class A have an inverter/charger. I assume the inverter/charger you are removing was original equipment and once removed a replacement charger needs to be installed. Need to choose something compatible with the battery.
 
If you get the inverter I mentioned above, you can skip all the extras. The 4024 has two sets of AC connections, AC out for inverter generated power, and ACin for shore/grid power. You would just need to wire a connection port that either the RV park AC or the generator AC can be plugged into. If you use a single connection port that you plug into you can dispense with the transfer switch. Here are some pics of how you do that. If it's for a hard-wired permanent connection, then yes, you still need a transfer switch.
1634484244279.png
1634484313559.png
 
The RV shop busted my budget and my emergency funds will only cover a fraction of the cost of a Victron Inverter, so purchasing additional solar panels would be impossible no matter how cheaply I could get them. Since I already purchased the inverter Will recommended for the 24V battery, I figured I could panel up and just use power sparingly until I can stabilize my finances.

How much would a transfer switch and battery charger run me?
 
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