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Old 15-01-2021, 06:22   #1
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Adding Inverter to Boat Electrical system

So......right now my question is this:

How the heck do ya'll wire in an inverter so that the outlets you use when plugged into shore power work when you are not on shore power?

The idea is when I leave the dock and unplug the shore power line I will have an inverter and be able to use the outlets in the boat off of the batteries.

So...I can't figure out how to wire it. Every way I see to wire in the inverter ends up looping the charger back to the batteries. Seems silly to charge the batteries while using the batteries.
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Old 15-01-2021, 06:39   #2
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Re: Adding Inverter to Boat Electrical system

I'm going to be doing an install on my boat this weekend. Plan for me is as follows:

Boat has 2 inlets, which we'll call leg 1 and 2. Leg 2 will be untouched by this project.

For leg 1, the panel is laid out with breakers in 2 rows. I'm going to remove the connection between them to effectively form a sub-panel. The leg 1 input breaker will feed the top row of breakers as well as the inverter/charger input. That leaves the top row as shore/gen only. The bottom row contains all of the outlets, etc. that I want the inverter to power. So the inverter output will feed that row.

The inverter I'm using has a built in transfer switch, so the inverter sub-panel will be powered on shore/gen when available and from the inverter the rest of the time. Things like the charger for the starting batteries, water heater, etc. are either on the leg 1 shore only panel or the leg 2 panel in my setup so the inverter won't affect them at all.
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Old 15-01-2021, 08:07   #3
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Re: Adding Inverter to Boat Electrical system

Quote:
Originally Posted by LostDog88 View Post
So......right now my question is this:

How the heck do ya'll wire in an inverter so that the outlets you use when plugged into shore power work when you are not on shore power?

The idea is when I leave the dock and unplug the shore power line I will have an inverter and be able to use the outlets in the boat off of the batteries.

So...I can't figure out how to wire it. Every way I see to wire in the inverter ends up looping the charger back to the batteries. Seems silly to charge the batteries while using the batteries.
If you are installing an Inverter Charger, you must have a transfer switch to prevent battery charging while under inverter power. Inverter Chargers will include a built in transfer switch that ends battery charging without shore/axillary power.

If you are installing an Inverter only, you will need to dedicate the circuits for the Inverter to power full time.

Loop charging from the batteries to an Inverter and back to the batteries will result in dead batteries.

What is the make and model number of your Inverter?
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Old 15-01-2021, 08:09   #4
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Re: Adding Inverter to Boat Electrical system

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Originally Posted by Henry J Fate View Post
If you are installing an Inverter Charger, you must have a transfer switch to prevent battery charging while under inverter power. Inverter Chargers will include a built in transfer switch that ends battery charging without shore/axillary power.

If you are installing an Inverter only, you will need to dedicate the circuits for the Inverter to power full time.

Loop charging from the batteries to an Inverter and back to the batteries will result in dead batteries.

What is the make and model number of your Inverter?
Exactly. Dead batts at sea is bad. Every time. I want to be able to flip back and forth from inverter to shore power. When there is shore power. Outlets work. When there is no shore power, outlets work off batteries. I am thinking I need some sort of transfer switch?
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Old 15-01-2021, 08:11   #5
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Re: Adding Inverter to Boat Electrical system

What inverter are you planning to install? Do you already have it, or are you still choosing an inverter?
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Old 15-01-2021, 08:12   #6
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Re: Adding Inverter to Boat Electrical system

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What inverter are you planning to install? Do you already have it, or are you still choosing an inverter?
Still choosing one. Probably gonna be something like 2000 to 2500 watts. We just wanna run a couple CPAPs, ice maker, tv, and maybe a laptop.

The solar charger system I have already designed and will install after I get the inverter/Shore power thing worked out.

Must be pure sine as we will have a few inductive loads that won't like the modified sine wave.
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Old 15-01-2021, 08:15   #7
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Re: Adding Inverter to Boat Electrical system

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Originally Posted by LostDog88 View Post
Still choosing one. Probably gonna be something like 2000 to 2500 watts. We just wanna run a couple CPAPs, ice maker, tv, and maybe a laptop.

The solar charger system I have already designed and will install after I get the inverter/Shore power thing worked out.

Must be pure sine as we will have a few inductive loads that won't like the modified sine wave.

In that case, choose an inverter with a built in transfer switch. Personally, I'm putting in a Victron Multiplus 12/2000/80. It's got a charger built in as well as a 50A transfer switch, so it can pass through plenty of power when on shore power or generator. They've got other models of various sizes and some also have a second AC output that's only powered when input power is available. Depending on your panel layout, something like that might make things simpler.
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Old 15-01-2021, 08:18   #8
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Re: Adding Inverter to Boat Electrical system

Yes, you will need a transfer switch. You can make your own with a DPDT relay, with the coil energized by the shore power. As mentioned above, you will need to organize your AC breakers into 2 buses, and put the battery charger, water heater, and air conditioner on the bus which is only driven by shore power.
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Old 15-01-2021, 08:24   #9
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Re: Adding Inverter to Boat Electrical system

A 2500 watt inverter will cost more than a 600 watt inverter, require much more expensive wiring, and have 4 times the parasitic draw. The only advantage of the 2500 watt inverter is if you want to run a microwave.
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Old 15-01-2021, 08:31   #10
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Re: Adding Inverter to Boat Electrical system

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A 2500 watt inverter will cost more than a 600 watt inverter, require much more expensive wiring, and have 4 times the parasitic draw. The only advantage of the 2500 watt inverter is if you want to run a microwave.

The parasitic draw thing is the big reason I went for the 2000 rather than the 3000. The parasitic draw is half as much, and the only thing I'd lose is the ability to run the microwave on the inverter (which isn't all that important to me). The important thing is that it can run the coffee maker and toaster to avoid me needing the generator in the morning when on the hook. Well, I could run the very low power microwave that's currently on the boat, but I'm planning to upgrade that, so I won't bother putting the microwave circuit on the inverter.
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Old 15-01-2021, 10:55   #11
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Re: Adding Inverter to Boat Electrical system

I use an inverter with built-in transfer switch.

https://www.westmarine.com/buy/kisae...37?recordNum=6

Pure sine keepes the microwave happier than the previous modified sine inverter.
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Old 15-01-2021, 11:34   #12
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Re: Adding Inverter to Boat Electrical system

Quote:
Originally Posted by LostDog88 View Post
Still choosing one. Probably gonna be something like 2000 to 2500 watts. We just wanna run a couple CPAPs, ice maker, tv, and maybe a laptop.

The solar charger system I have already designed and will install after I get the inverter/Shore power thing worked out.

Must be pure sine as we will have a few inductive loads that won't like the modified sine wave.
I have all of that other than that the icemaker is a freezer in our reefer-freezer box. As well I have a Linksys router for the times I want to distribute the incoming WiFi aloft (also 12VDC in both cases)

I don't use a laptop because I don't like it, but I'd bet there was a similar solution to my built-in, mini-itx computer - which power supply comes with a typical 19.2VDC wall wart but which also runs on 12VDC - and Mag Monitor (12VDC, ditto), with usb-dongle wireless keyboard and mouse, for your laptop. ( Pictures: Flying Pig 2011-2012 Refit/Computer Rebuild )

Everything other than a soldering gun or shop vac, or for the tiny number of times we might be at a dock, the space heater-blower, is 12V. Even the 4 external HDD I have for storage and backup purposes.

My BiPap pulls about a half-amp. My computer and monitor pull about 2 amps. We use the monitor for our TV equivalent; there are TVs which can be monitors. The reefer-freezer will vary by what load we're asking, of course.

But every bit of it is boat house power. I did take the caution of doing a 12-12 buck boost to assure continuous (vs varying due to charge or discharge) power for the HDD, controlled by a switch, as those don't run unless needed specifically, such as during a backup or playing a movie or the like (actually, I transfer the needed files to my computer HDD, so it's a brief time the HDD runs; ditto music).

And none of it has the overhead of standby, nor the cost in lack of 100% effective transfer to AC, all of which in our cases (and from what I can see, likely yours as well), need to be transferred back to some DC voltage. A travel adapter would accomplish all of the tasks you've listed if they can't utilize house power...

That said, I have a Xantrex XC2000 (2000Watt inverter, charger max 80A), for the times I need higher power and an inverter (as above).

YMMV but I'd look at that rather than obsessing over your challenges shown, if that's the only items you have which use AC...

As to connecting it all:

AC shorepower to the Xantrex, with pass-through automatic for times on shore power. We have that controlled to the boat outlets via a breaker; the light to the breaker is lit when AC is present, which is the case if we are using our Honda genset for on-the-water charging.

House bank to the Xantrex 12VDC input which is controlled by a switch; we also use a remote for convenience as our I/C is in the engine room; when energized, that enables the inverter circuit. That same input becomes the charge source when AC is present inbound, and the I/C does the conversion.

We also have, powered through our main panel, a separate shore power charger left from the time when we had a simple inverter; that breaker can be energized to make that charger work, but otherwise it's just there, waiting for the breaker to be flipped. So, when our first I/C got wonky, we'd switch over to the shorepower inverter (both when running the Honda genset) to finish it off. That's more complex than your installation but illustrates how you can manipulate your system.

So, at least as I understand your setup:

Shore power to charger to Battery; battery gets charged. Maybe you have an AC switch already, allowing you to use shore power throughout the boat.

Inverter from Battery to house AC power, preferably though a breaker. If you have an inverter-charger, it would work like ours without the separate shore power charger. It's not complicated so long as you have a breaker to control each link...
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Old 15-01-2021, 11:39   #13
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Re: Adding Inverter to Boat Electrical system

You will need a transfer switch that will open all wires (green, white, and black) at the same time. The inverter will most likely have green and white bonded together. When you are on shore power, green and white can not be bonded together. An example of this is the selector switch that will select if your power on the AC side is coming from shore/generator/inverter. Black can not only be the switchable wire.

Generator and inverter have the green and whites bonded together. If you are going through the inverter with shore power, the inverter should open this bond between green and white but remain closed without shore power.
I have my battery charger on a seperate breaker that is shut off while on inverter.
Transfer switches will most likely have connectors for all three wires of each source (white,green, and black). Please don't get these mixed up.
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Old 15-01-2021, 11:48   #14
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Re: Adding Inverter to Boat Electrical system

2 suggestions
Much of the time all the mains power is doing is charging a cell phone or a few batteries. Running a big inverter for this wastes a lot of battery power. Look at what you use A/C for and if you will spend significant time just running some small chargers on the chart table thing about a small (400w) one at the chart table and a remote switch so you only use the big one when you need it.
Many people do use an automatic or manual changeover switch with the main charger wired in on the shore power side, orks fine. Another way of doing it is to just wire the charger to shore power and always run A/C from the Inverter/batteries. This creates total isolation for the boat from shore power (same as an issolation transformer) so no worries about unstable voltages, power spikes, earth faults etc. Quite a few marinas have dubious A/C supply. If you travel internationally it also means you do not have to worry about 110/240v 50/60hz issues.
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Old 15-01-2021, 12:00   #15
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Re: Adding Inverter to Boat Electrical system

A simple KISS solution that is worth considering is to install seperate AC outlets for shore power and inverter use.

This saves the complication of a transfer switch and has some advantages in dealing with different voltage and frequencies of shore power supply. The AC wiring is only thin and the additional outlets are inexpensive and the system provides some redundancy as well as simplicity.

As has been noted, the efficiency and parasitic draw of the inverter is important if you are on an energy budget. This varies significantly with different models. Some large inverters have lower (or at least similar) parasitic draw to smaller models, so do not assume that a smaller inverter is always necessary.
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