Hard wiring an inverter

[YVRguy]

I purchased a 500watt inverter for the boat a couple of years ago. I use it by plugging it into the cigarette lighter outlet next to my breaker panel. The problem with that is the outlet is only rated for about 100 watts. According to the manual, for full performance you should use the supplied alligator clamps and cables to attach the inverter directly to the battery. I very much want the full 500 watt performance of the inverter but the batteries are accessed via the cockpit and the cables are only a few feet long. What is the best way to connect the inverter "in-line" such that it is conveniently located and is able to offer its full rated performance? Do I need to get an electrician to hard wire it inside the breaker panel?

 

[Hayden Watson]

I did the same a couple of years ago.
The reason for the hard-wire install was because when sailing with my 3-yr old granddaughter, she got fascinated by the pretty red and black knobs on the back. They were sized just right for curious little fingers, and she managed to get the red one off and found a shiny silver ring terminal. It just seemed like the right thing to do to move that ring over to the black to see if it would fit.
At the time, I was in the middle of enjoying some "quality time" in the head compartment when I hear a lightning bolt, screams all around and the yell "FIRE!" Needless to say, everyone saw more than they should have as I bolted out of the head. Did I mention that the alligator clips were connected directly to a Lifeline 4D?
What I found was a crying granddaughter, a screaming wife and a cabin full of smoke, and the smoldering charred remains of two wires disappearing under sittee cushion. The ring terminal had welded itself to the post and then both wires went white hot and vaporized. Fortunately, nobody got burned and nothing was actually on fire although the cabin was full of smoke and the sittee cushion now had a fashionable 1" deep black groove burned into the face.

It is now properly installed with nuts and lock washers and 8-AWG wire which is protected with a 40A fuse. I mounted the unit to the underside of my chart table using nylon standoff sleeves and fender washers that fit into the outermost cooling fins at four locations which held it quite well. It is standalone and does not have any AC connection to the boat which eliminates all of the grounding issues. The only output is the two built-in plugs on the face.

 

[dlochner]

First check the specs. Many inverters have a continuous draw and surge draw. Your 500 watt inverter will draw over 40 amps at 12 v, perhaps closer to 50 amps factoring in the inefficiency of the inverter.

It could be wired into the main DC panel if there is room for a new breaker and if the panel can handle the draw. Some panels have a 50 amp main breaker which could handle the max current draw of the inverter, but nothing else could be turned on.

Alternatively, it could be connected closer to the battery and appropriately fused.

If you are uncertain about all this, then hiring a qualified marine electrician would be a good idea.

 

[YVRguy]

First check the specs. Many inverters have a continuous draw and surge draw. Your 500 watt inverter will draw over 40 amps at 12 v, perhaps closer to 50 amps factoring in the inefficiency of the inverter.

It could be wired into the main DC panel if there is room for a new breaker and if the panel can handle the draw. Some panels have a 50 amp main breaker which could handle the max current draw of the inverter, but nothing else could be turned on.

Alternatively, it could be connected closer to the battery and appropriately fused.

If you are uncertain about all this, then hiring a qualified marine electrician would be a good idea.

Yep, I think putting this on the list for our boat tech is exactly the right move.

 

[Stu Jackson]

Yep, I think putting this on the list for our boat tech is exactly the right move.

Doug, I just read some of your delightful blog. Given your exploits and cruising areas, it would behoove you to not only hard wire that inverter, but learn all about it (and/or do it yourself), because when you're "out there" there just aren't any " 'lectricians." I'm surprised you don't do this stuff in your sleep by now, given your experience(s).

 

[higgs]

How about finding a cigarette lighter rated at 500 watts and do a search on wire size for that draw and rewire it all into the panel? I'm not sure if the breaker cares about the wattage or not. Hopefully someone here knows the answer to that.

 

[jviss]

How about finding a cigarette lighter rated at 500 watts

Because there is no such thing. Cigarette lighter sockets are usually rated at 10 to 20 Amps, i.e., around 240 Watts max. A 500W outlet would have to carry over 40A, which that system is not designed to do.

 

[Hayden Watson]

How about finding a cigarette lighter rated at 500 watts and do a search on wire size for that draw and rewire it all into the panel? I'm not sure if the breaker cares about the wattage or not. Hopefully someone here knows the answer to that.

500W is about 40A and you need to add another 15% for inefficacy. I have never seen a cigarette plug that is rated for more than 15A.

 

[jviss]

I think you would be looking at a 50A breaker, like the Blue Sea Systems 285-Series, and wiring it to the inverter with wire that can carry 50A, from your main DC distribution point, i.e., downstream of your main breaker.

 

[justsomeguy]

inefficacy

Yah, there is such a word...

 

[Captain Larry-DH]

I think you would be looking at a 50A breaker, like the Blue Sea Systems 285-Series, and wiring it to the inverter with wire that can carry 50A, from your main DC distribution point, i.e., downstream of your main breaker.

The breaker should be sized to protect the smallest wire, not the highest load. Keep that in mind when designing a system. Use appropriate wire sizes for the breaker and the minimal voltage drop. (There are tables published online for wire size and voltage drop. It’s a function of Volts, Amps load, and round trip distance).

 

[jviss]

The breaker should be sized to protect the smallest wire, not the highest load. Keep that in mind when designing a system. Use appropriate wire sizes for the breaker and the minimal voltage drop. (There are tables published online for wire size and voltage drop. It’s a function of Volts, Amps load, and round trip distance).

That's what I meant when I said "wire that can carry 50A." The independent variable is the current requirement for the load; the system upstream has to be designed to handle that, meaning the wire, and the breaker sized to protect the wire. I think we agree. That said, but not in this case, there are many cases where the breaker is sized to protect the distribution circuit, and there's a fuse downstream to protect the smallest wire or the load, as is typically the case with VHF radios.