12v Outlet

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jclays

Senior Member
Joined
Jun 8, 2010
Messages
467
Location
USA
Vessel Name
Freebird
Vessel Make
1997 Mainship 350
Good morning
I will be installing a 12v cigarette lighter style outlet in the cockpit area of my Mainship 350. I will mostly use it to plug in a 350 watt portable inverter. I can run my laptop when on the hook and also run my Christmas lighting when underway.
Should I fuse the positive leg to the battery?
How should I calculate the fuse size?
Thanks
Jim.
 
20 amp is the highest rating I've seen on a 12V outlet and would be plenty for your needs. You need to size the circuit wire to the total circuit length and acceptable voltage drop. If possible, I would buy a charger that can be DC powered to avoid dragging out additional cords and clutter each time you want to use the laptop in the cockpit.
 
Fuse those leads ESPECIALLY if the are run directly to the battery. They should be fused for your safety in case of a short.
 
Doesn't a 350 watt inverter if maxed out draw more than 20A?

Granted you have to see what the laptop or lights or anything else planned draws... but the amps for the full 350W is around 28A or so.

If so the wiring and socket should be fused for 20 so the inverter only will be capable of around 250W.
 
psneeld said:
Doesn't a 350 watt inverter if maxed out draw more than 20A?

Granted you have to see what the laptop or lights or anything else planned draws... but the amps for the full 350W is around 28A or so.

If so the wiring and socket should be fused for 20 so the inverter only will be capable of around 250W.
Click to expand...

30 amp fuse and appropriate wiring is needed to properly handle a 350watt inverter. However, if it’s only being used for a laptop computer then you could get away with a lot less. Check the power needs of the computer.

There are 30amp fuses available if you need to go that big.
 
Thanks
I will look into the 30a fuses.
The run is 15ft of wire to the battery with all its bends included. I have lots of 8ga wire leftover and will use that.
 
30A thru a cigarette lighter style outlet doesn't sound right to me. The ones I've seen (Blue Sea for example) specify a max of 10-15A.

Maybe there are higher-amp versions (from a quality provider) but I'm not aware of any.
 
Based on personal experience I would not use a cigarette type plug for this application.

THey are NOT rated for more than about 10A.

Aside for it being too light duty for your intended potential use I found they would lose the pressure holding the central plug contact against the central receptacle contact resulting in glitches and small inverter goofups from lack of reliable power and my small inverter goofing up.

I just looked at my spare and the internal fuse is 10A.

I still use my dash mounted unit for the USB only function to drive my two tablets and when not running recharge my handheld VHF. But the current going through is only a couple of amps so it seems to work OK with that.

I tried the cig. type plug for my small freezer, Danfoss BD35 drawing about 4-5 amps. Constantly got low voltage shutdowns. I figured out that I actually had to stand there holding the two plug parts together. Same type of problem as above.

The freezer connection I changed to the plug/receptacle type for Scotty
Downrigger motors which are set up for about 30A/12V loads. THey are a sealed twist lock plug/receptacle from Marinco and/or Scotty Fishing gear in my area.
Scotty p/n 2125
Marinco p/n 12VCPS2

Since I made the freezer supply change 3 yrs ago no more problems.


Or use a trolling motor plug/receptacle kit [Marinco}which are three pins and rated for higher current.
 
I did that conversion last year, removed the cockpit cigarette lighter entirely and replaced it with something like this. Much more useful and sophisticated. Even if you wanted to keep the cig lighter to use as a map reading light socket (as I initially did), you can just use a USB-powered map light instead.

https://www.amazon.com/YonHan-Charger-Waterproof-Aluminum-Voltmeter/dp/B07L9QST54/

Even comes with an in-line fuse. And a cap in case the LED glow is distracting or messing up your night vision.
 
Slight hesitation on my part to say anything here as I have a MS 400 not a 350 and they are different boats. But on my boat it would be an easier wire run from the cockpit to the main DC panel than it would be to go directly to the battery. Assuming the voltage drop would not be too much (you need to measure from the battery to the panel to the outlet AND back) a breaker on the panel would be a much better solution than an in line fuse.



I also don't like adding any more wires than absolutely necessary directly to the battery. You probably have some sort of positive and negative buss bars down there that you could pull from.


Inverters draw a lot of power when the load on them spikes, even at 350 watts. They are bad about tripping breakers, in my humble experience anyway.


Just my .02 cents. C-Electric and others on this thread know WAY more about this than I do.
 
I didn’t check other manufacturers but Blue Seas only has 12 volt outlets up to 15 amp that I found on their website. I have never seen a 30 amp one. And you would also have to find a plug that would carry 30 amps. Why not install the small inverter next to the main power panel and just use an extension cord to run out to the cockpit? Much easier to do and then you can use a circuit breaker on the main panel to power it.
 
I have a 89 Jefferson 37 Sundeck and in my cockpit inside the helm panel which has switches for Radar, Depth Sounder, etc., there are positive and negative bus bars that power is led from.
I have a Stanley inverter that I plug into my 12v cig adapter which I use to power my laptop. My laptop has all my charts and use PolarNavy as my chartplotter. I have charts from New Jersey, Hudson River, Erie Canal, All the Great Lakes, both U.S and Canadian waters. It keeps the laptop powered up all day long. I have never had an issue with lines getting hot or pulling too much power.
At the end of the day, whether I am in a marina hooked up to shore power or on the hook and run the genny for a bit when first dropping the hook and in the AM for coffee, I make sure the laptop is charged from 110v.
Coming from the bus bar the wire is short.
The upper helm is powered by a breaker on my DC/110 electrical panel in the main salon.
 
Before everyone goes crazy with suggestion...a 15A cig socket may be all he needs,

The inverter will still function if he is only drawing 60 or so watts for a laptop or some LED lights. That's why I posted look up the "needs".

As long as it is all protected by the right size fuse for wire and socket.

Lots of us have plugged a 50A boat into a 30A outlet and managed out electric needs.

I will say I very much dislike and mistrust cigarette lighters on boats. I switched to these.
 

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10a fuse should be fine. 350 watts is only 2.92 amps correct? The inverter is maxing out at 350 watts divided by 120v = 2.92 amps
 
Don't use a 30 amp fuse if the wiring you are using (given the length of the run x 2, and current) can't handle 30 amps.
 
jclays said:
10a fuse should be fine. 350 watts is only 2.92 amps correct? The inverter is maxing out at 350 watts divided by 120v = 2.92 amps
Click to expand...

He was talking about 12 volts not 120. So at12 volts, 350 watts is 29.1 amps.
 
Look at a trolling motor socket and connector. They can handle the amperage and waterproof.

Tom
 

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Cigarette lighter sockets would be my last choice for devices needing amperage. What you want to use are Anderson Power Pole connectors.

https://www.andersonpower.com/us/en/resources/PowerPoleResourcesPage.html

They come in a number of different sizes, have silver plated copper contacts, and are self wiping when you put them together.

Figure out what connector size and wire size you want. Then Google them to find a number of different vendors that sell them. They're really not expensive, and are a far superior design. A light spray of the contacts with Corrosion X or similar product would be advisable.

Ted
 
Comodave said:
He was talking about 12 volts not 120. So at12 volts, 350 watts is 29.1 amps.
Click to expand...
The load on the inverter is 120v ac.
12v powers the inverter to convert 12v to 120 v. What do you fuse for? The Ac load or the Dc supply?
 
jclays said:
10a fuse should be fine. 350 watts is only 2.92 amps correct? The inverter is maxing out at 350 watts divided by 120v = 2.92 amps
Click to expand...



NO, the inverter is using 12VDC to run itself and then produce 120V AC. What you have calculated is the output amps at 120VAC, NOT the input at 12VDC

That means the inverter will draw 350 W / 12V= 29.2A at 12 Volts. Actually to run itself at full tilt it will need about 10% -15% more power so in fact it will pull about 33.54 A DC.

Be very carefull about understanding how you do the conversions or you will have trouble.

I agree with OC Diver about the Anderson plugs but also the suggestion of using a trolling motor plug/receptacle at about 40A. ampacity. I am another that didn't think of these untill I started poking about the Marinco site.
 
The inverter is itself fused with a 40 amp fuse. Do I need to fuse the positive wire (12v) from the battery?

CORRECTION… inverter is a 300 Watt inverter.
 
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I would definitely do that. If you leave the battery wire to the inverter unprotected then any chafe or damage could result in a short circuit.
In fact the battery is the far more dangerous power supply.
 
jclays said:
The inverter is itself fused with a 40 amp fuse. Do I need to fuse the positive wire (12v) from the battery?

CORRECTION… inverter is a 300 Watt inverter.
Click to expand...

Absolutely. What C Lecteic said. Most boat electrical fires are DC related.
 
jclays said:
The inverter is itself fused with a 40 amp fuse. Do I need to fuse the positive wire (12v) from the battery?

CORRECTION… inverter is a 300 Watt inverter.
Click to expand...
Absolutely. Fuses should be placed close to the source to protect wiring. Fusevat equip protects the equipment but can allow a short in supply wiring that's can cause a fire. Best to review & try to follow ABYC wiring reqmts for DIY projects.... generally much safer and frequently an insignificant cost premium.
 
If a high amp 12v pull maybe convert to anderson connectors for a good dedicated power source?
 
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