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Old 12-07-2022, 09:51 AM   #1
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12v Outlet

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.
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Old 12-07-2022, 10:16 AM   #2
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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.
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Old 12-07-2022, 10:20 AM   #3
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I'm following because I plan to add the 12v socket and a USB-A and USB-C at each helm.
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Old 12-07-2022, 10:34 AM   #4
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Fuse those leads ESPECIALLY if the are run directly to the battery. They should be fused for your safety in case of a short.
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Old 12-07-2022, 10:53 AM   #5
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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.
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Old 12-07-2022, 11:05 AM   #6
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Have you considered just hard wiring your inverter and not have the plug?
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Old 12-07-2022, 11:05 AM   #7
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Quote:
Originally Posted by psneeld View Post
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.
30 amp fuse and appropriate wiring is needed to properly handle a 350watt inverter. However, if itís 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.
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Old 12-07-2022, 11:42 AM   #8
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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.
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Old 12-07-2022, 12:31 PM   #9
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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.
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Old 12-07-2022, 01:40 PM   #10
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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.
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Old 12-07-2022, 01:53 PM   #11
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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-Charge...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.
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Old 12-07-2022, 02:11 PM   #12
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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.
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Old 12-07-2022, 02:22 PM   #13
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I didnít 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.
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Old 12-07-2022, 02:31 PM   #14
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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.
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Old 12-07-2022, 02:35 PM   #15
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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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Old 12-07-2022, 03:05 PM   #16
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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
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Old 12-07-2022, 03:06 PM   #17
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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.
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Old 12-07-2022, 04:10 PM   #18
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Quote:
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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
He was talking about 12 volts not 120. So at12 volts, 350 watts is 29.1 amps.
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Old 12-07-2022, 04:11 PM   #19
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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.
Also if the socket and plug are not rated for 30 amps.
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Old 12-07-2022, 07:34 PM   #20
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Look at a trolling motor socket and connector. They can handle the amperage and waterproof.

Tom
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