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JimMcGee 08-02-2010 10:19 AM

Wiring Question
Iím going to install a 12v TV/DVD and rewire my stereo this week on my 95 Catalina 30; wiring both to a circuit direct to the battery so I donít have to rescan stations every time I get on the boat (boat is kept in a marina other than occasional overnights at anchor).

The stereo (Sony car stereo) is pre-wired with a fused line to run to the battery directly (P.O. didn't connect when he installed the stereo). I looked at the specs on the 110v adapter for the TV. Its output is 12vdc/5amps. So the plan is to add a 12vdc plug for the TV in an outlet box on the forward bulkhead, with a 5amp breaker in the box so the outlet will be switched. Then run a line from the outlet box to the battery with a Anchor 5amp slow blow inline fuse where it connects to the battery post.

Why create a switched 12v outlet rather hardwire it? I want the option of switching it off if Iím trying to conserve power or troubleshoot a problem; and the outlet gives me a place to plug in the extension cord for a spotlight at night.

My question is am I missing anything from a safety perspective? I want to breaker to trip before blowing the fuse. Is there any reason NOT to use a slow blow marine fuse in this application?


mitiempo 08-02-2010 11:06 AM

I don`t think you are missing anything from a safety perspective. But I would wire the stereo to a breaker (or fuse if that is what you have) and only run the memory wire to the battery direct. This will eliminate the risk of draining the batteries.
As for the tv, some are very voltage sensitive. 12 volts is what it requires but wiring around the power supply will give it as much as 14+ volts. Some tvs will tolerate this and some won`t. I also would not wire the tv direct to the battery. It should remember the channels whether powered or not.

JimMcGee 08-02-2010 12:27 PM

A couple of clarifications. only the memory wire for the stereo will run to the battery. The power for the stereo is wired to the accessory circuit.

The TV can run on 12v or 110v depending on which cord/adapter you use. I'm planning on wiring it into the 12v system. My old TV (110v only) lost its channel memory when unplugged. I'm assuming this one will as well.


mitiempo 08-02-2010 01:09 PM

That makes sense for the stereo. But the constant 12 volts the adaptor for the tv outputs is what the tv is designed for. The "12 volts" on a boat is anywhere from 12 to 14.4 volts in reality. Some tvs don't mind, some are very voltage sensitive. A dc to dc adaptor would be a good idea. It would keep it within the tv specs and there would be no possible issues.

JimMcGee 08-02-2010 05:18 PM

Hmm, now you've got me thinking.

Since the TV is designed as a 12v model that can run off a cigarette adapter I assumed its internal power supply would allow it to run on a range of voltages (say 11 to 14 volts) the way a laptop's will.

The TV is sold for trucks, RVs and boats.

mitiempo 08-02-2010 07:07 PM

In that case it should be ok. The tvs that I have had problems with were the household types with a separate power supply between the wall plug and the tv. Several manufacturers cautioned about plugging this type into a 12 volt battery system. Sharp and Sony specifically. I used to sell and install audio/video equipment.

JimMcGee 08-03-2010 06:23 AM

Thanks, my biggest concern is safety, and it sounds like I'm OK with this approach.


btrayfors 08-03-2010 08:32 AM


You said you want the (5A) breaker to blow before the (5A) fuse. It won't. Breakers will tolerate significantly higher amperage than their rating for awhile before blowing.

Another question: how much does the spotlight draw? Maybe more than 5A!

Options include, inter alia, putting a larger fuse or breaker near the battery on the line to feed the outlet, and putting just a switch at the outlet. Then, you'd want a fuse sized for the DVD/TV in the line or cigarette lighter plug to the TV.

I think I'd use a 15A fuse or breaker near the battery, use AWG12/2 marine wire to the outlet, and install a healthy-sized toggle switch at the outlet if you want to switch it. Then, just run the "constant on" wire to the hot side of the switch, not all the way back to the battery, with an appropriate (small) in-line safety fuse.



mitiempo 08-03-2010 10:38 AM

The fuse near the battery should be larger than 5 amps. This will solve the problem of the fuse going before the breaker. As well, you don't install a fuse in that location to protect the tv, but to protect the wire itself.

JimMcGee 08-05-2010 04:50 PM

I've modified my installation a bit based on feedback I received here and elsewhere.

I'll be staying with a 5 amp circuit, but changing from a slow blow to a standard inline Anchor fuse for exactly the reason that Bill mentioned -- the breaker will be slower to trip and I want to protect the TV.

I'll keep the breaker at the 12v outlet so I can turn off power to the outlet for troubleshooting or if I need to conserve power.

When I get to the boat this weekend I'm going to check my breaker panel and determine if Catalina installed a hot bus (always hot regardless of battery switch position). If not I'll add one as this will be a cleaner installation than tying multiple lines to a battery terminal.

I should be OK with the current draw from the spotlight. It's a standard West Marine light with a 12v plug that was previously used on a 5 amp circuit.

Thanks guys,

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