Blade fuse size for 12v sockets

[CamperJack]

My parents want to install a 12v "cigarette lighter type" socket into their MH. This will be to power their 12V TV.

On the power brick (pictured) it says it is 60W.

So to work out the amps I've done 60W / 12V = 5A
plus 25% = 5A X 1.25 = 6.25A so I could use a 7.5A fuse, assuming they will only plug in the TV. However I know they will end up unplugging the TV and using the socket for other things.

The socket is rated up to 20 amps. So if they put something into socket that is higher rated than my 60W TV I'll be blowing the 7.5A fuse intended for the TV.

So what size fuse would you use / do you use for your 12V sockets?

 

[Phill D]

as the tv lead has its own fuse in the socket plug, unscrew the end... so no worries there.. i would say max of 20 Amps as its the rating of the socket.

 

[CamperJack]

Cheers Phil,

I'm thinking of using a 15 amp fuse and 4mm2 wire which is rated at 41 amp.

I'm connecting the wires direct to the battery terminals with an inline blade fuse holder. (They have no 12v sockets or fuse panel in place already and only want one socket.)

I think this should be okay?

 

[CamperJack]

I assume it's okay to connect the 4mm2 wires directly to the terminals of the battery via this type of terminal extension and the appropriate size lugs and use an inline fuse?

I my van everything is conected via a 12v fuse panel / bus bar. I assume this inline thing does exactly the same thing.

 

[Lenny HB]

I'm thinking of using a 15 amp fuse and 4mm2 wire which is rated at 41 amp.

Size of cable depends on the cable length you want to aim for a volt drop of 3% or less.
If you want to be able to use it up to 15 amps for a 2.5m cable length 4mm sq is fine for 5m you need 8 mm sq. When buying cable if you buy thin wall auto cable it's not what is says as the size includes the insulation.

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[Lenny HB]

I assume it's okay to connect the 4mm2 wires directly to the terminals of the battery via this type of terminal extension and the appropriate size lugs and use an inline fuse?

I my van everything is conected via a 12v fuse panel / bus bar. I assume this inline thing does exactly the same thing.


View attachment 405064

Those are OK but for just one extra connection you could just use a ring terminal on the battery clamp bolt.

 

[CamperJack]

Thanks Lenny. The length of cable is about 1.5M so 4mm2 should be okay.

 

[Gellyneck]

As Phill D says there will be a cartridge fuse in the plug on the power block in your picture. It'll possibly be a 7A as that's what the input on the block says so it'll blow before any higher rated inline fuse you fit.

 

[Minxy]

Those are OK but for just one extra connection you could just use a ring terminal on the battery clamp bolt.

Exactly what I did when I installed an awning light and a socket.

 

[IRHP]

Fuses are there to protect the wiring. your fuse should blow before the wiring melts. Both need to be capable of supplying enough current to whatever you have plugged in. With items rated at 120 watts I've seen plugs and sockets get very hot.

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[Lenny HB]

Fuses are there to protect the wiring. your fuse should blow before the wiring melts. Both need to be capable of supplying enough current to whatever you have plugged in. With items rated at 120 watts I've seen plugs and sockets get very hot.

If drawing much more than a couple of amps better to use Hella plugs and sockets.

 

[Gromett]

I assume it's okay to connect the 4mm2 wires directly to the terminals of the battery via this type of terminal extension and the appropriate size lugs and use an inline fuse?

I my van everything is conected via a 12v fuse panel / bus bar. I assume this inline thing does exactly the same thing.


View attachment 405064

The only thing I will add to this thread is, if those cables coming from the terminal are not fused next to the battery then you are asking for trouble.

The fuse should be as close to the battery on the wires as possible.

In most systems you have a mega fuse next to the battery with a larger cable then going to the distribution board containing the per wire fusing.

 

[Phill D]

a bit like this