Hard wiring 12v socket via dash switch

[hembramacho]

Right, now it's the Easter hols (and snowing! ) it's time for another job on the bongo. This time it's attempting to hard wire a 12v (cigarette lighter type) socket to the LB.
My plan is to use cable to wire from the LB going via an in-line fuse to a switch in the dash before finally ending with a 12v socket behind the dash in the form of a cut off 12v extension cable (female end) This will then connect to a 4 way 12v extension to give me hopefully 4 sockets behind the glove compartment powered directly from the LB which can be switched on and off via the dash switch whenever.

Right, questions:

What amp cable do I need to go from the LB to the dash switch and what amp in-line fuse do I need (do I need one - I would think yes to be safer?)

Can I just take 2 wires from the LB, one from the + and one from the -, or would it be better to earth the - instead?

From the dash switch would it be OK to use the original wiring from the 12v extension cable, as there are 2 wires (red and black) and they seem really thick - is there any way to test what ampage they are? The original extension (before I cut the male end off) has a 3amp fuse in if that helps!

Is there an easier way, or am I biting off more than I can chew???

Cheers

Andrew

[Colin H F]

I dont see the nessessity fo a 12v socket behind the dash just go straight from the switch via the fuse (depending on what amps your going to draw) to your sockets. if you have any red 1.5mm / blue 2.5mm or yellow 6mm lugs you can try on the cable this will determine the size of the cable. the earth and the negative - should be the same potential , hope this is of help. Colin

[mikeonb4c]

I bought a 3 x ciggie socket from Halfords that had a self adhesive pad on it, and stuck it on the rear face of the centre console. Unusually, this self adhesive pad has stayed well stuck on and having 3 sockets in that position looks neat and is very useful (kids in back can plug in stuff and so can front seat occupants. I wired it from the LB using +ve and -ve (might as well use twincore as its eaiser than worrying about finding a tidy and effective vehicle earth) and put a (from memory) 10 amp fuse inline as thats what the socket unit was rated at (wiring was probably more like 15 amp rating. I've since rewired it a bit so when switched on, it also feeds a little dash mounted LCD voltmeter that tells me (unreliably!) what the LB voltage is. Haven't got a pic of the sockets as mounted but switch (out of focus) and LCD meter are below:

[hembramacho]

I dont see the nessessity fo a 12v socket behind the dash just go straight from the switch via the fuse (depending on what amps your going to draw) to your sockets.

Thanks Colin. The idea to have a single socket after the switch feeding to the 4 way is so that I can remove the 4 way if required somewhere else which I wouldn't be able to do if it was permanantly wired to the switch. Plus I've already got a single socket with the wires cut! I was also intending to have the in-line fuse between the LB and the switch and not between the switch and socket - is this wrong then?
The original wire seems to be 2.5mm.

I wired it from the LB using +ve and -ve (might as well use twincore as its eaiser than worrying about finding a tidy and effective vehicle earth) and put a (from memory) 10 amp fuse inline as thats what the socket unit was rated at (wiring was probably more like 15 amp rating.

Thanks Mike. I was actually thinking of a 5amp in-line as I'm sure that's what's been used by other people rewiring the rear socket (I think!). So would I go for 5 amp in-line and 10 amp cable, or 10 amp in-line and 15amp wiring? What would the benefits (if any) of a higher/lower rating? I'm going to be running a DVD player, Ipod charger, TomTom charger and DS lite charger from the 4 way if that's any help.

Cheers again

Andrew

[dave_aber]

The wire size and fuse size should be decided based on whatever you are plugging on, and the maximum current rating of the 'weakest link'. So, if you have a rating of 10A on the 4-way, then this is the maximum the whole circuit can draw safely.

So, 10A at the socket, I would use 15A cable to ensure that it doesn't overheat, and a 10A fuse to protect the circuit. The fuse should be positioned as close as is practical to the power source, so that there is a minimum of unprotected cable. This is assuming that the switch can carry 10A safely. I wouldn't try to use anything that will draw 10A as that is the maximum for the 4-way (and the fuse rating!). Stick to about 8A or below (96W). Bear in mind that the current limit applies to all the devices added up, so a couple of amps each.

[mikeonb4c]

The wire size and fuse size should be decided based on whatever you are plugging on, and the maximum current rating of the 'weakest link'. So, if you have a rating of 10A on the 4-way, then this is the maximum the whole circuit can draw safely.

So, 10A at the socket, I would use 15A cable to ensure that it doesn't overheat, and a 10A fuse to protect the circuit. The fuse should be positioned as close as is practical to the power source, so that there is a minimum of unprotected cable. This is assuming that the switch can carry 10A safely. I wouldn't try to use anything that will draw 10A as that is the maximum for the 4-way (and the fuse rating!). Stick to about 8A or below (96W). Bear in mind that the current limit applies to all the devices added up, so a couple of amps each.

Thats exactly right I reckon and very well explained - saved me a lot of typing

PS - the determining factor in my case was that the 3 x socket thing from Halfords made it clear its max rating was 10 amps - I worked it out backwards from there.

[hembramacho]

Thanks for the replies guys. Looks like 15amp cable with 10amp in-line fuse it is,

the determining factor in my case was that the 3 x socket thing from Halfords made it clear its max rating was 10 amps - I worked it out backwards from there.

although there is nothing on my 4 way socket to suggest it's max rating. Is there any way to test this? Will they all be a standard 10 amp, as there are some in Halfords now with a max of 8amp. Is it worth getting a new 4 way that I know what the max amp rating is to be sure? But if I get an 8amp max socket for example, do I need to get a lower amped(!) cable and fuse?

Sorry for all the questions.

Andrew

[dave_aber]

The size of the cable should be the max current you could possibly draw, with nothing faulty, plus a safety margin. So, if the 4-way is rated for 8 or 10 amps, then you need to use that as the limiting factor - so the cable needs to be rated for 8 or 10 amp plus a reasonable margin. For 8 amp load, I'd be looking for above 10 amp cable, for 10 amp load, I'd be using 15 amp cable. There's no electrical reason not to use 50 amp cable if you have it. However, the higher the current rating, the bigger the cable is. Bigger, heavier, and eventually too big to get connectors for that will fit the socket / switch you are wiring in.

The fuse is there to protect the circuit. So, if there is a fault, like a short-circuit, the fuse should blow. The fuse should be of a lower rating than the cable. That way, it will blow before the cable is subjected to its maximum current. There is of course a safety margin built into the cable ratings by the manufacturer - 10 amp cable doesn't burst into flames at 10.1 amps - but it's better to assume that it will, and design the protection to prevent the current reaching the maximum.

As for the rating of the 4-way adaptor, if it isn't stated on it then the only way to test it is to overload it and see what happens at a given current. Not something you should be trying at home! I'd be happier buying one with the limit stated on it.

[hembramacho]

The size of the cable should be the max current you could possibly draw, with nothing faulty, plus a safety margin. So, if the 4-way is rated for 8 or 10 amps, then you need to use that as the limiting factor - so the cable needs to be rated for 8 or 10 amp plus a reasonable margin. For 8 amp load, I'd be looking for above 10 amp cable, for 10 amp load, I'd be using 15 amp cable. There's no electrical reason not to use 50 amp cable if you have it. However, the higher the current rating, the bigger the cable is. Bigger, heavier, and eventually too big to get connectors for that will fit the socket / switch you are wiring in.

The fuse is there to protect the circuit. So, if there is a fault, like a short-circuit, the fuse should blow. The fuse should be of a lower rating than the cable. That way, it will blow before the cable is subjected to its maximum current. There is of course a safety margin built into the cable ratings by the manufacturer - 10 amp cable doesn't burst into flames at 10.1 amps - but it's better to assume that it will, and design the protection to prevent the current reaching the maximum.

As for the rating of the 4-way adaptor, if it isn't stated on it then the only way to test it is to overload it and see what happens at a given current. Not something you should be trying at home! I'd be happier buying one with the limit stated on it.

Thanks very much for that info - very helpful.
I think I'm going to go for 17amp cable with a 10amp fuse (as close to the LB as possible) and get one of these to be on the safe side as it has a 10amp max rating, or so it says on one of the reviews.

http://www.halfords.com/webapp/wcs/stor ... 65489#dtab

Will report back.

Cheers again

Andrew

[mikexgough]

did you manage to get this done?..... CBE and Roadpro do some more uprated sockets....just so you know...I have CBE ones...one is hardwired and fused to the LB...

[hembramacho]

did you manage to get this done?..... CBE and Roadpro do some more uprated sockets....just so you know...I have CBE ones...one is hardwired and fused to the LB...

Thanks for that info Mike. Haven't managed to get it done yet as waiting for a switch to be delivered and been doing family 'non-bongo' stuff all weekend. Hopefully get round to it this week at some point - will no doubt post questions along the way if I get stuck. .

Cheers

Andrew