Wiring multiple 12v sockets and inverter into W124

[Cleggmeister]

Hi again!

I use quite a lot of devices in my car and I'd love a wee project to wire in some more 12v sockets and an inverter (all of which I have purchased).

The issue is me, I have no experience working on car wiring.

Please could you suggest where I might locate a feed for my 12v sockets, preferably near the centre console or passenger footwell, and where I can get a feed for the inverter, preferably under one of the front seats?

The car is a base-spec 200E from 1990. No electric seats, windows, etc - absolutely base spec.

Many thanks in advance!

Cleggy.

 

[Ted]

Back of the fag lighter should be ok for the 12v sockets. Switched live, earth and illumination will all be available.

 

[Cleggmeister]

Finally getting round to this, going to mount the multi-block thing in the glovebox and wire it back to the cigarette lighter as recommended. I need to make an educated guess re the adaptor - it has a black wire and a black/white wire. Which would be positive??! It's not possible to see where it's wired to... Oh, and I guess that positive is the "centre" pin and negative is the "outer" on a car lighter?

 

[DSM10000]

Have you worked out the total load you will be drawing? The supply cable for the lighter soocket may not be up to supplying that amount of current.

 

[BlackC55]

I would take a direct feed from the battery.

 

[Merc Owner 2B]

+1 and through a suitable in-line fuse.

 

[janner]

You need to calculate the load first. How big is the inverter?

 

[richard]

You need
a) A fuse that is big enough for the load. If this is wrong, fuse will blow. You need to calculate this from the total load in Watts you will need and assume a battery voltage of 10V as in fact your car will probably start and run happily with 10V battery voltage. (We had a W211 in yesterday that was running on 9.1V just .. alternator had failed)

b) Wire that is thick enough (both power and ground) based on the size of the fuse. If this is wrong wire will catch fire instead of fuse blowing. This means the fuse is there to protect the wire. Thus it should be as near to the battery as possible if running back to the battery so as much of the wire is protected should it ever get damaged (say in an accident). I.e put fuse at battery end not at cigarette lighter end.

c) The power wiring the correct way to the socket. If this is wrong, because car bodies are earth, and one of the wires is going to the exposed part of the socket bad sparks will fly (and the fuse will blow, unless (b) is wrong then the wire may burn before the fuse). And the equipment you plug in may be ruined. The centre pin of the socket is +12, the outside is ground.

d) The way you connect any wires to existing wiring must be good enough to carry all the power (based on size of wire). if it is not it will get hot and catch fire at the joint. With cigarette lighter sockets this means soldering to existing wiring or running a wire back to the battery.

- It is best to run back to the battery with its own fuse. You could run to an existing lighter socket if the fuse on that is big enough to cover the load you want, but the wiring must be big enough and you will have to solder.

When doing your current calculations, remember the battery voltage can drop to about 9-10V and the car will still work, but most devices will use more current at 10V then at 14.4V (unless they are dropping the voltage down further internally).

1Amp at 240V is 20Amps at 12v and 24amps at 10V) so as you are running an inverter (and it is no where 100% efficient - I recall about 50%, so even higher loads) you will be running reasonable size wires and fuses.

If the above is scary information, then please please get an auto-electrician to do it.

Cheers

Richard

 

[richard]

Finally getting round to this, going to mount the multi-block thing in the glovebox and wire it back to the cigarette lighter as recommended. I need to make an educated guess re the adaptor - it has a black wire and a black/white wire. Which would be positive??! It's not possible to see where it's wired to... Oh, and I guess that positive is the "centre" pin and negative is the "outer" on a car lighter?

OK, further to my last email, I am going to assume you are running this to the existing lighter socket. So, you must
a) NOT guess.
b) Check the size of the existing fuse for the existing lighter socket (fuse chart!!)
c) Use a multimeter to work out which is ground and +12 on the block you have. Ground is the outside part, +12 is the contact in the middle of the socket at the bottom.
d) Determine whether the new socket's wires can cope with the current implied by the existing fuse. If not, get an additional fuse holder and fuse suitable for that size wire which will end up directly behind the existing lighter in series with the +12 feed to the new socket
e) solder your wires to the existing wiring and preferably solder the fuse holder wiring to the new wiring rather than using connectors.

Cheers

Richard

 

[Cleggmeister]

Sincere thanks for all your thoughts and time on this chaps. Here's what I've achieved so far...

Removed the centre trim, ashtray and glovebox. Drilled and bolted a 4-way 12v block with 10A fuse into the glovebox, then ran the wire back to the cigarette lighter switched positive and ground. Rationale for this is that the adapter/block is designed to plug into the lighter socket and now has its own fuse and that of the lighter circuit.

I've not installed the inverter yet as it's getting a bit parky up here, even in my garage. In all honesty I don't really need it right now, though when this changes in the spring I shall do my maths carefully and take a dedicated, fused, wire of sufficient capacity straight to the battery.

Again, my most sincere thanks to all for your contributions. I'll post some pictures when I can.

Thanks again.

Cleggy.