Can the fire wall be used as an earth???

[Datt]

I took the aux battery setup (traxide) out of my D1 and am setting it up in the D2. Can any of you auto electical gurus tell me if I can use the captive nuts that my aux battery tray bolts onto on the fire wall as an earth for the aux battery? Thanks in advance.

Matt.

[dmdigital]

There are a number of earth points on the D2. From memory there is one on the firewall. If its not the battery earth it shouldn't pose an issue, but I wouldn't earth the battery back to there.

Your best bet is to PM or phone drivesafe (Traxide) and ask him directly.

[grover7488]

hi Matt

I would take the earth from the aux battery to a bolt on the engine (i really need to work out how to post photos!)

[barney]

as a sparky, i would earth the body (the firewall or anywhere else) and the chassis.
no point earthing the engine, unless it is going to run off the aux battery.
the engine, chassis and body are all earthed from the main battery, so althourh you may not need it, the engine will be earthed to the aux battery anyway.
bear in mind that the "earth" as is colloquially known is actually the negative path for the battery circuit, which uses the metal in the car's body as a conductor.
keeping this in mind and the fact that the positive will be of no use at all without the negative, might help you in understanding the function and reasoning behind the connections of the earth and their importance.

a poor termination of the cable, whether it be a bad crimp or bad contact into the metal of the body (use a star washer for better effect), will create heat, whih will slowly get worse until either the wire burns off or your car bursts into flames.
have a nice day:D

[Bundalene]

Hi, I ran a decent size cable - 35 sq mm along the firewall across the top of the engine (cable tied onto the brake lines) and down the right side to the main earth point adjacent to the TD5 ECU. This then ties all earths together to one common point.

Connecting the 2nd battery to a riv nut or self tapper on the fire wall may be OK for a while but if you get any corrosion you can get unstuck.

Erich

[grover7488]

barney,

why would you earth the body (the firewall and anywhere else) and the chassis when you say they are all earthed together anyway?

[waynep]

beacause copper cables provide a much better path to all those little electrons than the various bad joints ( in electrical terms ) between panels and between panels and chassis.

As said before, the term "earth" is bit of a misnomer when applied to DC currents in motor vehicles, considering they are well insulated from the "earth" by big rubber tyres. It is the negative side of your circuit, and just as important as the positive side running via the wires. Using the car body to complete one side of the circuit ( either positive or negative ) really was a cheap way of getting out of having to run two wires to every device from the battery. The practice has kept the auto electricians in a job for decades tho ;), finding "earth" problems.

The idea of a common "earth" point where all your negative cables come together, is that the circuit is completed via cables, not the car body.

[Tombie]

And especially important when you realise that power actually flows from Negative to Positive :cool:

[barney]

And especially important when you realise that power actually flows from Negative to Positive :cool:
electrons run from negative to positive

[mcrover]

And especially important when you realise that power actually flows from Negative to Positive :cool:


electrons run from negative to positive

Semantics....:eek:

Just remeber that you need to beable to flow the same from both sides, so what comes out has to go back in theory and then your fine.

If you run 30mm2 cable on the Poss side you cant just run 5mm cable on the neg as you wont be able to carry the current.

I wouldnt personally attach a major grounding to the bulk head as if you get corrosion around it then your car may easilly become irrepairable if it rusts through.

I would there fore as one of the others has posted, run a main link cable for engine,chassis and body and ground your aux battery there.

There would be no probs picking up an earth off the firewall either side but you dont want your ground feed there in my opinion.:D

[Datt]

Sensational, thanks guys for all the inputs. I definatley don't want any corrosion issues with the fire wall so will buy some more cable and run it to the spot Bundalene suggested.

Matt.

[drivesafe]

Best practise is that you can ground a battery, cranking or auxiliary battery pretty well anywhere in the engine bay and you are highly unlikely to have a problem.

Once the battery cables have to leave the engine bay then you need to run both a positive and a negative, of the same diameter, form one battery to the other.

Stick to the policy and you shouldn’t have a problem.