Outer Limits 4x4 Board

Does the main battery earth on my V8 110 County really need to be 2m long?

It runs from under the seatbox, along the left chassis rail, across the bellhousing and terminates at a bolt on the back of the starter motor.
The lead is ratty and I'd like to replace it with a shorter/neater one either to the back of the x/fer case or the chassis rail below the battery box. (there is a braided earth strap linking chassis at LH engine mount to engine block).

Why would Land Rover have done it this way? Surely there'd be less resistance/ voltage drop through the x'fer and gearbox than a battery lead of this length?

(I did post this in Auto Electrical but didnt get much of a response)

Best replace it with another to the same point. The highest current draw is the starter, which is the reason they have done it they way. If you want to go to overkill you can run the new cable to the chassis and then the starter.

I had a GQ with a TD42 which would have drawn twice as many amps when cranking as a low comporession rover V8 and the main earth lead ran to an 8mm bolt on the inlet manifold. So I cant understand why Rover would have done it this way.

Cause they're better designers than the Japs.

Tech: Probably to better ensure a cleaner power soure to the bit of the car that pulls the most current.

I'd run one from the battery to the nearest chassis point. Then another from the chassis to the engine near (or on) the starter.

But that's just me.
Make sure the crimp joins on your earth leads are good.

Slunnie wrote:Cause they're better designers than the Japs.

Tech: Probably to better ensure a cleaner power soure to the bit of the car that pulls the most current.

Toyota (for example) have the worst diff breather design ever devised.

But - the manifold is probably not so far away from the starter on the TD42??? Much better than just running the lead to the chassis.

On my county the earth cable runs to the outrigger just behind the battery box. I then have another short earth strap from the chassis to the engine

isuzu110 wrote:On my county the earth cable runs to the outrigger just behind the battery box. I then have another short earth strap from the chassis to the engine

I had a look at the parts diagram for the 110 Perentie - this is the same way the army 110's earth as well. A V8 has got to draw a lot less cranking amps than a diesel so I cant see any reason why I cant do this either.......
- unless its something to do with running the cranking current through an alloy engine block versus an Isuzu cast block??????????

direct is way best - using other mediums to trasnsfer power is alway chancy, and cheap. Replace the cable with the same or bigger to the same point and you'll have no problems with shorts or with stray electicity stuffing your engine block or radiator thru electrolysis. The earth strap on Toyotas between the chassis and the engine always frays and breaks causing loss of power to the starter and other accessories. Much less reliable than a direct cable is.

Reddo wrote:direct is way best - using other mediums to trasnsfer power is alway chancy, and cheap.

What conducts better, the chassis or a copper cable?

KiwiBacon wrote:

Reddo wrote:direct is way best - using other mediums to trasnsfer power is alway chancy, and cheap.

What conducts better, the chassis or a copper cable?

Depending on the alloy - copper has somewhere between 10x - 40x the conductivity of steel.

ISUZUROVER wrote:

KiwiBacon wrote:

Reddo wrote:direct is way best - using other mediums to trasnsfer power is alway chancy, and cheap.

What conducts better, the chassis or a copper cable?

Depending on the alloy - copper has somewhere between 10x - 40x the conductivity of steel.

True - however the conductivity (resistance) is also directly proportional to the cross sectional area of the conductor so if the chassis is more than 10 -40x bigger in CSA, it is a better conductor.

The earth lead on my truck goes to the chassis but is bolted to the body on the way past.

Earth strap across an engine mount from chassis to block.

I've pulled 511 amps through it without problems.

OK then lets send all electricity this way! The obvious answer is that it is less reliable, and that is why positive and negatives supplies are increasingly sent dirct to the device concerned. The old approach of common earths is unreliable, and so is using the chassis, not to mention the possible electrolytic effects that result from from stray currents, and potential problems with multiple conections, mud, water ingress and so on.

Reddo wrote:OK then lets send all electricity this way! The obvious answer is that it is less reliable, and that is why positive and negatives supplies are increasingly sent dirct to the device concerned. The old approach of common earths is unreliable, and so is using the chassis, not to mention the possible electrolytic effects that result from from stray currents, and potential problems with multiple conections, mud, water ingress and so on.

If stray currents is your concern, then earthing everything (incl the chassis) is the way to stop it.

Common earth is not an old approach, it's the way everything DC works. Ever seen an automotive alternator with a seperate earth lead?

KiwiBacon wrote:The earth lead on my truck goes to the chassis but is bolted to the body on the way past.

Earth strap across an engine mount from chassis to block.

I've pulled 511 amps through it without problems.

Is yours a diesel or a V8?

Come to think of it, if all the output current from the the alternator is running through the block constantly, why should intermittent cranking current (albeit with a higher peak) through the block or transmission from the rear be a drama?

Yes absolutely, alternators with seperate earthing are common as are (increasingly) individual earth returns in wiring looms.

This is a strange discussion. We all know that the more connectors your have in the circuit and the less direct you supply is, the more chance of failure, shorts and unexpected outcomes there are. Mixtures of metals with different conductivities, and indifferent current pathways and shorts through gaskets, bolts, thread lock material and so on are simply less reliable than a direct cable carrying such high loads.

Mark2 wrote: Is yours a diesel or a V8?

Come to think of it, if all the output current from the the alternator is running through the block constantly, why should intermittent cranking current (albeit with a higher peak) through the block or transmission from the rear be a drama?

Mine is diesel and normally draws about 150 amps to start.

As you've mentioend, there is no problem with earthing through a block. If there was car makers wouldn't have been doing it for the last 100 years.
Your engine block and body need to be earthed to the chassis, if you run a earth cable directly to the starter then you need another one back to the chassis as well. It just doesn't need to take starting loads.

Electricity is lazy, it always takes the path of least resistance.

I haven't come across an alternator with a seperate earth. I'm sure they must exist but common they don't seem to be.

KiwiBacon wrote:I haven't come across an alternator with a seperate earth. I'm sure they must exist but common they don't seem to be.

We had 2 alternators blow up in my Dads 79 Volvo before we realised what was going on. There was an oil leak above the alternator somewhere and the oil was making the earth from the alternator to the block to be a poor connection. We gave the alternator its own earth wire and all was fixed.

Regardless of what is factory I think giving each component its own earth where possible, especially in a grubby Land Rover, is the best method.

Isuzu110,
My 110 County 3.9D had the same pathetic earth cable arrangement. I left it in place when I set up my dual batteries under tha pax seat but added a second 50mm2 earth cable out through the battery box wall and connected to the back of the LT95 transfer case. The old Isuzu cranked heaps better after that.

JohnS