Dual battery wiring diagram

[Garygls Senior Member Find all posts View Profile Close Garygls]

Hi all, I have just ran a cable from the engine bay to the cargo area to power my 80ltr waeco. I was told that all i needed to do is run power to the cargo & you can earth the Anderson plugg to the body/chassy. Is this right? or do i need a earth return to the Isolator??

Haven't bought the Redarc Isolator yet just thought i would run the cable first.
Has anyone got a diagram or is this ok.

Thanks Gary

[Walker Valued Member Find all posts View Profile Close Walker]

Yes you can earth to the chasis, but it is not the best method. While the chasis will act as an earth, you just never know how good it is, especially for higher amperage stuff.

For lights etc the chisi is fine, for fridges or compressors I would run a seperate earth back to the battery.

[AdrianLR Member Find all posts View Profile Close AdrianLR]

Before wiring up my NP I measured the voltage (using a reasonable quality multimeter) at the end of two 8g cables vs a positive and the body as the earth under load to a running Autofridge. There was negligible difference and using the body was very slightly better (it was a couple of years ago and I don't remember the exact measurements). I would expect this to be the result as the Paj has monocoque construction so the body IS the chassis and you would hope it has good structural as well as electrical integrity. You will still need to run a short earth wire to the plug - make sure that you clean the paint off the point where you attach this to the body.

Adrian

[john_char Valued Member Find all posts View Profile Close john_char]

I agree with Adrian. All you need to do is run a short wire to the body. Definitely grind out the paint when screwing the earth down too and add some lanotec or similar to prevent any corrosion. I have my Anderson plug on top of the rear RH kick panel at the back and I also wired up a more heavier cable to the ciggy lighter while I was there.

John.

[Garygls Senior Member Find all posts View Profile Close Garygls]

Thanks all for your help, sleave's are up when the Redarc Isolator turns up in the mail this week. Already ran the wire to cargo area. Battery tray, battery, anderson plug, next weeks purchase.

[drivesafe Member Find all posts View Profile Close drivesafe]

Actually folks, Walker is correct.

No professional installer who knows his trade would risk all the problems that can occur when using the body or chassis as the earth return in any high current installations.

For anything requiring a current greater than that needed to power a blinker globe, you need to run both a positive and a negative.

The problem is that there is no effective way pre testing to see if the body or chassis is a suitable earth return.

You can test all you like but the problem is that there only has to be slightest resistance at any one location and once out on the open road with a constant current being needed to recharge a battery and the resistance point will start to warm up, increasing the resistance and so on.

The only way you will find out that the chassis is not such a good earth is when you get to where ever you were going and find your battery has not charged.

There is only one way to be 100% sure of your earth return and that?s to run both negative and positive cables.

Bit late then.

Just out of curiosity, what size cable did you run?

Cheers.

[Garygls Senior Member Find all posts View Profile Close Garygls]

Drivesafe, the cable size I decided to go for measures 8mm across bare wire.
Sounds like an over kill just for a fridge,I have plans later to run a inverter for other electrics, like compressor, lights & so on.
Just another question with the return earth, can I run a smaller cable back to the battery for an earth??? Haven't got the room under the carpet to run along side the power, can run earth on the other side of car if needed.
Thanks for your input, Gary

[gp339gm339 Member Find all posts View Profile Close gp339gm339]

If you run the negative wire to the neg terminal of the battery, ensure that you use an inline fuse located near the battery.

Or Mount the negative wire to the battery / chassis grounding point.

I have seen radio equipment burnt to a cinder, due to the ground wire being connected to the battery. And the vehicle then develops a fault where the Chassis / battery ground wire fails, and the vehicle then tries to start via the ground wire of your accessory.

[drivesafe Member Find all posts View Profile Close drivesafe]

Unfortunately Garygls, you have to use the same size cable for both positive and negative other wise the thinner negative cable will rule how much current and voltage drop there will be, not the thicker positive so you will loose the benefit of the thicker cable.

Cheers

[Garygls Senior Member Find all posts View Profile Close Garygls]

Positive Chassis Vehicle

Just reading through some FAQ's of the Redarc Isolator & it asked if you can use this Isolator on a positive Chassis Vehicle.

Has my 05 NP have a positive Chassis????? & how would I test for this?????
Gary

[beaky Member Find all posts View Profile Close beaky]

you can check this for yourself. which battery terminal is connected to the chasis? Most cars are -ve and this is because the +ve is where most of the erosion (is that the right term) happens. So you wouldn't connect the positive to the chassis else it would erode away. having said that there are some cars that are +ve earth (mg's are one I think) so the effect of the above cant be that great.

[Tred Junior Member Find all posts View Profile Close Tred]

wiring dual batteries in np 3.8 petrol

Has anybody got any ideas what exactly i have to move to mount the second battery in. I got a quote $950 to fit but want to do it myself to save some money. I understand the electrical side of the wiring but Im not sure if I have to move cannister. I got a price for a tray off the net of $130 from 4x4 store is that good or does anybody no of any other companies that sell them.