Electrical earthing on camper

Submitted: Saturday, Aug 16, 2014 at 16:54
ThreadID: 109159 Views:4508 Replies:8 FollowUps:2
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I am building a hybrid style camper made of epoxy composite on a galvanised steel chassis and I am wondering about earthing all the 12 volt circuits. There will be a big LiPo4 battery bank and a large solar array, plus several big current draws in the camper.

My preference is to wire the thing up as you would a boat, with all 12 volt circuits terminating back to the camper battery. But it has been suggested to me that I use the camper chassis to earth the battery bank and to earth all circuits onto that. In either case there will be proper positive and negative connections back to the tow.

I am just wondering whether electrical connections to the camper chassis will promote corrosion over the years ahead like they do when you earth onto the hull of a metal boat. The body will be bonded to the chassis and any rust repairs down the track would be quite difficult.

Any advice would be appreciated.

Keith
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Reply By: Member - John - Saturday, Aug 16, 2014 at 17:14

Saturday, Aug 16, 2014 at 17:14
G'day, I have just built up a trailer and used 2 x 105amp/hr LiFePo batteries and earthed everything back to the batteries. Much easier that way, no earth issues with trailer plugs etc. Just my two cents worth. John
John and Jan

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Reply By: Member - Rosco from way back - Saturday, Aug 16, 2014 at 17:15

Saturday, Aug 16, 2014 at 17:15
I agree....steer clear of earthing via the chassis.

Why not run twin core wiring to your various appliances. They don't all need to terminate at the battery, creating a jumble of wires. You could run a heavy +'ve to a suitable fuse block and a similar -'ve to a suitable common earthing point that will accommodate all your various earths. This could be an 8mm bolt or two or three, fixed to a suitably robust mounting. That way accessing/changing your battery will be must simpler and also neater.
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Reply By: Allan B (Member, SunCoast) - Saturday, Aug 16, 2014 at 17:18

Saturday, Aug 16, 2014 at 17:18
Hi Keith,

In general, electrical corrosion occurs when there is some difference in potential (voltage) between two electrically conducting components. Therefore it is reduced if all such components are well bonded to each other, and potentials produced by volt-drop of currents flowing in components such as the metal body or chassis are eliminated.

This is best achieved if the return current paths from the various loads in the camper are not returned to the battery via the body or chassis but by a dedicated negative return wire to a negative link bar connected directly to the battery. This requires a two-core (+ & -) cable to each consumer with no connection to the chassis. It also reduces losses due to volt-drop and is much easier to wire and troubleshoot with this arrangement.

In the case of vehicles, single wire with body/chassis return to battery negative is used because it is cheaper and the low current flows in most cables makes volt-drop and corrosion less significant.

Sometimes the camper battery has the negative side bonded to the chassis but it makes little or no difference.

Cheers
Allan

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Follow Up By: Allan B (Member, SunCoast) - Saturday, Aug 16, 2014 at 17:33

Saturday, Aug 16, 2014 at 17:33
And as Rosco has said, do not run a multitude of wires back to the battery posts, use a multiple fuse block and negative connector block such as these, available from ABR Sidewinder and others.




But connect two 60A fuses close to the battery terminal, one for the cable coming from the vehicle and the other to feed the fuse block.
Cheers
Allan

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Follow Up By: Freshstart - Sunday, Aug 17, 2014 at 07:22

Sunday, Aug 17, 2014 at 07:22
An optional fused terminal block. 100 amp max and ten x 30 amp circuits each.

From jaycar: 10 Way Blade Fuse Block with LED Indicators



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Reply By: Ozhumvee - Saturday, Aug 16, 2014 at 18:11

Saturday, Aug 16, 2014 at 18:11
Yes run the earth/gnd/neg to each "appliance", nothing but trouble with using chassis as the neg return.
The best and tidiest way is to use the typical twin (red/black) in a black sheath available from places like Caravan Plus in an appropriate size for each appliance and use a quality fusebox like the Baintech ones with inbuilt negative connections here
Peter
1996 Oka Motorhome

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Reply By: Member - KeithB - Saturday, Aug 16, 2014 at 18:39

Saturday, Aug 16, 2014 at 18:39
Thanks heaps. Looks like a unanimous vote to wire it like a boat, with a common earth bus.
Keith
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Reply By: The Bantam - Saturday, Aug 16, 2014 at 23:55

Saturday, Aug 16, 2014 at 23:55
Further in support of wiring everything in two wire cable and perhaps not connecting negative to the chassis at all.

The notion of earthing is completely foreign to DC 12 volt electrics.

The only reason you would connect the electrical system to the chassis at all is to save on running a return wire to negative battery.

I know some may argue the point, But I do not believe there is any good reason to bond negative battery to the chassis at all.

Always best to have a full circuit of positive supply and negative return wires.

cheers
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Reply By: Member - Frank P (NSW) - Monday, Aug 18, 2014 at 18:04

Monday, Aug 18, 2014 at 18:04
Keith,

Are you going to use a battery monitor? With LiFePO4 batteries, I think you should because you MUST guard against over-discharge. Because they have such a flat discharge curve you should count amp-hours in (from your charging sources) and out (from your loads) to help determine the SOC. Monitoring voltage helps, but with that technique it's a fine line between being on the minimum and disaster. Monitoring amp-hours helps considerably as long as you have a reputable battery monitor (Victron, Synergex, BEP are suggestions).

Therefore, follow the advice in the above replies, but put the shunt for your monitor between the common negative and the battery negative.

Cheers
FrankP

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Reply By: Member - KeithB - Tuesday, Aug 19, 2014 at 11:41

Tuesday, Aug 19, 2014 at 11:41
Thanks for all the help.
Yes there will be a full battery monitoring and management system. These batteries are too expensive to risk damaging them.
Keith
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