Dual Battery Wiring

[MN GLXR]

Add a DC battery charger, some fuses and a 2nd battery. I have mine set up this way.

There is plenty of info with wiring diagrams on this site.

[headake]

Smart charger like a ctek? Or could I just use a voltage sensitive relay (vsr) ?


Battery----fuse or circit breaker-------vsr--------- Anderson plug Anderson plug -------- battery

[headake]

Should the vsr be mounted close to the cranking battery or can I attach it to the aux battery box in tub

[hvac guy]

Close to start battery due too voltage drop

[Dans Tri]

Where are you guys buying 6B&S cable from? ebay or locally? also whats a decent price per meter?

[myself62]

Where are you guys buying 6B&S cable from? ebay or locally? also whats a decent price per meter?

I got my cabling from Jaycar.

[irwazza]

Abr sidewinder, very good do deal with, very fast shipping

[Dans Tri]

Has anyone used these pre-made looms from Hotwiring-Oz from ebay?

http://stores.ebay.com.au/Hotwiring-Oz/ ... 513&_pgn=3

[Cowboy Dave]

I've bought other pre-wired looms from them - like a single anderson to a triple anderson, and a 3 metre cable with andersons either end etc. They seemed like pretty good quality and I've not had any issues with them. Wish they'd been selling those fused ones when I was buying though, that seems a great idea.

[Quinny]

Dans ... I went to a cable supplier (can't remember who it was ... L&H maybe ) ... and asked if they had a drum with a few metres still on it ... got 16mm/2, 7M of the stuff for $8/M ... (have to be lucky, to be honest...) ...and 7 metres sounds plenty but I used it all from front of the ute to the tub ...

[Cowboy Dave]

I've also bought that stuff from battery world - they had a roll of heavy cable with triple sheath if you know what I mean? Anyway lots of rubber around the actual wire. Very well protected I thought.

[Quinny]

I've also bought that stuff from battery world - they had a roll of heavy cable with triple sheath if you know what I mean? Anyway lots of rubber around the actual wire. Very well protected I thought.

Yep ... that's the stuff CD ... three layers of insulation

[Snooozy]

I get a lot of my wire & bits from these guys
http://www.12volt.com.au
lucky they are only 30 min away.
the base price might be a little high on their stuff, but I get a pretty good discount cos I've been such a good customer.

[alex_m_84]

Sorry if this has been mentioned as i haven't got through this whole thread.

I ran a dual battery setup in my hilux but they were right next to each other under the bonnet.

Just a question on running the second battery in the tray. Do you run the negative between the batteries (so end up with 2 runs of thick cable for positive and negative) or earth the second battery at the back somewhere and just have the positives on the batteries linked? If earthing at the back, what point do you use as a good earth?

[Cowboy Dave]

Better to run a dedicated earth all the way to the rear I reckon. If you buy some figure 8 cable with double insulation it ends up only being a single cable run really.

[1 Nathan]

Abrsidewinder will do a lead 6 m long 6b&s figure 8 twin core that's what is used lugs and anderson and a fuse ready to go 30 mins to install $80 or so I think

[alex_m_84]

Yeah thought that would be the better way. Thanks guys

[dougie123]

Guys thought I'd chip in, I use to fit out emergency services, SES and Military vehicles and then did the same for mine vehicle for years when I was first out of high school. Now do 4WD fit out for friends for beer.

You can terminate the negative of the second battery at any earth point in the car. This will make the over all cable length shorter and reduce voltage drop. Google Voltage drop for DC / single phase calculation for those that don't believe.

You'll need a multimeter or Ohm meter to measure that the earth point you have chosen has the same potential as the main battery. Make sure you take all the paint off the metal when you terminate to this point and then respray the area.

Those that are using a DC to DC charger like Ctek, they have a max current draw of 20Amps and that would be charging a completely flat battery. Lest say your alternator is a bit off and only putting out 13Vdc, so you can have a voltage drop of .3Vdc for your charger to work. Your total cable run is 6 meters (remember you can terminate the negative near the second battery), you will need after rounding up a 8mm2 section cable.

Now if connecting the two negatives of the batteries together would need a 2 x 14mm2 section cable.

If you have a good functioning alternator you'd only need a 2mm2 section cable BUT I wouldn't and don't use a cable that small, I use 6mm2 section cable with 30 Amp fuses.

[hvac guy]

I agree but disagree with what u are saying the best practice with new cars is the run a separate earth. The reason why is the computer control in todays cars use the ground plane to carry currents and low voltages. Once u add extra stuff on the plane it can upset the electronics of the vehicle.

[ag9111]

You can terminate the negative of the second battery at any earth point in the car.

This I do not advocate in any way shape or form. Circulating currents will develop between the 2 batteries causing corrosion on the secondary battery negative cable where it is bolted to the chassis. clean connections and sealing will delay the inevitable though. Always go post to post on the negatives.
It is made even worse if you connect the negative cable on any device fed by the second battery to chassis.
I always go as far as having a fully isolated negative bar for the secondary battery so the only connection between the two batteries is the charge cable. No possibility of circulating currents then.

If you have a good functioning alternator you'd only need a 2mm2 section cable BUT I wouldn't and don't use a cable that small, I use 6mm2 section cable with 30 Amp fuses.

I use twin 2.5mmsq cable with a 25A fuse on mine, with the 2nd batt in the tray. Finally someone else who gets it. You do not need 35mmsq cable unless you want to start the car through it.

[dougie123]

The only time you'll have issues if the prep work for the ground was not done correctly e.g. paint removed to bare metal and cleaned, or the point chosen did not have the same potential. Or you have used an existing point that does not have the same potential. Or the wire used for connection is something you found in the garden.

Where are you running this separate earth to? The battery, alternator, engine block? They all go to the chassis. Have a look in the engine bay or behind the dash, you'll see earth points everywhere.

That why I said "You'll need a multimeter or Ohm meter to measure that the earth point you have chosen has the same potential as the main battery"

[ag9111]

The problem is not the common chassis ground system that vehicles use but the fact that you are adding a second voltage source to that system.
If the two batteries were at exactly the same potential then you wouldn't have a problem.
Its the fact that you have two batteries at different potentials that causes the problem. Circulating currents are developed that continuously corrode the lesser terminals and you end up with black cable rot on the negative leads.
The more you isolate the 2 systems the better off you are hence all my secondary battery negatives go to there own bus bar that is not attached, mechanically or electrically,to the vehicle chassis. I have a negative cable that then runs to the secondary battery. The negative battery cable is then run to the front of the car and attached to the negative battery lead. This is the easiest & closest spot I can get to the battery so that we have equalisation of the negatives. This is more to do with maximum charging of the secondary battery. With only one point of contact of the two negatives then no currents can flow through the chassis that cause corrosion.

[dougie123]

@ag9111 are you using a DC to DC charger like Ctek dual 250s or direct charging?

[ag9111]

VSR.
The new electronic style chargers with their leakage current through the IGBT's, or whatever they are using, make this situation even worse. One brand that a colleague tested a few years ago had nearly 10mA leakage current, at elevated temps, that would be encounted in a locked car in summer. this particular unit is no longer manufactured.
Once a relay or VSR opens then the two batteries are completely isolated from one another

[ag9111]

@ag9111 are you using a DC to DC charger like Ctek dual 250s or direct charging?

It shouldn't matter. Isolate your volt sources as much as you can.