Dual Battery Wiring

[Naff]

You can mitigate the risk of cable problems by using anaconda - would take a hell of a lot of effort to break through it.

[ag9111]

Doesnt take an accident to damage the cable. Hell of a lot of vibration under there

[Naff]

Anaconda protects it from vibration too... just an extra measure if you can get your hands on some. If I didn't get it free, I wouldn't have used it... if you did have an accident and the anaconda was damaged leading to a cable short, it's probably the last of your worries.

[odie602r]

Just checked out the Redarc website - they recommend manual reset breakers over both auto breakers and fuses.

They also recommend path as follows:
Crank batt -> manual CB -> isolator -> cable run -> manual CB -> aux batt

Thats what I'll go with then

[big_bob_thefirst]

That satisfies all requirements. I like manual reset as well, will have to see where I can replace my 2 auto reset at some stage...

[odie602r]

So question regarding running a fuse box off the aux battery. One that I'm looking at has positive connections, no negative on it at all.

http://cgi.ebay.com.au/ws/eBayISAPI.dll ... _927wt_922

What's best practice - re dealing with the negatives for the accessories:

1. Running the negatives to the aux battery negative post (which in turn is grounded to chassis at front of vehicle
2. Ground all the accessories at some common point to chassis right near the aux battery (which for me is going behind rear seat)
3. Not sure what other options there are, but am wanting to know....


Or there's this one that has a 'common positive and negative'-
http://www.ebay.com.au/itm/FUSE-BLOCK-B ... 1573wt_922

I assume common negative means you wire up the negative of the fuse box to chassis, then each accessory negative gets attached to the common negative point on the fuse box?

[Naff]

I ground everything to a common point (terminals) with one larger ground connecting it to the battery. This just saves you removing a heap of individual grounds from the battery when you want to take it out for whatever reason.

[odie602r]

I ground everything to a common point (terminals) with one larger ground connecting it to the battery. This just saves you removing a heap of individual grounds from the battery when you want to take it out for whatever reason.

Thanks for the prompt reply. I still haven't got my head around this yet so don't quite get what you mean. Could you give a little more detail? Thanks

[big_bob_thefirst]

U can do something basic.

Wire all the negatives to a point, a bolt and 2 nuts... Then have 1 wire run from that bolt to the battery. That way of u take the battery out, it's only 1 connection and u know where all the other connections are...

[Naff]

Some might say this is a bit extreme, but it's similar to what I have done -



You can buy this bar from any electrical wholesaler. Each screw is a connection point for your earth. Then connect one larger cable from the bolt to your battery.

Otherwise you can just do what big_bob said, throw all your connections on to a bolt between two nuts.

[odie602r]

Got it. So definitely need to have one from a common earth point back to the battery? Out of interest, what happens if you don't (have a cable from earth point back to battery?

[Naff]

If you don't have a connection back to the negative on the battery you can't guarantee you have got a good return path (ground). It will save you heart ache trouble shooting accessories that don't work properly.

Also, have you got a negative cable running from your primary battery to your auxiliary battery? This ensures you get a proper charge. I initially only used a chassis ground but after time corrosion took effect and my ground was bad causing the auxiliary to not charge properly.

[odie602r]

Thanks again.

That was another question I just thought of - yes my intention is to run negative cable from primary to aux - sounds like I should continue ahead with that plan!

[big_bob_thefirst]

I found out the hard way that with the cteck, u need to run a negative from the cteck back to the starter battery. It connects to the same earth point as the aux.

I have to aux in the tub and use that as my ground. In the front, can use the starter bat as the ground.

[Snooozy]

for the -ve I went the Busbar also.


they normally have covers but are removed for pic.

you can get a fuse panel with a Busbar also. 1 for +ve & 1 -ve

Bluesea make some good products, although can be a bit on the pricy side they are good quality & are marine grade so will last.

http://bluesea.com/category/81

if you have a look through my build thread you will see the system I used for the aux battery too

[ag9111]

What are your thoughts then on manual reset circuit breakers, just out of interest Garth?

I have no real experience with the small manual circuit breakers that are available from Auotomotive/ebay Stores.

I personally use the DIN style circuit breakers that are rated for 240V ac. These are the breakers used in the domestic/commercial/Industrial distribution boards. Over the years these breakers have become more and more commonly used in the 24Vdc side of things in the industrial market. I have had an ongoing feud with my boss as to whether these CB's were actually any good for 24Vdc as they are no good for larger DC voltages such as 110 and 230. I contacted many of the distributers and only one at the time would confirm that their breakers were rated for the stamped current at 24VDC. This company was Schneider who market the Merlin Gerin brand. I use Merlin Gerin C60 breakers for convenience although would rate fuses as a better alternative.
I carried out some tests about 4 years ago and used a 24vdc supply into a resistive load to trip these breakers at their recommended loads. I must confess that I was surprised at how closely they followed their trip curves.
As an aside, some of the Circuit breaker manufactures are now starting to sell circuit breakers dedicated for DC voltages.
I am by no means egotistical enough to think that I caused these breakers to be developed but i hope push it along. These breakers sell, to me, for about $74. To the general public at about $150 each

[odie602r]

Okay, I'm still getting this straight in my head and have another question or two (thanks for being patient with me while I learn this)

1. With the cable run from the crank batt to aux battery, do I wire up the negative cable to the negative post of the crank battery, or the negative ground on the chassis where the factory cable from negative post of crank battery is? I think Naff was saying go to the negative terminal on crank batt, but I'm just checking.

2. Since there will be a negative/earth running from crank battery to aux battery, will I also need to have another short cable from aux batt negative post to the chassis, or will doubling up earths cause other problems?

3. With the fuse box or -ve buss bar (not sure which way I'll go yet) do I just wire up a negative/earth ground from box/bar to the negative post on aux battery, or do I wire up both a cable to negative post on aux battery AND a cable to the chassis?

Sorry about the questions - still new territory for me ....

[big_bob_thefirst]

Odie,

The negative side is relatively straight forward as there isn't that much of a current going thru it.

1. If you wire the neg of the aux battery to the neg of the crank battery, it is grounded. The aux battery will have a straight run to earth, just like the crank battery.

2. There is no need to run to earth. I don't think it will cause any problems but there won't b any current going that route if u have a cable running back to the battery.

3. Same as above. I'd recommend u run the negatives off ur accessories to the neg on the battery. This ensure a good connection and current flow. No need to b earthed.Saying that, some accessories (I have an inverter) which has a seperate earth port and cable. I think this is more a safety feature if there's an internal fault rather then a means to run the equipment.

Think 12v current as a water system. The water starts at the + terminal and run alongs a pipe (cable) to where u need it. The accessory then uses a bit of water. The rest of the water needs somewhere to go then. If u run a pipe back to the negative terminal, it has an easy path and everything works well. If u cable it to the chasis, the water will flow but rather then an easy path, it has to flow thru a dirty and unorganised (think soil rather then pipe) back to the negative terminal.

If there's no good earth connection, there's a block in the system and the water /current won't flow at all.

If u have two paths back, the majority will use the easiest path. It'll actually split up to the exact ratio of how difficult the chasis run is vs the cable run (resistance). Again, similar to water.

[odie602r]

Thanks big_bob, I think it's clicking now.

To sum it up (for my own learning benefit):
Negative cable from aux to crank battery, then both are grounded by the existing cable from crank batt negative to chassis.

Accessories negatives to aux batt negative (through either a fuse box with common earth point, or -ve buss bar) which is grounded/earthed by above.

If wired as above, there's no need for a separate/additional chassis ground from aux batt to chassis. And no need for a separate/additional chassis ground from accessories to chassis.

Flow is then constant, consistent and has only one path.

Correct?

[big_bob_thefirst]

Almost completely right. The crank battery negative connection is the earth. The wire goes from the car chasis to the battery....

Other than that correct. If the aux battery is connected to the crank battery (via cteck) then u have the full path.

If u don't have a cteck, I'm not too sure if u need the negative to negative cabling...

The accessories, if u run from a common earth point or a busbar to the neg terminal on the bat, it'll work.

U can run each accessory to the neg battery terminal, it just gets a bit messy and harder to manage...

[hvac guy]

Ok dc actually flows from - to +

You can never have to much grounding on a car

More the better. 99 % 0ff wiring faults are from poor earthing in the car.

[big_bob_thefirst]

Thanks big_bob, I think it's clicking now.

To sum it up (for my own learning benefit):
Negative cable from aux to crank battery, then both are grounded by the existing cable from crank batt negative to chassis.

This is the wrong bit. The - terminal IS the ground. The whole chasis is wired to the battery, rather than the battery is wired to the chasis...

[odie602r]

I don't have a ctek at this point, but I'll wire up so that it's done should I choose to go that path in the future.

Thanks - think this means I got it

[hvac guy]

The tubs on these cars are not grounded well
U have to run a ground wire from the tub too the chassis rails

[odie602r]

Thanks big_bob, I think it's clicking now.

To sum it up (for my own learning benefit):
Negative cable from aux to crank battery, then both are grounded by the existing cable from crank batt negative to chassis.

This is the wrong bit. The - terminal IS the ground. The whole chasis is wired to the battery, rather than the battery is wired to the chasis...

Right, I see. Thanks. Wrong understanding, but the wiring would be correct.