Dual Battery Wiring Questions (Fuses, Wire Sizes, Battery Linking for dual start)

[Davros Advanced Member Find all posts View Profile Close Davros]

An alternative to the crimping tools is soldering the lugs.

Here is a video of how it is done.
http://www.youtube.com/watch?v=q2XMkEGRzGU

That is how I do all of mine anyway.

[wooley Avid PP Poster! Find all posts View Profile Close wooley]

An alternative to the crimping tools is soldering the lugs.

Here is a video of how it is done.
http://www.youtube.com/watch?v=q2XMkEGRzGU

That is how I do all of mine anyway.

wayyyy too hard.

[Si & Rae Member Find all posts View Profile Close Si & Rae]

wayyyy too hard.

Have to agree with ya Wooley.
last time I did a dual battery, I just cut the cables to length and went down to a car audio store and had them crimp them for me. I didn't get charged but would have been happy to pay $10 - $20 if they had asked. Unless you are planning to do lots of this type of work, it really is not worth buying the crimps or soldering gear.

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

That video was nothing short of amateur hour.

The guy had never soldered that size cable before because he didn’t know, in advance, that the heat shrink was the wrong size.

The cable should have had enough insulation stripped off it so the copper could have been inserted into the terminal housing and enough copper was still above the housing.

This way, both the housing and the copper are heated and the resin core solder is feed against the copper and runs into and fills the housing.

Then at the end of the job you can both see that you have applied enough solder and whether the solder has bonded to the cable and the house and you don’t just have a dry joint.

There is no way that “MECHANIC” has any idea of how good or bad that joint is.

That is a very dangerous way to carry out a soldering job.

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

Hi Ryzz and just a few safety points.

1. ) 16mm2 cable is very similar in size to 6B&S ( 13.5mm2 ) and 6B&S has a continuos maximum current rating of 105 amps, not 140 amps, and even this is based on the cable being in open air.

When the cable is run through a vehicle, it’s maximum safe current rating is about 95 amps.

While this may not seem all that important it becomes very important when you are matching it with the correct protection device.

2. ) A 100 amp rated automotive circuit breaker or fuse is actually rated at it’s capacity for 4 hours, but to get that rate for 4 hours, it must be able to hold 135% of it’s marked rate for 30 minutes, and much MUCH higher amps for a shorter period.

NOTE, all automotive circuit breakers and fuses are rated this way and are designed to be so so they don’t blow every time you start a motor.

So in your set up, you will have a potential for your 95 amp rated cable being protected for up to 30 minutes with a 135 amp circuit breaker.

3. ) The most dangerous situation that occurs with dual battery systems, is current overload, not short circuits.

In a worst case scenario you could have a fire but the most likely situation is that you will heat the insulation up so much that it will become extremely soft and cause a short if the cable is near any earthed metalwork.

The maximum safe current rating for 6B&S cable is 50 amps.

To avoid having to continually reset a circuit breaker, fit auto resetting circuit breakers and you then have both short circuit and current overload protection in one.

Also, because of the ability of automotive grade circuit breakers to tolerate very high currents for very short periods, you can actually jump start through a 50 amps circuit breaker and it won’t trip unless you continually keep cranking.

[Hoags Lurker Find all posts View Profile Close Hoags]

Sorry to hijack the thread, but...

Where does everyone put the earth from the second battery? And pictures if able?

Also I was told to upgrade the earth off the main battery to accomodate the dual battery setup, has anyone else heard of this?

Cheers.
Hoags

[MidLifeCrisis Out of control poster! Find all posts View Profile Close MidLifeCrisis]

Perhaps, MLC should be encouraged to drop around my joint to get a few photos of the other crimp tools?

Only just saw this post. I don't need to, I keep them at my house while your away, you know, so they are safe

[Ryzz Advanced Member Find all posts View Profile Close Ryzz]

Sorry to hijack the thread, but...

Where does everyone put the earth from the second battery? And pictures if able?

Also I was told to upgrade the earth off the main battery to accomodate the dual battery setup, has anyone else heard of this?

Cheers.
Hoags

The general thought process on the earth is, dont trust the body of the car, just wire everything directly back to the second battery (relevant only for accesories running off the second battery obviously). I dont have photos, however its pretty simple, use a 4 Guage wire, take positive from the original battery, run in into the isolator (Recarc/Piranaha, etc), run the positive out of the isolator to the positive of the second battery. Then run a second 4 guage from negative on one battery to negative on the second battery.

Remember according to ADR, any power runs longer than 300mm (not 100% sure on length, but principle is the same), needs to be DOUBLE INSULATED, to do this, goto bunnings and buy some black flexible cable management tubing and run the negative in one, and positive in the other.

You now have a dual battery complete with isolator. I THINK you probably need to run earth from the second battery to the isolator too, but cant remember 100%, check the install manual provided with the isolator you buy.

[Hoags Lurker Find all posts View Profile Close Hoags]

Thanks Ryzz,

That's what I have done. When I read the instructions, it wanted the battery and Redarc to go to the cars earth. I wanted the battery to be independant of the car. However the earth from the Redarc needs to go to the cars earth to provide reference voltage for the isolator to turn on or off.

Cheers.
Hoags

[Ryzz Advanced Member Find all posts View Profile Close Ryzz]

Thanks Ryzz,

That's what I have done. When I read the instructions, it wanted the battery and Redarc to go to the cars earth. I wanted the battery to be independant of the car. However the earth from the Redarc needs to go to the cars earth to provide reference voltage for the isolator to turn on or off.

Cheers.
Hoags

The Redarc can go to the Second Battery as the negative is always linked with the primary battery. If you do it that way, you gurantee to have the most reliable earth connection.

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

There is some good info in this thread and I wish to add some more:

The following link is about electrical circuit theory - http://www.gtsparkplugs.com/pdf/Auto...cuitTheory.pdf

This one is for wire size. Read the writing above the calculator first - http://www.gtsparkplugs.com/WireSizeCalc.html

And last one is ohm's law when working out amps, watts etc. http://www.gtsparkplugs.com/Ohms_Law_Calc.html

For example if I am using a 600 watt 12vdc - 240vac inverter what will be the current draw on my battery?. Answer would be 50 amps @ 12vdc (in theory). You need this information to work out your cable size to your battery.
You would use 12v for your calculation and not 13.8v or what ever your alternator puts out because the amperage would decrease. In this case it would be 43amps if I use 13.8vdc.

This information apply's to any vehicle type on this forum.

With any electrical work, over calculate your loads and wire sizes. Use the above information at your own risk and always seek advice from at least 2 qualified person's.


Winston.

[winniliss Avid PP Poster! Find all posts View Profile Close winniliss]

There is some good info in this thread and I wish to add some more:

The following link is about electrical circuit theory - http://www.gtsparkplugs.com/pdf/Auto...cuitTheory.pdf

This one is for wire size. Read the writing above the calculator first - http://www.gtsparkplugs.com/WireSizeCalc.html

And last one is ohm's law when working out amps, watts etc. http://www.gtsparkplugs.com/Ohms_Law_Calc.html

For example if I am using a 600 watt 12vdc - 240vac inverter what will be the current draw on my battery?. Answer would be 50 amps @ 12vdc (in theory). You need this information to work out your cable size to your battery.
You would use 12v for your calculation and not 13.8v or what ever your alternator puts out because the amperage would decrease. In this case it would be 43amps if I use 13.8vdc.

This information apply's to any vehicle type on this forum.

With any electrical work, over calculate your loads and wire sizes. Use the above information at your own risk and always seek advice from at least 2 qualified person's.


Winston.

This site isn't working at the moment. I found another one that is easy to read. Do scroll all the way down to the bottom.:

http://www.solarhome.ru/en/basics/ba...ing_cables.htm

Winston.

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

Thanks Ryzz,

That's what I have done. When I read the instructions, it wanted the battery and Redarc to go to the cars earth. I wanted the battery to be independant of the car. However the earth from the Redarc needs to go to the cars earth to provide reference voltage for the isolator to turn on or off.

Cheers.
Hoags

I have a charge-master set-up. The negative cable from the auto solenoid to the negative terminal of the main battery has to be the last cable connected otherwise the solenoid won't operate properly. Not sure if the redarc is the same.