Battery relocation to boot , advice needed

[swampy]

hi
Due to the amount of stuff in the engine bay ,considering bat relocation .

*** battery mounting in boot advice - NO crappy half assed efforts
vented sealed box for wet / flooded battery and rego
[I am using a starter bat AGM type ]


**** cable size only assuming +/- 3.5 mtrs of Awg "0" 50mmsq minimum ?? Welding cable /orange 50& 70mmsq is common.
Mounting to floor ??

What is your experience ??

[Willie]

Hi Swampy, put an isolator switch under the bonnet for when you have to disconnect the power.

[BasicQ]

Definitely run earth to engine block (I reckon you’d be all over it anyway swampy).

I haven’t done battery in boot before but seen cars struggling to start that have and they have negative just running to somewhere on the body in the boot. Electricity will go where ever it has to and that could mean through the diff, up the tail shaft, trans and through crank and bearings if it has to to get to starter. Bigger CCA battery too.

[swampy]

hi
Yup I already have an AGM yellow top , could have gone bigger , plus any AGM loves to be in an ambient/low temp environment . There life is severely shortened by heat.
Earths are as per factory so engine block , F&R cabin body shell and front behind headlight . Plus an xtra to boot frame / floor .

[GtoGeoff]

You don't need a separate earth cable from the battery [ boot ] to the engine. What you DO need is good, clean connections. Your pos cable should be larger in CSA than the short original pos cable that was probably about 1m long. Now it might be 4m long & if same CSA it will have 4 times as much resistance. So in this example, you would need a pos cable that has 4 times the CSA of the original to have the same resistance as the 1m original cable.
Steel has 7 times the resistance of copper. So using the body &/or chassis as the neg keeps the res low because the steel acts as multiple pieces of steel connected in parallel. The neg cable CSA can be about the same as original because overall length is about the same. Run a short piece from rear of block to the f'wall.

Personally, I would keep the bat in the engine bay if possible. Thick copper cable is heavy & you are adding weight putting the bat in the boot.

[swampy]

hi
Starters draw around +/- 300amps
Voltage drop is your enemy
factory cable say 1mtr x 16mmsq 5Awg or 20mmsq 4AWG volt drop is .5

3.5mtr x 50mm 0Awg .70 v/drop this cable has about a 30 second run time at this amperage
or 70mmsq 00Awg .5 volt drop for highly loaded starter IMO


http://www.enerdrive.com.au/wp-content/uploads/2015/04/Cable-Chart.pdf
https://www.hampdon.com.au/assets/alt_1/500021-10m.jpg?20210309030146
www.voltagedropcalculator.com.au/index.php?fldlength=3.5&fldcurrent=300&fldvoltage= 12&fldcrosssection=50&submit=Submit%21

[swampy]

hi
double post
bugga

[swampy]

Agm Optima hold down [34/78 type]

https://www.ebay.com.au/itm/115276413899?_trkparms=amclksrc%3DITM%26aid%3D1110 01%26algo%3DREC.SEED%26ao%3D1%26asc%3D201608111141 45%26meid%3D4f10486844d84f3b9b4c96d038734e07%26pid %3D100667%26rk%3D1%26rkt%3D8%26sd%3D313676243463%2 6itm%3D115276413899%26pmt%3D1%26noa%3D1%26pg%3D233 4524&_trksid=p2334524.c100667.m2042

[GtoGeoff]

If that means you will be using an Optima, best of luck to ya!!!
My Optima red failed going a steep hill; engine died, no brakes or steering. Had to take the bastards to court to get a refund.

[Gregaust]

I use 70mm2 cable , have used 50 as a minimum
I have a couple 34R red tops , one is 11 years now , other is 7 years . But I do keep them topped up with a C-Tek weekly

[Gregaust]

I use 70mm2 cable , have used 50 as a minimum . Usually weld a nice solid point to the chassis for the earths
I have a couple 34R red tops , one is 11 years now , other is 7 years . But I do keep them topped up with a C-Tek weekly

[swampy]

hi
voltage drop is calculated on both the pos+ and -neg combined ,, caution some donot do this .
As a result of above pos+ will be 70mmsq [actual64mmsq] and the neg- will be 50mmsq .
Now we no earth circuits have volt drop also ,, gong with2 earths 1x main engine earth 50mmsq ,,, 1x body 13mmsq [so going to cheat by going thru body which has little to no volt drop ] As we no body earths are not reliable in the long term .

,,,,,,Where to get ???
cable 6mtrs 70mmsq and 6mtrs of 50mmsq

[immortality]

I use welding flex with extra benefit off been double insulated.

[swampy]

hi
If your going to 70mmsq cable double insulated is nice but costly option and besides it might not flex as well as single insulated . ie it would have a larger bend radius .
Xtra insulation can always be done at areas that rub thru .

[immortality]

Ever done any welding with a good ol' arc welder with heavy duty flex cable?

If you plan to run it under the car than double insulated is a good safety feature.

I get it at trade prices so not quiet as painful.

I think 70mm² is overkill, you run the starter for a few seconds at a time, even if we round that up to 7.5 seconds, that is the equivalent of 25% duty cycle on a 30 second weld (as per your earlier link) and is good for 645 amps. Even with a longer run and slightly greater voltage drop over the longer length it's overkill and just more weight to cart around.

If you are cranking the car for 30 seconds each time you start the engine you have other issues you need to resolve.

Go and have a look at the wiring in a VE or VF Commodore which has a boot mounted battery from the factory and see what size cable they use.