Thread: Auto elec question.

Originally Posted by Ben_R

Hello All,

I've got a question regarding a dual battery setup in the rear storage boxes of my D2.

I've based a lot of what I have done on previous posts about this subject through searching the forum.

The plan is to put an electronic controller and 2nd batt in the rear box. However, at the moment the 2nd battery will have to wait ($$$). I've run 8mm cable from both the positive and negative terminals of the cranking batt, all sleeved and cable tired to the ABS lines on top of the chassis. With a 30amp circuit breaker on Positive lead in the engine bay. So, right now, I just want to run my 40l Engle using this wiring direct to the cranking battery using an Anderson plug on similar.

My question, Is the 8mm cable too big for the engle to run properly over this distance?

Thanks in advance, cheers Ben

It will never be TOO BIG, is the 8mm the measurement of the section?
The calculation for minimum size is

Length in metres x current in amps x 0.017/conductor size in sq mm = voltage drop.

8mm, the Engle will be freezing even when its turned off! It'll be fine.

BTW, this is how I have setup also. I've also got a fuse block in the bin to distribute power.

Hi Ben_R, the 8mm is fine for the fridge and although it will work for charging a battery but it is bit undersized to be able to charge the battery properly located in the rear of your D2, particularly if the battery is low when you start to charge it.

Remember, you are going to be trying to charge the battery and powering the fridge, while the fridge is in it’s on cycle.

Bellow is a link to a great site for quickly working out what sort of voltage your going to get at the battery.

Your 8mm cable will be 8 AWG and I’m guessing you will have about 30 foot of cable.

Try loading in different current loads, like if the battery is a 100 A/H and is at 11 volts and your fridge is going to be needing about 5 amps and the battery could easily pull up to 30 amps initially, except for the voltage drop.

Your battery needs at least 13.8 volts to be able to charge properly.

Cheers.

http://www.currentsolutions.com/knowledge/vdrop.htm

Hi

Thanks for your replies.

So should I change the 8mm for something bigger? or will it be ok when I eventually put in the 2nd batt and need to both charge the 2nd batt and run a fridge off it. Is it something that I can live with or will having 8mm cable effect the proper running of this setup? Will the 2nd batt reach full charge?
At this stage, it is not too late to change it over for bigger cable.

cheers Ben

Hi Ben, it will do the job but if you decide to do some work and can upgrade the cable at a later date do so.

As a rule of thumb, if you have two batteries side by side you can use 6mm automotive ( 4.5mm2 ) cable to connect them.

If you have two batteries in different places under the bonnet then the minimum cable size should be 8 B&S ( 7.9mm2 )

For batteries in the rear of a vehicle or in a camper trailer or caravan, 10mm2 would be the minimum size and 6 B&S ( 13.5mm2 ) would be better for caravan or camper trailer installations.

In all cases this would be both positive and negative cables running between both batteries.

Cheers.

Originally Posted by drivesafe

Hi Ben, it will do the job but if you decide to do some work and can upgrade the cable at a later date do so.

As a rule of thumb, if you have two batteries side by side you can use 6mm automotive ( 4.5mm2 ) cable to connect them.

If you have two batteries in different places under the bonnet then the minimum cable size should be 8 B&S ( 7.9mm2 )

For batteries in the rear of a vehicle or in a camper trailer or caravan, 10mm2 would be the minimum size and 6 B&S ( 13.5mm2 ) would be better for caravan or camper trailer installations.

In all cases this would be both positive and negative cables running between both batteries.

Cheers.

Thanks Drivesafe for all your advice.

I've been reading old posts and this has obviously been dealt with at length in the past. The cable wire itself is more like 6mm. So the total thickness incl coating is 8mm. I'll use this for now anyway and If I have difficulties with it not charging fast enough I will be go bigger.

cheers Ben

Originally Posted by Ben_R

Thanks Drivesafe for all your advice.

I've been reading old posts and this has obviously been dealt with at length in the past. The cable wire itself is more like 6mm. So the total thickness incl coating is 8mm. I'll use this for now anyway and If I have difficulties with it not charging fast enough I will be go bigger.

cheers Ben

If you are running it to the back, a 6mm section cable will be too small, and this could affect the battery

Might be just okay for running your Engel for the short term - but I would recommend that you upgrade the size as soon as you can, and before you instal the 2nd batery.

Originally Posted by Ben_R

The cable wire itself is more like 6mm. So the total thickness incl coating is 8mm.

cheers Ben

Hi Ben, 6mm automotive cable is about 5mm across the insulation and so if yours is about 8mm across the insulation then it’s a fair bet that it is 8 B&S which is 7.9mm2 and it will do for now but it will mean slower charging rates.

If you intend to put a large battery ( 100 A/H or bigger ) you will have to up the size of the cable.

One way to save some money is to join the existing positive and negative cable together and use this as you negative and just run a new thicker positive.

The two existing cable combined will be similar to running a single 16mm2 cable, so you then only need to get a new cable up to 16mm2 to match it.

Cheers.