Thread: 16mm square twin cable?

Originally Posted by bacicat2000

I am man enough to admit defeat here, I'll go crawl back into my box now.... I'll stick to 240 volt stuff from now on...

Cheers - Gav.

Hi Gav and sorry if I came over as if this was a competition.

It’s not, it’s just a debate which is being viewed from different fields of electricity. From 240VAC and from Extra Low Voltage DC.

While I have a decent working knowledge of 240VAC, I make it a point of never discussing 240VAC topics other than very basic info relating to thing like the type or size of battery chargers or inverters. I am not an electrician and so it’s not my place to cover anything 240VAC.

But while I don’t venture in to the field of AC, and there are some similarities, there are also many differences, so 12v DC needs to be covered as a specific field of electricity.

As such, this was not a competition and there is no reason for you to “go crawl back into your box”.

Cheers, Tim.

Originally Posted by drivesafe

Hi Scoota, for what your planning to use the cable for, 6B&S or 16mm2 twin cable would be the minimum size but you will still get a voltage drop and you might be surprised at how much voltage drop you will get with this thick cable.

Just to give you an idea of what to expect, just last Thursday I was carrying out some operating experiments on a new isolator.

I needed to do this in a real world situation, so the day before, I discharged two 105 Ah flooded wet cell deep cycle batteries down to 12.04v. Thats a fraction under 50% SoC.

I had these two batteries strapped down in the back of my wife’s D4 and had them connected via 6m of 6B&S twin from the cranking battery, via the isolator and through two sets of 50 amp Anderson plugs ( that 2 x 2 plugs ).

I was not interested in the current draw just the ability for the set up to be able to charge batteries without having problems with the isolator, so I only took voltage readings and didn’t bother with current readings.

Just after starting the motor, the cranking battery voltage was 13.78v and the auxiliary batteries were 12.71v

After 20 minutes of driving, the cranking battery voltage was 13.80v and the auxiliary batteries were 12.90v

After 3 hours and 6 minutes of driving, the voltage at the auxiliary batteries were at 13.28 and was 13.66v at the cranking battery.

The two auxiliary batteries have been sitting for a week now so if I get a chance this afternoon, I’ll load test them and see what they were charged to.

Hi folks and sorry for the delay.

I finally got the time ( remembered ) to test the batteries.

Even though they had been sitting for just over 2 weeks, after putting a small load on them for about 10 minutes, the voltage settled at 12.47v.

This puts them at about 86% SoC.

So thats close to 75 amperes of used capacity replaced in a little over 3 hours driving time, with an alternator voltage of 13.8v.