Electrical Question

[SkiFreak]

There may be a terminology issue here.

You could be right, but they also call this a battery isolator.

 

[Turtle59]

There may be a terminology issue here. Projecta seem to use the term isolator broadly.
View attachment 316011
this is called an isolator but is an auto vsr.

Thanks for pointing that out Alastair. The one I have is actually an auto VSR.

 

[Turtle59]

With 2 x 105A/H house batteries you should get 4 to 5 days use of the fridge without any battery charging, assuming that nothing else is connected to the house batteries (which is unlikely).

What I would add is to keep your cable runs as short as possible, as voltage drop can be a real issue when it comes to charging batteries. You should also run a positive and negative cable from the start batteries to the house batteries. Don't be tempted to use the chassis as you earth connection.

Because my cable runs are only from one side of the chassis to the other (about 1m - 1.5m max) do you think the 16mm2 cable is adequate or shall I use some 28mm2 cable I have laying around? Should lessen the chance of voltage drop.

Great suggestions thanks.

 

[gait]

for 50Amps voltage drop for 3m of 5AWG (16.8mm2) about 0.3v (at 12v), for 3AWG about 0.2v.

Once up to about 90% charged the charging current progressively reduces, until its pretty low and the voltage loss is about 0.

 

[SkiFreak]

As gait has pointed out, for a 3 metre length of cable (1.5 metres of positive and negative cable) there is only a minor difference in using 16 or 28 sg/mm cable when it comes to voltage drop. My point was to use the least amount of cable as possible, as longer lengths can potentially cause issues (you had mentioned having 10 metres of cable).
I am well known for over engineering pretty much everything, so I would probably go with the larger cable, but that does not mean that you would want to do the same thing. Larger cable would probably lessen the possibility of the cable getting hot, which for me is a good thing. Put it this way... if you use larger cable it will definitely not be worse, but you may not see any noticeable difference.

 

[Turtle59]

As gait has pointed out, for a 3 metre length of cable (1.5 metres of positive and negative cable) there is only a minor difference in using 16 or 28 sg/mm cable when it comes to voltage drop. My point was to use the least amount of cable as possible, as longer lengths can potentially cause issues (you had mentioned having 10 metres of cable).
I am well known for over engineering pretty much everything, so I would probably go with the larger cable, but that does not mean that you would want to do the same thing. Larger cable would probably lessen the possibility of the cable getting hot, which for me is a good thing. Put it this way... if you use larger cable it will definitely not be worse, but you may not see any noticeable difference.

Thanks blokes for your input and knowledge. Most helpful.

Cheers.