Volt sensing relay calculation

[Pijeros]

Hello,
pls do no kill me for being this stupid (i am a videographer in nature , and i need to make an order before my electrician returns from hospital...

I want to add leisure batt to my 1987 VW t3 Caravelle along with volt sensing relay and i cant figure out how to calculate the system:

My current setup:
start batt: 75Amph
leisure: 115 Amp
alternator: 65 Amp

my Qs:

VSR: how do i calculate the neccesary amperage of VSR for my setup? I plan to buy 140Amp, is that not overkill? Does it depend on the capacity of leisure battery and its current drawing when charging? How much does it draw (max) or what is the factor

Wire: Based on what do you calculate its size from start bat to VSR and from VSR to leisure? Also leisure?

Fuses: Based on what do you calculate its sizes on both sides? On the size of the wire?

Thank you pretty much.
petr

 

[PEG]

Hi,i would strongly advise you not to bother with what is effectively,an idea from the 50's
I would get a Dc to DC charge controller,current limited,to suit both your alternator output,and size of leisure battery.
This time of the year,is the busiest,for this exact issue....i may start using the old "....i'm in hospital..." meself