This is one of those almost religious topics. You'll get very strong opinions on both sides!Richard77 wrote: ↑Sat Jan 11, 2025 9:01 pm If I go the post route and use 70mm² to the inverter, I suppose the 2x 35mm² would have originally fitted. So wouldn't need to go down the post route in the first place.
I really could do with finding out what size cable physically the 8kw SunSynk can take thickness wise.(seems it's 70mm²)
Update edit: maybe 2x 35mm² will fit.
What's everyone's thoughts on DC isolator between battery and inverter? I'm sure I read somewhere they are not recommended any longer.
You should be aware that every connection point is a source of heat/failure. A "Frankenstein" switch-fuse introduces a whole load of potential sources of heat. And breaking DC under load is no joke, so be very careful to source high quality components and overspecify (this isn't the time for Amazon/eBay).
While a point of isolation can make maintenance less perilous, there is no way around working with live conductors when installing solar/batteries.
I would as a first option connect both batteries to the inverter. However if the inverter cannot accommodate 2x cables then you need a junction. You don't need 2x 35mm² joining to a 70mm², that isn;t how it works. You can do the whole thing in 35mm² unless the cable from the junction to the inverter is long enough to require a bigger cable for voltage drop.
12V Planet has a good voltage drop calculator. you want to be below 3% for the whole system (AC side plus DC side) and some people allocate this as 1% DC and 2% AC. However, you really want your AC voltage drop as low as possible because it avoids your inverter switching off in high grid voltage situations (that are really common in the UK. I'd still keep the DC side below 1% for efficiency reasons.
