I am wondering  what the maximum distance is for batteries to be away from the inverter?

I  know normally they are close. In my kitchen set-up I may have to move them somewhat.

What cable size for the max distance?

It depends on your cable diameter, but generally thicker cable costs so much money that you tend to make this distance as short as possible for no other reason than your bank account!

If you use 50mm^2 for example, that has a resistance of 0.473 Ω/km (Edit: and it is DC so we can ignore the reactance). You want a voltage drop of no more than 2% (ideally just 1%!) of the total, so on a 48V system, that's 1V max, but ideally just 0.5V. A 3KVA inverter at 48V needs a good 60A at peak operation, so that's 0.473*60 = 28V per kilometer, so you can have one 28h of a kilometer or around 35 meters... but that is round trip (positive and negative cables combined), so it's more like 18 meters. And as I said, ideally you want to halve that too... so more like 10 meters.

If you see what 50mm^2 cable costs you won't ask any more questions 🙂

Edited April 17, 20197 yr by plonkster

Why are you making my solar so difficult!😀

I know cable costs are enormous.

5 minutes ago, Mistral said:

Why are you making my solar so difficult!😀

Well, consider this. At 60A and 1V loss, you're generating 60W of heat! Sure, that is spread out over 20 meters of cable so it's not too noticeable... 😛

 

12 hours ago, plonkster said:

If you see what 50mm^2 cable costs you won't ask any more questions 🙂

Ag nee man. It is not that bad. R80 per meter if you shop hard. 🙂 

2 minutes ago, The Terrible Triplett said:

Ag nee man. It is not that bad. R80 per meter if you shop hard. 🙂 

Times 20 meters... you can almost buy a small Axpert for that! 😛

Edit: Then again, I spent twice that on an Earth Leakage... so Touche!

Edited April 17, 20197 yr by plonkster

I just got gatvol and went 50mm2 - have not regretted the R480 for 3m x 2 wires.

No voltage drop, no worries about amps - nothing.

5 hours ago, The Terrible Triplett said:

I just got gatvol and went 50mm2 - have not regretted the R480 for 3m x 2 wires

You imply 50mm2 is over-sized for your 24V 3kW @ a 6m loop set up ... it isn't ... it's just about right, to be under 2% at full load.

Your Cu losses at full load = (125)^2 * .000478 * 6 = 45W. ( 1.5%).

Anything less would considered conventionally under-engineered.

4 hours ago, phil.g00 said:

You imply 50mm2 is over-sized for your 24V 3kW @ a 6m loop set up ... it isn't ... it's just about right, to be under 2% at full load.

Mine's only 35mm^2, but about half the distance from the batteries. Same thing... I can not call it oversized. At full power I drop as much as 0.5V, which is bang on 2%!

Edited April 18, 20197 yr by plonkster

23 hours ago, Mistral said:

I am wondering  what the maximum distance is for batteries to be away from the inverter?

I  know normally they are close. In my kitchen set-up I may have to move them somewhat.

What cable size for the max distance?

Hi Mistral,

there's a calculator available for this. Here's the simple one (unfortunately non-english): http://www.ekoproud.wz.cz/v_prurez.htm

As a template, here are the values that I've put in for my system (9m circuit length, 150mm2 cable):

 

And here's the sophisticated calculator (english), that is usable for DC, AC and even for a 3-phase system too: https://myelectrical.com/tools/cable-sizing-calculator

 

5 hours ago, phil.g00 said:

You imply 50mm2 is over-sized for your 24V 3kW @ a 6m loop set up ... it isn't ... it's just about right, to be under 2% at full load.

Your Cu losses at full load = (125)^2 * .000478 * 6 = 45W. ( 1.5%).

Anything less would considered conventionally under-engineered.

You are 100% correct. I had it much shorter like 1.5m, therein the "impression" I had left in mind that is was oversized.

Edited April 18, 20197 yr by Guest

"As close as possible" is the preferred answer.

But looking at the circumstances, a long thick cable will work. On cars, when they put dual batteries in, the battery cables are often 7 or 8 m long, with very little side affect. So if you're happy with the cost, it's fine.