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cable size 48v system, 4x250ah batteries, 4m

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Depends on the maximum current draw of the inverter... the one thing you didn't specify :-)

Let's say it is 5kva. That's about 100 amps give or take. You want a voltage drop of less than 3%, preferably around 1%.

35mm^2 has a resistance of 0.65Ω per kilometer. You have 0.004 kilometer. So

0.004 * 0.65 * 100 ~= 0.3V. That's less than 1%.

25mm^2 has a resistance of 0.9Ω per km.

0.004 * 0.9 * 100 ~= 0.4V. That's also less than 1%.

If you look at some wiring ampacity tables (google) you'll see that the 25mm^2 will run quite hot at full load. So 25 in open air is fine if you only run full load for short periods. I'd go with 35.

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  • 5 months later...

So cable is expensive, that is true, but you buy it once. On the other hand, cable that is undersized hurts you day by day.

Even Voltronic updated their latest manuals to say 0 gauge for the battery (that is approx 55mm cable).

50mm welding cable is about R65 per meter when I bought some recently (that was only phoning about 3 places, I'm confident I could have found cheaper if I tried). It is expensive but it is once off and considering the cost of everything else it is nothing.

After 50mm things get expensive really quickly. 70mm I couldn't find cheaper than around R120 per meter. In that case I would simply double up on 50mm.

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  • 2 weeks later...

So far I've gone with 35mm2 on a similar battery bank and inverter. For volt drop reasons but also for pragmatic reasons: anything above 35mm2 becomes a real pain to terminate. Both finding the right termination and the actual task of clamping/crimping (not to mention the cost of tooling). I'd like to hear from others who have used anything above 35mm2 what their termination methods are. 

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1 hour ago, Jaco de Jongh said:

lucky enough to have my own

For a long time I used to have my cables crimped at the shop where I bought the cable. Finally this came past on gumtree at half price.


Then I got one of these as well, not this specific brand, this is a random picture from the internet, but it looks similar. Cheap, I think it was R130. Friend of mine says get a cheap set of garden shears, apparently nothing cuts copper cable cleaner than that :-)


I love tools. I tend to not buy the Metabo/Makita, I don't use it enough to justify that, but it still helps to have a tool or two.

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3 hours ago, Jaco de Jongh said:

After work I stopped at the Electrical wholesaler to pick up some spares, and found this on the counter.. 

16mm to 240mm...


And 16-300mm


Special till end of September.. Its pretty decent prices... 


That's cheap, but a real pain in the arse to properly crimp anything above 120mm by hand. Next time I'll buy a battery driven one ;)

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