DIY: Cable thickness for 250w 12v Wind Turbine 40m

[Solar2020]

DIY . Hello, I own a Marlec Rutland 913 250w , 12v Wind Turbine that I want to erect on land outside my caravan. The turbine will be 10m in the air and will be located about 15m from my caravan. I will size to 30 meters of cable. The charge controller the wires terminate to has a 20amp fuse.

What thickness wire do I need to use? From my calculations online, i can buy 30 meters of 6mm2 which will give me a 6% voltage drop. I will terminate that into a 20amp breaker before linking it to the wind turbine charge controller. Are my calculations correct?

I would add to get the full 250w or 20AMPs, I would need a 40 knots or 40mph wind so that would only occur in storm conditions.

Thank you for your help

 

[Lucien Nunes]

The online calculator result is way out.
6mm² conductor is about 3.1mΩ/m.
30m cable run is 60m conductor length.
60 x 0.0031=0.186Ω
Voltage drop at 20A:
0.186 x 20 X 100 / 12 = 31%

25mm² and 35mm² lie either side of your 6% drop.

 

[Solar2020]

25mm² and 35mm² lie either side of your 6% drop.
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Hi Lucien, thank you for your reply. 35mm2 is huge and would cost about 250 GBP and would not terminate in the charge controller; i struggled to get 6mm2 into the + and - terminals.. This is where I get confused.

In the manual, see attached image it says I can use 6mm2 over 31-45 meters, but when I use the calculators on voltage drop it says I cannot.

What are the implications of using 6mm2?

 

[Lucien Nunes]

They are obviously permitting a much greater drop than 6% for reasons of practicality, and for most situations it will probably be fine. They would not sanction the use of a cable of such high resistance that it makes their product look bad.

If you want maximum efficiency over long 12V circuits, particularly charging circuits where the voltage available to drive current around the circuit is only the difference between the charger voltage and the battery voltage (often only a volt or two) then you will need heavy cables. That's why the supergrid runs at 400,000V.

On long cable runs using heavy cables, it is sometimes necessary to terminate the main run onto something smaller that will fit into the target device.

 

[Solar2020]

Hi Lucien, thank you for the reply, I understand the thicker the cable, the better. I think just on cost I am going to be limited to 10mm2 at the most, even that will set me back 80 GBP and give me a voltage drop of about 17%

I guess it will come down to trade off , if cost v efficciency