Vosser Posted July 17, 2019 Share Posted July 17, 2019 (edited) Good day, Guys I'm planning my system and need some advise, please. Broadly I'm planning an off-grid system using the following: 12x Canadian 405W panels (3 strings of 4 each) MultiPlus II 48/5000/70-50 CCGX MPPT 250/100 2xPylontech US3000B (a diesel generator and maybe more batteries later will follow) Using the Victron MPPT Excel calculator for temperature variation between -5 to 80 degree Celsius tells be the current per 4 panel string will vary between 36.4A to 27.7A (206V to 124V). The panels will be on the roof of the house and the rest of the equipment will be in a outbuilding which is about 1-2 m away. I am uncertain about the size of solar cable from the panels. The combined cable length (+ and -) from the panels will not exceed 30m. When using this calculator (https://www.solar-wind.co.uk/info/dc-cable-sizing-tool) with the worse case values (36.4A, 206V and 30m) it gives me 10mm cable (for 3% loss) and 6mm cable (for 4% loss). Am I doing the calculation correct? Should I go for the 10mm or 6mm cable? When going with the 10mm it looks like not all MC4 connectors is made for 10mm (most are up to 6mm)? Will I need a bigger MC4 crimping tool (or are all of them capable to do 10mm)? Thanks for reading. Any advise is highly appreciated! Edited July 17, 2019 by Vosser Quote Link to comment Share on other sites More sharing options...
Jaco De Jongh Posted July 17, 2019 Share Posted July 17, 2019 16 minutes ago, Vosser said: Am I doing the calculation correct? Yes. 16 minutes ago, Vosser said: Should I go for the 10mm or 6mm cable? Volt drop on 6 mm over 30 meter will be 8.62 volt and on 10 mm it would be 4.99 volt, so on 6mm you will have (8.62V - 4.99V) x 36.4A = 132wh extra losses during full production Although 6 mm is within SANS regulation, it is better to use the 10mm to minimize your losses. SANS regulation state that you should remain below a 5% volt drop, but for solar applications a 3% is recommended to minimize losses. 16 minutes ago, Vosser said: Will I need a bigger MC4 crimping tool (or are all of them capable to do 10mm)? I am not sure what crimper you have, but mine can has different slots in the jaws to accommodate different size lugs. Vosser 1 Quote Link to comment Share on other sites More sharing options...
Jaco De Jongh Posted July 17, 2019 Share Posted July 17, 2019 41 minutes ago, Vosser said: The combined cable length (+ and -) from the panels will not exceed 30m. Wait, I have read to fast and missed this part. In this case do not worry about the distance from the panels to the combiner box. They are sold with 4 mm and 4 mm per sting would be sufficient. How far will the combiner box be from the Inverter? That Distance is important to determine the cable thickness after combining the strings. Quote Link to comment Share on other sites More sharing options...
Vosser Posted July 17, 2019 Author Share Posted July 17, 2019 Jaco, thank you for the replies. The 4 panels per string will be connected in serie with their pre-installed 4mm cables. I was wondering about the size of wire that I will have to install from the positive side of the nearest panel and the negative side of the furthest panel in the string to the combiner box. The combined length for those two wires will be about 30m. Quote Link to comment Share on other sites More sharing options...
Jaco De Jongh Posted July 17, 2019 Share Posted July 17, 2019 32 minutes ago, Vosser said: I will have to install from the positive side of the nearest panel and the negative side of the furthest panel in the string to the combiner box For a single string, you can keep it on 4 mm up to the combiner box. After combining the 3 strings, that is where you have to think about bigger cables, depending on the distance from the combiner box to the inverter. Vosser 1 Quote Link to comment Share on other sites More sharing options...
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