6mm or 10mm for solar extension lead





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  1. #1
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    Default 6mm or 10mm for solar extension lead

    Hi guys I want to make a 8m extension lead for my dad's 2 x 55w solar panels to his National Luna box.

    Is 6mm sufficient?

    Regards
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    Default Re: 6mm or 10mm for solar extension lead

    4mm is probably fine, but if you have 6mm even better

    To give you an idea i have 2x 80w 36v panels in parrallel so its 160w at 36v and i use a 4mm 10m twin cable and it works a bomb
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    Default Re: 6mm or 10mm for solar extension lead

    I use the 4mm solar installation cable that I got from AC-DC. I was told that 4mm will be fine for any application up to 20 metres in length from the solar system expert at AC-DC.
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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by whatyamacallit View Post
    4mm is probably fine, but if you have 6mm even better
    Pretty much this. I made a 10m lead with 6mm and the voltage drop is negligible.
    Last edited by HeavyG; 2019/10/02 at 05:40 PM.

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    Default Re: 6mm or 10mm for solar extension lead

    With the tiny current two 55w panels will make 2,5mm would also be enough but it starts getting a bit thin and can be easily broken. 4mm will not give to much resistance over a short distance and the price difference is not much.

    If you want to get technical then you can check the resistance of your specific cable and work out the volt drop over the distance you want but with such small camping set ups it's not really necessary, just get a 4mm or higher twin cable that is flexible and tough enough to lay on the ground or to roll up and pack away.
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    Default Re: 6mm or 10mm for solar extension lead

    I have 2 x 120w solar panels on a 30 m 6mm twin flex. The panels output voltage is 19 to 21volts so the volt drop you get has no effect on it as the voltage at the regulator is in excess of 15 volts.

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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by whatyamacallit View Post
    With the tiny current two 55w panels will make 2,5mm would also be enough but it starts getting a bit thin and can be easily broken.
    I use 2.5mm sq on my 80w panel. ...10 m there of.
    Not sure about thin and easily broken, it is flexible. Mine is quite sturdy & the thinner profile rolls into a smaller parcel to stow.

    In fact all my 80w panels (12 of them) on roof are stringed with 2.5mm sq. All distances less than 10m, longer next size up.
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    Default Re: 6mm or 10mm for solar extension lead

    Per info, DC likes fine stranded wire, not solid house wiring type surfex etc. You will see in 99,9% of DC installations the wiring is fine many strands as DC travels around the perimeter of the wires. In your application you also need the finer wire to enable the rolling/packing up easier. A coarse wire will not roll up very easily and eventually break, it's designed to be put in place and left there.
    Obviously the thicker the better but as stated the amperage carried is very low (around 7 amps max) Even 2,5mm would do the job, go to the 4mm and smile

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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by peyperj View Post
    Hi guys I want to make a 8m extension lead for my dad's 2 x 55w solar panels to his National Luna box.

    Is 6mm sufficient?

    Regards
    At 8m you can easily get away with 2.5mm with 110W panels.
    However for future proofing I would suggest to make up a 20m cable of 4mm.

    4mm at 20m has about the same resistance as a 2.5mm at 8m.
    The extra length of cable will come in handy when your camp is set up in an area with lots of trees or shade
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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by Dave Faddel View Post
    DC travels around the perimeter of the wires.
    I don't believe this is true at all. Any expert care to chime in?

    Quote Originally Posted by Dave Faddel View Post
    you also need the finer wire to enable the rolling/packing up easier. A coarse wire will not roll up very easily and eventually break, it's designed to be put in place and left there.
    This is the real reason for solid vs. stranded core as far as I know.

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    Default Re: 6mm or 10mm for solar extension lead

    [QUOTE=HeavyG;4241710]I don't believe this is true at all. Any expert care to chime

    Ok, did some homework, you may in fact be right. My currents may have been crossed ... it seems more applicable for AC ... my apologies ..
    Last edited by Dave Faddel; 2019/10/04 at 03:33 PM.

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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by peyperj View Post
    Hi guys I want to make a 8m extension lead for my dad's 2 x 55w solar panels to his National Luna box.

    Is 6mm sufficient?

    Regards
    Hi Peyperj

    To answer your question : Yes.

    Why do I say yes ?

    Well to do a proper calculation I would actually need to know what solar panel is being used. Worst case scenario in this case would be a 55 W panel with a 18 V output that has a maximum current rating of 3 A - Higher voltage rated panels will have lower current ratings for the same power output.

    So combined the two panels (Again assuming you are connecting them in parallel) will give a total current of 6 A.

    We are interested in the losses that a undersized cable will introduce, especially for solar panels where every watt counts.

    For a 6 mm2 cable the total resistance of the cable can easily be calculated as follows

    Resistance per rating of of a typical multi strand 6 mm2 copper cable is 0.0033 ohm per meter.
    You have a total of 8 m x 2 = 16 m (both cores)
    The total cable resistance is 16 x 0.0033 = 0.0528 ohms

    Cable Losses = I2R = I x I x R = 6 x 6 x 0.0528 = 1.9 W ( at 20 C)

    The cable resistance will increase as the temperature increases. If the cables are laying on the hot ground in the African sun it can probably increase the losses to about an acceptable 2.5 W
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    Default Re: 6mm or 10mm for solar extension lead

    2.5 sq mm cable cant do any work, I was told by an electrician.

    I use a 10m x 10sqmm cable.
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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by JLK View Post
    2.5 sq mm cable cant do any work, I was told by an electrician.

    I use a 10m x 10sqmm cable.
    Based on the great figures supplied by Tiaan earlier even a 2.5 sq mm will work fine at 4.7W power loss vs 1.9W loss with 6 sq mm. 4.7W loss on the 110W of the total the panels provide is no train smash using 2.5 sq mm. 10 sq mm looks like an over kill.

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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by Dave Faddel View Post
    Per info, DC likes fine stranded wire, not solid house wiring type surfex etc. You will see in 99,9% of DC installations the wiring is fine many strands as DC travels around the perimeter of the wires. In your application you also need the finer wire to enable the rolling/packing up easier. A coarse wire will not roll up very easily and eventually break, it's designed to be put in place and left there.
    Obviously the thicker the better but as stated the amperage carried is very low (around 7 amps max) Even 2,5mm would do the job, go to the 4mm and smile
    Conductors are made for specific purposes. Where the conductors are not going to be moved or subjected to vibration the normal house 7 strand or even solid cable is used, The finer the strands the more resistance the conductor has. Compare 25mm welding cable's physical size to 25mm GP wire.

    Trailing cables for cranes and such are made of fine strands as the equipment constantly moves and the conductors are subjected to constant bending and vibration stresses. Automotive wiring is always fine stranded to cope with vibration stresses.

    Get the right fine stranded cable as thick as you can afford and you will be 100%. Remember the volage drop on a 8m extention is calculated on 16m. It is 8m there on red and 8m back on black
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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by ekkekan View Post
    Based on the great figures supplied by Tiaan earlier even a 2.5 sq mm will work fine at 4.7W power loss vs 1.9W loss with 6 sq mm. 4.7W loss on the 110W of the total the panels provide is no train smash using 2.5 sq mm. 10 sq mm looks like an over kill.
    I have never worked with W loss we work with voltage loss and this is affected by the size of the conductor as well as the length and important the load. Voltage drop is a nasty circle as the more amps you draw the more voltge you lose and the more voltage you lose the more ampere the device will draw to compensate for the drop in voltage. tis is one of the reasons electric edge trimmers pop so often, the thin wires in the electric motors on the appliances are not enough to handle the amps drawn on a long extension

    Here is a link to a site with a proper 12v loss calculator just fill in your figures and be prepared for a surprise https://www.12voltplanet.co.uk/cable...selection.html
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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by peyperj View Post
    Hi guys I want to make a 8m extension lead for my dad's 2 x 55w solar panels to his National Luna box.

    Is 6mm sufficient?

    Regards
    Yes I think so.
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    Default Re: 6mm or 10mm for solar extension lead

    Quote Originally Posted by ekkekan View Post
    10 sq mm looks like an over kill.
    I use up to 240 Watt panels. 6sq mm will probably also work. I just tried to use the panels as effective as possible.

    Watt is also Volts x amps. Thus the volt drops gives you less watt. With a PWM charger it probably doesnt matter as the charger dont use the surplus volts from the panel?
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    Default Re: 6mm or 10mm for solar extension lead

    Henk thanks for a very handy link for DC systems.

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    Default Re: 6mm or 10mm for solar extension lead

    A copper conductor of 1sq/mm area presents 0,017 ohms for every metre of its length.

    Doubling the length doubles the resistance. Doubling the area, halves the resistance.

    Your 16 (8 x 2, you count both strands) metres of wire will have a total resistance of 0,136 ohms.

    Your panels connected in parallel will deliver up to 8 Amps maximum.

    Hence the volt drop across the conductor will be 0.136 x 8 = 1,088 Volts, nothing to worry about since the output voltage from the panels at full load will be over 16 Volts. If you want by all means use 2,5 sq/mm auto wire. That will reduce your volt drop to 0,435 Volts, no significant advantage other than the wire is physically more rugged, being auto and not domestic wire.

    This is why copper wire can handle up to 9 Amps per each sq/mm in auto wiring applications. 4sq/mm wire is rated for 36 Amps. 6sq/mm for 54 Amps.

    Wire is made multi-stranded to make it more flexible.

    At radio frequencies you get 'skin effect' whereby the current flows mostly near the surface of the conductor. I can assure you you won't experience skin effect in your fridge wiring.

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