Advice for solar cable sizes (1 Viewer)

[BILL 875]

Hi,
At the moment i have 1 x 120 w solar panel fitted and i am adding another 120 w panel i have changed the charge controller to a votronic 250w/15 amp controller, at the moment the wire from the existing panel via controller to the two leisure batterys is 2 x 2.5mm, the new solar panel wiring is 2 x 4mm, there is no way i can get to the connection on the existing panel which is 2.5 mm cable, so if run the 2 x 4mm to the controller put a branch connector to join the 2 x 2.5mm into the 2 x 4mm cables and change the cable from the controller to batteries with 2 x 6mm cable, its 2 meters in length with a 20 amp in line fuse. Also there is already a 20 a fuse in the controller.
Does the above sound like the best way to wire all this up?
Also is a 6mm cable the same size as a 6mm sq cable.
I look forward to any advice.
Many Thanks
Bill

 

[Richard n Ann]

Yes sounds like a plan. Just check what size cable comes with a 250w panel. It might be ideal to upgrade to whatever they come with.
With automotive cable the 4mm sometimes means overall diameter as that's what the manufacturer needs to calculate the space needed for bundles of cables. I'm no expert mind.

 

[Lenny HB]

Sounds good as Richard says Auto cable is often spec including the outside diameter. Proper Solar cable is cheap and you can buy it with the connectors already on. Solar cable is a bit bigger as it is double insulated (for high voltage domestic sytems where the panels are in series) has the advantage of the outer sheath being UV resistant good for any exposed cables on the roof.
If I need two 5 meter cables one with a female connector and one with a male cheaper to buy a male-female 10m cable and cut in half.

As for cable size anything above 4mm will be fine.
Voltage drop will be at it's highest in summer in full sun. In these conditions you will be getting the best out of your panels and the load on your electrical system will be at it's lowest.

Votage drop will be at it's lowest when the panels are producing low output. In these conditions you will be getting the lowest output out of you panels when you need the most system power but the volt drop will be low.

Example:
100 watt panel in full sun producing 6 amps with a cable run that gives a 5% volt drop net result a 5% reduction in power, the panel will still be giving you 5.7 amps this is not going to worry you in summer.
In winter with the same panel producing say 2.5 amps a 5%reduction in power, the panel will still be giving you 2.375 amps again not enough to worry you.

^{_{Subscribers  do not see these advertisements}}

 

[Freespirit1]

Always best to wire similar panels in series to give a higher combined voltage if your controller will take the sum of the individual panel voltages giving reduced cable runs too!