solar panel cablling

Submitted: Monday, Dec 02, 2013 at 15:20

ThreadID: 105348 Views:3201 Replies:12 FollowUps:15

This Thread has been Archived

avidcamper

We have two 60W solar panels roof-mounted on our goldstream wind-up camper. Up until recently, they have worked perfectly to keep our two batteries charged - the main draw on the batteries being our electric-only fridge.

The cable from the panels is connected to an anderson plug mounted under the trailer which is wired into the solar panel regulator. The wiring into the anderson plug from the solar panels broke, so my husband re-attached the plug - it broke again and we now realise that the actual copper wiring is exceptionally poor quality & is crumbling. We obviously need to replace the cable.

My question is where do we go to purchase good quality cabling, and what should we be asking for??? We have read, and tried to absorb, an article on exploreoz regarding solar panels & cables, but it has left us feeling less confident of buying the correct sized cable.
We would appreciate some advice on this to enable us to properly make the necessary repairs.

Thanking you in advance,

avidcamper

Back Expand Un-Read 0 Moderator Share

Reply By: Member - Rosco from way back - Monday, Dec 02, 2013 at 15:51

Reply By: Herbal - Monday, Dec 02, 2013 at 15:57

Reply By: Ross M - Monday, Dec 02, 2013 at 16:01

Monday, Dec 02, 2013 at 16:01

avid
Although not a Jaycar line, they do sell twin core red/black in 3mm 4mm 5mm 6mm with a plastic sheath over it.

The 5mm will be quite reasonable for the current over the distance you are working and not cause much voltage drop.

What you should aim for, if not already done, is the to feed the regulator and have it as close as practical to the battery. Then the maximum energy/voltage level available is then regulated and delivered to the battery/ies.

The 5mm, that is the dia of the red or black over the inner copper will flow 27 amps without significant heating of the cable due to it's own resistance, so 120W is only a few amps, maybe 8 on a good cool day and so that size should be ok. $2.75/m

6mm is more better of course.

You may be able to source similar off the WWW ebay thingo at a cheeeeper price.

Make sure non of the cables are free swinging as movement will cause fractures and failures in anything. Cables ties are your friend.

AnswerID: 522480

Follow Up By: avidcamper - Monday, Dec 02, 2013 at 16:58

Monday, Dec 02, 2013 at 16:58

Hi Ross M,

Thankyou for your help.

The regulator is installed close to the batteries (good!) .... our problem is the cable from the solar panels - obviously of inferior quality.

The panels are roof-mounted & the cable runs down the side of the camper to the anderson plug - 2.5 metres in length - do you think that we should aim for the 6mm rather than 5mm? What I don't understand, is the difference between 5mm & 5mm²????

Regards,

avidcamper

FollowupID: 803556

Follow Up By: Ross M - Monday, Dec 02, 2013 at 18:04

Monday, Dec 02, 2013 at 18:04

Avid
I use 5mm (cos i had it) on a similar length run with 160W (2 panels) and that is OK.
Bigger is better, but if the 5mm is sufficient then 6mm is not going to be any more benefit but has capability for expansion of panels though.

FollowupID: 803563

Follow Up By: Terry 12 - Monday, Dec 02, 2013 at 21:58

Monday, Dec 02, 2013 at 21:58

( What I don't understand, is the difference between 5mm & 5mm²?? )

5mm is the width of the copper core as a diameter, 5mm across.
5mm² is the total end area of all the strands that make up the wire, this could be 40 of 50 very small strands or copper, as one solid square of wire it would be 2.24mm x 2.24mm ( 5mm² )

FollowupID: 803572

Reply By: Member - wicket - Monday, Dec 02, 2013 at 16:51

Reply By: bks - Monday, Dec 02, 2013 at 17:18

Reply By: Member - Bruce C (NSW) - Monday, Dec 02, 2013 at 17:21

Monday, Dec 02, 2013 at 17:21

Hi Avidcamper,

It has not been mentioned so far but it is accepted that 4 mm2 is the preferred size from the panels to the regulator.
As I explained in follow up to Wicket a minimum of 6 mm2 for regulator to batteries but keep the reg to battery cables as short as you can so that you minimize line drop or losses.
Ebay is also awash with sellers selling suitable cable but you can depend on ABR for a quality product and good advice.

Cheers, Bruce.

At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

Lifetime Member
My Profile Send Message

AnswerID: 522487

Follow Up By: Brian 01 - Monday, Dec 02, 2013 at 20:14

Monday, Dec 02, 2013 at 20:14

I'm at a bit of a loss as to why there would be a blanket acceptance of 4mm2 being the preferred size from the panels to the controller but then 6mm2 from the controller to the battery.
First point would be that the length of run from the panels to the controller is likely to be considerably longer than that from the controller to the battery and therefore should have the larger cable size.
Second point is that if using a series type controller (PWM) then the current in both sections of wire is the same, so why have different sizes?
If using an MPPT controller, then there may be a slightly larger current in the controller to battery cable, but even so, the larger cable for the longer run is still sensible practice.
Third point is that surely the length of the run, the current being carried and the tolerable voltage drop are the wire size deciders, not some rule of thumb.

FollowupID: 803568

Follow Up By: Member - Bruce C (NSW) - Monday, Dec 02, 2013 at 20:55

Monday, Dec 02, 2013 at 20:55

Hi Brian,
There is no blanket acceptance of 4mm, just a general acceptance from most of the reading I have done on the subject and from the more experienced installers here. Also it works fine on my installations.

I guess that the 4mm theory it is due to the higher voltage at the panels (19 to 21V) where as the reg drops that down to 12V to the battery connections. This is why it is generally accepted that a larger sized but shorter cable is required between reg and battery.

This is my understanding on the subject anyway.

Accepted that the larger the better when dealing with DC but there is such a thing as over engineering I guess and that may account for the 4mm versus the 6mm thinking.

Mind you, I am happy to be enlightened if I am misguided on this.

Cheers, Bruce.

At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

Lifetime Member
My Profile Send Message

FollowupID: 803570

Follow Up By: Brian 01 - Monday, Dec 02, 2013 at 23:15

Monday, Dec 02, 2013 at 23:15

If the controller is a PWM type as most still are, then the voltage of the panel is pulled down to that of the battery, so you won't see anywhere near 19 to 20v on those cables when the controller is on, 13 to 14 is more likely, and that is the exact same voltage that will be present in the other bit of wire as well.
Even if it is an MPPT controller where the voltage at the panels will be higher during the boost stage, it will still absorb and float in PWM mode, with all voltages being the same throughout, so, no matter which size you use, there really is no point in different size cables.

FollowupID: 803575

Follow Up By: Ross M - Tuesday, Dec 03, 2013 at 08:58

Tuesday, Dec 03, 2013 at 08:58

Any percentage of loss through voltage drop in panel to reg is going to cause some loss of efficiency. You only need a small resistance to be in the panel to reg to batt line and you will easily cause 1/3 of the charging ability to be lost.
It is because of the difference of the resulting applied voltage level over and above the battery level.
With an faulty/affected resisting circuit (wire too small) the applied voltage may be only slightly above the battery voltage and than means the current energy won't flow very much at all = less performance.

You want the reg to be able to deliver and the regs characteristics to control charge to the battery not the cables cos they aint smart.