solar panel cable size

[lesrollins]

What size cable do i need from 2 x 140w solar panels to a 40amp mppt controller and what size cable would i need from the controller to the batteries. Is there any maximum length of cable that should not be exceeded in any of the runs.

On solar panels what is the difference between 36 cells and 72 cells and can 72 cell solar panels be used on a 12v system. Thanks

[NMEA]

You will need to provide the cable run lengths (round trip) for both the runs you mention before anybody can give you any meaningful reply on the actual 2mm of the cable. Or you could work it out for yourself using one of the many cable voltage drop tables available. There is no maximum length but the longer you go the bigger (and more expensive) the cable cross section so keep as short as practical. You should be looking for no more than 3% ( preferably less) drop as this is a highly voltage critical aplication. Bear in mind that the quoted rating of the panels will rarely be acheaved in UK.

Edited May 31, 2012 by NMEA

[lesrollins]

Any chance of that in lay mens term that answer goes beyond me i,m new to this. Cheers

[matty40s]

Any chance of that in lay mens term that answer goes beyond me i,m new to this. Cheers

 

It was rather technical wasn't it!!

 

You need to let us know how far from controller to batteries to ascertain the best cable size.

 

The panels to controller would be 4mm or 6mm pholtovoltaic cable in normal set-ups. The further your lemgth of run, the larger cable you should use due to voltage drop.

[lesrollins]

The two panels will be sitting adjecent to each other forming a run just over 3 metres. From the end of the last panel to the controller will be about 2.5 metres. And the controller to the batteries will be a run of about 2 metres. These measurements have allowed for the cables to be fixed in a tidy fashion. Thanks

Edited May 31, 2012 by lesrollins

[jenlyn]

The two panels will be sitting adjecent to each other forming a run just over 3 metres. From the end of the last panel to the controller will be about 2.5 metres. And the controller to the batteries will be a run of about 2 metres. These measurements have allowed for the cables to be fixed in a tidy fashion. Thanks

I tweaked mine a little by connecting the battery cables from the mppt to a domestic choc block in a box, thus only using one cable to the battery bank. I think you can also parallel the panels.

I should point out that my setup came as 2 panels with 2 mppt controllers :-$

Edited May 31, 2012 by jenlyn

[lesrollins]

I thought i would only need one set ( positive and negative ) of cables to the battery bank from the controller. The batteries are already joined in sequence. Sorry missed the last part about two mppt controllers i will only be using one 40amp controller.

Edited May 31, 2012 by lesrollins

[Ex- Member]

What size cable do i need from 2 x 140w solar panels to a 40amp mppt controller and what size cable would i need from the controller to the batteries. Is there any maximum length of cable that should not be exceeded in any of the runs.

On solar panels what is the difference between 36 cells and 72 cells and can 72 cell solar panels be used on a 12v system. Thanks

 

Hi Les

 

You should get away with MC4 cable for the solar panels with no problem. If you have 12v panels I'm not sure weather they come with the MC4 connectors & box fitted to the rear.

 

I would say 16mmS would suffice from CC to batteries. You should check out lengths and v drops though, there's a voltage drop checker on line here.

 

http://www.calculator.net/voltage-drop-calculator.html

 

This thread is also worth a good read, it's recent and there's a couple of members actually fitting panels as the thread goes on so some really helpful info. You'll probably need to fues on the solar side of the charge controller as well as the battery side, rated around the same as your charge controller. It all sounds more complicated that it actually is once you get your head around it.

 

Here's the thread

http://www.canalworld.net/forums/index.php?showtopic=46249&st=260

 

 

 

[Higgs]

I bought my panels, 3x100w, from the boatyard I worked at. Must have asked what wire I needed. I've ended up with 8.5mm sq'd cable, for a run of about 35' to the control box and engine room. Going to use the same wire size to run back to the 12v fridge.

[Ex- Member]

I bought my panels, 3x100w, from the boatyard I worked at. Must have asked what wire I needed. I've ended up with 8.5mm sq'd cable, for a run of about 35' to the control box and engine room. Going to use the same wire size to run back to the 12v fridge.

 

I wouldn't use standard cable on the roof.(If that's what you've used) Solar cable has a casing that can withstand the elements, if you use standard cable you'll need to use some conduit or sleeving to protect the cable. 12 volt panels often don't seem to come with MC4 connectors, the larger type panels for fitting to roof's (usually around 160 watt +) do but are higher voltage and need a MPPT controller for best results. Although you can wire 3x 12 volt panels to produce 36 volts, but again need a MPPT controller to cope with the higher voltage I believe.

 

 

 

[lesrollins]

So whats the difference between 36 cells and 72 cells and can a 72 cell solar panel be used on a 12volt system. When choosing solar panels is it best to use brand names or can cheapies be just as good.

[bottle]

Les

 

To compare solar panels look at their specifications. Wattage, voltage, open circuit voltage, open circuit amperage etc.

 

That with the correct controller, PMW or MPPT will tell you if they are suitable for your needs.

[Grace and Favour]

So whats the difference between 36 cells and 72 cells and can a 72 cell solar panel be used on a 12volt system. When choosing solar panels is it best to use brand names or can cheapies be just as good.

 

Can cheapies be as good as brands - - - that's an impossible question to answer accurately - - -

It depends upon the cheapie, it depends upon the brand, it depends upon what you want?

 

It's a "reasonable" maxim that one 'often gets what one pays for' (but we are generalising aren't we?)

 

I've recently bought some really first-rate Sanyo HIT panels (240w each) for £300 a pop - still expensive compared to some cheapies (but not nearly as dear as they were . . .) -= but (I'm led to believe) the performance profile of them is brilliant . . . . so I'm glad I bought them instead of 200w cheapie panels for £200.

 

Performance, build/component quality, and longevity are all factors in the difference between cheapie and branded, just as the retailers profit margin may well make a major difference too

 

 

At the end of the day, some people will tell you to buy one thing, as opposed to another, and be completely convinced they're right, but it's you that has to make the judgement I'm afraid.

 

There are some rubbish panels out there - - for there are sellers that will offer a 10 year guarantee, safe in the knowledge that they'll have closed the business in under two years.

 

Personally, I'll always buy the 'best' that I can afford - - only time will indicate whether I'm right

[Higgs]

I wouldn't use standard cable on the roof.(If that's what you've used) Solar cable has a casing that can withstand the elements, if you use standard cable you'll need to use some conduit or sleeving to protect the cable. 12 volt panels often don't seem to come with MC4 connectors, the larger type panels for fitting to roof's (usually around 160 watt +) do but are higher voltage and need a MPPT controller for best results. Although you can wire 3x 12 volt panels to produce 36 volts, but again need a MPPT controller to cope with the higher voltage I believe.

 

 

The cable is for internal use once the panel cables have been fed through the roof. Haven't fitted yet. The way I intend to do the fitting, all the panel cables will go through under the panel and non exposed directly to the elements.

 

Cheers.