Solar panel wiring

[panamea]

I'm rebuilding a Class C and I might be redoing the roof soon. I would like to run the wiring for solar panels now instead of doing it through the fridge vent later. The thing is that I won't be able to install the max wattage from the beginning so is it possible to run the wires now and keep on adding/ changing the panels later or do I have to decide now what the system will be and run the right gauge.

Thanks

[OldSmokey]

westend wrote:
I don't think you've calculated the voltage drop correctly. I'd bet you are dropping voltage 3-4% over 40' of 10 ga at 54V w/17 A.

A better practice may be to install the largest wire possible from the roof to the controller location. That will insure that all the current produced gets to the controller.

yeh.. I messed up, I'm tired and have had a few beers..
here is the revised calculations.

The resistance per foot from the standard AWG tables is 0.9989 milliOhms per foot for 10AWG copper.
my panels Vmpp is 18.8 V and I have approx 40 foot run inclusive from panels to charge controller.
so assuming I could actually get 160W from each panel on a perfect day then: as a 3S2P string I get 18.8V*3 = 56.4 Volts from each string. (160W*3)/56.4V = 8.51 Amps. with 2P = 8.51*2 = 17.02 Amps
therefore: 40ft * 0.0009989 Ohms * 17.02 Amps = 0.68005 Volts drop
0.68005/(56.4/100) = 1.2%

you lost the bet.:p

[westend]

OldSmokey wrote:

pianotuna wrote:
Just run the wire for the most amps you dream of having. #4 would be great.

er no, you don't need 4 AWG

I have 960 W on my roof ( 6 * 160 W ) configured as 3S2P and the max current is 17 Amps @ 54 V, 10 AWG is more than enough.

Vdrop over 40Ft of 10AWG at 17 A is less than 1V.

if you think you need 4 AWG then you need to think again..
unless you have cash to burn..

I don't think you've calculated the voltage drop correctly. I'd bet you are dropping voltage 3-4% over 40' of 10 ga at 54V w/17 A.

A better practice may be to install the largest wire possible from the roof to the controller location. That will insure that all the current produced gets to the controller.

Without knowing the OP's plans, use, and dimensions, it is difficult to advise a wire gauge. I always tend to install larger wire as the price is not significant and I will be sure it is large enough to handle the loads.

[OldSmokey]

pianotuna wrote:
Just run the wire for the most amps you dream of having. #4 would be great.

er no, you don't need 4 AWG

I have 960 W on my roof ( 6 * 160 W ) configured as 3S2P and the max current is 17 Amps @ 54 V, 10 AWG is more than enough.

Vdrop over 40Ft of 10AWG at 17 A is less than 1V.

if you think you need 4 AWG then you need to think again..
unless you have cash to burn..

[panamea]

Thank you all for your answers.

[pianotuna]

Just run the wire for the most amps you dream of having. #4 would be great.

[Boon_Docker]

panamea wrote:
Was thinking of running 2 or 3 different gauges cables and use the corresponding one for different setups but not sure what the prices are for wires and I'm on a tight budget.

Also, What will happen if I install a wire for a higher amperage and start with a lower amperage system? (in order to add to the system later

Thanks

High amperage wire (larger wire) is better even for a low amperage system. The larger the better, there is less voltage drop with larger wire.

[Lwiddis]

"Was thinking of running 2 or 3 different gauges cables"

If you had 25 amps coming from your panels to controller within 12 feet, 8 gauge wire would be appropriate. I'm using 8 for 10 feet and 18 amps.

[azrving]

Get the measurements for various panels then make cardboard patterns and go up there and see where and how many could fit. Just say you could get 600 watts up there, 600 watts is going to give you a max of about 30 amps. If you run an PWM controller you would be carrying more amps than if you used an mppt controller.

If I only knew that I had the potential to put 600 watts up there I would install number 6 uv protected wire through strain reliefs at the frig vent with enough extra up top and down below to reach your possible combiner box and controller near the battery. If you said you can only get 300 watts up there I would then probably use 10 gauge.

If you want to go through the roof you could use something like this but there may be better quality others available. It's just an example of how to go through the roof. Some also go down the vent pipe using strain reliefs.

[mike-s]

panamea wrote:

WNYBob wrote:
In home construction they run plastic pipes from the attic to the basement, for future network cables. I don't see why you couldn't do it on a camper, just seal it where it goes through the roof.

Can wires be pushed through pipes that are bent on 90 degrees when going from roof to the wall?

Thanks

If you're trying to push wires through conduit, you're doing it wrong.

[dfletch]

I would just run 10 or 8 gague wires now while it is easy to do it. It doesn't hurt to lhave larger wire than you need other than the cost of copper and allows for future expansion. As a matter of fact the larger wire will have less voltage drop on long runs.

[time2roll]

I would do nothing until you are ready to go solar. That way you just make the hole you need for the system you are installing. Already plenty of holes in the roof. You just drill and seal it up like the rest.

[panamea]

Was thinking of running 2 or 3 different gauges cables and use the corresponding one for different setups but not sure what the prices are for wires and I'm on a tight budget.

Also, What will happen if I install a wire for a higher amperage and start with a lower amperage system? (in order to add to the system later

Thanks

[panamea]

WNYBob wrote:
In home construction they run plastic pipes from the attic to the basement, for future network cables. I don't see why you couldn't do it on a camper, just seal it where it goes through the roof.

Can wires be pushed through pipes that are bent on 90 degrees when going from roof to the wall?

Thanks

[Boon_Docker]

Your best bet would be to decide now what the system will be and run the right gauge.