61 replies to this topic

[kmacafee]

I have searched high and low in advance to see if anyone has run heavier gauge wire from the roof to the battery box. Currently, the camper has 12 ga installed and I am thinking of going to 10, maybe 8 ga. So far I have not found any references.

 

I know where the box is in the ceiling and I know the wires run behind the front lift panels and down to the battery box over the water tank. Its the section between the ceiling box and the front panels that I am unsure about -- is it run thru conduit (unlikely) or just bundled and zip tied to roof supports?  I am hoping I can get some info from Brenda at FWC but was hoping someone here might have attempted it.

 

 Currently, the camper has 12 ga installed and I am thinking of going to 10, maybe 8 ga.  

 

Thanks in advance for any help.

 

Cheers

[pods8]

How many amps are you trying to carry?  Even with a pair of 100watt panels you'd have ~11amps max in the wire and it'd be starting around 17-18volts, you'll have about 5% voltage lost.  That's still plenty of voltage going into a PWM controller which is just chopping it down and wasting off the extra voltage.  If you have an MPPT controller you're only casing a couple % of efficiency.  Hardly seems worth trying to swap the wire out in the roof after the fact, 12ga isn't too bad up there.

[JaSAn]

Can't help with the routing, cuz my Grandby is OLD.  But I ran AWG 4 gauge wire from solar to batteries based on length and amperage:

http://circuitwizard.bluesea.com/#

 

The explanation of my solar setup is in post #3: 

http://www.wanderthe...interior-build/

[pods8]

 But I ran AWG 4 gauge wire from solar to batteries based on length and amperage:

 

You have a PWM controller, it chops down the excess voltage that gets to it, really anything over 12ga wasn't needed.  That said running 8 or 10ga on a new installation sure doesn't hurt for the little extra cost.  4ga seems to have crossed into extra money and having to deal with stiff/bulky wiring for no real need.  Not trying to attack, just confused.

[kmacafee]

In talking with many people who are very knowledgeable about solar, they are unanimous in their opinion that 10 ga wire is the minimum that should be used for almost any 12 volt solar setup and 8 is preferable.  Even for 100-200 watt panels, the voltage drop can be significant.  

 

I was checking to see how easy it would be to run new wire.  Brenda at FWC says that the wire from the ceiling box to the front of the camper runs thru a channel but I have not heard how it runs back under the bed to the battery box.  I may just live with 12 ga which I agree, is not the end of the world.  And if/when I do wire, I will use welding cable which, even in 6 and 8 ga forms is quite flexible.

[JaSAn]

pods8:  Being a Mechanical Engineer, I just went with what the 'sparkies' told me 

 

The 'experts' I followed: HandyBob, MaineSail, Jack Meyer, insisted that one of the biggest mistakes made in solar installations was undersizing the wire from panels to battery.  (Going from memory) for panels in parallel, HandyBob recommends AWG 6 minimum, Jack Meyer recommends no smaller than AWG 8.

 

I ran my refrigerator all last summer.  Every time I looked, I was at 100% by noon; usually earlier.  I think my system works well.

 

I did oversize the wire for the possiblity of adding more panels if needed.

 

kmacafee:  I'd hook them up and see if they will keep the batteries charged.  Worst case is you will have to rewire.

 

The 4 gauge welding wire I used was like a wet noodle, very flexible.

 

Another possiblity is running another set of 12 gauge wires in parallel and combining them at the controller.

[Fallbrook]

12 gauge is all you need!

[Advmoto18]

I am by no means an electrical or solar SME!

 

But, having worked with such SMEs in remote locations, they had different length and gauge wire bundles to select from based on...

Solar panel array output voltage.

Total amps the solar panel array produced

Length of run from panels to controller anf to batteries

 

While using a heavier gauge wire then needed will not have adverse effects, you will be toteing around a lot more weight in copper wire, perhaps reducing your loadout of other needed supplies.

Edited by Advmoto18, 21 April 2015 - 10:54 AM.

[ntsqd]

The thing to consider is NOT the ampacity of the wire. If you do you will end up with too small of a wire gauge. If you use the vastly common National Electrical Code based ampacity charts you will for sure be undersized as due to the cooling effect from the reversing polarity AC power is much different than DC power with regard to wire size.

 

The thing to consider is voltage drop, ideally you don't want any!

 

Search generically and specifically for the "Handy Bob" blog both here and on the greater net. Jasan gave some other, supporting author's names as well. There isn't universal agreement, but there is a trend that is pretty obvious.

 

In that searching I hope that you find the argument against paralleled smaller gauge wire. I wish that I could recall the details, but there was stated a good reason not to do this. The counter argument is/was that the stated reason isn't universal in application, so some can probably do it and have it be OK, while others can not.

[JHa6av8r]

I'm a mechanical engineer and by no means an expert in electrical set up, but DC voltage drop calculations for wire lengths of 20' or shorter are less than 0.5% for 12 gauge wire and less than 0.1% for 8 gauge are larger.  Seems like a lot of work to rewire for minimal return.

 

For me it's like spending more for an MPPT over a PWM controller for small systems.  The bang for the buck just doesn't seem justified.  Handy Bob puts out a lot of good information which would be beneficial for building a system from scratch.  However if 12 gauge wire is already in place, I fail to see how a properly sized solar pane/array (150 to 200 W), PWM controller, and a pair of deep cycle batteries will not meet the electrical needs most of us have.

 

I would install using existing wiring and see how it performs first.  Rewiring would only be done as a last resort.  Anyway, just my two cents.