Solar power: Wire gauge and length questions....

Martinjmpr

Wiffleball Batter
As I posted in the other thread, I went ahead and got the HQST foldable 100w solar panel with the PWM controller attached.
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Works fine but I need to tweak it a bit and so I'm soliciting some input from the experts here. :sombrero:
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I need to make a cable that runs from the controller (which is mounted on the back of the panel) to the truck or trailer (I'm going to set it up so I can use it on either one.) My T@B already has an SAE connector attached to the battery, but my understanding is that it was specifically made for ZAMP solar panels and for some weird reason is wired "backwards" from most SAE plugs.
.
My plan is to switch the wires on the built-in SAE so it is no longer backwards and will work with other accessories (like a battery tender, etc.) Then I will make a cable to run from the PWM controller (mounted on the solar panel) to the truck/trailer.
.
My questions are: 1. What gauge of wire should I use? I Had some old 10 gauge wire in my toolbox and man, was that tough to work with! Too thick, too stiff, and I couldn't attach the wires to the SAE plug by twisting and taping (I don't have a soldering iron - yet.) I would rather use a smaller gauge wire - maybe 12 or even 14 gauge - just for light weight, flexibility and ease of working with it. But would 12 or 14 be too small and cause too much loss of power?
.
Second question, if I go with 12 or 14 gauge wire, what should be the max length? Obviously, the longer the wire is, the easier it is for me to park the trailer or truck in the shade and put the solar panel in the sunlight. But, again, I understand that having a wire that is too long will cause me to lose power through the wire length. So is there a formula for figuring optimum length? Ideally I'd like to have at least 20' of wire, that should allow me to offset the panel no matter where the sunlight is.
.
Thanks in advance for any help! :ylsmoke:
 

AndrewP

Explorer
Martin-I helped a friend with the electrical on his TAB and found the same backwards SAE connector. In general the stock wiring on that trailer is poorly done as you have probably seen. On my friends, when his fridge came on, the voltage drop would hit the automatic cut off, so his fridge would never really start. Plus, the OEM single battery is junk, I assume you have replaced. I can tell you that two 6 volt golf cart batteries fit perfectly in the tongue box and triple your onboard power. You do have to move the propane tank to the side of the tongue box. He's in great shape now with the batteries and much better heavier wiring to the fridge on a dedicated circuit.

Regarding your set up, using a portable panel, if you insist on leaving the charge controller out in the elements on your panel, the 10 ga landscape cord is a great suggestion. The PowerPole SB50 connectors work great, are basically weatherproof, tough (you could drive over them). They are larger than regular 15/30/45 powerpoles but they are more robust too. One other thing I use for my portable panel is a 25 foot 10 gauge extension cord with powerpoles on each end. This also works well but is bulkier. It's got a heavy industrial coating though so is very robust.

If you wanted to get clever with your solar and TAB, I'd get a better charge controller, mount it inside the tongue box with a nearby Powerpole connector. Then it's just a matter of setting up the panel, plugging in 2 connectors and enjoying a cold one.

Regarding length, I did the experiment with my 100 watt folding panel a year ago and really had no significant resistance losses out to 75 feet. You can read about that here in post #49:

https://forum.ih8mud.com/threads/camp-solar-setup.876038/page-3
 

Martinjmpr

Wiffleball Batter
Thanks for all the tips. Andrew, to answer your question, I haven't yet replaced the factory 75AH battery with the dual 6v golf cart batteries yet but it's on my 'to do' list. The T@Bs don't actually have a "tongue box", what they have is a cheap "propane cover" that just hides the propane tank and battery. My goal is to buy (or build) a platform that goes all the way across the front of the trailer that will then mount a proper tongue box, at least one (and preferably two) 20lb propane tanks and the dual battery box.
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I was hoping to get that done some time this year but now the wife and I are talking about selling the T@B and moving to a bigger trailer - since it looks like we may have the opportunity to camp with the grandkids (ages 2 and 5 now) in the coming years and a bigger camping space would be needed. We'll probably make a decision later this year as to whether we're keeping the T@B or upsizing, and if we're upsizing I'm not going to spend a lot of time and money upgrading the T@B.
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We don't actually have a critical need for the 2 x 6v batteries because we don't typically run the fridge in the T@B (as we have a Truckfridge in the tow vehicle.)
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As far as mounting the power controller on the T@B, while I know that is the preferred location, having it mounted on the panel gives me the ability to use it on either the T@B (when camping with the family) or using it on the truck alone (when camping solo.) My plan is to put a simple SAE connector on the house battery for the Suburban so that I could easily just plug the solar panel in to charge that when I don't have the trailer.
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Also, as stated above, we are contemplating moving to a bigger trailer and in that case, keeping the controller on the panel again gives me the option of using the solar panel on whatever trailer we have.
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Thanks again for all the ideas and suggestions.
 

Burb One

Adventurer
Not sure where the wires are on the trailer, but I do like the 12 gauge landscape wire on the exterior (roof etc.) Quality landscape wire is formulated with UV protection. Not sure under a truck/ trailer where it may contact salt, debris, rubbing, oil, grease, fuel, etc., but on a roof and in trim, etc., it works great.
 

dwh

Tail-End Charlie
Quality landscape wire is formulated with UV protection. Not sure under a truck/ trailer where it may contact salt, debris, rubbing, oil, grease, fuel, etc., but on a roof and in trim, etc., it works great.

Back when I was a working electrician I ran about a million miles of that stuff up in Beverly Hills where every estate seems to have a few hundred landscape lights (usually high voltage, but low voltage for some stuff).

I can tell you from years of experience...

It will survive being tangled up in a Mexican gardener's industrial strength weed eater.

It will usually survive an encounter with a shovel.

50/50 surviving being hit by a lawnmower.


Up there they fertilize and water constantly. It eats away galvanized pipe in the ground and Bell boxes in a few years, but does nothing to the low voltage cable except corrode the connections at the ends if they aren't properly waterproofed.


The only time it had any real problems, was at Ivan Reitman's house, where it seemed at least once a week the gardeners would manage to cut it with something (hoe or shovel). We finally just dug it all up, sheathed it all in ENT plastic conduit and reburied it. Fixed.
 

verdesard0g

Search and Rescue first responder
Be careful of a full width tongue box or platform, it will limit the turning radius of your rig. That's why most tongue boxes are shaped the way they are!
 

vicali

Adventurer
I just finished working on my 90w Coleman kit, I shortened up the lead on the panel, replaced the 6ft extension with a 20ft extension cord, mounted the controller into a spare peli-case I had, put a port in the side of the case, then made up a permanent harness for the trailer batteries- and then re-did the clamp leads with longer better wires in case I need to use them on the truck. All I'm waiting for now is my dual 12v meter displays to mount on the side of the box.

It's a 90w panel and a 7 amp controller- less amps than a set of driving lights.. Most of the kit was wired with 18g tiny wiring, so my update bumped it up to 14 between the panel and controller and 16 out to the batteries.
 

vtsoundman

OverAnalyzer
As I posted in the other thread, I went ahead and got the HQST foldable 100w solar panel with the PWM controller attached.
.
Works fine but I need to tweak it a bit and so I'm soliciting some input from the experts here. :sombrero:
.
I need to make a cable that runs from the controller (which is mounted on the back of the panel) to the truck or trailer (I'm going to set it up so I can use it on either one.) My T@B already has an SAE connector attached to the battery, but my understanding is that it was specifically made for ZAMP solar panels and for some weird reason is wired "backwards" from most SAE plugs.
.
My plan is to switch the wires on the built-in SAE so it is no longer backwards and will work with other accessories (like a battery tender, etc.) Then I will make a cable to run from the PWM controller (mounted on the solar panel) to the truck/trailer.
.
My questions are: 1. What gauge of wire should I use? I Had some old 10 gauge wire in my toolbox and man, was that tough to work with! Too thick, too stiff, and I couldn't attach the wires to the SAE plug by twisting and taping (I don't have a soldering iron - yet.) I would rather use a smaller gauge wire - maybe 12 or even 14 gauge - just for light weight, flexibility and ease of working with it. But would 12 or 14 be too small and cause too much loss of power?
.
Second question, if I go with 12 or 14 gauge wire, what should be the max length? Obviously, the longer the wire is, the easier it is for me to park the trailer or truck in the shade and put the solar panel in the sunlight. But, again, I understand that having a wire that is too long will cause me to lose power through the wire length. So is there a formula for figuring optimum length? Ideally I'd like to have at least 20' of wire, that should allow me to offset the panel no matter where the sunlight is.
.
Thanks in advance for any help! :ylsmoke:

1. 20' is shorter than you think in the field - especially if parking in the shade and keeping the modules in peak sun all day. Don't forgot to account for curve/loops in the wire when running around tires, out of the truck, up to the modules etc. #14 is a waste unless the run is very short.

2. Optimal solar & battery wire sizing is based on % voltage drop and NOT on capacity.
The power lost across the wire is the voltage due to ohmic resistance.Use an online calculator to help determine % loss. So 3% voltage drop at full current equates to ~3% power loss and ~2% energy loss in a given solar day. Easiest way to do it is take the MPPT current rating from the module and put it into a voltage drop calculator. Then figure percentage using the MPPT voltage -> this will give you the net % power loss. Total energy loss over a given solar day is about 75% of the power loss.

3. Guidelines: Run no more than 1/2 rated current for a given length. Ex: I'd run a 120V 15A skilsaw on 50' of cord #12 all day - an acceptable voltage loss for a 120V extension cord. For solar, I'd expect to use NO MORE than 7.5A on that same #12 50' run. (This guideline only applies to this niche application).This will yield about 1.19V drop - which is significant at our low voltage levels -> it could be 8-10% of the total voltage lost & similar amounts of power lost. As a comparison, most well designed 1kv & 1.5kV util scale solar plants shoot for ~1.5-2% voltage drop from module to inverter.

I currently run #12 wire for up to 50ft w/ 150W - @ ~8% loss, it is way too lossy for my taste, but it what I had laying around. Optimally it would be no more than 75W per 50ft of #12. Next iteration I will be switching to #10 landscape or 10/2 cord (which ever is cheaper) once I pickup enough remnants. I use 25ft lengths connected via 30A MC4 connectors in series up to 50'. All of my modules are connected in parallel. The 25ft runs keep the wire mess to a min and lets me deploy as much as I need. MC4 is much cheaper than Anderson and I have a ton of them. Right now I am using #12 HF extension cord with MC4 connectors on the module end and a single MC4 to Anderson whip to connect to my CTEK 250S controller.
 
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rayra

Expedition Leader
Martin, fine-stranded wire will give you greater flexibility, as will the coating on the low-volt outdoor lighting wire, as opposed to cutting up a an extension cord or using thicker gauge wire.

Another option to consider, especially if you are buying wire adn couplings anyway, would be to make a few segments, so you can make the run as long or as short as you want. Or just go with the 10AWG and something up to 100' and put a couple dogs on the back of the panel and just wind the cord up on the panel and unwind whatever you need for wherever you put it.
 

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