Wire AWG for Movable extra panel

RebTech Registered Users Posts: 3
edited June 2021 in Solar Beginners Corner #1
Hi all I'm a noob when it comes to solar, i'm trying to wrap my head around what I need to make one solar panel as a backup. On some sites they say as long as you match the wire on the panel others give you a calculator and I'm looking at welding wire?
I'm so Confused? 
I just want to have this 150W panel for chasing the sun when i'm parked under the trees when my RV panel isn't getting the sun it needs. I prefer to chase the sun than run a generator.

This is the panel I bought
VMP 17.1V
Imp 8.7A
Voc 21.5V
isc 9.2A
Max system V 1000V

Here's my existing setup;
280w mono panel on the roof of my RV that is connected my MPPT epever Tracer2215BN
2- 6V 230Ah batteries wired for 12V
2000W pure sine wave Inverter

My Trailer has a Zamp SAE plug at the rear and I've wired it in to the controller to make it an easy to hook up for the 150W panel.

My question is what size of wire can I get away with for about 50 feet of total distance away and I plan to put a connector half way so that sometimes I won't need the whole 50 feet

2nd question?
Does it matter that the wire awg at the panel and zamp plug in the RV wall are lower awg?


  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
    Welcome to the forum RebTech,

    My first question--Are you planning on running the two solar panels (280 Watt and 150 Watt) in parallel to the single MPPT solar charge controller?

    Or are you planning on getting (for example) a simple/less expensive PWM charge controller to run the 150 Watt panel?

    I am guessing that the 280 Watt panel has Vmp~30-36 volts (typical) vs the 17.1 volt Vmp 150 Watt panel... The two panels will not work in parallel to a single controller. And the 150 Watt panel is a bit on the low voltage side for Vmp (you really want 17.5 volts or higher--Especially when you take into account the long cable's voltage drop).

    Voltage drop wise... Say you aim for 1% voltage drop @ 8.7 Amps @ 50 feet one way run.

    Using a simple voltage drop calculator, try different AWG wire size to 1% voltage drop (or less):

    Using 6 AWG cable:
    Voltage drop: 0.43
    Voltage drop percentage: 2.50%
    Voltage at the end: 16.67

    So--practially speaking, 6 AWG cable is heavy and expensive... And if you are in very hot climate, the Vmp ~17.1 volts is going to drop (hot panels, Vmp falls)... It can fall below 14 volts on a hot day, and with another 0.43 volt drop, you are looking at Vbatt charging ~13.57 volts or so... And you really want 14.8 volts charging for flooded cell lead acid batteries...

    Now, the Vmp curve is a bit rounded... So you could get decent charging current at 14.5 volts or so--But you are sill looking at some pretty heavy cable.

    For example, the heaviest extension cord you can easily buy is around 10-12 AWG--The voltage drop on a 12 AWG cord would be:

    Voltage drop: 1.75
    Voltage drop percentage: 10.23%
    Voltage at the end: 15.35

    Just too much drop for "effective" charging of your 12 volt battery bank with the 150 Watt panel @ 12 AWG.

    So--Here we are... Figuring out if you are going to use 1 or 2 solar charge controllers, parallel the two sets of panels or run separately, etc.

    If you can justify it (and get a second 150 Watt pane) l matching your present panel), placing the two 150 Panels in series... Gets you Vmp-array ~ 34 volts... Perhaps close enough to the Vmp of your 280 Watt panel, and now high enough Vmp-array voltage that you could easily use 12 AWG or even lighter) 50 foot cable...

    Then you also need to look at the max current output for the Epever... 20 Amps into your 12 volt battery bank... The maximum "cost effective" array would be:
    • 20 amps * 14.5 volts charging * 1/0.77 solar panel+controller deratings = 377 Watt array
    280 Watts + 300 Watts (150W*2) = 580 Watts...

    So a second charge controller would be needed if you want to efficiently charge with both sets of solar panels at the same time (more power!).

    Anyway... Sorry for the long/confusing answer to what looked like a simple question... Sending lots of low voltage DC power any significant distance requires a large (and expensive) copper cable. And is frequently not really cost effective or user friendly (6 AWG extension cords are heavy, bulky, and kind stiff).

    So--What are your needs/plans?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RebTech
    RebTech Registered Users Posts: 3
    Thanks Bill

    What your saying makes sense and I think the best way to go, would be to just get another cheap controller and have it installed near the battery and just hook up the 150W on its own when I need it. 

    My wants are simply to have a portal unit for when my main panel is stuck in the shade.

    I was thinking about getting another 150W panel, but this thing is a big bulky panel and I can't imagine carrying two of them around all summer.

    What would you recommend for a inexpensive controller that I can purchase in Canada.

    Also, does any one make any good foldable panels that would suit my needs and then I could maybe get rid of the big beast.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
    I am not in the solar business... So I tend to avoid giving more than "general" recommendations (a couple of known good vendors, what to look for).

    One interesting charge controller that can take "low" voltage solar panel and step up to battery voltage (good for your existing 150 Watt panel on extension cord):


    For a "remote" panel, getting a higher voltage panel (see wire sizing) and an inexpensive MPPT charge controller (EBay, Amazon, etc.) can be a good deal... And if something breaks, you are not out of pocket very much (and got a bit of an education).

    For example, a 215 Watt panel (Vmp~37.65 volts) with a decent MPPT controller would be a nice fit (this is a link to our host in Northern Arizona--But probably not practical for you--Again just and example what to look for using a higher Vmp rated panel):


    Sonali SS-215W 215W 24V Solar Panel

    All Manufactured Modules are tested 100% by EL (Electroluminescence) during the Production Process and Free from Micro Cracks. Our high-performance modules are highly efficient, reliable, and provide optimal output. The company manufactures solar modules in compliance with global standard including MNRE, IEC 61215, 61730-1, 61730-2, 61701, UL 1703 ISO 9001:2008 and ISO 14001:2008 and 18001:2007

    High Module efficiency is obtaining top performance even in diffused light conditions. We are leaders in providing out customers with maximum sunlight conversion.

    Residential and Commercial Rooftops, Car Ports, Solar Farming, Balconies, Awnings, Street Lights Fences, Canopies, etc.

    Sonali solar has a 25 year performance warranty. Integrated manufacturing of cells and modules in one production line guarantees optimum performance.


    • Max. power: 215 Watts
    • Max. power voltage Vmp: 37.65 Volt
    • Max. power current Imp: 5.71 Amp
    • Open Circuit Voltage Voc: 46.21 Volt
    • Short Circuit Current Isc: 6.20 Amp
    • Cells per modules: 72 Cells
    • Dimensions: 62.2 in x 31.81in x 1.3in
    • Weight: 35 lbs
    • 215 Watt * 0.77 solar panel+charge controller derating * 1/14.5 volts charging = 11.4 Amps suggested minimum MPPT controller rating (10, 20, amp etc are fine).
    Generally, 140 Watt and smaller are around Vmp~17.5 volts (PWM controller land). The larger panel are generally in the Vmp=30-38 volt range--Much better for your "remote" panel and wiring.

    Glass panels--They are easy to break (single weight tempered glass)... So being careful and staking to avoid wind blowing over helps (shattered panels are not repairable and will fail over days/weeks/months).

    I also suggest not using "Locking" connectors for the cords. If you drive away and forget to put away the panel--You don't want to drag it down the road (one suggestion is to put a "female" 120 AC outlet on the van/charge controller, and a "male" plug on the solar panel... You can use a standard 120 VAC extension cord (multiple uses for the cord--Solar charging and 120 VAC cord--As needed) "backwards" and sort of avoid somebody plugging in (for example) your Van Solar Charger into a 120 VAC shore power connection.

    If you are really worried, you can put a simple lock or bolt and nut on the solar panel "male plug" to avoid somebody helping you and plugging the panel into 120 VAC (not good).

    (insert 50+ year old story--Local fire department members were tired of "kicking" out the 120 VAC standard plug used to keep the truck charged between uses. Installed locking plug and outlet--Some number of runs later, forget to disconnect, drove away, and ripped some wiring out of the wall.

    Another item to watch for... Always connect 12 VDC battery power first and disconnect last to solar charge controller. Connect Solar Panel power "last"... Most controller need stable 12 (or 24) VDC power to boot reliably and auto configure. If you connect solar panel first, the controller may not boot correctly and, in some cases, can "fry" the charge control (panel power, no battery power).

    Our host, Northern Arizona Wind & Sun, has quality solar products, stands by their products, and has engineers on site to help with customer questions and configurations. Again, probably not cost effective to ship to Canada, but you can see some better brands and what models are out there:


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,046 ✭✭✭✭✭
    There are some (up to 200 watt) 12 volt panels I've seen on eBay , US made, that are physically the same size as the older 120'ish watt size. 58.35inch×26.57inch so easier to handle and deploy.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • RebTech
    RebTech Registered Users Posts: 3
    Thank-you guys I will absorb all this info and try my best to set this up right!
    If I can give you an example of my recent needs and uses maybe someone can point out my faults or maybe some tips on my last trip a day ago.

    Went on a camping trip (no services and in AB Canada) good sun location and my batt showing 13.2 -14 v most of the day (2 costco 6V 230Ah batteries in 12v config with a 280w panel on the roof

    Cooked two huge briskets at home on my pellet grill and took them camping. I was able to Vac seal all the leftover food for our friends while camping and just used my external 300W pure sine wave for the vac sealer, no issues vac sealing over 25lb of brisket!

    The next night I wanted to treat my wife with her fav (sous vide tiger prawns shrimp for 30 mins) This is our first time we took the Sous Vide out camping

    There was no way my 300W or my 2000w Go Power pure sine wave inverter would even handle it! so confused...every time I tried I would get trip errors?
    I do know from experience that anything that has a heating element is a HUGE drain on the system, just so confused that I can't even run a small Sous Vide? but I had no issues running a cheap Walmart kettle for a full boil..Yes that did drain my system to a very low level, but I was able to do it!

    Maybe too many beers before the our attempt to cook or i don't know Sh**? only thing coming to my head is that when I turned on my Inverter that my fridge also switched over to AC via the Inverter and might have caused an extra drain on my system with the Sous Vide, maybe not enough to run both!