Connecting two solar panels with different watts through one battery controller

DLKDLK Registered Users, Users Awaiting Email Confirmation Posts: 4 ✭
in Solar Beginners Corner #1
New to the solar power world. I have two coleman solar panels, 1 40W and 1 100W. The 40W comes with a battery controller while the 100W does not and seems to be more heavy duty, intended for fixed installation. I would like to find 1 battery controller that I could plug both panels into, that would than feed my two 12V batteries within my RV. If anyone could recommend a fairly straight forward option, that's not going to break the bank, that would be appreciated!
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  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    #2
    You need to look at the Vmp/Imp of the panels... For paralleling, you want Vmp to be "close". Using a PWM (less expensive solar charge controller), your typical Vmp range is ~17.5 to ~20 volts.

    You would have the choice of removing the charge controller from the 40 watt panel, and paralleling with the 100 Watt panel (assuming Vmp voltages are a "match"), and get a new/larger PWM controller... Roughly:
    • 140 Watts / 17.5 volts Vmp = 8 amps...
    So a 10 amp or larger PWM controller would be appropriate. Install the controller near the battery bank (short/"heavy" wire from charge controller to battery bank is best). The longer wire run(s) should be from the controller to the solar panels.

    When connecting charge controllers, connect them to the battery bank first, then the solar array. And disconnect array first, then the battery bank. It is possible to "confuse" a charge controller if you connect to the solar panels first--The controllers are designed to take their operating voltage (for booting the microprocessor, determining bank voltage, etc.) from the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • DLKDLK Registered Users, Users Awaiting Email Confirmation Posts: 4 ✭
    #3

    Bill, thank you for the feedback, very helpful.

    I double checked the VMP and based on my calculation (140 Watts / 17.1 volts = 8.2 amps), the 10 amp controller should work well.

    I found a 10 amp Wanderer on amazon that appears to be well suited for my application as a reasonable price point.


    https://www.amazon.ca/Renogy-Wanderer-Amp-12V-24V/dp/B07NPDWZJ7/ref=sr_1_3?dchild=1&keywords=wander+battery+controller&qid=1591191890&s=lawn-garden&sr=1-3


    Appears I will have some wiring / connector configuration to deal with but this looks to be fairly straight forward.

    If you have any other tips or better options for a controller, please let me know.

    Much appreciated!


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  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    #4
    You are very welcome DLK,

    There are lots of other questions... What are your loads, the size and type of batteries, where you will be using solar, will you be using a genset too, are you trying to use solar for all your power needs, using fuses/breakers to protect hour DC wiring from short circuits, etc.

    It is very common for folks to underestimate their loads, and over estimate the energy generated by solar... And end up with short battery life from undercharging and over discharging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • DLKDLK Registered Users, Users Awaiting Email Confirmation Posts: 4 ✭
    #5
    I have a very basic setup with 2 x 12V deep cycle batteries on my RV. Goal is to be off the grid for 3 to 4 days at a time with a fairly manageable load (lights, fridge, water pump plus charge the odd device). Not sure if that changes your thoughts or recommenddations
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  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    #6
    What is your fridge? Propane running on propane with a little 12 volt?

    Roughly where and what seasons will you be dry camping?

    Will the panels be flat to roof or tilted during the day?

    If you have something like 12 volt @ 210AH batteries, you want something like 5-13% or so rate of charge. For example 10% would look like:

    210 ah * 14.5 volts charging * 1/0.77 panel & controller derating * 0.10 rate of charge = 395 Watt array nominal

    And the math for you array assuming 5 hours of sun per day (summer):

    8.2 amps * 5.0 hours of sun per day = 41 AH per day harvest (average) @ 12 volts

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • DLKDLK Registered Users, Users Awaiting Email Confirmation Posts: 4 ✭
    #7
    Yes, the fridge is propane and I'm located in Ontario, so your 5 hours of sun on average during the summer season would not be far off.  Sounds like as long as I'm conscientious on the power usage, this arrangement will get me by for a few days off the grid. Thanks again for the help!
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  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    #8
    Just to give you some details on energy harvest:

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Toronto
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:

    JanFebMarAprMayJun
    1.53
         		2.35
         		3.29
         		4.35
         		5.12
         		5.88
     
    JulAugSepOctNovDec
    5.87
         		5.02
         		3.92
         		2.64
         		1.55
         		1.24
     

    You pick the location and tilt (or flat) array... Deep winter in Canada is not great for solar harvest.

    Have fun!
    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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