Solar charge controller comparisons?

lalakailalakai Registered Users Posts: 12 ✭✭
Getting ready to pick up a solar charge controller but not certain of the differences between the different models. Currently looking at either the SunSaver 20 Amp 12, the ProStar 15 Amp 12/24, or the Schneider Electric C35. They are all in the price range i'm looking at. I'll be using either a single or double panel set up(130 watts each), running them parallel to keep 12 volts, going into a 12 volt car battery. I will be upgrading the battery to a deep cycle. I'm setting the system up for portable dc power. Primary use will be led lights and possible inverter use (very light). It's an experimental set up.

Any feedback would be appreciated. Thanks

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,849 admin
    Re: Solar charge controller comparisons?

    What is the Vmp/Imp ratings of your solar panels?

    What is the AH rating of your current and new batteries (12 volt battery bus?)?

    Will you want to log information from your charging system? Will you want a remote battery temperature sensor (recommended for controllers that are not in the "same box/temperature" of the battery bank).

    How far from the solar array to the charge controller?

    Will you want anything like automatic on/off control (such as outdoor LED landscape lighting)? Will you want to set exact charging voltage/other parameters for your battery (AGM, GEL, flooded cell, etc.)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lalakailalakai Registered Users Posts: 12 ✭✭
    Re: Solar charge controller comparisons?

    Hi and thanks for looking.

    Vmmp - 42.7
    Imp - 3.05
    Voc - 56.5

    unknown AH of current battery: NAPA 7565 880 CCA. I have no specific replacement battery identified yet.

    I'm not planning on logging the information. Have considered remote sensor but wasn't planning on it for now. Controller could be mounted in battery box. Will be using fan in battery box.

    Distance from panels to controller: longest run will be 8 feet of MC4 cable. Distance from controller to battery: 10 feet max.

    at present I have no plans to use the system for an automatic lighting system. Uncertain regarding setting a specific charging voltage. I thought most of the controllers operated under a "3 phase" system of trickle, charge, float.
  • BB.BB. Super Moderators, Administrators Posts: 29,849 admin
    Re: Solar charge controller comparisons?
    lalakai wrote: »
    Hi and thanks for looking.

    Vmmp - 42.7
    Imp - 3.05
    Voc - 56.5

    With a Vmp that high (outside of the range of 17.5 to 18.6 volts or so), you will need a MPPT charge controller.

    If you use a PWM controller with Vmp~43 volts and Vbatt~12 volts, you will only get about 40% the power of those solar panels

    PWM controllers cannot "efficiently" down convert from high voltage/low current to low voltage/high current like a MPPT controller can.

    If you do use a PWM controller, then you will probably need a PWM controller rated higher than 24 VDC nominal maximum. Such as the Schneider/Xantrex C40 controller. Such a controller will work OK (PWM with "high" Vmp solar panels)--It just will not be very efficient.
    unknown AH of current battery: NAPA 7565 880 CCA. I have no specific replacement battery identified yet.

    Call it an 80 AH battery... using 5% to 13% rule of thumb for charging, and 10% as a "nice healthy" value:

    80 AH * 14.5 volts * 1/0.77 controller+panel derating * 0.10 rate of charge = 151 watt array

    So, 155 watts would be on a well matched PWM controller plus ~18 Volt Vmp solar array on a 12 volt battery bank.

    With a PWM controller and a Vmp~43 volt array:

    151 watt array * 1/0.40 efficiency pwm miss-match = 377 watt array using PWM controller
    I'm not planning on logging the information. Have considered remote sensor but wasn't planning on it for now. Controller could be mounted in battery box. Will be using fan in battery box.

    Distance from panels to controller: longest run will be 8 feet of MC4 cable. Distance from controller to battery: 10 feet max.

    Would be better to have short/heavy cables from charge controller to battery bank. Too long of cables can give excessive voltage drop and issues with battery/controller temperature differences.
    at present I have no plans to use the system for an automatic lighting system. Uncertain regarding setting a specific charging voltage. I thought most of the controllers operated under a "3 phase" system of trickle, charge, float.

    Yes, the are three or more charging stages... But different type batteries require different charging set points... AGM/GEL around 14.2 volts and flooded cell around 14.7 volts for absorb voltage.

    Float for both are probably around 13.6 volts. (all at ~77F/25C).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lalakailalakai Registered Users Posts: 12 ✭✭
    Re: Solar charge controller comparisons?

    hmmmmmmmm...............hadn't wanted to go with the MPPT controller due to costs but if I want to consider "futur-ability" of changes, might have to spend the extra $ now to give me room to upgrade later without needing to purchase new controller. Now I have to start looking at the differences in the MPPT controllers.

    Thanks a bunch Bill, you've answered most of my questions and given me answers to some I hadn't considered yet. I'll update the thread as the project continues.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar charge controller comparisons?

    Without an MPPT controller panels that have a Vmp of 42.7 are going to be pretty useless on a 12 Volt system. They will put out their Imp, but at battery Voltage meaning essentially they will be (3 * 17.5 typical Vmp) 53 Watt panels.

    I'll hazard a guess your panels are not standard polycrystaline panels like these: http://www.solar-electric.com/solartech-spm130p-s-n-130-watt-multicrystalline-solar-module.html

    Unless you've already been saddled with them I'd reconsider the panel choice. Maybe even if you have.
  • lalakailalakai Registered Users Posts: 12 ✭✭
    Re: Solar charge controller comparisons?

    i'll double check on the panel info.....that was the info I had written down. I'll verify it. I don't have a lot of money invested in the panels...only bought 2. Might have to reconsider the set up. and here I thought I had done some of my homework. Oh well :blush:
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