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  • Charge Controller settings Trojan T105s

    Looking for advice on charge controller settings for my RV Solar set up.

    2 x 24 volt panels 265w connected in series. MPPT controller

    4 Trojan T105 series Parallel 12V 440 Ah

    current settings on controller, please share adjustment suggestions

    High Volt disconnect 16
    Charge Limit Voltage 15.5
    Boost charge Voltage 14.8
    Float charge voltage 13.5
    Boost charge return 12.8
    over discharge volt 11.1
    discharge Limit volt 10.6
    Boost charge time 150


    Any advice would be appreciated

    Richard
    Last edited by NutinElse2Do; 10-21-2018, 12:13 PM.

  • #2
    Hey Rich how are you?

    Being in an RV I assume means part time use?

    If that is accurate then you have a bit of wiggle room. Just be aware there is no correct voltage, it is a moving target. You best bet is to get a decent battery hydrometer with temperature correction. They are inexpensive and the best $10 you will ever invest in insurance. The hydrometer will tell what voltage to charge at. If specific Gravity is low, crank up th evoltage in .1 volt increments daily until you reach full charge..

    OK let's get to some specifics. You got an odd charger where they use made up names, but there are only a couple you need to worry about.
    Starting with Float leave it at 13.5 volts and never change it. Easy enough..

    What is throwing me off a bit is what they call Charge Limit and Boost Charge. I think Boost Charge is the same as Bulk/Absorb and that is the voltage setting you are looking for with the hydrometer. It will be the moving target and vary from 13.5 to 15 volts. Without the controllers spec sheet to look at I am going to say for now treat Charge Limit and Boost the same equally. Better yet give me your controllers manufacture and model number so I can figure out exactly what those terms are.

    Boost Time = Absorb Time. For now 150 minutes is OK.

    Rest of the settings don't mean a whole lot you have no use for. What they call Discharge Limit is Low Voltage Disconnect which you have no use for and could careless about. Sounds like your Controller has a Load Output Terminal for a nigh-lite that has a built-in relay so if the battery voltage dips below 10.6 volts will disconnect the battery to the Output Terminal you do not use. Only place you take battery power from is directly from the Battery Term Post.

    Solar and RV's do not play well with each other. When you are actually using the RV, your batteries will never be fully charged unless you are smart enough to use a Electronic Battery Isolator to allow you to use the engine alternator to charge the batteries while driving and change location ever couple of days. If your trips are limited to 2 or 3 days, you really do not need solar. When the RV is parked and not in use, your batteries get cooked from over charging because charge controllers manufactures assume you discharge the battery everyday and thus each morning resets and starts another full charge cycle on a battery that is already over charged. Of course you can work around that and lower Boost to Equal Float = 13.5 volts. On the road when in use crank the voltage back up.

    It is a moving target in the dark you have to hit. The only light you can use to see the target is your hydrometer.

    Reply back with your controller info so I can look it up and be more specific. In the meantime break out a credit card, go online and buy a hydrometer like this one

    You are looking for OTC 4619 hydrometer. Go find one. We are talking $10ish
    Last edited by Sunking; 10-21-2018, 01:43 PM.
    MSEE, PE

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    • #3
      Hi Sunking

      Thank you for the reply and I am doing awesome thank you for asking.

      Appreciate the advice on the Hydrometer, and let me make some clarification points.

      I "full time" in the RV and travel constantly. The controller I have is a GS-MPPT-Zenith-40.

      We "dry" camp for week to a month with no connection to power so the panels keep up with our load and recharge usage during the day.

      When we are hooked to power for more than a few days, I will probably flip the breaker so the panels do not fight with the inverter/ charger

      The setting that is confusing me the is boost return charge, I think that means when voltage gets to xxxx then return to Boost / Absorption charge but I a lost

      Will await your reply and advice, and if you need more details please let me know..

      Richard aka NutinElse2do


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      • #4
        OK I had a look. Like I suspected they are using their own unique terms rather than industry terms. So here we go, with setting and comments.

        Equalize = 16.2 volts. You do not have listed, but that is what is needed for the T-105.
        High Voltage Disconnect = 17 volts. You have it set too low, less than Equalize. It disconnects the charger if the battery voltage gets to high. It has to be above Equalize.
        Boost Voltage = Determined by Specific Gravity and can be anything from 14.2 up to 16 volts. This is also known as Bulk/Absorb Phase in the Industry. Trojan specifies it to be 14.82 volts. In the manual on page 6 describes what it is titled Fast Charging (aka Bulk or Constant Current), Sustaining (Absord or Constant Voltage) , and Boost Charging is the Time the charger stays in Absorb before switching to Float. This is one you will play with using your hydrometer. Being in an RV full time use I suspect what you are going to discover, there is no voltage high enough to reach full charge as indicated on a hydrometer.
        Float Charging Voltage = 13.5 volts. Leave it there and never change it.
        Charge Limit Voltage = Beats me. It is not defined in the manual unless that is what they call High Voltage Disconnect.
        Boost Charge Return I would set to 12.5 to 12.8 volts. You are correct. If the battery voltage slips below that voltage say in the afternoon after the charger has fully cycled, will start the charge cycle over again when the battery is starting to discharge, but good sun available. Makes the panels pick up the load with Sun available.
        Boost Charge Time = 150 minutes or whatever you want really. You can use this value to help with Specific Gravity. If you are having trouble reaching full charge before sunset, increase the time to maximum. There is no such thing as too long with solar. With AC chargers you have to worry about it, but not solar because time is not a commodity you have.

        As for the rest of the setting leave to factory default. As for being connected to Shore Power and using the built-in charger, there is no harm, no foul leaving the solar connected or disconnected. Shore Power is a Stiffer Source and essentially when connected turns the solar off.
        Last edited by Sunking; 10-21-2018, 05:05 PM.
        MSEE, PE

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        • #5
          Well, you are a rock star!!!

          Thanks for taking the time to help, I will start tweaking things as you described and move this forward.

          Again thank you very very much, and take $50 out of petty cash and have dinner on me

          Nutin

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          • #6
            Originally posted by NutinElse2Do View Post
            Thanks for taking the time to help
            You are welcome.

            MSEE, PE

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            • #7
              I have four panels with total of 400watts, i need to run cables 150feet long. Whats the cheapest cables? What gage do i need? Thank you

              Comment


              • #8
                Originally posted by Teco View Post
                I have four panels with total of 400watts, i need to run cables 150feet long. Whats the cheapest cables? What gage do i need? Thank you
                How are those 4 panels wired and what is the voltage that will be on those cables?

                If they are wired in parallel you will need some very big wires.

                If they are wired in series you can get away with smaller wire.

                Either way that 150 feet to run the DC voltage to a CC is going to be a killer and very expensive.

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                • #9
                  Its a 12v system.

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                  • #10
                    Originally posted by Teco View Post
                    Its a 12v system.
                    Sorry that really does not mean anything except you are using "12v" panels which usually have a Vmp = 17V to 18V.

                    If you mean all 4 panels are wired in parallel then the voltage on the 150 ft run will start at about the Vmp rating of a panel which is usually around 18v and a system about 4 x Imp or say 20 amps.

                    I may be making a mess of this calculation but a quick formula would be; Max wire Length = 2%VD(system) x Circular mill of the wire / Amps on the wires x 22.

                    Or the Circular mill of the wire = Wire length x amps x 22 / 2%VD.

                    You need to either increase the voltage coming from the 4 panels or drastically reduce the distance.
                    Last edited by SunEagle; 10-27-2018, 09:03 PM. Reason: removed calculation due to an error

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                    • #11
                      You can just look up the resistance per foot of the wire you are thinking of using, and multiply by the 300 foot
                      loop. And multiply that total resistance by the desired current, ohms law to get the voltage loss. For example
                      10 gauge cooper at .001 ohm per foot will total 0.3 ohm, at 20A will drop 6V. That will stop a 12V system from
                      delivering. Super heavy wire will help if you can afford it, but usually the practical solution is put your panels
                      in series to run 4 times the voltage at 1/4 the current, percent losses will be 1/16 as much. With the properly
                      voltage rated MPP controller. Bruce Roe
                      Last edited by bcroe; 10-28-2018, 02:04 PM.

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                      • #12
                        Originally posted by Teco View Post
                        I have four panels with total of 400watts, i need to run cables 150feet long. Whats the cheapest cables? What gage do i need? Thank you
                        You are going to learn a very expensive lesson and why 12 volt systems are called toys. Hope you have a few hundred dollars to waste and throw away. You will understand once you figure out what size the wire should be and how expensive it is. Assuming you wire the panels 2S2P 300 feet of of 4 AWG. That will cost you around $300.

                        MSEE, PE

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