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Small MPPT Charge Controller?

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  • #16
    Originally posted by Sunking View Post

    So what is your point? You asked for unreasonable electric prices, outages and problems. What are you complaining about? Anything you take off-grid is going to cost you 5 to 10 times more than just buying it from the POCO and have many days without power. You are getting exactly what you asked for.

    Couple that with an undersized system to start with, and you have to start over and do it right. Your system has to be designed for WORSE CASE, half the year is not going to cut it and destroy batteries. Battery replacement cost alone is going to be many times more than just buying power. That is what off-grid solar is all about.
    My point is, that although the existing system is not set up to get the maximum life out of the batteries, it ain't going to kill them by the end of the week. It's a hobby greenhouse that is in use only 5 months out of the year (they float with no load the other 7). It appears to be undersized for just 2 months out of the 5 that it's in use. I am looking to make some minor tweaks to get more life out of the batteries I have, not spend nearly double their worth to maybe get them to go one extra season.

    This is for fun and education, not some misguided attempt to stick it to the POCO. I am still messing around with how best to garden up here and may change the greenhouse set up substantially at some point, I don't know, hence I don't want to spend money on a whole new system right now.

    Heck, if I really wanted to just waste money, I'd take up something like golf.
    Last edited by NorthRick; 04-13-2017, 05:25 PM.

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    • #17
      It is hard to believe there aren't industry devices ready to serve this market. Solar panels are the cheapest thing in the system and you want to double or triple them and run nearly without a battery at all using linear current boosters. That would make the system very cost effective. If the sun isn't shining, you don't need a fan and at lower light levels they just run slower. Alas, the world is battery centric and stuck with stupid control systems. Find yourself a sharp 12 year old to get involved with this experiment.

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      • #18
        Rick you biggest mistake is using PWM controller with 2 195 watt panels wired in parallel. What you have done is turned your potential 390 watts panels into 220 watts. That is what you get using PWM controllers You shot yourself in the foot from the start. At best you can only generate 9 amps of charge current which is not near enough for a 205 AH battery. Ideally you want 20 to 25 amps.

        Simple fix, buy a good 15 to 20 amp MPPT charge controller and something amazing happens. You actually get about 390 watts from 390 watts of panels. Who would have thought that was possible? PWM controllers are antiquated 8-Track tapes. That is why they are so cheap.

        Small MPPT Charge Controller?
        That was the title of your thread right? Now go get a good 15 to 20 amp mppt controller and wire the panels in series and correct your mistake. What more do you want?

        OK get a Morningstar Sun Saver MPPT, and sell the Sun Saver PWM to a sucker who does not know the difference and will loose 30 to 50% of the power from the panel using PWM.

        If it were me I would have just dug a shallow trench, and ran an AC circuit. Lot less expensive and works.
        Last edited by Sunking; 04-13-2017, 08:27 PM.
        MSEE, PE

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        • #19
          Originally posted by NorthRick View Post

          Actually the panels are 37v and are currently in parallel, which I believe is fine for a 24v battery bank.
          37Voc is a 60 cell panel. That is nominal 20V, designed for grid tied solar. 44Voc 72 cell panels are for charging 24V batteries. (22Voc is 36 cell 12V nominal panels) It will be fine in cool weather, but in hot weather, the voltage drops, and may not be high enough to effectively charge the battery. Trust me on this one. If you are switching to MPPT, switch the wiring to series. You also get a bonus of lower voltage drop and lower current in to the charge controller.
          Solar Queen
          altE Store

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          • #20
            Originally posted by Amy@altE View Post

            37Voc is a 60 cell panel. That is nominal 20V, designed for grid tied solar. 44Voc 72 cell panels are for charging 24V batteries. (22Voc is 36 cell 12V nominal panels) It will be fine in cool weather, but in hot weather, the voltage drops, and may not be high enough to effectively charge the battery. Trust me on this one. If you are switching to MPPT, switch the wiring to series. You also get a bonus of lower voltage drop and lower current in to the charge controller.
            Maybe I'm using the wrong terminology. The panels are 37 Vmp. They are 45 Voc and are 72 cell panels. It's a short run from the panels to the controller and the wires are sized correctly. I ended up going with a Prostar PS-MPPT-25 charge controller, so the input from the panels in parallel is well within it's limits. Is something else significant to warrant climbing on the roof and rewiring things?

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            • #21
              Originally posted by NorthRick View Post
              Hmmm. $200 for another panel and $300 for a 25A MPPT charge controller, so, $500 to maximize the life of $340 worth of batteries.
              Pretty much. If it saves you two battery replacements over ten years it's paid for itself.

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              • #22
                Originally posted by NorthRick View Post

                Maybe I'm using the wrong terminology. The panels are 37 Vmp. They are 45 Voc and are 72 cell panels. It's a short run from the panels to the controller and the wires are sized correctly. I ended up going with a Prostar PS-MPPT-25 charge controller, so the input from the panels in parallel is well within it's limits. Is something else significant to warrant climbing on the roof and rewiring things?
                With 72 cell panels and a short run, you are fine in parallel for 24V. Sorry for the confusion, too many voltages without enough details.
                Solar Queen
                altE Store

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