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  • Super Noob question(s)

    Hello, and I'll apologize in advance if this question is obvious to most of you. I did some searching and didn't find an obvious answer.

    I'm setting up a remote security monitoring system for my boat (I live an hour from where it is moored) so I set up a very simple configuration: 1 50 watt panel, a cheap controller rated for 20amps, a 15ah battery, and an inexpensive 12v webcam (Wifi available at marina for connectivity / stream).

    All is well for the most part and I'm happy with my little science project - but first problem that I discovered was that cam would eventually drain down batter below a point (sub 10v) that the solar controller would no longer recharge it. Apparently this is to prevent battery damage - makes good sense. So...I put a circuit between the batteries and the cam that will drop power to the camera if the battery drops below 11v. Then the controller (when sun comes up in the morning) is happy to recharge the battery again.

    I was struck by the fact that this must be a super common issue in panel > controller > battery > load equations, and I was frankly surprised that my Controller didn't manage this? And i really didn't see much in the way of the 'low voltage disconnect' in the retail market (sort of repurposed one from another science project).

    Is it just me...or is this something that should be accounted for in any solar powered / battery system??

  • #2
    I can't tell you if you got a good or bad controller, but you did use the word "cheap", so perhaps they left out that key feature.

    In addition, different batteries have different requirements for long life.

    I'm guessing that you have a lead-acid battery. Lead acid batteries, whether sealed or liquid (aka FLA), last longest if you keep them always charged. The deeper you discharge them and the longer you leave them discharged, the quicker that the plates suffate and the battery becomes unrecoverable. Then it becomes a balancing game between buying a huge battery and allowing a small battery to die quicker. There's an optimum, but if in doubt, larger batteries and higher cutout voltage is always safer, although more expensive.

    LiIon batteries are completely different. They last longest if kept between 20% and 80% of charge. Leaving them fully charged or allowing them to remain fully discharge is bad and shortens life. I've been told that deep discharge and full charge isn't too bad, if you don't leave it in that condition for too long.

    And all batteries hate heat. If possible, keep them <75F. It is also good to avoid getting batteries too cold. Each battery has a different minimum safe temperature, but staying above freezing 32F is safest.

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    • #3
      Thank you Bob - much appreciate the knowledge. If I'm understanding you correctly - the controller (or a better one) should be managing the low battery voltage disconnect for me then?

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      • #4
        Many mid-grade controllers have "Load Terminals" that will disconnect the load when the battery is dangerously low. The terminals are often only good for a low amp device, Cam & Router should be OK. Seat of the pants experiance has me thinking that a 50w panel is quite small, and a 200w panel with a 80ah deep cycle battery would be a better mix.
        https://www.morningstarcorp.com/products/sunsaver-mppt/
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

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        • #5
          Does your controller have solar, battery and load output terminals? The load terminals are where you get Low Voltage Disconnect.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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          • #6
            Originally posted by JackFromSac View Post
            Thank you Bob - much appreciate the knowledge. If I'm understanding you correctly - the controller (or a better one) should be managing the low battery voltage disconnect for me then?
            Before you spend any more money on a CC your 15Ah battery can probably give you less than 60 watt hours which is probably not enough to power that camera all night long.

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            • #7
              Thanks all for the great responses. Really great of you all to chime in and I really appreciate it. I'm really enthusiastic about solar power implications. As an FYI: I work in IoT and I see dozens of use-cases that are largely not being accounted for that would classically be considered 'off grid'. Solar power will is an area that I think will open up a lot of remote asset management, security and monitoring types of opportunities that are largely being ignored at the moment.

              On my controller - it was configurable - but no matter which load cutoff threshold I used - it was low enough that the controller (on the battery side) would consider the batter too low to recharge again - which really seemed to defeat the ability for the controller to manage this without intervention. (Disconnect the controller, recharge the battery, reconnect. rinse repeat). Thus i connected the 'load' directly to the battery with the low voltage disconnect circuit between the battery and the Cam. This actually worked: it prevented the battery from going too low for the charge controller to allow the recharge. Was just a PITA (pain in the @ss) to have to add additional components and complexity to what I thought would be an obvious feature of a controller.

              On the battery size: The cam is only 2A draw in full use and much lower in standby - but part of this 'science project' was to size the panel and battery requirements. In summer sun (I'm pretty far north) the setup actually worked quite well overnight if I didn't stream the camera often overnight. Winter has been a very different story, as expected.

              Phase II will be adding battery capacity - and bump to 100 watt panel (or add another 50 in series with the existing 50). Looks like I'm needing a better controller so I can eliminate the LV circuit and simplify.

              Any recommendations for a lower-end price (trying to keep build cost down) controller would be greatly appreciated!

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