Basic 12V solar charged battery setup

Discussion in 'Electronics & Electrics' started by dufflover, Mar 4, 2019.

  1. dufflover

    dufflover Member

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    TLDR version: is the basic combination of 3 components (small 12V panel, charge controller, and small 12V SLA battery) sufficient, and safe, to act as a solar charged power source for a 12V circuit that operates at night.

    I am wanting to set up a basic night time light circuit where the battery is solar-charged through the day and the light runs off the battery during the night. I know all those existing solar LED lights that work on trickle charging a single LiPoFe4 (typically) will come to mind, but in my case just bear with me in running 12V, maybe 3~5W, intermittently. A 9V solution may be ok too, yet to test that.

    So I have things like the light and sensor controller part figured out, the only thing I don't have figured out is the battery side of things. I've worked with Li-ion 18650 cells before but in battery pack building or pack charging. I know you can get BMS boards but then they don't manage the charging, so looking for a 12V capable balanced charger, etc. it just seems a bit much.

    After more looking to how people typically use the 12V panels in vehicles and stuff, it looks like that might be the way to go and from reading it all I would need is the panel, controller, and battery.
    e.g.
    SLA: https://www.jaycar.com.au/12v-2-2ah-sla-battery/p/SB2482

    Controller: https://www.ebay.com.au/itm/3A-12V-...=item213e7b98e2:g:HN8AAOSw1nRa7Aq9:rk:32:pf:0

    Panel: https://www.ebay.com.au/itm/High-Po...8acb451c:m:mRMxXaRBY2MlQn8HS7dx6Jw:rk:16:pf:0

    • Would that all be it to it as a solar charged 12V DC power source?
    • Are the consumer level "security alarm" SLA batteries safe to have in roof spaces (i.e. can get warm)?
    • I do not have to go with this SLA route by all means if anyone knows of existing controllers for other battery types, or something easier for less coin.
    The part of the roof I am thinking of poking this out on gets a lot of afternoon sun.
     
  2. _zak

    _zak Member

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    I'd say that an SLA is probably the best option for a hot roof space, but this Battery University article indicates that you might want to adjust the charge voltage to maximise the battery life. Other than that, I don't see any problems?
     
  3. merlin13

    merlin13 Member

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    Tin or tile roof, and worth fitting a roof vent if the cavity gets screaming hot?

    Either way, may be some (!) additional dicking about but also ponder relocating the battery (and maybe even the charging/monitoring "smarts") down out of the hot roof cavity perhaps - top of the linen cupboard for example. Bonus on this is it'd also give you easy access for keeping an eye on the system status as well, not only for those dark 'n gloomy days but the long-term battery condition.

    You're only indicating less than half an amp actual power draw, so a longer run of suitable heavier gauge wire up out to the actual lights would be fine...
     
  4. OP
    OP
    dufflover

    dufflover Member

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    It's a tin roof. Although I only just realised I may not have the easy required access I want anyway lol.

    I'll have to check that this weekend before doing anything further.
     
  5. aXis

    aXis Member

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    I've tried to do similar before and really struggled with SLA batteries, they have pretty rubbish cycle life and charging performance. You'll want to keep the depth of discharge really low so that means having excess batteries.
     
  6. rainwulf

    rainwulf Member

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    SLA batteries are very very good... but are also snowflakes.

    The number 1 reason people hate them is that they get treated like a standard lead acid battery. They can NOT be treated like that. 13.8 volt charge on standby, or you must use an intelligent current monitoring charger.
    Most solar chargers are designed around standard car/truck/marine batteries. SLA/AGM are annoying, but amazing if they are looked after.

    Charge properly, keep cool.
     
  7. aXis

    aXis Member

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    My limited experience with the small AGM SLA's is that they are great backup batteries (like in UPS's), but suck for repeated cycling. I had a lot of trouble getting them to accept charge on a daily cycle solar system.
     
  8. OP
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    dufflover

    dufflover Member

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    Thanks for the feedback all.
    I noticed solar charger boards for lithium ion also exist. e.g.
    https://www.ebay.com.au/p/12v-MPPT-...-Battery-Charge-Auto-Switch-Cn3722/2147640455
    And presumably the output of this would go into a 12V BMS board since it doesn't have the individual battery connections.

    Of course no idea about reliability, but the SLA battery costs more than 3 18650s or equiv source anyway. Also much smaller size than an SLA.

    But this board says the input is a "18V nominal board". So not a standard 12V panel?
     
  9. Recharge

    Recharge Member

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    you haven't explained what the lighting is for, it's application and weather you want constant light and for what reason.
    it all depends on this to offer real ideas.

    lead acid are shit in hot places, every degree above 25c shortens the live of the battery, at 30+ this is a significant amount.
    you also need to calculate your total draw over night and then account for multiple cloudy days to work out how much storage you need and/or how many panels, which VERY quickly become economically silly to consider over cheap arse solar floodlight options from aliexpress.

    https://www.aliexpress.com/item/120...lgo_pvid=8ab46737-2260-4290-a993-f31708db62d2

    i mean this is crazy cheap for what it is and will cover a LOT of general security lighting applications, and there are dozens of similar and different options.
     
  10. cvidler

    cvidler Member

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    you also don't want to run the battery flat, a full discharge will shorten the life of the battery, lead acid and SLAs are bad for this. Calculate on a 80% minimum charge level (i.e. you only use 20% of the capacity), unless you like buying new batteries frequently.

    depending on panel orientation/efficiency, it's only making useful power for ~8 hrs a day (assuming a pretty worst case scenario for a badly aligned, cheapie panel).


    Once you have some numbers on what your requirements are then you can start considering what to buy.
     
  11. rainwulf

    rainwulf Member

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    Yea those aren't actually designed to be cycled. The plates are too thin, they were designed to get as much capacity in a small area as possible. The thin plates buckle after repeated cycling. Solar storage AGMs use much much thicker plates, which is also why they are so freaking heavy.
     
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  12. slavewone

    slavewone Member

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    I need to do something similar for a vergola. It’s got a small BP branded solar panel charging a 7.2A 12v SLA in the eave.

    When the SLA no longer had the juice to run the vergola, I pulled the SLA out thinking it needed replacing, but it has charged up and cycled fine so no I think the solar panel is kaput. Panel’s Sealed electrics at the back are no longer sealed so it’s feasible as kaput.

    eBay panels look similar and I might as well just replace the panel, putting in a small BMS sounds sensible to install at the same time.

    Or should I upgrade everything to a 3S lipo?
     
  13. pivot

    pivot Member

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    I don't think it is worth going solar for this. Here is why:

    1. Amount of power required in 24hr period: 5w x 8hrs = 40whr (That is a 12v5w light running for 8 hours)
    2. Amount of power required in a 24hr period due to inefficiencies: 1.5 times amount in 1. = 1.5 * 40 = 60whr
    3. Solar isolation for Melbourne: the lowest during the year is 2kWh m2 (from here)
    4. Solar array size: Amount in 2. / amount in 3. = 60/2 = 30w (so you would need at least a 30w solar panel)
    5. Battery size: 12v x the amount of days in reserve = 12v x 5 days = 60amp/hr (you would need a 12v 60amp battery)
    6. Solar controller: Solar array size / 12v = 2.5amp controller.

    PMW controllers not as efficient as MPPT controllers, so you might need to go to a 40w solar panel to account for this. Once you take all the about into account it is a lot of money to invest over a pre-built light.

    If you feel like reading have a look at this thread
     
    Last edited: Mar 15, 2019 at 1:52 AM

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