Trying to use Solar Panel to charge Lead Acid powered lighting

Discussion in 'General Electronics Chat' started by jamesgjatkin, May 23, 2016.

  1. jamesgjatkin

    Thread Starter New Member

    May 23, 2016
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    Hi all,
    I have a bunch of LED lighting that is powered from a 12v sealed Lead-Acid battery.
    I would like to add a solar panel into the equation to keep the battery topped up, and cut off when it is fully charged.
    Are there any 'standard' circuits that are designed for this type of application?
    I am familiar with PIC programming so if any active monitoring is needed this is okay.
    Any help would be appreciated.
    Many thanks,
    James
     
  2. #12

    Expert

    Nov 30, 2010
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    Give us a guess on the amps and amp-hours per day. The kind of low efficiency stuff we do for a couple of yard lights isn't fit for a whole house full of LEDs.
     
  3. jamesgjatkin

    Thread Starter New Member

    May 23, 2016
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    Sorry, I should have included this in the post!
    I am essentially running only a small number of lights from this to illuminate a small area of the garden.
    I would guess at around 10-15W of LEDs
     
  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    To get the maximum energy out of a solar panel you need a MPPT (maximum power point tracking) system as well as controlling the battery charge. All this generally means some sort of switched mode system.
     
  5. #12

    Expert

    Nov 30, 2010
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    Oh C'mon. Nobody is going to buy a MPPT system with motors and pivots and sensors for some garden lights.

    Again, more information (about the solar panel). On way to do this is to use an LM317 voltage regulator chip and set it for 14.2 volts...if you can get about 16 volts out of your solar panel. That will float charge your battery without boiling it. If you can't get 16 volts out of your solar panel, you might use a shunt regulator to waste the excess power to ground when the battery is full. See? It's all a balancing act. A lot of people think a 12 volt solar panel will charge a lead acid battery. It won't. A lead -acid battery has about 12.6 volts when it's full and it takes more than that to drive current backwards through the battery.

    If your solar panel is really low on volts, that's when we get into using a boost regulator.
    So, what do you have for a solar panel?
    Volts, amps, that kind of stuff.
     
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Tonyr1084 likes this.
  7. #12

    Expert

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    I had the wrong idea. I thought a MPPT was a way to angle the solar panel. Now I find its a converter to adjust the amp load and the voltage for the best efficiency at whatever angle the panel is at.
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Try something like this. KISS
     
    #12 likes this.
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    We have a simple system running some unattended lights (they are on a lighthouse in the middle of a harbor) that has run for years now. No controller, just batteries and the lights, standard 12 volt exterior spots.

    The solar panel puts out up to 20 v when in full sun, at about 5 amps max. This is directly connected to two parallel deep discharge batteries. There is a diode built into these panels.

    The batteries have 200 amp-hour capacity. Even in full sun they don't put out enough current to negatively affect the batteries. Crude but it works pretty reliably. With a charger we may get an extra year or two out of the batteries, maybe not.

    15 watts of 12v garden lights is a bit over an amp, call it 15 or 20 amp hours over night. You don't want to come even close to draining the battery completely for long life, so a battery of 80 or 100 amp hour rating is good.

    Now you need find a solar bank rated for some 5 amps, no more than 1/10 the capacity of the battery.

    If you have some of these parts already please post them and we will have a look how to best connect them together.
     
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  10. jamesgjatkin

    Thread Starter New Member

    May 23, 2016
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    Thanks so much for all the comments...
    I think maybe I should have explained more fully exactly what I am trying to achieve.
    Essentially I would like to add some LED lighting on a BBQ - encased within the inner side of a roof structure - without having to run mains.
    In the event of an evening BBQ, the LEDs could be turned on and they would run from a battery.
    I would like a solar panel located on the top of the roof to the BBQ to trickle-change the battery, ensuring that the battery is always charged when needed. My main concern was leaving the solar panel trickle-charging the battery when it is full may eventually lead to damage - I could be wrong on that!
    What I had not considered was that a 12v Solar panel would not be sufficient to change a lead-acid battery though...
    I am not fixed into using Lead Acid, I just thought that would be the simplest way to have a higher capacity battery when needed.
    As for the panel or panels themselves, I was thinking about something very cheap-and-cheerful like the ones you can get on ebay, eg.
    http://www.ebay.co.uk/itm/141964968845
    These are typically 12v @~400mA each.
    As they are pretty small I can use multiple units to boost the voltage or current if necessary.
    I could then use a buck converter to drop 24v down to the charging voltage...
    Maybe looking at the above I need to calculate exactly what I need...
    At a guess, the usage would be about 2 hours max, at say 1.5A would be 3Ah
    The NP7-12 gives 12v @ 7Ah which would provide up to 4+ hours from full charge.
     
  11. AlbertHall

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    Jun 4, 2014
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  12. #12

    Expert

    Nov 30, 2010
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    I've been keeping my lawn mower battery floating at 14.2 volts for 3 years.
    It's an AGM battery. When it gets charged up, it only accepts 2ma to 3ma.
    It still works every time.
     
  13. jamesgjatkin

    Thread Starter New Member

    May 23, 2016
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    The MPPT looks like a very strong contender for what I am trying to do - and seems very cheap!
    Looking at the details, it takes 12v from a Solar panel and charges to the full 13+v the battery takes.
    Is this correct? Are these specifically designed for charging Lead Acid batteries in these situations?
    Sorry if I sound surprised - I am very new to this (as you can tell) and I haven't come across these before!
     
  14. Lestraveled

    Well-Known Member

    May 19, 2014
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    If you read about MPPT controllers you will find that they become effective (cost and performance) on systems over 200 watts. Also don't confuse a switching power regulator with MPPT. They are two different functions.

    On a small system it is much cheaper to buy a larger panel and not use all of the power being generated. All you need is a panel(s) that produce more voltage than your battery and a charge controller. If you have the skills to build a buck converter, like a "Simple Switcher", you are way ahead. Or, just buy a charge controller. They are cheap and some of them have excellent charging profiles.

    Don't over think this. Keep it simple.

    Although if you want a nice build it project, look into a Texas Instruments BQ2031. It is my favorite lead acid battery charger chip plus it has a buck controller built in.
     
  15. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    If in doubt ask the supplier but looking at the battery voltage specs it is:

    Color-changing LED working voltage indicates area:
    Red LED 10.5V-11V
    Orange LED 10.5~11V-13.7V
    Green LED ≥13.7V
     
  16. Lestraveled

    Well-Known Member

    May 19, 2014
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    It is both. Maximum Power Point Tracking (MPPT) can be a physical pointing system or an electronic power optimization. MPPT is a very misunderstood term.

    Edit: MPPT is also the most lied about term when buying cheap charge controllers.
     
    Last edited: May 23, 2016
    #12 likes this.
  17. Lestraveled

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  18. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Good lord, you DO NOT NEED A MPPT CONTROLLER (or any controller) to keep a simple battery charged for the occasional use. A diode will do. If you are worried about efficiency use a Schottky diode.

    When you connect a solar panel to a battery the battery "regulates" the panel voltage and near the maximum current will flow. I'm doing this, #12 is too. It's how every solar garden light works too.

    Works with lead acid and NiCad batteries. Possibly others, but these are what I know. Just have to have a panel that puts out greater than the charging voltage.

    If you are worried about overcharging the batteries (I wouldn't) don't put an ON/OFF switch and let it run every night.

    The only thing I would worry about the grill roasting the panel or battery. ;)
     
  19. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Indeed, and for this particular case, you don't even need a solar panel. Keep the battery indoors, charged by a mains powered charger, and take it outdoors when a BBQ beckons.
     
    ErnieM likes this.
  20. jamesgjatkin

    Thread Starter New Member

    May 23, 2016
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    Thanks so much for everyone's input on this.
    I'll take a look at the options and see how things go :)

    Thanks again for a very informative discussion.
     
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