Advice on adding a Solar Panel to Trickle Charge battery

Discussion in 'The Projects Forum' started by PaulHollingsworth, Jan 13, 2016.

  1. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    So please excuse my lack of knowledge as Im very new to this industry...But I am making push button audio boxes that will be housed outside of the enclosures in an animal sanctuary here in the UK.

    The set up I have at the minute is.... 3AA batteries hooked up to the Adafruit sound FX board (with built in 2W amps) This board needs 3.5-5V DC. When a button is pressed it triggers audio that plays out of the 3W mylar speaker. It is all contained within a weatherproof box.

    However, to save having to replace the battery's every few days I want to add a small solar panel that will trickle charge some rechargeable batteries. The solar panels that I have and fit perfectly onto my box are (5V 1.5W 300Mah).

    I have just ordered the Adafruit USB DC Solar Lithium Ion/Polymer Battery Charger. Would this be suitable to use for this project? And that leads me to my next question...what battery would you recommend to use that will be safe to leave on trickle charge every day...Lithium ion or NiMH seem to be the best? Would I need a diode between the solar panel and battery?

    Also is there a way I could make the Adafruit FX soundboard automatically turn off when the button is not being pressed. At the minute it is constantly using power even when the audio isn't being triggered.

    Thank you for any help.. I have put all the links below to the parts I have bought already...

    Solar Panel: http://www.ebay.co.uk/itm/201450011824?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT
    Sound Board: http://www.maplin.co.uk/p/audio-fx-sound-board-2x2w-amp-wavogg-trigger-2mb-n61ea
    Push Button: http://www.ebay.co.uk/itm/291300140890?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
    Speaker: http://www.maplin.co.uk/p/3w-mylar-square-speakers-77mm-vc88v
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I am familiar with two dirt simple solar battery chargers. First are those garden solar night lights. The other is Adair of 100 AH deep cycle marine batteries connected to 150W solar panels.

    Neither system has a charger per say, they both rely on using solar panels where the panel max output is the same as the charge rating of the battery. Both systems have diodes to keep the panel from discharging the battery at night; schotkey types work better.

    Garden lights use ni-cad batteries. I would just get enough ni-cads in series to support your device and a set of panels to make somewhat more voltage at the charge rate. If you don't know the charge rate just take the capacity as amps and divide by 10 or 20. Don't worry about the voltage rating being more than the battery voltage, it will be limited by the battery itself, that's one of the good things about how solar panels work.
     
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Use Nicads,if your solar panel gives out 5V, the battery is 4.5V a schokley diode will drop 0.2v that will give 4.8V to charge the battery, might be better with two solar panels in series.
     
    Last edited: Jan 14, 2016
  4. marcf

    Member

    Dec 29, 2014
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    What about this:

    http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
    A quote from this site:
    “Li-ion cannot absorb overcharge. When fully charged the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To minimize stress, keep the lithium-ion battery at the peak cut-off as short as possible.”
     
    Bernard likes this.
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Stick with Ni-Cd if possible, they can stand unlimited trickle charging.
     
  6. marcf

    Member

    Dec 29, 2014
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    Interesting.

    Seems that the NICAD (and also NIMH? ) are the only commonly used battery types that will tolerate constant trickle (float) charging.

    I understand that even then they cannot tolerate greater than 0.1C (10% of their Amp Hour rating) charging rates without problems.
    (Venting, getting very hot, blowing up, etc)

    At charging rates of 0.1C they are not damaged, but their lives are shortened slightly. It is best to remove the charging current when they are fully charged, but it is not easy to tell when this is.

    I see a current of 0.1 (0.1C) of the total AH rating (1C) is recommended for 12 hours.
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    OK, Simon sez do not do that, so do not do that.

    I said use ni-cad batteries, and the last time I checked neither nickle nor cadmium are made out of lithium.
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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    You can probably just add a diode to your panel and then charge NICD batteries.
    Can you make a little diagram of where the switch goes right now.
     
  9. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    Hi everyone. Thanks for all of your input so far its been very helpful. I have chosen the batteries now and thought it would be a good idea for me to draw a circuit so you can see what I have so far. Please excuse the unprofessional schematic, Im very new to it all so I have not learnt proper symbols yet.

    I think I am using a good enough diode for the circuit? But I would love to have some sort of regulator or safety component so the batteries do not overcharge or if there is a sudden problem with the panel or the batteries then it will all shut off safely? Any ideas how I could do that?

    The soundboard when idle still draws 35mAh which is a waste of power. So instead I was wondering if there is some way of powering the circuit up so that it is only on whilst the audio is playing, and then shuts off again. I need some sort of adjustable timer or something? Of course, I could just use a rocker switch. But the interface has to be a momentary push button. I thought about using capacitors but it seems too complicated and I don't think they would hold enough charge for the amount of time that a push button is held down for?

    Any ideas will be much appreciated. Thanks
     
  10. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Best way is to make a 555 Cmos monostable timer, and use that to power the sound board, so when you press the button it triggers the timer and activitates the soundboard, then times out.

    OR you modify the soundboard.
    The nicads wont need to be monitored for charging, they're ok to be left on.
     
  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Your schematic is actually very good. Most jobs start as sketches, sometimes literally on the back of an envelope (back in the days when mail actually came printed on paper). Knowing the symbols will come one day, but for now using a box to describe a module works well. Using a straight edge just keeps the sanity in the drawing.

    On the solar end you have 3 cells each of 1.2 V for a total of 3.6 volts. You have a 5V solar cell and a reverse protect diode; if we call the diode drop at 0.7 V (typical for most common types) you still have 5 - 0.7 = 4.3 volts to charge the Ni Cads.

    Solar cells work in a way that they limit their voltage to what the circuit needs since they act as a current source up to their maximum.

    That is a long winded way of saying from the battery to the left is a good working circuit.

    Using a '555 can be done but you have to be very very careful about current draw even using the CMOS type. Things like the timing resistors will draw real current that can drain the battery. It would be best if you can somehow make the timer not only turn the sound board on and off but also turn itself on and off.

    I'd do the timer part using a simpole micro controller, but learning those is not simple.

    Last, let me show you the battery symbol:
    [​IMG]
    The positive side is the longer bar so you need not mark + and - on it. A single cell is one long and short bar, multiple cells inside one case (such as a 9V or a 12 V car battery) use multiple bars, and you need not match internal cell count with bars on the symbol: after 2 or 3 cells we get the hint you have a battery.
     
  12. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    The algorithm of your charger will protect lions from overcharge, but it's not the best for solar panels. A bq24210 for instance maximizes panel power. Take a look at your sound board specs. You will note the operation of the power button as well as the 'activity' output. You should be able to utilize the latter to tie a pnp switch in with your momentary.
     
  13. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    Hi, Thanks for your input. Iv just looked on my sound board and it does have an activity output which sends a trigger once audio has finished playing. However, as im still new to this circuitry world, I still cant figure out how I can use that to switch the board off and back on when the momentary button is pressed. Please help.

    Thank you
     
  14. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    What voltage does the activity output pulse give when the audio has finished, that can be used to reset a flipflop.
     
  15. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    Hi Dave,

    The activity pin reads 0.08V whilst audio is playing and then shoots to 3.30V when audio is not playing.
     
  16. Dodgydave

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    Jun 22, 2012
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    So it goes zero on playing and 3v when finished, have you measured the current when its not playing and when it is playing sound?
     
    Last edited: Feb 2, 2016
  17. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    Yep, Apparently thats called "low mode" when audio is playing. I haven't measured current. I will do that now.
     
  18. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    I cant seem to get a reading unfortunately. :(
     
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