Will buck-boost regulator protect NiMH battery for arduino?

Discussion in 'The Projects Forum' started by mortonc, Jun 6, 2014.

  1. mortonc

    Thread Starter New Member

    Jun 6, 2014
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    I'm trying to find a way to power an arduino via solar with enough battery backup to last several days.

    The conclusion I've come to is to create a battery from 12 NiMH cells resulting in 7.2v and 36AH. I estimate the arduino will be using up to about 400mA and running almost constantly.

    From the battery I would run a 5v regulator to the arduino.

    Now the bit where I'm stuck is how I can charge the battery from a solar panel and ensure that I'm not overcharging it or anything else that might break it.

    I've seen a number of posts where people suggest using a buck-boost regulator like this http://m.ebay.com/itm/321234751122?cmd=VIDESC that I would set to 7.2v.

    1) Will this stop it from overcharging etc.?
    2) will it waste much energy?
    2)what voltage panel should I get?
    3) would I be better with a 6v or even 5v battery?
     
    Last edited: Jun 6, 2014
  2. sirch2

    Well-Known Member

    Jan 21, 2013
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    400mA seems very high, what are you using the Arduino for? If you need long battery life you should use an ATMeag328 on it's own and avoid the other parts of an Arduino (e.g. FTDI) that use power unnecessarily. I have a board that is programmed via the Arduino IDE but consumes 150uA when sleeping so would run for 27 years* off your 36AH battery, no solar panel needed.

    Google "Low Pwer Arduino" to get some idea of what is possible.



    *Of course battery self-discharge would use more than the Arduino, but you get the idea
     
  3. mortonc

    Thread Starter New Member

    Jun 6, 2014
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    Blimey, that is very low, might be the solution then.

    Currently using a Yun connected to Wifi with it taking sensor readings every minute or so. I haven't tested it yet but that seems to be the information I've seen online.

    Perhaps the solution is an uno plus wifi shield or even as you say just program the chip.
     
  4. sirch2

    Well-Known Member

    Jan 21, 2013
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    Depends on your requirements, do you really need the processing power of the Yun and always-on WiFi, or can you just blast the data across once per day?
     
  5. mortonc

    Thread Starter New Member

    Jun 6, 2014
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    Not sure I really need the power of the yun but I do need to be using wifi to send the data live.

    Any idea whether that regulator would be any good?
     
  6. sirch2

    Well-Known Member

    Jan 21, 2013
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    Sorry, can't help with the regulator but I'm sure someone will be along who knows all about it. My hunch is you should still think about shutting down as much as possible between readings or you are going to need a fairly large solar panel to deliver 400mA to your board and have enough spare to charge the battery to cover overnight and cloudy days.

    Knowing where you are in the world, how much sunlight you get etc. will help the solar experts help you...
     
  7. crutschow

    Expert

    Mar 14, 2008
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    12 NiMH cells in series have nominal voltage of 14.4V. How did you get 7.2V? Are you using two parallel strings of 6 cells each? If so that won't work since such cells don't charge properly in parallel.
     
  8. mortonc

    Thread Starter New Member

    Jun 6, 2014
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    That was going to be the plan yes. What's the issue with parallel charging and is there a solution?
     
  9. crutschow

    Expert

    Mar 14, 2008
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    The issue is that one of the strings will have a slightly lower voltage, due to small differences in the batteries, and that string will tend to hog the current and possibly overheat. The best solution is to have a separate charger for each series string. You might get by with a small series resistor in each string during charging to help equalize the charge current.
     
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