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Solar Charging Circuit with a Prop? — Parallax Forums

Solar Charging Circuit with a Prop?

Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
edited 2011-05-30 10:18 in Propeller 1
A little noodling for my engineering friends here on the forums.

Is there any reason why a Propeller couldn't be placed into the same job as this 555 chip to create a Propeller based solar charging circuit?

http://www.mdpub.com/555Controller/

It might be overkill, but then one could take advantage of the Propeller's various video/control objects to make a very interesting circuit for it.

Does this look like a doable Propeller project?

OBC

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2011-05-27 21:55
    Sure, it's a doable Propeller project. You could use the Sigma-Delta ADC described in AN001. Use a voltage divider.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-05-27 23:05
    Personally I would want to automate the Dump/Charge, and have the 'Dump' go towards a grid-tie instead.... but in answer to your question, yes totally doable with a Propeller.
  • JonnyMacJonnyMac Posts: 9,208
    edited 2011-05-28 07:50
    It's beyond my present skills but I think it would be neat to create a circuit that could control the charge of the battery and drive and, using another cog of course, drive an AC output into an appropriate circuit to provide power for the target device.
  • StefanL38StefanL38 Posts: 2,292
    edited 2011-05-29 02:51
    when using a propeller I guess it will even be possible to do MPP-Tracking.
    (Maximum Power Point Tracking) http://en.wikipedia.org/wiki/Maximum_power_point_tracking

    And If I remember right somebody here in the forum was already working on it.

    @PhiPi or any other EE-guru: could the control of the charging current simply be realised through PWM or is anything more complex requiered for that?

    Edit: I did a search with google on MPP tracking circuit and came up with this hit:
    http://www.hamill.co.uk/pdfs/smpptfpa.pdf simple maximum power point tracker circuit.

    If you take a look at the schematic it is still quite simple. 6 ICs simple things like LM318, LM311, CD4030, 74HC74, AD633.
    Here I have to state I love the propeller but sometimes other things are better suited. For what it does (maximum power point tracking with a responsetime of milliseconds!)
    this circuit is simple. And then I love simple solutions. It's like my first ultra-simple waterlevel control:

    purpuse: only if a water container reaches a maximum level a pump should switch on and pump out the water,
    until a minimum-level is reached only then the pump switches off and stays off until maximum level is reached again (then repeat)
    .
    Piece of cake to bore a propeller-chip. I realized it with three components: two floatswitches and one relay with two change-contacts.
    What a pure KISS-solution.

    Anyway: if people enjoy to pimp up bobby cars http://upload.wikimedia.org/wikipedia/commons/5/5c/Bobbycar.jpg
    to run races http://i.auto-bild.de/ir_img/58184250_f2063b7935.jpg http://www.wiesentbote.de/bilder/bcr2.jpg
    why not using a propeller to do MPP inlcuding displaying XY-charts on a VGA-screen showing harvested energy, maximum voltage maximum current etc.

    best regards

    Stefan
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2011-05-29 04:38
    Generally, MPPT uses a Buck Converter to transform the maximum power point voltage to the lower voltage higher charging current on the battery.

    The propeller could control this in 2 ways:
    1. Simply supply a voltage to the converter to control the PWM. In this case the Propellor is on the side.
    2. Directly generate the PWM for the converter. In this case the Propeller is an integral part of the converter.

    The Propeller is amply fast enough to do the MPPT calculation while generating the PWM signal.

    Duane
  • LawsonLawson Posts: 870
    edited 2011-05-29 07:52
    StefanL38 wrote: »
    Edit: I did a search with google on MPP tracking circuit and came up with this hit:
    http://www.hamill.co.uk/pdfs/smpptfpa.pdf simple maximum power point tracker circuit.

    Cool link you found. I've been thinking of trying something similar myself. My inspiration was PDH locking from optics, as locking to a cavity or atomic absorption is a similar maximum/minimum point locking problem.

    Lawson
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2011-05-29 12:39
    To implement MPPT most measure power by multiplying measured current & voltage.
    This is required for the "general" MPPT algorithm.

    However, it can be simpler in solar panel & storage battery application by just measuring the battery voltage.
    This is a subset of the general algorithm.

    The first order approximation of the battery is the voltage is constant.
    The second order approximation is the voltage varies in proportion to the charging currevt.
    The goal in the MPPT is to maximize the charging current,
    By differentiating the battery voltage one can tell if the charging power is increasing or decreasing and passed to the MPPT algorithm which generates the PWM signal.

    I have done this algorithm quite successfully and worked well both with simple cmos logic gates and software in a Z80 micro.
    The clear advantage of this technique is multiplication is not required.

    Of course, when the battery nears full charge the PWM will be determined not with MPPT but with conventional methods.

    Duane
  • BigFootBigFoot Posts: 259
    edited 2011-05-29 16:47
    Using a prop to charge a battery is sort of overkill, why not use a single chip that was designed for this.
    I like to use SEPIC converters (Single Ended Primary Inductance Converters) .

    They have the ability to charge a battery that is below the supply voltage when dead and above the
    supply voltage to full charge. You could call them Buck Boost converters :)..

    Anyway I enclosed the one I use and an inexpensive gas gauge for it. It was designed for 1.25 amp
    charging for a 9.6V Ni-cad but will work for Li also. It uses dual servo loops, one sensing current and
    the other voltage. It charges a dead battery in constant current mode then switches over to constant
    voltage to complete the charge.
    GasGuage.jpg
    1024 x 451 - 32K
    BatChg35.jpg
    1024 x 451 - 51K
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2011-05-29 19:20
    BigFoot wrote: »
    I like to use SEPIC converters (Single Ended Primary Inductance Converters) .

    They have the ability to charge a battery that is below the supply voltage when dead and above the
    supply voltage to full charge. You could call them Buck Boost converters :)..

    Technically a SEPIC converter is not a BUCK-BOOST converter. They have different basic topologies.
    Yes, the SEPIC can output voltages greater than and less than the input though.
    See a good discription of the different converter types:
    http://www.redrok.com/an9208.pdf

    I like your circuit.
    And, in addition, its circuitry can be driven from an external PWM signal provided by the Propeller to implement MPPT algorithms.

    Duane
  • BigFootBigFoot Posts: 259
    edited 2011-05-30 10:18
    I realize the topologies are different but have a tendency to over simplify sometimes. That is a good app note
    though, and I added it to my collection.

    The input is driven with a propeller 1 but it dosent do much good if the battery is charging with the power switch
    off :(...
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