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Thread: MPPT Solar Charger

  1. #1
    Team BlackSheep RiSCyD's Avatar
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    Post MPPT Solar Charger

    Hi guys,
    I want quickly introduce a small side project I have done recently.
    I planned a solar electric glider with 14-18pcs Sunpower C60 solar cells which gives me in the best case 50-60W of energy in full sunlight. The voltage I get from 14 cells is about 7V, with 18cells it would be around 9V.
    Flight battery are one or two 3S2P 18650GA packs: https://www.gettitanpower.com/collec...120w-endurance

    My first tests I did with a simple Step Up (claimed to be for solar applications too), quite similar to this one:

    With that setup I get about 60-70% efficiency, which is not bad but also not great at all, as this basically means that 30-40% of the cells installed are literally worthless.

    Looking for a proper MPPT (Maximum Power Point Tracker) I failed. First of all are MPPT with boost configuration much more rare than buck and then most called and claimed MPPT trackers do not MPPT at all!
    Most units requires to set the mppt voltage using a potentiometer, that means the working voltage always remains the same which is not the best and efficiant way to do it. Real trackers adjust that voltage either chip internal or they use microcontrollers to do it.
    There are literally just two real MPPT chips which do what I need: SPV1020 and LT8490 whereas the SPV1020 requires less components and easier design but the chip is end of life...

    For this reason I designed in my spare time a real MPPT tracker based on LT8490 chip.
    It accepts 10-40V input, coming from the solar panel. It is possible to go as low as 6V input, however with quite some chip limitations.
    Therefore I prefere to use C60 cells cut in half to get double the voltage with half the current.
    The output is fixed to 12.6V with max. charge current of 5A which is ideal for 3S Li-Ion and LiPo packs.
    The design was done as small as possible while still remain very high efficiency by using high spec components. Size is 70x35x12mm.

    With minor adjustments it is possible to change the output voltage and charge settings for any battery up to 30V.
    Mass production is not planned at that time unless there would be quite some demand which I don`t expect.
    Right now one prototype is up and running (bigger form factor), the final unit shown below goes to pcb production right now.

    Comments welcome


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  2. #2
    FPV Techanic RonSII's Avatar
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    Good work RiSCyD!!!

    I was finding the same problem with the mppt setups I looked into for a solar setup, I tried a few cheap imports with low to moderate success but nothing really worked as well as I needed for the intended purpose and they weren't very efficient in the configuration I had... so I never did much other than a couple static tests and breaking a lot of cells.

    Great to see you blazing a trail in this new frontier I for one am very interested to see how this progresses.

  3. #3
    Pilot Blizzard1287's Avatar
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    Nice job RiSCyD, have you been working with mictronics by chance? He was working on some custom MPPT using the LT8490 for the past few years but he never followed up with anything other than his initial design.

    What are the output limitations of the design? Can you achieve higher than 5A output with more solar cells or would you have to vary the output voltage?

    Very interested in how this project progresses, I tried to look for exactly this a few years back but gave up because there wasn't a viable option for small scale FPV. If you ever make a production run, consider me 2nd on the list.

    Just a side note... you're not planning on putting that setup on a caipi are you?
    Last edited by Blizzard1287; 15th March 2017 at 09:25 AM.
    Some fly for attitude, others for altitude

  4. #4
    Pilot ivc's Avatar
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    Great project! I think he means gliders more like this:

    Click image for larger version. 

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    Solius 2.85M Solar Powered Sailplane

    If you need a proper regular 18 to 75V 15A MPPT controller, I use and recommend the Victron BlueSolar MPPT 75/15. There's also a chinese clone by Fangpusun if you just want to experiment. But it's too big, even without the case, for a model plane.

  5. #5
    Team BlackSheep RiSCyD's Avatar
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    Quote Originally Posted by Blizzard1287 View Post
    Nice job RiSCyD, have you been working with mictronics by chance? He was working on some custom MPPT using the LT8490 for the past few years but he never followed up with anything other than his initial design.

    What are the output limitations of the design? Can you achieve higher than 5A output with more solar cells or would you have to vary the output voltage?

    Very interested in how this project progresses, I tried to look for exactly this a few years back but gave up because there wasn't a viable option for small scale FPV. If you ever make a production run, consider me 2nd on the list.

    Just a side note... you're not planning on putting that setup on a caipi are you?
    Hi,
    No did not worked with Microtronics at all, but knew it exists. Unfortunately he does not sell it otherwise I would have got me one for sure. Also it seems that there might be some limitation on his design but I haven`t put any effort in studying it, having no access to CAD data makes it complex.
    For this reason I decided to do it myself, that way I also have it customized for the application I need.

    Output limitation from my prototype is 5A but that is defined by the shunt values, the inductor and FETs can handle safely 10A. For more it would require an even bigger inductor which then is quite some higher (15-18mm) and would not fit due to size issues. The choosen Würth flat wire wound inductor is the ideal compromise in between size and effectivity for me. Going up with the battery voltage would make sense at that point. However, it needs to change more than just one resistor value which is kind of a pitty using that chip.

  6. #6
    Navigator parajared's Avatar
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    Seems kinda silly to me. You are charging lipos not saggy lead acid batteries, you don't need a charge controller to manage those tempermental charge curves.

    Why not either
    1)PWM activated switch: you turn on your solar panels once you get in the air. Keep an eye on your voltage to avoid overcharging.
    2)simply serialize your solar panels to exactly reach battery full charge voltage and not worry about on/off.

  7. #7
    Team BlackSheep RiSCyD's Avatar
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    Quote Originally Posted by ivc View Post
    If you need a proper regular 18 to 75V 15A MPPT controller, I use and recommend the Victron BlueSolar MPPT 75/15. There's also a chinese clone by Fangpusun if you just want to experiment. But it's too big, even without the case, for a model plane.
    Thanks. Have seen that, however that is much too big for my model and ten times heavier than my board

  8. #8
    Navigator parajared's Avatar
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    Also your batteries will pull your panel voltage down to their level so if you have a 20 volt panel that outputs 5 amps and a 12 volt battery you will only get 12 amps x 5 volts of charge = 60 watts instead of 20 volts x5 amps = 100 watts like your solar panel has potential to output. My point being that it makes sense to have your voltages match up and forget the controller all together.

  9. #9
    Team BlackSheep RiSCyD's Avatar
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    Quote Originally Posted by parajared View Post
    Seems kinda silly to me. You are charging lipos not saggy lead acid batteries, you don't need a charge controller to manage those tempermental charge curves.

    Why not either
    1)PWM activated switch: you turn on your solar panels once you get in the air. Keep an eye on your voltage to avoid overcharging.
    2)simply serialize your solar panels to exactly reach battery full charge voltage and not worry about on/off.
    LiIon and LiPo needs no charge controller, that`s right. Simply set the max voltage and you`re good to go.


    That is one approach, but not specially the most efficient one. The optimal working point is not always the same, it might shift with changing situations. Only a tracker is actively taking care of that and adjust to the most efficient working point.
    And it requires cell count that exactly match your battery voltage to work at least some kind of normal. On my model I want to be able to place as many cells as I am able to fit to get the most out of my surface, the buck boost switcher does the rest.


    Also I do not want to manually flick a switch to enable or disable the panels, that should run autonomous. That might be easy to do with an MCU but then that MCU could do MPPT straight away
    Last edited by RiSCyD; 15th March 2017 at 01:59 PM.

  10. #10
    Navigator parajared's Avatar
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    Well cool,
    Looks like a fun project.

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