Way to solve the 12 volt charger issue

Discussion in 'Mavic Pro Discussions' started by JustinVV, May 11, 2017.

  1. JustinVV

    JustinVV Well-Known Member

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    The cheap 12 volt charger DJI used for the Mavic wont charge if the voltage is below 13 volts, this is when you vehicle isnt running.

    Here is my fix.

    Power supply from here
    Items in solaluna88 store on eBay !


     
  2. Cyberpower678

    Cyberpower678 Well-Known Member

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    There's a reason why it won't charge at less than 13V, and it's to not damage the battery. There's a voltage switch in there that has that cutoff in there by design, to give the battery clean voltage.
     
  3. JustinVV

    JustinVV Well-Known Member

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    Maybe, but the battery has smarts to protect it, but why didn't they put a proper power supply in it that would regulate to the correct voltage. Like everyone else does. Its all about price.

    The regulator I used will supply a rock solid regulated 13.6 volts, no matter what you throw at it. Just what the charger needs.

    Is there a limit switch in the power supply? or is it just the battery that has the smarts.. I will check, but I bet its the battery that has the smarts. I bet the power supply only regulates on the high end.
     
  4. Cyberpower678

    Cyberpower678 Well-Known Member

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    The charger plug has a voltage cutoff switch in it. If you want to bypass it, take it out, but I wouldn't recommend it. It's easier to regulate down than up.
     
  5. dwallersv

    dwallersv Well-Known Member

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    Disappointing that something as ubiquitous and cheap as a switching supply wasn't the design -- something that could deliver the necessary 3S LiHV final stage charge voltage (13.05V) at a wide range of input voltages (say, 5-25V). A.k.a. the classic Buck Converter, and many other common designs.
     
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  6. JustinVV

    JustinVV Well-Known Member

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    Why would I want to take it out?? I solved the issue..

    Yes, its cheaper by a few cents to only regulate the high side.
     
  7. Cyberpower678

    Cyberpower678 Well-Known Member

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    You know it could also be that they don't want to drain the car battery accidentally and designed it to only take power when the car is running.
     
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  8. JustinVV

    JustinVV Well-Known Member

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    I think I am big and ugly enough to make this decision myself. I actually have a second battery in my vehicle protected with a VSR, so I am good as far as that goes. Also a few charges on a set of drone batteries wont flatten you car battery.

    Its just cheaper.
     
  9. JustinVV

    JustinVV Well-Known Member

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    Actually it doesn't have a "switch", I just checked it. If you feed the power supply 10 volts it will output 10 volts, if you feed it 13 volts it will output 13 volts, if you feed it 15 volts, it will output 13 volts. It only regulates the high side.

    So as I suggested the battery is doing all the work protecting its self.

    Where ever you got the information about this switch, you might want to correct them..
     
  10. Cyberpower678

    Cyberpower678 Well-Known Member

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    I got that information based on the fact someone took their plug apart and there was a simple voltage switch circuit inside. @Robbyg and I being Electrical Engineers analyzed it and came to that conclusion.
     
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  11. Plawa

    Plawa Well-Known Member

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    I would hardly call this "solved"... I bought the car charger to be able to charge batteries on my bike, I don't really see myself carrying another brick twice the size and weight just to be able to use the charger with the engine off..
     
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  12. JustinVV

    JustinVV Well-Known Member

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    Well, I totally seeing myself doing this, so yes, I have it solved.
     
  13. Robbyg

    Robbyg Well-Known Member

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    Justin I know we analyzed the circuit several months ago. My memory is not as good as Cyberpowers. I have worked on a lot of circuit designs since then and have forgotten what we found. Maybe somebody who remembers the post can link it.

    Many Amateur Radio operators use DC-DC converters for their radios because they also have issues if the voltage drops. The concept works fine if you have dual car batteries but for the 99% of us with a single battery we can easily come back to the car and find the cars battery level at 8V and be stranded at a remote location.

    Rob
     
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  14. JustinVV

    JustinVV Well-Known Member

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    OK, maybe it doesnt work, or mine is broken, I tested the input and output with meters.
     
  15. JustinVV

    JustinVV Well-Known Member

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    I am going run all batteries out, and the controller and set it up on my bike and look at the draw and see what happens, and I have to know anyway. Will post results. But I have charged up the drone batteries using inverters, even less efficient, and not come close to flattening the battery. But this was just one charge in 3 batteries. But the battery in my car is quite big being a diesel SUV 4x4.
     
  16. Cyberpower678

    Cyberpower678 Well-Known Member

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    Are you measuring the current at all?
     
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  17. JustinVV

    JustinVV Well-Known Member

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    I did on the input of the dc-dc. With only the Mavic battery it was drawing 4 amps at 13 volts, and an amp of 2 more as you reduce the input voltage.
     
  18. Dragonfly

    Dragonfly Well-Known Member

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    You can easily charge three Mavic batteries from your car battery while its stopped with no problems at all.
    Three (3) Mavic battery's at 15% flatt = roughly 3000mha or X3 9000 mha or 9amps.
    The average car battery, Small is 400amp, large 600amp.
    So even after an hour charging 3 Mavic batterys 9 to 10 amps from 400 amp battery isn't going to flatten it. And a five minute idle with a good alternator will replace that back into car battery.
    Now the DJI car charger seems to need a full 13.8 volts to provide the battery circuit an even current to charge the cells.
    The problem is the car battery is an lead acid and at peak charge per cell of 2.3 is 13.8 but once that float discharge is removed the nominal voltage per cell is 2.1 or 12.6 volts.
    And 12.6 is not enough to hold open the input gate on the Mavic car charger.
    So you have to use a Buck Converter which takes a lower voltage of between 8 to 12v and supplies a steady output of 13.8 volts. They come in flavors of 5,8,10or15 amp so you would need at least 10 amp minimum for 3 batteries at once.
    Or you could go the 12v to 240v inverter route and use your home charger plugged into the inverter.
    A little more inefficient but still a cheap fix as you already have home charger and a 12v to 240v 300w can or gigarette plug inverter is only $15 to $20.
     
    #18 Dragonfly, May 12, 2017
    Last edited: May 12, 2017
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  19. mark_t

    mark_t Well-Known Member

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    The car charger isn't just a cheap dumb device, it is capable of handling up to 30V, but the pack could well be the limiting factor on allowing the charge to take place.

    If you feed the charger with 12.3-16 V or 25-30 V charging should take place, outside those ranges it won't...
     
  20. Cyberpower678

    Cyberpower678 Well-Known Member

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    Little detail, 400-600 amps refers to how much it can deliver at once to cold crank it. No indication of the capacity. I personally have 665 CCA battery.
     
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