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New PWD Board - Smoke from main power terminal

Discussion in 'Electronics' started by Ben Freedman, Feb 7, 2013.

  1. Ben Freedman

    Ben Freedman Member

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    Howdy...

    Just dropped another $800 for a new PWD, due to my recent issue.

    I have now attached the main power leads around 3 times, but each time I power-up, I get a thin thread of smoke coming from the main power attachment tabs. I've made sure there's no short, and the solder connection is very good (I've redone it 3 times!), but I'm still getting a little thread of smoke from the main power terminal.

    Oddly enough I didn't see this smoke when I powered up with no motors hooked up, but with the motors attached, I'm getting that little thread of smoke.

    The motors chirp normally at powerup, but then I power back down again because of the smoke thread..

    Any thoughts?

    Best,

    Ben
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Ouch. That does not sound good at all (he said, stating the bloody obvious....)

    Do you have a volt-ohmeter? Can you measure the resistance across the main power leads?
    It's also possible that you have a solder "whisker" from one side of the power distribution board to the other.

    I think you've got to determine the actual resistance -- it might not be a dead short, but if it's a static low resistance it could produce this effect....something's heating up burning off solder resin or something it's got no business burning off.

    Andy.
     
  3. Tabb Firchau

    Tabb Firchau Administrator
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    I think you should invest in a current limited power supply, it will save you a LOT of money in the long run.

    Best,

    Tabb
     
  4. Ben Freedman

    Ben Freedman Member

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    I believe when we measure the resistance, it increases as the capacitors are charged by the battery in the meter, correct? As per your video? How do we go about measuring the 'actual' resistance?

    It wasn't smoking before the motors where hooked up, however... Could that mean something?

    Probably a good idea, Tabb.

    Ben
     
  5. Gary Haynes

    Gary Haynes Administrator
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    Ben look at getting one of these. Mastech HY1803D Won't run a quad at full speed but can do anything else and you can increase power gradually. Pretty cheap and I use it all the time for testing purposes rather than batteries. About $80 from Amazon.
     
  6. Ben Freedman

    Ben Freedman Member

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    Sounds like a good deal, however I'm sure with a low-current supply, the wire won't smoke, so I wouldn't notice the problem until up in the air...not a good thing... I think it's vital to be able to diagnose the issue on the bench, so at some point, you have to use a LiPo...

    Any idea why it'd only smoke when the motors are attached? Maybe it has to have a complete circuit, or something?

    Best,

    Ben
     
  7. Gary Haynes

    Gary Haynes Administrator
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    Maybe Adam Paugh can chime in if they have seen anything like that during their RTF builds at QC. Magnifier check for stray hair like wires strands anyplace? Some rosin runoff from one side to the other that is melting off (that one is a stretch I think). Basically the stuff Andy suggested.

    Why with the motors only? More current, more heat. Did you have the FC plugged in? Can you shoot a photo of your setup just before adding power, focusing on where you see the smoke?
     
  8. Ben Freedman

    Ben Freedman Member

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    Yes, will take some photos tomorrow. Will also ask Josh to come and take a look...

    Is it just me, or does it seem that putting the two LiPo tabs on top of each other is just asking for trouble? Why not have them on opposite sides of the board, across from each other, so no short is possible or even likely?

    Hey... Has anyone thought of using another of the large + or - tabs that are on the circuit board? Would that be a more intelligent place to attach the LiPo?

    Best,

    Ben
     
  9. Gary Haynes

    Gary Haynes Administrator
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    Ben

    Location probably so as not have split leads for the power and any resulting EMI/RF. When I built mine I also wondered the same thing but just really scoured the area for strays. I'm not at home but think that I also put electrical tape around one lead as close as I could get it to the board to reduce the chance of something like a piece of grass with dew on it somehow causing a short. And lastly, again speculation, when the MK team designed the board the wire size imagined wasn't 8/10 gauge but probably 14/16/18 which is of course much smaller.
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    With the assembled PDB you cannot get a measure of the actual resistance if the caps are charging up -- on the other hand, if you see that there's a static resistance that tells you that you have a short circuit of some form -- either a direct short or some low ohm value.

    Either one spells trouble with a capital T and, as you see, the smoke comes out of the wires.... :)

    Smoke = heat. Heat = current. Current = low resistance. :)

    Andy.
     
  11. Ben Freedman

    Ben Freedman Member

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    There's no static resistance...but the caps charge up as per your DVD.

    Best,

    Ben
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    OK. Sounds like you found the source of the smoke based your other thread, right?

    Andy.
     
  13. Ben Freedman

    Ben Freedman Member

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    Maybe. We switch out the leads for spade plugs, and that seems to have solved the issue. Can't say I really knew what the issue was, however...

    Best,

    Ben
     

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