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Thread: Fusion Brain Reverse Polarity... Fuse blown?

  1. #1
    FLAC
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    Fusion Brain Reverse Polarity... Fuse blown?

    I just accidentally hooked up my fusion brain with reverse polarity and now it's not working. Did I blow a fuse? Frankly I'm not too worried about blowing another fuse, so are there just to points I could solder together to bypass the fuse?
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  2. #2
    FLAC
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    Nevermind, no fuse blown. Regulator solder joint simply melted off. Fixed.
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  3. #3
    Fusion Brain Creator 2k1Toaster's Avatar
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    Good to see it working.

    As for the fuse, it is thermal. Give it an hour or so and it should work again if it happens. However obviously this can do much much more damage depending on what is connected when it happens.
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  4. #4
    FLAC
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    Hmm actually it's not working. Only output 0 works. Plugging into any other output makes the blue power LED on the board get brighter. Led for 9 is stuck on, but if you plug a relay into its pins, the light goes out and the relay doesn't click?

    Any idea what the heck is going on? Would there be something simple for me to fix myself?
    My Nearly Complete Car:
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    Micro Control Center... Control Your Car Across the Internet
    http://www.mp3car.com/fusion-brain/1...-internet.html

    Website: (It's a work in progress, really. All my projects have taken me from ever really developing it.)
    http://paulfurtado.com/

  5. #5
    Fusion Brain Creator 2k1Toaster's Avatar
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    That weird behaviour suggests you fried it beyond repair.
    Fusion Brain Version 6 Released!
    1.9in x 2.9in -- 47mm x 73mm
    30 Digital Outputs -- Directly drive a relay
    15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
    Buy now in the MP3Car.com Store

  6. #6
    Raw Wave
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    I'd agree - a few shorted transistor eh?

    Big difference between (over) current protection and reverse-polarity protection (albeit fixed with a 20c diode).

  7. #7
    Fusion Brain Creator 2k1Toaster's Avatar
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    Well I have connected the same MCU on a breadboard with reverse polarity as well as +12v directly into VDD (don't ask...) and it worked fine afterwards. However it was a couple seconds at most. So the chip itself has some protection. It sounds like it was on for a while if the solder joint desoldered itself from the heat.
    Fusion Brain Version 6 Released!
    1.9in x 2.9in -- 47mm x 73mm
    30 Digital Outputs -- Directly drive a relay
    15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
    Buy now in the MP3Car.com Store

  8. #8
    Raw Wave
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    It's more a case that the chip has certain tolerance - there isn't any protection.

    Just add a reverse-connected diode after the thermal fuse (IN4004 etc), else full protection (same diode in line, or diode in a series relay's coil circuit if voltage drops are unacceptable).

  9. #9
    Fusion Brain Creator 2k1Toaster's Avatar
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    Right. The chip can take abuse in moderation, that's it. More protection is possible but all designs have tradeoffs.
    Fusion Brain Version 6 Released!
    1.9in x 2.9in -- 47mm x 73mm
    30 Digital Outputs -- Directly drive a relay
    15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
    Buy now in the MP3Car.com Store

  10. #10
    Raw Wave
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    Yep - a 20c tradeoff. But I often reverse polarity protect. Some things are quite easy - that last was an Oatley "smart battery isolator" kit (~$20; 80A) where I simply added a small signal diode on the board in place of an optional resistor for 24V operation. (It protected the chips etc but did not effect the voltage sensing - that was done before the diode.)

    But for 12V etc circuits that drop to 5V, it does surprise me that designers do not include the protection diode. (But that's sometimes an intentional omission.)

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