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Thread: flexmod spikes-not

  1. #1
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    Default flexmod spikes-not

    Ok so I was looking at my flexmods again and I killed some diodes. Then I remembered the whole flap about this. I also just happened to watch the EEVBLOG on bypass caps. Well folks the flexmods are fine. Add a 10uf and a 0.1uf cap is parallel with the power to the board and your problems vanish. That board is very sensitive to power supply noise it seems. Once I did that I could not pop any diodes or make any kind of spikes at all. I then after added the pangolin protection thing as well. Mystery solved as far as I am concerned. My switching cheap breadboard supply sucks.

  2. #2
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    If I remember correctly, the earlier models had a wire-wound resistor for current sense. So there was a possibility of back-EMF killing diodes.

  3. #3
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    It’s a dale resistor and it’s still inductive. The ones I have are from the last batch. Great design. Very reliable shame no more. The caps really helped. My breadboard supply is total garbage. Whenever I used a good supply no issues.

  4. #4
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    DZ hit the nail on the head. It was the current-sensing resistor causing the problems with the ones I tested. Original spec was for a non-inductive unit, but somehow that got missed on one of the production runs. I had the 'scope traces to prove it but no one believed me until I cut one of the resistors open and took a picture of the wire-wound element inside.

    Adam

  5. #5
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    Indeed. I just replaced mine. They were all inductive. So the spike was the collapsing field.

  6. #6
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    There is a type of wirewound resistor where two wires are in parallel and going in opposite directions. The effect cancels out the development of a magnetic field so inductance is severely reduced.

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