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Thread: Bizarre simpledrive II driver problem

  1. #41
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    Quote Originally Posted by Bbe View Post
    Pots don't need to be swapped

    Digikey has one that you can use for replacing
    https://www.digikey.com/product-deta...FECT-ND/678963
    OK, that's great! Someone much more knowledgeable than I told me that wire wound resistors may generate a spike when the magnetic field they create collapses when powering down. As such, wouldn't a metal or carbon film resistor be a better fit? Maybe this one?

    Also, can you identify which resistor needs swapping? I have a picture of the v2.5A r1 on the left and an r4 on the right.

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    Many thanks!

    -David
    "Help, help, I'm being repressed!"

  2. #42

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    Yes, and these "spikes" has a negative polarity, which is much more dangerous for a laser diode. But.. low-impedance metal resistors have negligibly small parasitic inductance, which can be neglected. And in any case, these "spikes" (if they have a dangerous amplitude) will be absorbed by the onboard Schottky diode. A much greater threat is represented by wires, between the driver and the laser diode. Their parasitic inductance can be enough to generate a fatal negative spikes. For this reason, the absorbing diodes (Schottky + TVS) should be connected in close proximity to the laser diode (regular rectifying diodes are ineffective for this).
    Someone much more knowledgeable than I told me that wire wound resistors may generate a spike when the magnetic field they create collapses when powering down
    They are on the front side - you don't confuse them with anything.
    Also, can you identify which resistor needs swapping?
    Too high temperature coefficient I think. I use 50ppm in v500, but I could not find the one suitable on digikey. Anyway they will work too - they have no choice.
    Maybe this one?

  3. #43
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    What would be the longest recommended wire run to the laser? the max I have ever used was 6.5 inches with the Lasorb at the diode it's self, the UV leds that I use, I use the same rules to keep the wires as short as possible from the driver to the LED, I started that test run about 3 years ago on a thread on this forum, I should find it and update it as the leds are still running strong with over 1k hours on them, the cheap Chinese ones with plastic encapsulation died long ago but the Nichia and LED Engine ones with a ceramic body and glass are still going strong, there price though is still 30 bucks a pop though worth the money, got to use them twice now on 2 shows we did
    Polk SDA SRS, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  4. #44
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    i am going out on a limb here but the resistor that needs to be swapped is the main current sense resistor, the big white ceramic resistor on the top side of the driver
    , it's hard to not notice as it's the largest resistor on the driver
    Polk SDA SRS, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  5. #45

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    Parasitic inductance is very individual for different conditions. Much depends on how the wires twisted or how they are laid inside the case. No simple answer to your question
    What would be the longest recommended wire run to the laser?
    I think they died their own death, no good wires or drivers would not have saved them
    Chinese ones with plastic encapsulation died long ago

  6. #46
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    Quote Originally Posted by Bbe View Post
    Too high temperature coefficient I think. I use 50ppm in v500, but I could not find the one suitable on digikey. Anyway they will work too - they have no choice.
    Quote Originally Posted by Draco View Post
    i am going out on a limb here but the resistor that needs to be swapped is the main current sense resistor, the big white ceramic resistor on the top side of the driver, it's hard to not notice as it's the largest resistor on the driver
    Got it! Thank you both!

    -David
    "Help, help, I'm being repressed!"

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