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Thread: what resistor for 445 diodes in parallel?

  1. #41
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    so, you won't be running the diodes at more than 0.25 amps, rite?
    you are almost good to go if it is for LOCs, but not sure about the 445s...
    "its called character briggs..."

  2. #42
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    Quote Originally Posted by LaNeK779 View Post
    so, you won't be running the diodes at more than 0.25 amps, rite?
    you are almost good to go if it is for LOCs, but not sure about the 445s...
    yeah red diodes
    Eat Sleep Lase Repeat

  3. #43
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  4. #44
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    Just to complicate things I would like to know how the resistor choice might change if we want to protect the diodes (LOC's or 445's) if say a 4 diode parallel string had one diode go open circuit or a dead short. The latter is more plausible with the LOC as when a drive wire contacted the grounded case. I think the resistance may need to be significantly higher especially if we are running the diodes close to their upper limit. Any thoughts?

  5. #45
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    Quote Originally Posted by planters View Post
    Just to complicate things I would like to know how the resistor choice might change if we want to protect the diodes (LOC's or 445's) if say a 4 diode parallel string had one diode go open circuit or a dead short. The latter is more plausible with the LOC as when a drive wire contacted the grounded case. I think the resistance may need to be significantly higher especially if we are running the diodes close to their upper limit. Any thoughts?
    There is little saving grace in either failure mode.

    O/C diode/wiring: the remaining diodes absorb the programmed current, failure highly likely.

    S/C diode/wiring: the resistor on that diode will absorb the addition Vfwd of the diode (2.5 to 4.5V depending on 660/445) and could exceed the resistor rating, resulting in resistor failure, then it's the same as an O/C failure. Not to mention the sharing imbalance that will result before the resistor fails.

    Rating the resistors to cope with shorts is possible, but either way the results are less than ideal. 1 driver per diode OR diodes in series really is the only safe method.
    This space for rent.

  6. #46
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    a simple yes or no will do, no techy elecy speak

    when driving 4x 445 diodes with 12v and using these 3watt resistors as advised in this thread, they get mega fooking hot. they burn my fingers they are so hot, is this normal?
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  7. #47
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    If you using them as balance resistors, there is no reason you need to use 1 ohm, I am using .47 ohm 1/2 watt for my LOC's @ 500ma and they barely get warm.


    you could do the same with 445's by going to a lower value, which should drop the heat a lot. Depending on the current you are running through them, those 3W resistors are having to dissipate a lot of heat. ~1.5 W @ 1.2A

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