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Help with PSU (Temp control fan, load bank, & PWM circuit)

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by jocanon, Jul 23, 2012.

  1. jocanon

    jocanon Member

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    That really might not be a bad idea, even if just to prevent the case from getting so hot that you can't touch it.
     
  2. ronv

    ronv Well-Known Member Most Helpful Member

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    Actually it is a resistor to ground. My bad. You were faster than my edit I bet.

    Out of curiousity it would be interesting to know what the part # of the componet is on the heatsink and how hot the heatsink is with just pin 4 grounded. We might be able to estimate how close it is to the spec.
     
  3. jocanon

    jocanon Member

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    Sure, I will see when I get home if I can find the part number. What component should I be looking for will it be obvious from what is attached to the heat sink?
     
    Last edited: Oct 23, 2012
  4. dave

    Dave New Member

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  5. ronv

    ronv Well-Known Member Most Helpful Member

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    I would guess something like the FETs you used in the load box.
     
  6. jocanon

    jocanon Member

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    I wonder what is the best way to get a temperature reading on these components. I have an infrared thermometer that is just point and shoot, but is there a more accurate way to measure?
     
  7. Dusey52

    Dusey52 New Member

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    A resistor from pin 4 to ground will set a new minimum fan speed...
     
  8. jocanon

    jocanon Member

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    Hm, is there a way to keep the min fan speed as is, but just lower the temperature at which it reaches max speed, in other words make the thermal control more sensitive.
     
  9. ronv

    ronv Well-Known Member Most Helpful Member

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    That's kind of what we did with your circuit.
     
  10. jocanon

    jocanon Member

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    yeah, I guess you are right, but how difficult would it be do you think to modify the existing thermal control without having to add another thermistor and op-amp? That's more what I am getting at now.
     
  11. ronv

    ronv Well-Known Member Most Helpful Member

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    It would probably be pretty easy if we had a schematic of it. Might be difficult to trace it out from the board.
    I wouldn't give up to soon on the resistor to ground. Without checking it is hard to say how much higher the low speed would be to get the top speed sooner.
     
  12. jocanon

    jocanon Member

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    Appearently there are two pots on the one daughter board according to a guy in the rcg forum. Once I find what he is talking about, I can try and see what those adjust.
     
  13. jocanon

    jocanon Member

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    I took apart a broken unit. Should I get part numbers for the big black one (it's the bridge rectifier and you can see the part number of that one in the picture, it's GPJ15M) in the first picture and the white ones in the second pic. Anything else you can see in the pictures I should get part numbers for? I will be offline for a while but back on later tonight.
     
    Last edited: Oct 23, 2012
  14. jocanon

    jocanon Member

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  15. jocanon

    jocanon Member

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  16. jocanon

    jocanon Member

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  17. jocanon

    jocanon Member

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    I think it is well within spec. I ran it for about 20 minutes on 50 amps and it was as hot as it was going to get. The heat sink was only 45C, the transformer was a little hotter at 110C. Would you agree with me that it is well within spec and no further mod is needed at this point other than shorting pin 4 to ground?
     
  18. ronv

    ronv Well-Known Member Most Helpful Member

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    The bridge is probably the easiest. Just rough numbers..... If we get 50 amps at 12 volts the bridge needs to be able to provide 5 amps at 120 volts plus say 15% for losses - 6 amps. If you go down the derating curve it can be 130C and provide 6 amps. This is absolute max.
    Actually the things that will probably fail are the 470 Ufd. capacitors right next to the heatsink. Electrolytic capacitors don't like heat especially when they are working hard as they do in switchers.
    I'm guessing these are good ones rated for 105C.
     
  19. jocanon

    jocanon Member

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    yep, 105C
     
  20. ronv

    ronv Well-Known Member Most Helpful Member

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    I think you are ok.;)
     
  21. ()blivion

    ()blivion Active Member

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    Electrolytic caps used to be the most common point of failure for SMPS's. A lot of units "had cancer" do to a major Taiwanese manufacturer using a bad electrolyte formula. You can read about it *HERE*. Not really relevant to your setup, ("HP reportedly purged its product line in 2004") but interesting read none the less. The problem still persists to this day, but is much less frequent.
     
    Last edited: Oct 23, 2012

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