transistor heating up

Discussion in 'The Projects Forum' started by piranha3380, Jun 23, 2013.

  1. piranha3380

    Thread Starter Member

    May 28, 2013
    30
    3
    heya everyone,
    ime working on making my aquarium into a vivarium and ive stumbled on a stupid problem,
    i have set up 2 computer fans for fresh air and circulation inside the tank and lowered rpm whit a power transistor on a sink and a potentiometer, this works fine as is,
    but now ive made my verry own cold steam vaporizer whit 2 0.2A comp fans driven by the same transistor (2n5430) for some reason these fans chew up my components, i had a bd677 driving it at first but that blew up and destroyed my potentiometer, so i moved on to my 2n5430 again and that chew up another pot, so ive put 13k in series whit the base to get the rpm i whant and placed a big heatsink but now my heatsink gets realy hot,
    they both run of the same 12v supply so why dos it work whit a small print pot on 1 set of in total 0.4A fans and dosnt on the other set witch is identically made ?
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Most likely the new fans require much more current than the ones you used before, so the power dissipation on the transistor is much greater. Can you post a schematic so that we are sure on what you acutally are doing?
    Maybe you could use a 555 to drive the fan with PWM signal, this would dissipate very little power in the transistor.
     
  3. piranha3380

    Thread Starter Member

    May 28, 2013
    30
    3
    whel the fans arent controlled by a pwm signal but a solid 12 volt whit a feedback to let the computer know at what rpm its going,
    the fans itself are rated 0.2 to 0.21A at 12 volt so that wil make around 0.4A,
    the positive of the fans is connected to the supplie and the negative to the collector,
    then connected a pot (now 13k 5w ressistor) from 12v to base and gnd to the emitter, i am using this transistor http://alltransistors.com/transistor.php?transistor=4894
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Can you measure the voltage on the fan when you have the rpm you want?
     
  5. piranha3380

    Thread Starter Member

    May 28, 2013
    30
    3
    9.77 volt, burned my finger on the sink tho haha
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,979
    744
    Use a regulator like an LM317t it will give a better response.
     
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