120vAc to 12vDc@4A for temp regulated fans

Discussion in 'The Projects Forum' started by mpdube113, Apr 2, 2011.

  1. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    Hello I'm looking for some guidance. i currently have 3 "T5 electronic ballast" that i'm in the process of building a air cooling system for. I have mounted aluminum heat sinks on metal housing of these 3 ballasts via some 6-32 screws an some thermal paste. I have 3-12vDc .43A brushless fans that I'm wanting to control with a temp sensor.
    EASY RIGHT! well heres the catch i've searched all my salvaged parts an can't find any IC that could make this really simple.(i won't be purchasing any parts) i have tons of salvaged power supplies from TV's, COMPTERS, AND MANY other different types of electronics.

    please give any advice

    thankyou
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Welcome to the forums

    you can make a temp sensor with LM339 as a comparator and some diodes as a sensor. Pretty simple
     
  3. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    thankyou
    is there anyway around using a specific IC
     
  4. R!f@@

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    Apr 2, 2009
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    There is this LM34, a temp sensor. you can use this instead of a diode.
    Rest is just basic comparator. Whether it be a μC or a simple op amp comparator like LM339

    You do know what a comparator is, don't you?

    The temp sensor and fan switching circuitry is nothing too fancy. It's basically what I said one way or the other
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    One of the questions you need to answer is how deep your electronics expertise is. I like to design stuff from scratch, some people can assemble things if given a schematic, while others want to know what those little arrows mean next to the diode.

    We can better answer your questions if we knew your expertise. Rifaa's replies made sense to me, but they may not help you much.
     
  6. R!f@@

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    I did made it using diodes and comparators as level sensors. Quite easy. And it was way before I join here.
     
  7. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    i'm not an expert by any means. but i have a good understanding of basic electronics. its my hobby. i have no training of any sort. i'm a licensed master electrician. so with some guidance from these forums i'm hoping to learn more.
    a comparator seems like a very simple concept. i'm going to do some digging an see if i can find one. if not what are my other options?
     
  8. R!f@@

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    Actually this is the simplest option as far as I can see.

    I will give you by design. I do not have a schema as of now but if you follow what I say and Google it you will learn a lot more. Reading and experimenting will teach u a lot.

    First you have to decide which sensor. There is NTC , PTC and ready made temp sensor like LM34. Silicon diodes can also be used but their variation is very little. You will have a large margin if you use thermistors or stand alone sensors.

    Next is the comparator designed around a Voltage comparator opamp such as LM339.
    This circuit basically compares two voltage levels. One input senses the sensor voltage drop at a specified or required temperature and compares it to a reference voltage at other input.

    This reference determines the triggering point. A hysteresis should be given between the max temp trigger and minimum temp trigger. This will prevent the opamp triggering errors.
    U can use either input for the threshold and sensor, and the design can be an over voltage type or an under voltage type.

    This the complicated part.

    Next is easy part.
    The output of the opamp can be coupled to any thing, an indicator, or a transistor driven relay or mosfet maybe. no big deal here.

    Other concern is actually where the sensor is located. for example is it far away to the comparator input or close. Precautions should be taken if far away. like noise filtering to prevent erratic triggering
     
    Last edited: Apr 4, 2011
  9. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    ok this are the IC's i've come up with

    http://pdf1.alldatasheet.com/datasheet-pdf/view/251927/FOSLINK/FSP34063N.html

    http://pdf1.alldatasheet.com/datasheet-pdf/view/12713/ONSEMI/UC3845BN.html

    http://pdf1.alldatasheet.com/datasheet-pdf/view/33711/WINGS/KA3842A.html

    http://pdf1.alldatasheet.com/datasheet-pdf/view/3073/MOTOROLA/LM358N.html

    and the thermistor I've come up with is a TTC-103 it's in a little Aluminum housing with a mounting hole ( PERFECT ) Covered in Thermal paste

    now a little direction :)


     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Have you decided what to get or checked what you have.
    did U know that u can salvage parts for ur problem from a computer power supply.

    try it first
     
  11. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    the parts listed on my previous post are salvaged parts i have in my possession :) just need some help applying one of the 4 listed IC's to my specific situation
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    OK ..let's see now..
    {ed}
    You have a dc to dc converter and some SMPS PWM chips. Which cannot be used for ur current project.
    But the LM358 can be used as a comparator.

    Post a pic of the thermistor that you have.
    and try to find a 4 pin or 8 pin IC labeled LM339. I bet there will be one if you have some PC junks.
     
    Last edited: Apr 4, 2011
  13. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    i'm sorry i don't have a camera ATM. um... i'll describe It it's green and labeled TTC 103.. i think i remember seeing another one i'll try and dig it up..
    but as far as the LM339 i searched all my stuff the first time you mentioned that IC. i couldn't find it. Can we make use of the LM358
     
  14. R!f@@

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    Apr 2, 2009
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    We can use the 358.
    You have to take some measurements.

    Tell me the resistance of ur thermistor. at room temperature. Do not touch the thing when measuring.
    Make a table. Heat the thermistor and note down it's resistance variations.

    Post the table
     
  15. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    room temp (60-70F) = 10.55k Ohms

    heated temp (soldering Iron about 3" from the Sensor ) = 8.76k Ohms

    do i need to take more precise measurements or are these sufficient
     
  16. R!f@@

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    Apr 2, 2009
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    So what you have is a NTC.
    Which R drops to the applied heat.

    Now ask your self how should and when should the fan operate
     
  17. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    well i don't wanna make it to complicated but.. if possible i want them to Turn on when a set temp is reached (low speed) and then Climb in RPMs ( or just jump to a set RPM)as the temp rises, and then once the heatsinks on my ballast (where my temp sensor will be mounted) start to cool down i want the fan to throttle back down to Low speed and turn off..
    but if that is to much i can settle for just a on off set up
     
  18. R!f@@

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    Apr 2, 2009
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    Hmm!! Just what I thought.

    For dual speed you have to utilize both the op amps.
    How do you plan to give power to the chip. Stand alone former or tapping into the current circuit.

    You can run a fan from the current circuit. It's no big deal. If the fan is a standard PC PSU type of fan.
     
  19. mpdube113

    Thread Starter New Member

    Apr 2, 2011
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    umm the fans are 12vdc .43A each and there's only 2 of them but i want to Keep enough room in the Circuit For an extra fan around the same Amp rating. i've got tons of Transformers that i can make a regulated PS from. i've got a few of these guys also along Caps in every shape an size
    http://pdf1.alldatasheet.com/datasheet-pdf/view/14721/PANJIT/GBU4K.html

    i haven't made a Regulated PS yet so i think this would be a good Time to practice ??
     
  20. R!f@@

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    Apr 2, 2009
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    OK then..Let's see what I can cook up.

    You have to give me the trigger points. Like say the resistance of the NTC at the low speed start temperature.
    Since I cannot find any data related to the NTC and you haven't shown me the thing, I cannot speculate.
    So you have to mount the thermistor on the sink and measure the resistance. Note down the value at which you like the fan to start and toggle speeds.

    The sensor should be mounted in a position where air does not flow. In other words , do not mount the thermistor anywhere between the fan and the sink
     
    Last edited: Apr 4, 2011
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