Using a second supply to boost a variable 0-12V DC

Discussion in 'General Electronics Chat' started by Barry M, Sep 1, 2015.

  1. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    I have an electronic fan controller for a PC that I can set between 0-12V DC. My problem is that it cannot supply enough power. But I also have the PC's 12V as well with more amps than I would ever need for fans.

    Can anyone please tell me where I can start on how I can use the PC's supply to supply the fans while taking the same voltage set on the controller?

    I'm not being funny (or looking for the sympathy vote) but I probably have the parts lying around -I have about every timer and a lot variation of Arduino boards but an illness has sort of fried my brain.

    I have the funny feeling it's a timer and altering the duty cycle based on the analogue input from the controller. But I keep getting mental blocks and feel like beating my head off a wall :D
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    If you just want to boost the current of the controller output, you could use an opamp configured as a voltage follower with a transistor on it's output. Like this:
    curBoost.jpg
    Choose an opamp appropriate for your voltage and slew rate requirements and a transistor that can handle the desired current.
     
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  3. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    Thanks.

    Tomorrow I will set up the controller with one fan and get the multi-meter out and get a close enough slew rate. I'd imagine it will be close to zero. In fact, I don't think it will matter because its not going to be that sensitive an application.

    I will need to look through my transistors. It only has to handle about 3 amps at the very most with max volts probably 12.25. (LM138?)

    Then I will breadboard it and post pics to make sure (probably) :)

    Thanks for the solution.

    I will let you know how I get on.
     
    Last edited: Sep 2, 2015
  4. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    I don't know why I posted 'tomorrow' when it was 6:30AM when I posted that, lol, yup ... fried.

    Same sort of problem again for another device, this time a pump.

    I have a voltage booster to feed my pump, so it will be 24V and I will be taking that off the 12V ... not a problem, but ...

    How would I modify the above to have the 12V control between 8V and 24V?

    So 0V = 0V. 1V (or first increment) = 8V. 12V = 24V.
     
  5. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    Would using a UA741 and IRFZ44N be ok?
     
    Last edited: Sep 2, 2015
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Lets back up a bit to the fan. An LM138 is a 3-terminal regulator, not a transistor. It can do the voltage regulation and handle the current, but the max voltage to the fans will be around 10 V, not 12, because of the headroom required for the regulator to do its thing. The 138 datasheet has the standard circuit. If you use the circuit in post #2 with a rail-to-rail opamp and an NPN power darlington transistor set up as common emitter, max fan voltage will be 11 V or a little more. Note that these are linear regulators, and will heatsinks and air flow to regulate a 3 A load.

    What is the application for the pump and what is its max continuous current at 24 V? Also, is PWM an option for either the fan or the pump?

    ak
     
  7. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    I think I probably posted as you were posting. I changed to the UA741 and IRFZ44N.

    The pump is for my CPU waterblock and I believe it is 35 watts continuous.

    The fans are PWM fans, so you can't use PWM on them. I have ordered a couple of touch screens and another few bits and pieces and I plan to make a controller for them using the PWM fan signal.

    I wouldn't say PWM is really an option for either right now (the pump never probably). I bought a touch screen voltage controller that fits into my bays. The controller uses voltage to control the speeds, but it only has 15 watts per channel @ 12V and I need 8 fans on one channel and six on another, then the pump etc. So the easiest solution is to use the controllers voltage to control 'something' that would power the fans.

    Heatsinks aren't a problem, scavenged a few I can bolt on and airflow isn't a problem. I'm using something like 15 fans and making sure there are no dead zones.

    The controller I am using: https://www.nzxt.com/product/detail/144-sentry-3-fan-controller.html
     
    Last edited: Sep 2, 2015
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    14-15 fans in a computer? :eek: :D silly overkill

    NO ONE needs that many fans in any personal computer..
     
  9. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    Found a TIP41C TO-220 ... But if there are any 'best' parts to use I could see about ordering them.
     
    Last edited: Sep 2, 2015
  10. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    It's my new baby. 8 are for the quad 120mm radiator. 64GB of RAM, 6 HDD's -2 are SSD, Hex core Intel Extreme that I already had way over 4GHz on air.

    I run virtual machines on it, one is Ubuntu Server. Instead of everyone just saving photos and work and stuff to their local hard drives it is also backed up to a RAID array. I basically went backup mad.

    It was supposed to be a twin CPU. I plan to upgrade to that at a later date and keep the case.

    But if you look at the specs of the case, like 65cm long and high you can see where 15 fans will go.

    http://www.corsair.com/en/obsidian-series-900d-super-tower-case
     
    Last edited: Sep 2, 2015
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Don't forget the extra fan you'll need, to get rid of the heat that the other 14 fans will generate :).
     
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  12. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    True, true. If I am going to do that though, I would be as well upgrading to a fridge, but the back of them heat up so I may as well go for air conditioning and that kills two birds with one stone -because I'd like it.

    Problem solved, project replaced with 'save pennies for air con' project :)
     
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