noob question/checking. On/off + DC voltage select circuit

Discussion in 'Electronics & Electrics' started by bennyg, May 10, 2019.

  1. bennyg

    bennyg Member

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    Circuit diagram.png

    From the components I have on hand, using a 2 way SPST switch (top circuit) would be better looking from a size perspective.

    The bottom seems more fault tolerant, as I'm not sure what would happen (in the top diagram) if both switches are opened? Could I reliably have a 3rd speed (somewhere in between 5V and boost controller output voltage) by closing both switches? How would I predict the outcome and calculate the load through each part of the circuit in that case? I think I understand the basics of circuits well enough, but not yet how the equations apply to parallel situations like this.


    Background:
    Building a watercooled laptop, the small pump needs power. Advertised spec is "6-12VDC max 0.35A @ 12V" so I'm assuming single digit watts at max load.
    5V DC and grounds are tapped from the motherboard's slimline SATA port (for what used to be optical drive)
    The small manual screw-adjustable boost controller takes 5V in, outputs 5-24V.
    It is desirable for noise/vibration to run pump at 5V.
    However bleeding, and maximal performance, require a higher voltage (9-10V).
    A no boot scenario occurs with the pump connected (perhaps on POST the EC is thinking it's detected a short). After POST has completed the pump can be connected and runs just fine without issue from there. Thus the desire for the pump to be able to be disconnected entirely.
    I have a theory that a pull-up resistor to ground on the slimline SATA detect pin *might* fix this issue, but regardless the speed select switch is still desirable.

    Thoughts? Any errors in my logic or diagram (self taught so far)?

    Thx :thumbup:
     
    Last edited: May 10, 2019
  2. merlin13

    merlin13 Member

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    A water cooled laptop?? Steampunk perhaps? Else someone has to be the first to ask - apart from the novelty value, why?...

    Somewhat off topic to your questions, but first Headscratch here would be how and where are you going to fit the cooling radiator?

    Back on topic - bleeding all the air completely out of the system might help negate the higher pump voltage requirements, but that'll be a fun concept to joust with methinks.

    Yup, that suspiciously sounds about right. You might have to rethink your power tap and try it off one (or even a couple) of the actual USB ports perhaps ,they'd handle higher current requirements on boot. Possibly even directly off the battery pack terminals if you still need the high pump purge volts.
     
  3. OP
    OP
    bennyg

    bennyg Member

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    Yeah mostly novelty, because a gaming laptop drawing 500W+ from the wall getting 20K total Firestrike with minimal noise and load temps in the 60s/70s is a complete novelty ... let alone one from 2012!! The one thing that has bothered my about my units over the past few years is the noise, that's why I've been playing with watercooling mods for a couple of years now, and a fully internal system (with the ability to connect external rads for extra cooling capacity) was the next logical progression

    There's a few other reasons too, my son gets off on hearing things explained in the answers to his million questions about what I'm doing and why I'm doing things certain ways as I'm cutting, soldering, dremeling, gluing, disassembling/assembling, etc. It's also something away from screens that I feel I need at the moment to stay sane.

    I have a few more pics and more of a build log here: http://forum.notebookreview.com/threads/fully-internal-watercooled-sli-system-diy-project.828059/

    The higher pump speed helps bleed air trapped in the pump. Once bled 5V is more than enough, the noise and vibration isn't worth the couple of degrees drop in temps most of the time.

    Anyway I settled on some different switches that settle all the needs and wants and won't have any parallel weirdness going on:

    Circuit diagram.png

    190515-IMG_20190515_155718 (Large).jpg
     
    Last edited: May 15, 2019
  4. merlin13

    merlin13 Member

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    Fairy's Muff. Almost anything can be engineered for personal preference, done horrible things in various hardware environments over the decades myself.

    Mucking about inside a lappy though, I might be inclined to drop some filter caps in, to help kill any switching spikes form the switch operation(s). And any idea what the snap-loading of the boost convertor and pump is like like when they first get hit with power?

    Let us know how it goes.
     

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