Electronics PWM speed sensor probes

Discussion in 'Modding' started by eaterofpies, 7 Mar 2002.

  1. eaterofpies

    eaterofpies What's a Dremel?

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    this is probably a really stupid idea and i will probably be branded a n00b for it but what the hell

    couldnt you just constantly supply the motor with the minimum voltage ie instead of running it at 12v when on 0v when off run it at 12v when on but 2v when off?
    just an idea

    edit corrected spelling it title to probe not prob (DOH)
     
    Last edited: 7 Mar 2002
    eaterofpies, 7 Mar 2002
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  2. mcduffiem

    mcduffiem What's a Dremel?

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    I don't think the available PWN controllers can do this. I guess you could build your own custom circuit w/ 555s...

    My first question is why? If your using PWM to contol fan speed, just increase you duty cycle if you want a faster speed. I don't understand what 2v instead of 0v is going to accomplish.


    Cheers, Mike
     
    mcduffiem, 7 Mar 2002
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  3. eaterofpies

    eaterofpies What's a Dremel?

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    the built in speed sensors of fans require power all of the time if u only go down to 2 v instead of 0v they may still work (well that was my idea) but i dont know how the speed sensors work hence this thread
     
    eaterofpies, 7 Mar 2002
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  4. cpemma

    cpemma Ecky thump

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    The sensor is usually sending out 2 pulses every rev, and if pulse event coincides with a space (zero voltage) on the PWM signal, no pulse possible, so wrong speed calculated.

    You wouldn't want the 2v base voltage going through the switching transistor, that would create heat, as the transistor would be part on & full on, not on/off.

    You may need a higher base, say 5v, to keep everything working, but I'm guessing here.

    Stay linear - pwm is efficient but won't save you the price of a birthday pint. :D
     
    cpemma, 7 Mar 2002
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  5. linear

    linear Minimodder

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    Hmmm...linear....birthday....pint....

    I think you're on to something.
     
    linear, 7 Mar 2002
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  6. eaterofpies

    eaterofpies What's a Dremel?

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    edit removed all junk posted last night about being drunk

    the reason i want to use pwm is because of my diy digidoc thingy it is probably the easiest way of controling the fans with a pic and i kinda like seeing the fan speeds not really sure why cos its not really useful

    oh the 2v bit was just as an example i dont know what voltage it needs either was hopeing one of you lot would . . . ho hum

    /me is now hung over DOH
     
    Last edited: 8 Mar 2002
    eaterofpies, 7 Mar 2002
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  7. cpemma

    cpemma Ecky thump

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    That other PIC fan controller mentioned in some recent thread calculated the fan speeds based on duty cycle.

    Its generally a very linear relationship with volts in the 7-12v range.

    Probably as good as the chipset method - MBM5 gives me either 3590, 3629 or 3668 RPM, nothing in between :rolleyes:
     
    Last edited: 8 Mar 2002
    cpemma, 8 Mar 2002
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