Loading ...
Sorry, an error occurred while loading the content.

Re: Resistor or regulator?

Expand Messages
  • AlienRelics
    That will have to be a really monster capacitor to have a long enough RC time constant. And if the fan gets jammed, or some other long-term (ie, a few 10s of
    Message 1 of 12 , Sep 4, 2011
    • 0 Attachment
      That will have to be a really monster capacitor to have a long enough RC time constant. And if the fan gets jammed, or some other long-term (ie, a few 10s of seconds) failure, it gets over-voltage anyway.

      Your fan will have a really slow start, too.

      You would have to really match the RC time constant closely with the time to full speed for the fan. However, the time to full speed will be much longer with the RC circuit, so it will be quite a cut-and-try job. Which will change if the in- or outtake vents become partly blocked by dust. As will the motor current.

      My verdict is that a motor is much to complex a load to get good regulation with a resistive voltage drop.

      Steve Greenfield AE7HD

      --- In Electronics_101@yahoogroups.com, Donald H Locker <dhlocker@...> wrote:
      >
      > How about a resistor in series (to get the main drop) with a cap in parallel with the fan (to provide some cushion for max/min current events). One disadvantage - takes three terminals now, instead of two (supply+, supply-, fan+.)
      >
      > Donald.
      > --
      > *Plain Text* email -- it's an accessibility issue
      > () no proprietary attachments; no html mail
      > /\ ascii ribbon campaign - <www.asciiribbon.org>
      >
      > ----- Original Message -----
      > > From: "Derek" <derek@...>
      > > To: "Electronics 101" <Electronics_101@yahoogroups.com>
      > > Sent: Sunday, September 4, 2011 1:19:12 AM
      > > Subject: [Electronics_101] Re: Resistor or regulator?
      > > Inserting a resistor for the 12V drop is one thing, but takes
      > > experimentation as to what value. Other option is to use a resistor to
      > > drop the voltage and a 12V zener (in parallel with the fan). This will
      > > ensure 12V across the fan. But the resistor will still dissipate
      > > power. Both cases you are effectively doing a linear regulation.
      > >
      > > Better yet... put the 12V zener in series with the fan. 12V drop
      > > across the zener, balance across the fan.
      > >
      > > Derek Koonce
      > > DDK Interactive Consulting Services
      > >
      > >
      > > --- In Electronics_101@yahoogroups.com, DaveC <davec2468@> wrote:
      > > >
      > > > Small 12vdc fan needs to run from 24vdc supply.
      > > >
      > > > Simplest solution is measure current and insert a v. dropping
      > > > resistor.
      > > >
      > > > More elegant solution is to use a voltage regulator.
      > > >
      > > > If I understand correctly both will consume (waste) about the same
      > > > power.
      > > >
      > > > For such a simple application, is there any reason to use other than
      > > > a resistor?
      > > >
      > > > Thanks,
      > > > Dave
      > > >
      > >
      > >
      > >
      > >
      > > ------------------------------------
      > >
      > > Please trim excess when replyingYahoo! Groups Links
      > >
      > >
      > >
      >
    • Chris Robinson
      BY far the easiest possibly the cheapest, and still a fairly resilliant little setup. I recently burned a small 12V fan because of over voltage, spike hit at
      Message 2 of 12 , Sep 4, 2011
      • 0 Attachment
        BY far the easiest possibly the cheapest, and still a fairly resilliant
        little setup. I recently burned a small 12V fan because of over voltage,
        spike hit at about 20Vdc to it and puff as a tiny white cloud and a nasty
        smell. So my solution to all this mess was to get a bigger fan, and use a
        regulated supply, not the cheapest method by any means, but what else do I
        do with a million and one power supplies from various ages and designs. I
        found that I could controll fan speed by this method as well. The supply was
        an old kit from about 20 years ago. It worked first time, and was a variable
        power from 1.5 to 37Vdc claimed but only measured about 32V, as well as a
        constant rwegulated non variable 5Vdc output also worked for running a
        handfull of LED's so I could also see in my server/radio closet.

        If you go the way of the resistor, may I suggest something that will
        dissipate enough heat to not worry about a failure from it. Something I am
        learning about a few LCD TV manu. under rated Caps, and all 9 may have to be
        replaced as well as a resister that cooked from a little to much dust and
        other Sugar Honey Ice Tea!



        On Sat, Sep 3, 2011 at 10:19 PM, Derek <derek@...> wrote:

        > **
        >
        >
        > Inserting a resistor for the 12V drop is one thing, but takes
        > experimentation as to what value. Other option is to use a resistor to drop
        > the voltage and a 12V zener (in parallel with the fan). This will ensure 12V
        > across the fan. But the resistor will still dissipate power. Both cases you
        > are effectively doing a linear regulation.
        >
        > Better yet... put the 12V zener in series with the fan. 12V drop across the
        > zener, balance across the fan.
        >
        > Derek Koonce
        > DDK Interactive Consulting Services
        >
        >
        > --- In Electronics_101@yahoogroups.com, DaveC <davec2468@...> wrote:
        > >
        > > Small 12vdc fan needs to run from 24vdc supply.
        > >
        > > Simplest solution is measure current and insert a v. dropping resistor.
        > >
        > > More elegant solution is to use a voltage regulator.
        > >
        > > If I understand correctly both will consume (waste) about the same power.
        > >
        > > For such a simple application, is there any reason to use other than
        > > a resistor?
        > >
        > > Thanks,
        > > Dave
        > >
        >
        >
        >



        --
        Mr.C.Robinson
        73 DE KF6NFW


        [Non-text portions of this message have been removed]
      Your message has been successfully submitted and would be delivered to recipients shortly.