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Re: [beam] Some Miller SE help?

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  • wrigter
    Here are some more comprehensive comments in the order in which they appeared in your email. ... SE One of my favorite applications of a SE ... 10uF is pretty
    Message 1 of 7 , Nov 15, 2010
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      Here are some more comprehensive comments in the order in
      which they appeared in your email.

      >one of my first projects - a wind chime powered by a Miller
      SE

      One of my favorite applications of a SE

      >I've got a a 10uF timing cap (lower timing cap?)

      10uF is pretty big and may actually waste a lot of energy
      (relatively speaking)

      That is because the timing cap will hold the SE in the
      triggered state long after the main cap has been fully
      discharged, all the while shorting the solar cell current
      through the load to ground. You can test this by measuring
      the voltage across the timing cap. It will show a rising
      voltage that triggers the 1381 at its rated SE "trigger"
      voltage after which this timing cap voltage slowly decays
      until it reaches the SE "reset" voltage. If that is long
      after the motor has stopped turning, the charging output of
      the solar cell is wasted. The correct timing cap value
      should cause the 1381 to "reset" at the same time that the
      motor stops turning.

      >I need to drive my walkman motor, which seems to
      >want about 30-40mA to shift (tested w. 2x 1.5V AAA
      >batteries and a resistor).

      Electric motors have a variable impedance (resistance) and
      draw more or less current depending on the mechanical load
      and the speed of rotation of the motor shaft. The current of
      an efficient unloaded motor with a steady state RPM draws
      less than 1/20 of the current when starting (shifting) a
      motor from 0RPM. The actual current which a stalled motor
      will draw can be determined by measuring the dc resistance
      of the motor winding or by measuring the motor current while
      blocking shaft rotation. Knowing the stall current of the
      motor at 3V (without any series resistor) will make it
      easier to understand the behavior of the MSE circuit.

      >Is my expectation unreasonable? More storage caps?

      Just see what happens when you charge a given storage cap to
      3V and firmly touch the storage cap to the motor terminals.
      If it spins vigorously, then the storage cap value is
      correct and all that is needed is a more efficient MSE
      circuit with a low forward voltage drop when it triggers.

      wilf

      ----- Original Message -----
      From: samfosteriam <potatosculptor@...>
      To: beam@yahoogroups.com
      Subject: [beam] Some Miller SE help?
      Date: Tue, 16 Nov 2010 01:27:03 +0000

      >hi Beamers,
      >
      >I've been struggling to get off the ground with one of my
      >first projects - a wind chime powered by a Miller SE (
      >specifically:
      >http://www.solarbotics.net/library/circuits/se_t1_mse.html
      >) Its basically working, but I'm not getting anything like
      >the charge I need to drive my walkman motor, which seems to
      >want about 30-40mA to shift (tested w. 2x 1.5V AAA
      >batteries and a resistor).
      >
      >I'm using the 24x33 solar cell from solarbotics (
      >scc2433b-mse ) and using the circuit that shipped with it,
      >with the single BC548B (sub-ing in for the 2N3904
      >transistor), no R1, and a diode between pin 3 of the 1381
      >and ground. I've got a a 10uF timing cap, and I started
      >with a 4700uF storage cap.
      >
      >In this configuration I can watch the voltage grow across
      >the storage cap, and with my DMM in series I can see a
      >pulse of current to the motor. It seems to max out at about
      >11mA.
      >
      >I'm using a 1381J, but I've now put a diode in there now so
      >it trips at more like 3.3V. That bit works, and I can put
      >an LED in there and it goes on for a few seconds just under
      >a 60W bulb before fading off.
      >
      >I just added 2 more caps in parallel to push the
      >capacitance up to 6700uF. That seems to have got me close
      >to 15mA. But its still not enough. IIRC, 40mA to spin the
      >motor is pretty good efficiency-wise, last time I looked
      >into this stuff. And I've now got a great ugly stack of 3
      >pretty large storage caps. Granted the solar cell is small,
      >but converting that charge to a form that'll spin my motor
      >is the work I want the solar engine to do. Is my
      >expectation unreasonable? More storage caps? Lower timing
      >cap? Did sub-ing the 2N3904 do something horrible?
      >
      >thanks for any thoughts,
      >/Sam
      >
      >
    • samfosteriam
      ... Wow that could absolutely be it. I had marked the emitter originally, but when it came to soldering it in, I just followed the little drawing that came w.
      Message 2 of 7 , Nov 16, 2010
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        --- In beam@yahoogroups.com, wrigter <wrigter@...> wrote:
        >
        > > Did sub-ing the 2N3904 do something horrible?
        >
        > Only if you put the BC548B in backwards. Easy to do since
        > its pin order is the reverse of the 3904 and even with e and
        > c swapped it would still provide some current gain.

        Wow that could absolutely be it. I had marked the emitter originally, but when it came to soldering it in, I just followed the little drawing that came w. the solar cell/circuit - which is of course of a 2N3904. I really hope that's the answer, I'll check this evening (or earlier if I can't stand the anticipation)

        thanks Wilf!

        /Sam
      • samfosteriam
        Wilf I owe you one. Flipping the BC548B over did the trick, and now its firing like a champ. I even dropped back to the single 4700uF cap. I ve left the timing
        Message 3 of 7 , Nov 16, 2010
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          Wilf I owe you one. Flipping the BC548B over did the trick, and now its firing like a champ. I even dropped back to the single 4700uF cap. I've left the timing cap as-is for now and will tweak when I have the bell ringing mechanism sorted out and a better idea of the load/resistance it'll give.

          (inline)
          > Electric motors have a variable impedance (resistance) and
          > draw more or less current depending on the mechanical load
          > and the speed of rotation of the motor shaft. The current of
          > an efficient unloaded motor with a steady state RPM draws
          > less than 1/20 of the current when starting (shifting) a
          > motor from 0RPM. The actual current which a stalled motor
          > will draw can be determined by measuring the dc resistance
          > of the motor winding or by measuring the motor current while
          > blocking shaft rotation. Knowing the stall current of the
          > motor at 3V (without any series resistor) will make it
          > easier to understand the behavior of the MSE circuit.

          Invaluable info, duly stashed away.

          I'm happiest that everything I thought I had learnt and understood wasn't all delusional rubbish. While it occurred to me I might have stuff in the wrong away around, it didn't occur to me that it might still work kinda with the transistor wired up wrong.

          thanks again,
          /Sam
        • samfosteriam
          To follow up on this: I got the solar engine working thanks to help received here, and put together the rest of the thing last week. Its been hung up (inside)
          Message 4 of 7 , Nov 29, 2010
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            To follow up on this: I got the solar engine working thanks to help received here, and put together the rest of the thing last week. Its been hung up (inside) the kitchen window announcing the sun since.

            A little video of it in action:
            http://www.vimeo.com/17295373

            It was a lovely little project. This one needs to get packed up and shipped for christmas, but I'll definitely make another to replace it. The only bits I paid for are the 1381, transistors and the solar cell. Maybe $5 outlay in all.

            thanks for all the help here.

            /Sam

            --- In beam@yahoogroups.com, "samfosteriam" <potatosculptor@...> wrote:
            >
            > Wilf I owe you one. Flipping the BC548B over did the trick, and now its firing like a champ. I even dropped back to the single 4700uF cap. I've left the timing cap as-is for now and will tweak when I have the bell ringing mechanism sorted out and a better idea of the load/resistance it'll give.
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