Incapacitated -- trying to wire up a small 35v 3300 mcf electrolytic to a little 18vdc @ 2A motor

Discussion in 'General Electronics Chat' started by Dynamo1, Nov 22, 2015.

  1. Dynamo1

    Thread Starter New Member

    Nov 19, 2015
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    Hello all; I'm new to this community and have a small problem. ..I was just searching out a possible solution to my incapacitated capacitor knowledge. I'm trying to wire up a small 35v 3300 mcf electrolytic to a little 18vdc @ 2A motor. I'm running off power out of a transformer rated @ or a little above motor rating. My goal is to run motor directly off transformer continually without need for a battery. My capacitance is probably to low for one thing and I'm not sure whether to connect it across or inline...Any input would be well appreciated.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Does the "transformer" put out AC or DC? Wall-Wart type?

    The capacitor should be placed in parallel with the motor, +end of capacitor to the more positive voltage...
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
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    Capacitor is in parallel. You also need to rectify the AC to protect the cap from reverse voltage. Full wave would give you better efficiency.
     
  4. Dynamo1

    Thread Starter New Member

    Nov 19, 2015
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    Yeh, it's a ac to dc transformer used for recharging the battery that would have originally run the motor. I'm start/running the motor with the batt. and intend to take the batt. out of the circuit with the motor running only on the trans.
     
  5. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    If, as I understand post #4, your PSU supplies DC then yes! 3300uF @35V is applicable to your application:) --- That said, one wonders why you require the capacitor at all?

    Best regards
    HP
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    In most of those unregulated DC wall-warts, the internal filter capacitor is quite small, typically only 500uF, so adding an external, bigger capacitor reduces ripple...
     
  7. Dynamo1

    Thread Starter New Member

    Nov 19, 2015
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    I'm only assuming the need for a cap. because when I switch the batt. out of the circuit, after switching in the transformer, there's not enough from the trans. to run the motor. Now when I introduced the cap. on the positive side of the transformer, the neg. leg of the cap. toward the trans. and pos. to the motor, there's a slow rundown before stopping of the motor.
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Your description of how it is wired makes no sense. Draw it out!
    Reread post #2. The capacitor should be in parallel with the motor...
    Say it another way: substitute the capacitor for the battery, observing polarity.
     
    Last edited: Nov 22, 2015
  9. Dynamo1

    Thread Starter New Member

    Nov 19, 2015
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    I've tried connecting the cap. in series and across with neg. to trans. neg. and pos. to pos., nothing. That's why I was thinking maybe a need for greater capicitance so when the switch is made there's a good stored punch to the motor.
     
  10. Hypatia's Protege

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    If there is little or no internal filtration then capacitively shunting the PSU will increase the EMF (the limiting factor being 2^.5) -- That said, it sounds as if the PSU is not supplying sufficient current -- are you quite certain the cap is paralleling the PSU and load?

    Best regards
    HP
     
    Last edited: Nov 25, 2015
  11. Hypatia's Protege

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    If you've inverse polarized the cap - even momentarily - it may be damaged! -- Unless otherwise marked electrolytic are unipolar!

    Best regards
    HP
     
  12. Dynamo1

    Thread Starter New Member

    Nov 19, 2015
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    The power supply is a simple wall trans. charger so I assume there's a sufficient filter cap in it. But what you were saying about EMF factor, I don't understand your formula as you annotated it.
     
  13. Hypatia's Protege

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    Based upon your description, it seems you require a PSU better suited to the motor... Please check the EMF across the motor when you think it should be running...

    Best regards
    HP
     
  14. Hypatia's Protege

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    For a sinusoidal function E(Peak) = E(RMS)*2^.5 :)

    Best regards
    HP
     
  15. Hypatia's Protege

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    Or... to 'prettify' it: E(Peak) = E(RMS)*√2 :):):)

    But, again - this is a limit -- loading will radically (NPI) affect the actual EMF...
     
  16. Dynamo1

    Thread Starter New Member

    Nov 19, 2015
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    I never wired it any other way but (-) to Neg. be it inline on the pos. with the neg. toward the source or across with the neg. on the neg. side from the source and the pos. to the hot. I guess I can check the cap with my ohmeter since it doesn't have a cap check on it.
     
  17. Hypatia's Protege

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    That being the case, it seems I misinterpreted post #9....:oops:
     
  18. Hypatia's Protege

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    Please try this:

    Connect:
    PSU (+) to Cap(+) and Motor (+)
    PSU(-) to Cap(-) and Motor(-)

    Then check the EMF across the Motor

    Best regards
    HP
     
  19. Dynamo1

    Thread Starter New Member

    Nov 19, 2015
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    Man, your gonna cause me to search out my old Floyd textbook...But I can definitely see major drop in EMF when the load is applied...The trans. is putting out 19.5vdc noload and 17vdc loaded.
     
  20. Hypatia's Protege

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    That to be expected --unregulated 'wall wart' style PSUs tend to exhibit OC EMFs markedly in excess of their ratings...

    Best regards
    HP
     
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