halfwave 200v dc

Discussion in 'General Electronics Chat' started by joes, May 12, 2008.

  1. joes

    Thread Starter New Member

    May 12, 2008
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    Hi,
    I have a piece of Japanese equipment and I need to build a 200 volt half wave rectifier to power a 200 volt electromagnetic coil for a vibratory feeder to control the amplitude.

    I don’t know the amp draw but it’s pretty thin wire so I would imagine less the 5 amps

    Any ideas on how to approach this from 120v or 220v?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    If you want 200V DC its better to use a full wave rectifier unless you need the waveform the half wave rectifier gives.

    What is the resistance of the coil?

    what is a vibratory feeder?
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    Is that like the vibrator car radios used to make AC when they needed B+ for the tubes?
     
  4. joes

    Thread Starter New Member

    May 12, 2008
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    need half wave to pulse the coil

    47.8ohms

    a vibratory feeder is like a conveyor with no moving parts instead of a moving belt there is a solid sheet of metal that is attached to an electromagnetic feeder that vibrates the product down the line.
     
  5. joes

    Thread Starter New Member

    May 12, 2008
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    Not a clue before my time... as far back as i go is remembering 8-track tapes my father used.
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    What i would make is to make a half wave rectifier by just using a single diode and drive the coil. But this is a bit risky because the maximum voltage of the mains will be 311 Volts (220 Vrms*1.41) and maybe the core of the coil will saturate at such a voltage and thus the current through the coil will increase for a small amount of time. With this increase in current you may overheat the coil and destroy it. Also the dc value of this halfway rectifier will be approximatelly 100V which may be not enough to drive your vibrator.

    Also you have to put a diode in parallel with the coil to absorb the back EMF.

    I dont say do it!! but if you want have a try but be aware of the mains voltage.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Don't do what Mik3 suggests.
    It is too dangerous. EVERYTHING will have high voltage on it.

    In Europe and Asia, they have a neutral line, and a 50Hz, 230v line.

    In the US, we have a neutral, and 60Hz, L1 and L2. L1 and L2 are 115v each to the neutral (which is a transformer center tap) and 230v to each other, because they are 180° out of phase with each other.

    If you really want to do this safely, you will have to purchase what is known as an isolation transformer, rated for 230V input and 230v output. You need to consult the documentation of your appliance to determine the wattage required.

    Along with your L1 and L2, you must have a ground line. If you don't have one, you should have an electrician install a proper one for you. There are places to save money. This is not one of them. Funerals are expensive.

    Connect your fused L1 and L2 to the primary side of the isolation transformer (each line must be fused) You should use a double-pole single-throw switch on the input side to turn the power on and off; both L1 and L2 must be switched, after the fuses.

    On one side of the secondary, connect your ground wire, and another wire connect to the exposed side of the vibratory feeder.

    The other side of your secondary, connect one side of a diode/rectifier that is rated for at least 400V, and of sufficient amperage for your load. Connect the other side of the diode/rectifier to your vibratory coil input.
     
    Last edited: May 13, 2008
  8. mik3

    Senior Member

    Feb 4, 2008
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    SgtWookie whats does an isolation transformer do actually? i have an idea but would like to know more.

    why do we connect the ground to one of the secondary's wires?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    An isolation transformer:
    1) Insulates the circuit on the secondary from the mains.
    2) Removes the reference to neutral and (ultimately) ground, so that it may be re-referenced to ground.
    3) Limits the current on the secondary side by the rating of the transformer.

    The way they wire residences in the US, the power company's transformer has three connections on the consumer side:
    1) L1 (One end of the transformer winding)
    2) Neutral (the center tap)
    3) L2 (The other end of the transfomer winding)
    Neutral is connected to Ground at the breaker panel for safety. Otherwise, the system could "float" to thousands of volts, which would obviously be quite dangerous.

    I don't know offhand why, but in Europe and Asia, the power company transformers have only two connections, which are roughly equivalent to our L1 and L2, with no center tap. They also use 50Hz instead of 60Hz. At any rate, since they don't have a center tap, they reference the L2 end of the transformer to ground at the breaker panel and call it Neutral.

    In what I recommended the O.P. do, on the output side of the isolation transformer, L2 is grounded. Basically, it becomes the "neutral" line of this secondary, more or less replicating Asian/Europe power except for the frequency. L1 exists only until the diode; then it becomes DC+ after rectification.

    The OP should connect the GND side to the chassis of the vibratory feeder. This will protect life, both human and fowl. The DC+ is connected only to the coil. If there is a fault in the vibratory coil, the isolation transformer will limit the current until the fuse(s) blow.

    If the isolation transformer should happen to short windings from primary to secondary, the ground connection will cause a fuse to blow before anyone or anything becomes endangered from electrocution.

    Had the OP followed your original advice, the first rainy feeding day could have resulted in far worse than fowl play.
     
    Last edited: May 13, 2008
  10. mik3

    Senior Member

    Feb 4, 2008
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    If you dont ground the secondary and the transformer works fine, if you touch one of the ends of the secondary only you will be shocked?
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    You ground one end of the secondary so that it doesn't float.

    If you didn't ground one end, it's possible that it could float to some arbitrary value, but there would be no current.

    If you touched only one end of the secondary and the other end wasn't grounded, you wouldn't get a shock, because there would not be a complete path for the current. That is, as long as the transformer windings stayed "good".

    If the primary and secondary windings should happen to short together (which occasionally happens when transformers overheat and the insulation melts) then the ground will keep the exposed end at a safe potential, while the primary side blows the fuses, because there will now be a short between L1 or L2 and neutral and ground back at the main breaker panel.

    The possibility of being exposed to high voltage is minimized when one end of the secondary winding is grounded, and the other end is kept insulated.
     
  12. mik3

    Senior Member

    Feb 4, 2008
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    I think you will feel a little shock due to static electricity discharges if you left the secondary floating.
     
  13. joes

    Thread Starter New Member

    May 12, 2008
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    Japan uses 200v 60 cycle power.

    could a scr be used to limit the power so I don't kill the coil with the peek voltage?
     
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