charge stored up in power supply caps

Discussion in 'The Projects Forum' started by owhite, Jun 11, 2010.

  1. owhite

    Thread Starter New Member

    Jun 11, 2010
    4
    0
    Folks,

    I built a full wave bridge power supply based on this schematic:

    http://www.plitron.com/images/tech7.gif

    (68VDC + 2) * 0.8 = 56 VAC.

    This uses 55VAC toroid from plitron. I estimated would need two 15,000uF, 80V electrolytic caps wired in parallel for this circuit. The power supply is used to drive servo motors, you can get more information here:

    http://nilno.com/laser_intro/power_supply.html

    Its not a problem when I fire up the power supply with the motors attached as a load to the circuit, however if I ever turn that thing on and the servos are not attached the caps store a viscious charge. So there's been a couple times that I've turned on the supply without the motors, flipped it off, and then gone to hook up my motors to the screw terminals and I get a firecracker-sized explosion. This is annoying.

    Does anyone have any suggestions for what I could add to the circuit to bleed off the charge in the caps? If the answer involves adding some large power resistors please give me an idea of how I would calculate the resistance and amperage.

    thanks much,

    owen
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    see the attached.
    Take a look at the inrush current limiter

    I use to limit the cap inrush current and when the supply is off the relay switches connecting the cap bleeder discharging the cap.
    The voltage is almost identical to ur application I think

    Other part of the circuit is changed to make improvements so please don't think the regulator will work, but the current limiter is same as before and works
     
  3. owhite

    Thread Starter New Member

    Jun 11, 2010
    4
    0
    Thanks, this is helpful.

    Can you confirm that a resistor rated at 5Watt 30ohm is used to bleed the charge stored in the capacitors?

    Another question: was it necessary to use the transistor labeled "MPSA2222A" to get the relay to activate? Could the relay just be activated when the power switch turns on the voltage from MAIN (220VAC)?

    owen
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    R is 30ohm 5W is the bleeder and comes into play at mains power off , relay activation can be any way you like, I used the relay I had on hand at the moment

    {ed}
    Mains activated relay shud have a coil voltage of 220VAC.
     
    Last edited: Jun 11, 2010
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