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Power supply problems

  1. Jul 10, 2017 #1
    I've got an old laptop charger 19v 3A for my solenoid.
    I used a multimeter to check the charger without and with load. I used a solenoid of insulated 22gauge of approx 150 turns as the load. On my first try without any load, it gave 20v DC on the multimeter.
    When I connected the load and connected the multimeter ,it gave values on AC part fluctuating back and forth from 0-1.5v . Can anyone help me out in this? Is there anyway to get DC out of it while on load ?
  2. jcsd
  3. Jul 10, 2017 #2


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    Staff: Mentor

    You are shorting out its output, so it is in current limit until you remove the short.

    You need to put a load of about 19V/3A = 6.3 Ohms on it to keep it out of current limit.
  4. Jul 10, 2017 #3
    I tried 6ohms ( I don't remember correctly,but it's close to 6ohms) and the solenoid literally ceased to function :(
  5. Jul 10, 2017 #4


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    Staff: Mentor

    What wattage resistor did you use? I^2 * R = 54W, so you would have needed a pretty big power resistor...
  6. Jul 10, 2017 #5

    jim hardy

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    Science Advisor
    Gold Member

    #22 is 16 milliohms per foot.

    How many feet of #22 would it take to make six ohms ?
    On your solenoid's diameter, how many turns would that be ?

    Do you understand the relation between amp-turns and magnetic field strength ?
    You might look that up . Train your search engine - it wants to please .
  7. Jul 10, 2017 #6


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    2017 Award

    not surprised .... your LOAD, the coil, needs to be around 6 Ohms ... not a 6Ohm resistor in series with it :smile:

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