High initial current on Relay

Discussion in 'General Electronics Chat' started by superway, Jan 11, 2010.

  1. superway

    Thread Starter Active Member

    Oct 19, 2009
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    0
    Hello,
    Can you please help methis question?
    I have a 12vdc-3.4Adc supply. I used to power up 4 different type of relays. There are 2 relays(kilovac EV200 AAANA) are powered up by 12vdc. But some time when I energizes this relay, the inital current reached 3.3 or 3.5 adc and casued other relays starting clattering and shut down.
    In order to reduce this initial current, what is the best simple circuit can I use?
    Thanks in advance!

    Ken Ng.
     
  2. sceadwian

    New Member

    Jun 1, 2009
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    37
    You can use a resistor to limit the initial current.
     
  3. superway

    Thread Starter Active Member

    Oct 19, 2009
    128
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    Please give more details. Thanks
     
  4. sceadwian

    New Member

    Jun 1, 2009
    499
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    What is the required holding current of the relay and it's DC resistance?
     
  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Those relays have a high inrush current, but only for a very short time (130mS according to the data).

    A limiting resistor would not work with this type of relay, they need the high current pulse for the initial pull-in.

    An extra smoothing (resovoir) capacitor should supply the current and avoid the dropouts.

    Try something like 10,000 uF at 16V, it should get rid of the problem.
    You could go for a larger size of you have anything available.
     
  6. superway

    Thread Starter Active Member

    Oct 19, 2009
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    I did tried cap 1000uf, 35vdc that i have on hand now. But this relay still clattering and caused my 12 vdc supply drops down voltage (8V).
    The holding current is about 0.18@12vdc.
    Thanks

    K
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Have you tested your coils? It sound like you have excess noise from a bad coil. If you pull the relays and energize the coil from your supply, do you get proper amperage? any fluctuation?

    You may want to try a much larger cap. Are there any diodes separating the relays?
     
    Last edited: Jan 11, 2010
  8. superway

    Thread Starter Active Member

    Oct 19, 2009
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    I tested relay just fine. There is no external diode added.
    I checked relay by manually it works just fine. When I run automatic test ATE, the relay start clattering.

    K
     
  9. Paulo540

    Member

    Nov 23, 2009
    188
    0
    As Jenkins said, don't use a resistor.

    The best thing to do is use a larger power supply. If you want to go the capacitve route, put ten of the previously mentioned caps in parallel.

    But honestly, I've done cycle testing on those very contactors with that same power supply and it is possible to burn up the supply over time running it at max current. They are only like 50 bucks so using a second one would solve all your problems and future headaches.

    Just curious but what kind of power are you switching with these?
     
  10. sceadwian

    New Member

    Jun 1, 2009
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    Is the power supply has short circuit or current limiting it'll go into protection mode if something with that much capactiance (discharged) is plugged into it.
     
  11. Paulo540

    Member

    Nov 23, 2009
    188
    0
    Yeah, those types are actually V and I limited. You really can't reliably operate more than one of those relays at a time with that supply. That's the sad truth. Especially if you are using some sort of testing/cycling program.
     
  12. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Yes sir. The inductance from the relay is really doing a number on that power supply.
     
  13. lmartinez

    Active Member

    Mar 8, 2009
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  14. superway

    Thread Starter Active Member

    Oct 19, 2009
    128
    0
    I am using a Condor DC power supply.
    Model: HC 12-3.4A - A+G.
    This DC supply is installed in Switch Box to supply power for all relays.
    I don't think it does have current limit.
     
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