ac volage stablizer

Discussion in 'General Electronics Chat' started by TAKYMOUNIR, Nov 9, 2013.

  1. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    I have transformer 120 vac in and 24 vac out and this 24 vac feeding the coil of contactors and it feeds 4 contactors my problem is if i need to run 4 contactors in the same time some times the contactors not pull in ,and i did try transformer with high va but the problem is the same ,so how can i hold the 24 v from dropping,because at the begiing i need high current to pull the contacors
     
  2. ScottWang

    Moderator

    Aug 23, 2012
    4,855
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    It looks like the current is not enough for the contactors, how is the current of transformer and the current of each contactor?
     
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  3. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    You obviously need a larger transformer.
     
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  4. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    the current needed to supply the contactor is about 5 amp and the transformer is ok with this current but i see that the voltage is dropping down because in beginning we need higher current
     
  5. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    is there any thing can i do it to make the voltage not dropping ,is like if coil is dc i can put capacitor which not allow the voltage to drop quickly so is there any thing with the ac voltage which make the voltage not drop quickly
     
  6. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Don't load the transformer so heavily.
    Use lower current contactors.
    Use a transformer capable of higher current.
    Use separate transformer for one or more of the contactors.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,566
    2,379
    The answer as stated is either a higher Va rated transformer or use DC coils.
    AC contactor have high initial inrush, this is aggravated by the fact that the inductive reactance does not come into play to restrict the current until the armature has sealed in.
    Max.
     
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  8. #12

    Expert

    Nov 30, 2010
    16,345
    6,829
    Use the transformer to fire small relays that connect power line voltage to larger contactors with coil voltage requirements according to the power line wherever you might be in the world.

    Don't fire all 5 contactors at the same time.
     
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  9. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
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    Exactly!

    Most systems can tolerate .5 second delays.
    If it can, put a .5sec delay on one and a 1sec delay on another.

    Think of the load side of the contactors. Must be fairly large loads to require contactors with 120 watt coils.

    This will make the power side happy too. :)
     
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  10. ScottWang

    Moderator

    Aug 23, 2012
    4,855
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    If the contactors unnecessary to turn on at the same time, then this is a good way to do, maybe using a LM324 op amp to set up 4 comparators to detecting 4 voltages levels as 4 sections delay time, using 4 resistors and 4 caps to be the delay time.
     
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  11. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    can you draw the circuit
     
  12. ScottWang

    Moderator

    Aug 23, 2012
    4,855
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    There is another way to do is using LM3914 and one RC delay time.

    LM3914 Dot/Bar Display Driver - it can be set for 10 levels, you just need 4 levels.

    12V Car Battery Monitor - You can using RC to do the delay time from pin 5 of LM3914, and comparing with the comparators inside of LM3914.

    You can using LM339 or LM393 comparators or LM324 op amp to do the job of comparator, the following circuit is the same with LM3914, you just need 4 level, so if you using LM324 is easier more than LM339 or LM393.

    4 Level - voltage Detector - it's close to the bottom of the page, you may also see the "Comparator Timer Delay Schematic 3", it is at the 2/3 page.

    To see all the infos, if you still have the problem then you just post it.
     
    Last edited: Nov 10, 2013
  13. #12

    Expert

    Nov 30, 2010
    16,345
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    You could use 4 small relays to fire 4 big contactors or change the outputs to triacs and fire the big contactors with them.
     
  14. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
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    Until we know the logic involved now bringing in these contactors the delay logic is not easily solved.

    Say for example it's 4 random turn on signals.
    Chances are remote that all 4 come on within a couple hundred ms.

    The only need then would be different delays on each for power cycling or drop out when all are on.

    Maybe just on one or two.

    If the rare event of random simultaneous starts needing to be solved, an interlock would be needed between at least two.

    Reason being random starts could still be simultaneous even after fixed delays.

    Always comes down to needing more information.

    As far as delay timers go, off the shelf timers are the way to go. They are packaged nicely and have the necessary no/nc instant and timed contacts needed for interlocking.

    Two terminal series delay modules work well, but I haven't found 5-amp ones.

    120vac coils as suggested in an early post would sure solve a lot of problems.
     
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