what can be used if cant use resettabble polyswitch fuse

Discussion in 'The Projects Forum' started by Dimpi, Dec 28, 2013.

  1. Dimpi

    Thread Starter Member

    Sep 6, 2013
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    helo all,i want to protect the relay contact from the overcurrent caused by ac mains....the rating of relay is 12vdc,20A...

    i was searching for a ptc resettable switch whose trip current may be 8a,9a 0r 10a at 240V.but i dint find any...can any1 suggest me the alternative that what what can i use in place of ptc resettable switch for overcurrent protection of 12vdc relay...

    any help would be highly appreciated.
     
  2. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    So wait you are using a DC relay for AC correct ????
     
  3. Dimpi

    Thread Starter Member

    Sep 6, 2013
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    yes i am using 12v dc relay for switching ac loads
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The problem is that the points on that relay are designed to switch 12V dc loads (automotive). The points may not open far enough (small gap) to extinguish an arc when switching off an inductive load powered from a peak voltage of 339V. Not a good idea!
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    @Dimpi, there are relays that have 12VDC pull in coils for AC loads, if that will help you in your design.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you require to switch high current/voltage AC using a 12VDC supply with resettable over loads there are many sources on such as ebay for motor contactors, Telemecanique is a nice brand and have clip on resettable/adjustable overloads on the load side.
    These also have a range of coil voltage options.
    These O/L's normally have two auxilliary contacts for interlocking the coil itself, for e.g.
    The other N.O. contact can be used for indication of some kind.
    Incidentally these resettable O/L's come in stand-alone as well as the clip on type.
    Max.
     
  7. Dimpi

    Thread Starter Member

    Sep 6, 2013
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    but sir i think that will cost me more isn't it??
    and more thing i want to ask,if the term overload and overcurrent protection same??i think both are diffrent isn't it?guide me
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Overload usually refers to thermal or electronic overload protection between contactor and motor and often are attached to the contactor and have an adjustable range, this device often wired to drop the contactor out on a fault.
    Over-current can be a overload breaker or fuse also of some kind on the supply side.
    They both essentially perform the same function.
    You asked for something re-settable in place of a replaceable fuse.
    Max.
     
  9. Dimpi

    Thread Starter Member

    Sep 6, 2013
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    yes sir i wanted to use resettable fuse for overcurrent protection of relay adainst ac load..but i was searching of 8A,250v(or 240v)ptc polyswitch fuse.but its not available..

    so my ques was if i cant use ptc polyswitch fuse for overcurrent protection then what is its alternative???please bare with me i am very new to the domain.n guide me
     
    Last edited: Dec 30, 2013
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    How about a regular circuit breaker? PTC's typically aren't available in "higher" voltages as you have already found..
     
  11. Dimpi

    Thread Starter Member

    Sep 6, 2013
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    circuit breaker is expensive..isn't it?
     
  12. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    You can get a 7A 250V on digikey for as little as $0.80
    8A @250V for $1.72

    is the "expensive" for you? I'd hope not..
     
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