Relay becomes hot

Discussion in 'General Electronics Chat' started by natiz, Mar 16, 2010.

  1. natiz

    Thread Starter New Member

    Mar 16, 2010
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    Hi,

    I have used four 12VDC relays (each has diode on them) where I am using 12VDC with 1Amp current from a transformer. Problem is after 30 minutes of working, transformer and all relays becomes too hot that its hard to hold my finger on them. why its so ? Please guide me as i want them under normal temperature throughout days till they run.
    Even I used 9Volts with 1 Amp , but still they become hot. and when I use 12V with 500ma even then scenerio is same.... is there any resistance i need ? or any other thing???

    Please help me out...
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Are you sure that relays have the correct voltage? Can you give us some more specs and your schematics
     
  3. R!f@@

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    Apr 2, 2009
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    I think OP is using 5V relays
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    Well he says he is using 12vDC relays. It sounds like you are not limiting enough current to the relays. If your relays are not recommended or rated for continuous use, there may be a problem. Also, Are you SURE of your transformers output?

    Measure the output of the transformer, and for gods sakes, be careful.

    Rifaa, you may be correct. The relays may be rated for 12v on the load side. and have a lesser rated coil
     
  5. natiz

    Thread Starter New Member

    Mar 16, 2010
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    no Relays are of 12VDC on coil side and 220V AC for switch side as written on them. but there is no specification of amperes on it. So I dont know what amperes should i give them.
    Tell me what should i use to make a 9VDC 1amp current to 7.5VDC 1amp? resistance ? or what ? and of what value ?
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Measure the coil resistance on the relay. Icoil =12V/Rcoil.
    What is the actual output voltage (measured) of the transformer when the relays are activated. Most wall warts output the stated voltage (12VDC) only when the load current in at or near the maximum stated value (1A). At lighter loads, the voltage is closer to 1.4*12V.

    Ken
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    Sounds like the relay is not rated for continuous duty.

    hgmjr
     
  8. natiz

    Thread Starter New Member

    Mar 16, 2010
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    i never know that relays are of two kinds .. one is for continous use and other is for short time usage. is it so?
    how can i check what kind of relay im currently using?
     
  9. R!f@@

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    Apr 2, 2009
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    can u measure coil resistance, and also post the label written on the relay
     
  10. t06afre

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    Also post your schematic;)
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    Some relays are reated for continuous operation while others are rated for pulsed (short duration) operation. The only way to tell for sure about your relay is to track down the /manufacturer's published specifications for the relay. It will provide all of the operating parameters for the relay.

    hgmjr
     
  12. hondabones

    Active Member

    Sep 29, 2009
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    If he has step-up transformer I believe it is going to high for the max VAC rated relay. I think the problem is in the transformer.
     
  13. natiz

    Thread Starter New Member

    Mar 16, 2010
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    sorry for late replying... actually there is no complicated circuit behind this ... I am just using one adapter 12VDC 1 ampere and connected it with a 12VDC coiled relay with a diode on it .. I have four relays of different kinds but 12VDC coiled , but same prob is all become too hot to touch after few hours.. But when i use 9VDC with 1 amp current on same relays , they become hot gradually and in two days of continous working , they become that hot again. I just wanna confirm , if these relays are on some heat will it be burn out? or its safe to use them in same condition?
     
  14. retched

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    Dec 5, 2009
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    The transformer is the likely culprit. It seems like a over voltage problem.

    Any chance you are using the wrong taps?
     
    Last edited: Mar 19, 2010
  15. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Just did a bench test on a hunch. I put a 6V "AC" relay on a DC supply. At 6VDC it was drawing 1A and getting warm. I then put it on a AC supply. At 6VAC it was drawing 0.33A(RMS). Any chance your relays are AC instead of DC. Look for a copper ring on the top of the coil core.

    Ken
     
  16. natiz

    Thread Starter New Member

    Mar 16, 2010
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    no its DC relay ... and 12VDC is written on it and im just giving 9VDC .. also i confirmed and measured voltage with meter.
    tel me how much a relay can become hot where we can say its still normal and it will never burn..? and what are symptoms of temperature where it can burn or malfunction?
     
  17. retched

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    If you are using an intermittent duty relay as a continuous duty relay, it will heat up after a while.
     
  18. Wendy

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    Mar 24, 2008
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    And part numbers of the relays.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    If they are plastic-cased relays designed for PCBs, and you have small-gauge wiring connected to them instead of nice, wide PCB traces, that could be your problem.

    PCB-mount relays get much of their cooling from the PCB traces. The traces act like a heat sink, carrying the heat away and radiating it into space.

    Connecting up insulated wires won't have the same cooling effect, as the insulation on the wires also prevents heat from being radiated. Therefore, there is no place for the heat to go - so it builds up in the relay.
     
  20. theamber

    Active Member

    Jun 13, 2008
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    Post a picture of your circuit. I think your transformer is passing out heat to the relays. You can use a colling fan or heat sinks.
     
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