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I bought an 8 channel dc 5v relay module for Arduino from an on-line store. When i power on my system, the modules become really hot.

My connections are,

  • Vcc to 24vdc
  • Gnd to ground
  • In(1-8) to the digital outputs of my arduino.

Everything seems to be connected correctly. Another thing, when I tried pulling out the jumper connected between Vcc to JD-VCC, then powered it up; the relays and other components didn't turn hot, but the problem is that it does not respond to the digital inputs that I send from the Arduino..

** We assume it is this module, please confirm.

enter image description here

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  • \$\begingroup\$ Do you have a link to your module? Also Can you clarify exactly what you connected to what - e.g. Gnd to Ground means nothing - what ground to what ground? Ardunio? Relay? Mains? \$\endgroup\$
    – Oli Glaser
    Jul 16, 2012 at 3:46
  • \$\begingroup\$ This might help arduino-info.wikispaces.com/ArduinoPower \$\endgroup\$
    – Piotr Kula
    Jul 16, 2012 at 13:43
  • \$\begingroup\$ Could you check the addition to your question? Is this the module you're talking about? \$\endgroup\$
    – stevenvh
    Jul 17, 2012 at 7:30
  • \$\begingroup\$ @stevenvh:No, it is the one you guessed below. Sorry for my carelessness. \$\endgroup\$
    – user10768
    Jul 19, 2012 at 5:18
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    \$\begingroup\$ @user10768 - thanks for finally looking at it. Try to understand us people who want to help you. You show little appreciation for our efforts: you never accept an answer. It doesn't cost you anything, but it's like saying "thanks". Just decency. Once you have 15 rep you can also upvote answers you find useful. Please do so. And respond to questions for information. You'll find that users are very helpful, but something has to come from you too. Just read the comments to my answer here. Have a nice day! \$\endgroup\$
    – stevenvh
    Jul 19, 2012 at 5:46

3 Answers 3

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If the heat came from the output (on the relay) you probably driving too much current through your relay, try add resistance to control the current to acceptable range.

If the heat came from the ICs, double check your module connections.

Note: Can help you better if you provide more information of where the heat came from and a link to the datasheet of the module you purchased.

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    \$\begingroup\$ "try add resistance to control the current" seems a bit pointless advice. If the load is a 100 W bulb then adding enough resistance to significantly decrease the current will reduce it to a 50 W bulb. \$\endgroup\$
    – stevenvh
    Jul 21, 2012 at 8:32
  • \$\begingroup\$ @stevenvh, if not adding resistor; what would be a better way to limit the current flowing through the output? \$\endgroup\$
    – JeeShen Lee
    Jul 21, 2012 at 8:37
  • \$\begingroup\$ If it's a 100 W bulb, and you want the light of a 100 W bulb, you'll need that current. Nothing you can do about it. You can try a relay with a lower contact resistance to reduce the dissipation in the relay. \$\endgroup\$
    – stevenvh
    Jul 21, 2012 at 8:41
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I guess you're talking about these.

If they're 5 V relays you should operate them at 5 V, not 24 V. At 24 V the relays will get 23x (!) too much power, and that may destroy them in a short while.

Maybe you are confused about the "DC30V" in the product description. But that's the contact rating, not the coil's.

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    \$\begingroup\$ @user10768: You've asked 6 questions so far and accepted zero answers. If Steven's answer solves your problem you might accept. It's also useful to others to know when a problem is solved. Once you get 15 rep you'll also be able to upvote answers you find useful. Do so, it shows appreciation. \$\endgroup\$
    – Federico Russo
    Jul 16, 2012 at 9:23
  • \$\begingroup\$ @stevenvh: yes, I think I know who you mean :) \$\endgroup\$
    – Federico Russo
    Jul 16, 2012 at 10:44
  • \$\begingroup\$ Thanks. I didn't noticed the feedback information. Sorry for that. You guys are being helpful. I should thank you more than words. \$\endgroup\$
    – user10768
    Jul 17, 2012 at 7:01
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    \$\begingroup\$ @user10768 - So how about accepting some answers? Doesn't have to be mine, but if an answer solves your problem accepting is just saying "thank you". It's those small things that keep the site running. \$\endgroup\$
    – stevenvh
    Jul 17, 2012 at 7:28
  • \$\begingroup\$ @stevenvh:By saying accepting answers, do you mean answering" was this post useful to you?" \$\endgroup\$
    – user10768
    Jul 20, 2012 at 7:32
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Your connections are

  • Vcc to 24vdc---------THIS IS YOUR PROBLEM should be 5VDC

  • Gnd to ground

  • In(1-8) to the digital outputs of my arduino.

Typically when you see Vcc on any electronics board it wants 5Vdc. Your relays and relay driver chips are all 5Vdc not 24Vdc. The relays have a 5 volt coils to actuate the contacts which are rated for high voltage and current 10A 250VAC, 10A 125VAC, 10A 30VDC and 10A 28VDC. I'd be surprised if the circuitry on your relay board is still working, sorry but you might have toasted the board.

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  • \$\begingroup\$ Welcome to EE.SE please reformat (edit) your answer and make it look nice. \$\endgroup\$
    – Voltage Spike ♦
    Mar 29, 2016 at 21:15

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