I am using a SainSmart 5V 2-Channel Relay Module for Arduino to drive a hot plate (110V, 1000W).

I plugged my Arduino VCC and GND to the VCC and GND pins of the relay board and I drive both relays simultaneously through one of the digital output pin. The relays are controlling both the phase and the neutral of the cooking plate. In order to control my temperature, I turn the relays on or off in a 15 seconds window.

Twice, already, my relays appeared to die. The LED still works, and I still hear the noise when it is toggled, but the contact is not made anymore.

What am I doing wrong? How can I fix it?

  • Increase relay rating to 15A or more. – Tony EE rocketscientist Aug 17 at 23:08
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    With 110 V, 1000 W you are near the 10 A limit of the relays. Are you sure you are not going above that? I suggest bigger relays for this application anyway. – Vladimir Cravero Aug 17 at 23:09
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    Use a 15A Triac instead. – Tony EE rocketscientist Aug 18 at 0:09
  • datasheet generationrobots.com/media/JQC-3FF-v1.pdf says that relay can't be expected to switch 10A repeatedly (assuming it's "JQC-3FF-S-Z") - life curve bottom of page 2 – Jasen Aug 18 at 2:03
  • When the hot plate is cold the resistance is lower and the current may exceed the design safety margin of the relay contacts. Use larger relays, as a temporary unreliable fix you could use both relay contacts on your hot (or either if not polarised) wire and gain more (not double but perhaps enough) current handling if they are switched simultaneously. If one relays fails the other will too so not a long term fix. – KalleMP Aug 18 at 15:35
up vote 3 down vote accepted

If possible increase your time base to double or triple the 15 seconds.

A better relay will last longer- you could also go to an SSR, but it would require a fair size heatsink to dispose of around 9-10W.

The lifetime of a mechanical relay will be specified in the data sheet, but typically it’s around 100K at full load, so at 15 seconds that’s a bit over 2 weeks 24/7. If it’s 50K, obviously half that.

  • What about this SSR, then: Model: SSR-25DA Input voltage: 3-32V DC Output voltage: 24-380V AC Output current: 25A How do you compute the heatsink dissipation? What about: amazon.com/Ogrmar-SSR-25-3-32V-24-380V-Solid/dp/B074FT4VXB/… ? – tibur Aug 18 at 0:39
  • That one has terrible reviews. SSR dissipation is around 1W/A for AC output models. Fotek may be a better offshore brand. There is not enough information to be sure but my guess is it's okay for that size of heatsink provided the environment isn't too hot. With an SSR you can make the time base shorter if you want, a few seconds perhaps. – Spehro Pefhany Aug 18 at 1:37
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    and, also, please don't do this to yourself: Amazon is not the appropriate place to buy electronic components. You want someone who guarantees that the values in the datasheet apply to the device. (and where you get a datasheet at all). Get your components at mouser, arrow, digikey, element14 … – Marcus Müller Aug 18 at 1:43
  • I agree with @MarcusMüller- your original problem is from not having specs to understand and evaluate. Price will be higher, but value also higher. – Spehro Pefhany Aug 18 at 1:45
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    @SpehroPefhany admittedly, if we give that box nice fins … – Marcus Müller Aug 18 at 14:24

A hot plate is just a resistor. Like a good old incandescent light bulb. Just with slightly less visible light emission.

So, use a simple 1000 W light dimmer; these are cheap.

I have never seen one but I guess a hot plate is like an incandescent light bulb.

Its resistance is much less when cool then its current is much higher than its rated current when it is hot. Then the overloaded relay contacts melt away.

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