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Relay trouble with ATX power supply

dukeofmarshall

Full disclosure: I'm a beginner electronics enthusiast. Here is my setup:

 

(1) Arduino Nano

(1) Arduino 24v 3 amp Relay Shield

(1) MR5A001A1 12v 30 amp Relay from an Isuzu Rodeo

(1) ATX Power Supply Model ATX-1956D

(1) 12v 50w Halogen Light Bulb

 

So the end goal is to drive the halogen bulb with the Arduino. Be able to turn it on and off as needed. For my first setup, I connected the Arduino to the relay shield, ran a 12v line from the power supply unit to the common on the relay, and the NO from the relay to the halogen bulb. I did not take the amps of the bulb into account at first but soon realized my mistake when the relay fried. I replaced the Arduino relay and the PSU just to be sure and added the car relay. My current setup is Arduino Nano connected to the Arduino relay, one 12v line from the PSU is connected to the common on the Arduino relay, the NO on the Arduino relay is connected to the trigger(?) of the car relay, one 12v line from the PSU is connected to the common on the car relay, and the bulb is then connected to the NO of the car relay. The Arduino and the Arduino relay shield are both powered from a 5v line from the PSU.

 

The issue I'm having is when the Arduino relay switches on and turns on the car relay, the PSU just shuts down. Now, I can power the bulb directly with the PSU, no problem. But when connected up in this setup something's causing the PSU to shut off. Strangely enough, If I connect the bulb to the NC of the car relay, the bulb powers up with no problem. Then, as expected, when the Arduino relay switches on the car relay, the bulb goes off, but when the Arduino relay switches off and turns off the car relay, activating the NC of the car relay again, the PSU immediately shuts down like before.

 

Anyone have any ideas or suggestions about this? All the parts seem to be in order. There's not too much voltage going into any part and, now, all the parts should be able to handle the amperage with the PSU being more than enough to power the whole system. What am I missing here?

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  • Hi Todd,

    Another possibility is that you are getting enough of a voltage spike from the relay coil to trigger the ATX into protect mode. Make certain that you have a diode, reverse biased across the relay coil. Another possibility is the way the load of the bulb is being applied. A 56 watt halogen bulb could easily draw 10 amps for a few milliseconds until the rising temperature of the filament brings the resistance up to operational levels. Make sure that you are using the 12 Plus supply of the ATX as the negative 12 volts may only be rated for a couple amps.

    John

  • in reply to jw0752

    Mr. Wiltrout,

    Thanks for the information and the suggestion. I applied a PR1004 diode across the coil and looked up some schematics online to make sure I was doing it right. Unfortunately I'm still getting the same results.

     

    Just for giggles I added my benchtop ATX PSU that I use for other projects/testing. So even with two power supplies providing two separate 12v lines in combination for the bulb I still got the same results.

     

    Another test I performed is taking my spare, identical bulb and hooking up directly to the power supply unit. The bulb powered up and glowed like normal. Then I disconnected the 12v line, turned the PSU back on, waited a few seconds, and reconnected the 12v line to the bulb. The PSU immediately shut down like before. I did the same test with a 5v line off the same PSU and there were no failures. The bulb, on the 5v line, would dimly glow each time, as is expected, but it did not affect the PSU like the 12v line no matter how many times I disconnected and reconnected the live wire.

     

    So I think your second suggestion may apply here, but if so, why would it work with the bulb connected when the PSU powers up, but fails when connected after power up? Also, the PSU states it can supply 12 amps on the 12v line and the failure occurs even with two PSUs powering the bulb. It's all confusing to me, but then I'm still rather ignorant about this subject matter at this time.

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  • in reply to jw0752

    Mr. Wiltrout,

    Thanks for the information and the suggestion. I applied a PR1004 diode across the coil and looked up some schematics online to make sure I was doing it right. Unfortunately I'm still getting the same results.

     

    Just for giggles I added my benchtop ATX PSU that I use for other projects/testing. So even with two power supplies providing two separate 12v lines in combination for the bulb I still got the same results.

     

    Another test I performed is taking my spare, identical bulb and hooking up directly to the power supply unit. The bulb powered up and glowed like normal. Then I disconnected the 12v line, turned the PSU back on, waited a few seconds, and reconnected the 12v line to the bulb. The PSU immediately shut down like before. I did the same test with a 5v line off the same PSU and there were no failures. The bulb, on the 5v line, would dimly glow each time, as is expected, but it did not affect the PSU like the 12v line no matter how many times I disconnected and reconnected the live wire.

     

    So I think your second suggestion may apply here, but if so, why would it work with the bulb connected when the PSU powers up, but fails when connected after power up? Also, the PSU states it can supply 12 amps on the 12v line and the failure occurs even with two PSUs powering the bulb. It's all confusing to me, but then I'm still rather ignorant about this subject matter at this time.

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