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Pi 3 and SainSmart 8 channel SSR - Not able to turn on all 8 relays

  • Environment: Raspberry Pi 3
  • OS: Raspian
  • Language: Python3 and Java/Pi4J
  • Control: SainSmart 8 channel Solid State Relay
  • Issue: Unable to turn on all 8 relays at the same time

Using a Pi 3 installed with raspian that I picked up from a convention, and instructions from Instructables and YouTube, I intended to make a programmable 8 channel Christmas Light outlet box.

After doing a simple python test, I was able to switch all 8 of the relays on and off one at a time in succession. Thinking that was sufficient, I mounted the board and outlets.

However, I discover now that when I try to turn on more than 3 / 4 lights at a time, the others turn off. I dissected a micro USB cable with 5v / .7A phone charger to deliver separate power to the SainSmart, but it appears not to work.

I assume that either the pi is not delivering enough power to each pin to turn on all the relays or that not enough power is being delivered through the micro USB cable to the SainSmart.

Not being familiar with electronic schematics, does anyone have an idea of the possible culprit?

  • Could you add a link to the specs of the SSR you are using? Ordinary relays need quite a lot of power to keep each coil energised. – joan Nov 6 '18 at 9:54
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If this is close to what you are using, it says that when all outputs are on, it draws 160mA at 5V which is 0.8W (or .1W per channel if it scaled linearly)

The rpi gpio is only 3.3V (which should be ok as that relay board treats anything over 2.5 as high) But the GPIO pins should only source 50-100mA total which is 0.165W-.33W This 50mA rating is probably lower then what the board can actually output, as you were able to do more then one, but not able to turn on all of them.

When attempting to use a separate power source, you would still need a shared ground between the two, and depending on how the board is designed it may still be drawing enough power from the logic input pins to take you over the threshold for GPIO output

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