3

I've reviewed many questions on the list, but still having difficulty driving my Fotek SSR-25 DA Solid State Relay (Spec Sheet - http://www.fotek.com.hk/solid/SSR-1.htm) from my Raspberry Pi.

Here's my circuit: 

GPIO 26 -------1kR -----+
                        |               +------------+
                        |               |            | 
                         -- +        +--+             = Fan
                               SSR                   |  
                         -- -        ---+             = 120v
                        |               |            |  
                        |               +------------+  
GND --------------------+

Here's what I know:

  1. Circuit works fine when input cycled from +5v to 0v with another controller (Labjack).
  2. Circuit causes fan motor to buzz when hooked up as shown (never turns on).
  3. Tested input switched between Pi's power rails +3.3v to 0v. Same behavior.

Here's what I suspect:

  1. +3.3v is not enough to drive my specific SSR (although specs would indicate it should), or,
  2. Pi not supplying enough current by GPIO26 to fully trip SSR.

Questions:

  1. Any tests recommended?
  2. How do you adjust current output on a GPIO pin (I'm using Python and it's associated libraries)?
  3. Would reversing the logic provide better switching (e.g. Wire SSR+ to 3.3v and switching SSR- between 0.0v and 3.3v)?
Aurora0001
  • 6,357
  • 3
  • 25
  • 39
Coach443
  • 61
  • 7

2 Answers2

1

Your SSR has integrated resistors so you might wanna try it without the 1k resistor. The datasheet states that it draws 7,5mA at 12V, so the impedance should already be around 1,6k (you could test this). If you add another 1k the current @3.3V is limited to less than 2mA which might be a bit too low to drive the LED.

Domme
  • 375
  • 2
  • 11
1

Answer:

Although the device specs says otherwise, 3.3v is NOT enough to control my Solid State Relay (SSR).

I purchase a 4-relay SAINSMART board:
http://www.sainsmart.com/4-channel-5v-relay-module-for-pic-arm-avr-dsp-arduino-msp430-ttl-logic.html

I connected Vcc to 5v on my Pi.
I connected In1 to GPIO 26 on my Pi.
I connected GND to GND.

Then I connected my 120v to the normally open side of the relay and it works!

Power flows when my logic is LOW.
Power does NOT flow when my logic is HIGH.

Coach443
  • 61
  • 7