ESP8266 wifi disconnect issue

Hi All!

I'm not sure if this is the right board for this question, so if this isn't the right place to post this please feel free to move it elsewhere or let me know and I'll repost in a different place.

I have a small project using an ESP8266 ESP-12 board to control a pool pump. Its fairly simple: I have the pump wired through a solid state relay, connected to the ESP-12 on one pin. The SSR can be controlled using 3-12v and the ESP-12 doesn't seem to have any trouble turning it on and off. ESP-12 is powered by a 3.3V 500ma external power supply.

What I'm experiencing is that the ESP-12/ESP8266 will initially stay connected to WiFi after it starts up for some random amount of time (ranging from 10 minutes to 24 hours) and it will then disconnect. Once it disconnects from WiFi it does not recover the connection or appear in my list of connected wifi devices from the perspective of my router.

I'm fairly convinced that the ESP-12 is still active because it is continuing to send the "HIGH" signal to the SSR, keeping the pump activated even though it is not connected to WiFi.

Any ideas on why this might be happening?

Thanks!
Stephen