Measuring current using ACS712 interfaced with ESP8266
ACS712 is a family of parts, if you bought the 30A version instead of a 5A one you will not see only 66mV/A change in the output (vs 185mV/A for 5A version).  That entire line of parts suffers from offset voltage issues and I believe they just use 1/2 Vin as the ref voltage, so if you have any variance in your power supply it will directly affect your offset voltage.
Bottom line: expect to perform a gain &amp; offset cal on every serial number if you want good data.  Once you adopt that strategy those parts offer very good performance at a very good price point.