Measuring AC Current


I’ve created this webpage as reference information for my presentation at the 2018 Maker Faire.

When I replaced my 20+ year old heating system with a new high efficiency heat pump along with a propane furnace for backup I wanted a way to keep track of the system operation. In particular I was interested in the energy use and duty cycle of the heat pump itself and what the requirement for backup heating was. I was also interested in somehow measuring the level in the outdoor propane storage tank that is dedicated to the backup furnace as running out of propane was something that I didn’t want to happen!

I was already monitoring the temperature at outlet of a heat register and from that I could tell when the propane furnace was operating because the air temperature is quite a bit higher. At least this was easy to do by eye when looking at a graph of the temperature.


I thought that if I could monitor the AC current going to the components of the heating system I would have all the data I needed.

I found two types of AC current sensors at one of my favourite electronic components suppliers (The Robotshop - see links below).

The first one I tried was the i-Snail-VC sensor manufactured by ELKOR.


I was attracted to this sensor because it is calibrated and has excellent accuracy (0.5%) and comes in a number of current ranges. It also produces a DC signal voltage output that is linear with respect to AC current. It is a bit expensive however and when I received it I realized that it required the circuit that is to be measured to be disconnected to install it. I didn’t really want to do that myself so I would need an electrician or find something else.

I then decided to get one of the low cost clip-on sensors packaged by Seeedstudio and to compare the two sensors in a test setup.


The clip-on sensor produces an AC signal voltage (not DC like the other one) and so the software to process it is not as simple. Fortunately there is an open source library that works well with this sensor:

For this sensor I used the Adafruit ESP8266 Huzzah as a processor which can run an application linked to that library no problem.

Ultimately I ended up using this sensor because of its low cost and ease of installation and for my purposes the accuracy seemed to be good enough.