Looking to get impExplorer + current sensor - will this work?

[orchid]

I’m new to electric imp but it looks really cool! I want to get one to measure temperature of an air-conditioned room, and check the power usage of the a/c unit, and create reports for both wirelessly.

It looks like if I got the impExplorer kit that should cover the temperature sensing, and then I was thinking of the SCT-013-020 to measure power usage. It looks like the cable on that goes to a 3.5mm connector - what would I need to connect that to my impExplorer?

Thanks!

[hugo]

You’d need to plug that into one of the non-i2c grove connectors, with a “burden” resistor across the coil and the coil between the input pin and ground; this will then turn the current flow sensed by the clip-on transformer into an analog voltage that you’d sample with the sampler (as it will vary at your mains frequency) and then integrate.

Not super straightforward, but not impossible either. Have a look at this old post on the forums for some code (use the version that uses the sampler):

https://discourse.electricimp.com/t/electric-imp-and-non-invasive-ac-current-sensor/824/69

[orchid]

@hugo

You’d need to plug that into one of the non-i2c grove connectors, with a “burden” resistor across the coil and the coil between the input pin and ground; this will then turn the current flow sensed by the clip-on transformer into an analog voltage that you’d sample with the sampler (as it will vary at your mains frequency) and then integrate.

Thanks very much @hugo! So, it seems from reading here that all the SCT-013 series apart from the SCT-013-000 come with ‘burden’ resistors. In particular:

Therefore, if you require a 0 - 20 A input range, your best choice is to use the -000 variant and calculate your external burden resistor value to give you a peak-peak voltage across the burden that is few percent less (*) than the maximum input voltage range on a 20 A primary current.

So, given that my appliance (a/c unit) will be <20A, would I be best to get the SCT-013-000 instead of the SCT-013-020 and add a ‘burden’ resistor? If so, what should the value be?

Possibly this is too complicated for someone just starting on the SBC road!

[rocketfire]

The SCT-013-100 doesn’t have a burden resistor, at least the one that I have doesn’t but they probably come in different variations.

It does have a protective zener diode though. I hate to think what the voltage would be on the 3.5mm plug without a burden resistor or diode.

The voltage across the burden resistor will follow the AC cycles, so for my hobby project I sampled it quickly into an array for a fixed time then did some maths on the results. Undoubtedly there’s much better ways to measure the varying voltage but it gave pretty good results above 100watts (0.24amps).