Current sensors - Power Measurement

[Guest Alphonsox]

I need to start getting a handle on the electricity consumption of my many devices/circuits around the house. I intend to log this information along with temperature and other such info via a Node Red instance running on a RPi or similar.

I need at least 8 current measurement channels ideally using clip on current sensors/CTs. Has anyone got any pointers as to suitable hardware for this ?

[PeterW]

I used 2 of these for a basic sensor circuit and they were reasonably accurate. 

 

Current Sensor

[billt]

I started off with three of these http://www.brultech.com/ecm-1240/

when there was little else available. I'd now use one of these http://www.brultech.com/greeneye/

Then tried a couple of Open Energy Monitor Arduino boards, but had  a few failures and ended up making one of these https://boredomprojects.net/index.php/projects/home-energy-monitor which is may be the cheapest option if you don't want to design your own.

 

The ECM1240s came with lots of CTs, mainly doughnut ones, which are used with the Boredom projects system as well as the ECM1240s; they suit my purposes better as they are small and easier to fit into a consumer unit, but you can use clip on CTs as well.

[SteamyTea]

Do you really need 8 channels.  Two or 3 is generally enough.

You can try and pick up an old CurrentCost Envi and the appropriate clamps and transmitters,  You can then get 10 circuits monitored.

eBay usually has some for sale.

Dead easy to then hook it up to an RPi with a serial cable.

[Guest Alphonsox]

Thanks for all the thoughts.

I was intending to have multi-channel measurement as a pretty much permanent feature. I guess this may be overkill and I good get away with 2-3 channels and switch things around as required. @billt point regarding the size of the sensors is a good one. Having checked the size of the units @PeterW has used seems to show them being too big for easy use inside a consumer unit.

Having thought some more about this I may look at build my own around a Pi and an 8-channel ADC HAT, it looks to be the cheapest solution at the moment.

[MrMagic]

I recently ordered a 3 channel board from this place - http://lechacal.com/wiki/index.php/Main_Page - works really well. You still need to write your own code to 'do something' with the data that comes out of the sensor board but theres some examples on their wiki on how to do basic integrations. They do a 7 channel version for £35 (ex clamps).

 

Still uses the same CT clamps from the beginning of this thread so not ideal for stuffing inside a consumer unit.

 

This one is monitoring my garden office/shed at the moment - 

 

[SteamyTea]

I fancy something like that, but notice that it uses the same pins as an RTC on the RPi.

I would have thought that it was not too hard to make ones own circuit to use a simple CT clamp and an RPi.

 

Just cobbling together an energy monitor at the moment.

These are some of the bits.

 

[Guest Alphonsox]

On 17/04/2018 at 11:08, MrMagic said:

I recently ordered a 3 channel board from this place - http://lechacal.com/wiki/index.php/Main_Page - works really well. You still need to write your own code to 'do something' with the data that comes out of the sensor board but theres some examples on their wiki on how to do basic integrations. They do a 7 channel version for £35 (ex clamps).

 

Still uses the same CT clamps from the beginning of this thread so not ideal for stuffing inside a consumer unit.

 

This one is monitoring my garden office/shed at the moment - 

 

 

@MrMagicThat's very close to what I'm looking for - what's the lowest power you can realistically measure with this ?

 

[MrMagic]

@Alphonsox Good question - Just been trying to think of anything low power with a live wire that I can clamp... not sure I've got anything readily available at the moment, sorry.

 

Perhaps try contacting the vendor? I'll have a dig around and see if I can find something that I can modify to test with...

 

EDIT: The folks over at OpenEnergyMonitor look to have done some low current testing using similar hardware - general consensus seems to be that anything <50w may be incorrectly reported.

https://github.com/openenergymonitor/emontx2/blob/master/accuracy.md

https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/measurement-implications-of-adc-resolution-at-low-current-values

Edited April 19, 2018 by MrMagic
Updated.

[SteamyTea]

7 hours ago, MrMagic said:

<50w may be incorrectly reported

That is my experience when using CTs.  Though I found, on average over the whole range things tend to sort themselves out.

The only large inductive loads I have are the washing machine, vacuum cleaner and the bathroom fan.  They are no used that much in the scheme of things.

Edited April 20, 2018 by SteamyTea