Best solution to monitore 20 or 30 clip-on current sensor CT?

Do you know what’s the simplest and cheapest solution to monitore 20 or 30 (up to 50) clip-on current sensor CT without wireless necessity??
Maybe for 20 sensors, i need 5 * EmonTx Shield with 5 * Nanode style board ?
I have a 3G ethernet gateway and maybe add a switch?
What’s your advices?
Thanks so much !

Look at Boredom Projects

Possibly not the simplest, as you must build the hardware yourself.

I can vouch for the Boredom Projects device, having built one.

A much simpler option would be a Brultech GEM, 32 channels per device.

Haven’t used those but its predecessor the ECM1240 is good.


Simpler, definitely. But with a base price of 399 319 USD, not the cheapest.
(adding in the ancillary hardware can bring the total close to 700 USD)

The OP asked for the simplest & cheapest solution.

Reminds me a sign I saw in an automotive repair shop.
We do three kinds of work here: good, fast and cheap.
If you want it good, it won’t be fast or cheap.
If you want it fast, it wont be good or cheap.
If you want it cheap, it wont be fast or good.
(also seen as we do three kinds of work… pick two)

I was offering a simple option, which the Boredom projects one isn’t.

The Brultech GEM starts at 319 CAD, which translates to £193 (plus delivery, plus taxes), so it isn’t actually outrageously expensive. You would have to buy the CTs whatever you use.

Edit. I see that they now price in USD so it’s a bit more expensive at about £255, but I still don’t see that as ridiculously pricey. (Presumably if you’re monitoring up to 50 feeds it’s a semi-professional project and it’s reasonable to expect to spend a bit more than peanuts on it!

Nice solution, exactly what i need! Expensive right but simply, any review ?

Definitely not knocking the GEM. It appears to be a solid product as does their ECM-1240.

A bit over a year ago, I suggested the GEM as a solution and got this response:

I’m ready to made by myself the system but don’t have enough time to dévelop, only clone :wink:
How the arduino méga system communicate to internet? I don’t want wireless and i think it’s impossible to add ethernet shield?

If you check out the link Bill posted from the start it is about connecting the Boredom Projects board via USB, that method for connecting multiple devices to one Pi running emonHub is discussed further in the Does the emonTx Shield need an actual Arduino? thread, since a Due is already USB I suspect this would be somewhat easier than using emonTx’s. An advantage of USB “serial-direct” devices is that you can upload firmware, reset the devices and power them directly from a RPi.

A couple of Boredom Projects boards (or more) connected via USB to a PI could give you a pretty tidy and powerful monitoring solution with lots of channels.

My Arduino Due (Boredom Project) uses the USB port via a USB/serial adapter connected to a PC. The PC runs a Python script to send the data to a local instance of EMon CMS.

I’m still not convinced of the value of making an Arduino system for such a large number of ports. For 30 ports you’ld need 3 Arduino Dues, 3 break out boards, an enclosure and all the ancillaries. The boards alone will be about £100. then you are going to have to spend a lot of time putting all the bits together and calibrating it. Yes, you can save a bit of money and if you enjoy playing with electronics and software it’s a good idea. If you value your time and don’t want to do all the fiddling then maybe not such a good idea.

I concur. The problem posed by the initial post was 20 - 50 current channels and “simplest and cheapest”. I do not know where you can find a simple (i.e. off-the shelf) and cheap solution to handle that many sensors.
There’s a parallel discussion in another thread about the desirability of using a much higher powered processor and a much faster ADC (STM32 Boards for Energy Monitoring)
This problem would seem to be ideally suited to something like that - even multiplexing 50 inputs would seem to offer better performance than the Atmel 328P. But it would almost inevitably mean a one-off solution, or failing that, a modular and expandable design, because I cannot envisage a great demand for a 50-channel monitor.

This is a discussion I have almost daily with one of my clients, nobody wants to spend money on extra channels they don’t need and yet it is an even bigger issue when an entire second device is needed to add one more channel, especially as that then presents more redundant channels, which avoiding such was the under lying reason we are short one channel and require the additional device…

The “simplest” solution of all is possibly to pick up the phone and get someone else to do it, but that fails dismally on the “cheapest” requirement, the cheapest would be to roll your own to your own exact requirements which isn’t so simple, anything in between will be a compromise, as are many decisions.

I agree the Due approach isn’t perfect and my “USB connections” suggestion followed the OP’s question about connectivity. That being said, if it were me I would choose open-source tech I am more familiar with or has a good support community (such as this) over other options more often than not.

the Due shield option is however easier to stagger the work and costs perhaps, “Maybe for 20 sensors” might only involve 2, “or 30” would require 3 and as for " (up to 50) " could involve 4 or 5 Due’s, but the decision doesn’t need to be made upfront, the others can be added along the way.

The use of a RPi and Due’s might provide additional IO that can be be utilized, I would put money on the Pi/Due combo being more flexible in that way than the commercial systems. hosting your own server on it is a good example.

The mcu used in the Due actually has a 16way mux, so if it was the basis of a whole new device not just a shield the costs per CT channel could be spread further. Perhaps even a 4 channel (1 ac + 3 CT) emonTx “master” could have upto 3 additional and stackable, 4 channel slave boards that just break out more ADC’s from the master, those boards could come in 2 flavours all CT or 1 AC + 3CT to allow up to 15 CTs on a single phase, 13 CT’s mixed across 3 phases or 14 CT’s for US users,

This unfortunately doesn’t help josselin much now, but it is a question that pops up frequently enough to be considered in future development. I use multiple emonTx’s on each site to get the number of channels I need and I consider it an expensive way of doing things, but it is flexible and modular’ish, so IMO still much better option than installing a large commercial system, until we develop something better.