IotaWatt three phase discussion

It does work for me but that said, the WIFImanager service that manages the connection is not the most robust thing I’ve ever used. Most likely you were connecting ok but your device wasn’t doing the captive portal web screen to configure. Note from the OEM quickstart guide:
Note: If this page does not display automatically browse to http://192.168.4.1

In any event, it’s not something you would be doing regularly and you got through it.

New user here. I’m in AU with 3 phase power very interested in setting up an iotawatt based monitoring kit. I’ve got 27 circuits in total that I want to monitor (including the 3 main lines). I have got access to each of the three phases where the devices will be installed, so tapping into each for voltage references is no problem.

I was hoping to do this with two iotawatt devices, but after reading this thread, the documentation for the device, and playing with the demo UI, I have a few questions about how this might be possible.

I understand that I can use one of the CT inputs as a voltage reference input; hence one of the two iotawatt devices will have two voltage references. What I can’t get my head around is how I would configure the voltage references for each of the three phases in a way that somehow identifies the phase of each of them in order to “link” each of the respective CT inputs. To put another way, I assume that I would need to specify which phase each CT input must reference; it is this that I cannot immediately see a method to do.

The second apparent issue is that there will have to be some circuits from, say, phase C that will need to be measured by the iotawatt device that only has a voltage reference for phase A (given that the other iotawatt device has the voltage references for phases B and C, and all circuits from both phases B and C will exceed 13). This would either need to be done from EmonCMS, or the iotawatt devices will need to talk to eachother in order to share voltage reference data. I have a feeling that neither are possible.

A curly one, I’d say. Does anyone have any ideas?

…Or perhaps I should just get three iotawatt devices :slight_smile:

In the interest of keeping it simple, I don’t expose three phase complexity in single phase configurations. The demo app at iotawatt.com is a little outdated, but nevertheless contains what you are asking about. If you run the demo and configure a second VT, you will find that an additional field is presented when configuring CTs. It is a dropdown menu from which you would select the voltage reference for that CT. Try it.

The way I might approach this, given you intend to use two IoTaWatt, would be to use the primary voltage reference channels for two of the phases. So for instance IoTaWatt 1 would have (in your terminology) phase A. IoTaWatt 2 would have phase B. Then I would split the output of a third VT on phase C and connect it to both IoTaWatt, using adapters. So you would have A and C on IoTaWatt 1; B and C on IoTaWatt 2. As long as there are not more than 13 CTs on either A or B, you should be OK.

That scheme would allow for 26 circuits to be measured.

The IoTaWatt do not talk to each other to share voltage data, or anything else. They are each independent. Aggregation of the measurements from multiple IoTaWatt would need to be worked out in Emoncms or some other service.

Bob have you got a circuit diagram for connecting the extra VT’s?

Regards
Dave

Bob,

Grateful for the quick reply.

Your answer makes absolute sense, and I did give it a shot in the demo and can see what you mean. I should be able to get by with 26 CT channels, so I will try that and see how it goes.

A subsequent question: What do I need to do about the internal resistor on inputs 1-14 if I wish to use them as VT inputs, and is the process to connect an AC transformer to one of those inputs the same as connecting it to input 0? Apologies if this is documented elsewhere - feel free to redirect me if so.

Looking forward to getting my hands on your creation!

Best,
Brad

With the method I’ve been using, the internal burden resistors remain in place as part of a voltage divider created with the external resistor. It’s not the ideal setup, as it uses more power than the primary VT (~400mw vs 10mw) but it is so simple and requires no modification to the IoTaWatt - the holy grail.

I’ve been using 1/2watt 287 ohm resistors, which are dissipating 70% of their rated power and get slightly warm, but it’s not a lot of power and could be easily built with greater power handling margin. Going forward, I’m going to recommend using a bundle of three 1K and one 2K resistors in parallel to get 286 ohms and a lot more surface area to dissipate the power. Unlike the 287 ohm .1% 1/2 watt resistors I’ve been using, the 1K and 2K are more commodity and the bundle would actually cost less than the one 287 I’ve been using.

The power through the internal 24 ohm “burden” resistor is exactly the same as when it is used as a CT channel.

I’ve had other questions about this today, so I’ll be publishing a diagram later, and I’ll break out the extra circuitry you will need to make a splitter adapter.

As an aside, OEM only had a few IoTaWatt available as of the end of their sale last week, and manufacturing lead times have the next batch out in mid-January at the earliest, so if you need two…

See below.

You will need an adapter such as the lower one pictured here. It will accept the output from the phase C VT and provide two 3.5mm plugs to go into the two IoTaWatt. Resistors should be 1/4watt or better. These are all standard resistor values, so they should be available in 1% or better. If you don’t have a decent rms voltmeter for calibration, try to get .5% or better.
image

I got the following hardware.
1 x IoTaWatt with Power Supply 5V DC, AC Voltage Sensor Adaptor.
6 x 100A max clip-on current sensor CT
I described my situation some weeks ago here: Beginner, new to IoTaWatt
After some network problems I made some attempts.
Now just for clarification, as I have only one voltage sensor I will have a mistake on 2 phases? The same at 2 phases on solar side? The mistake will be the difference of voltage from phase 1 to the other 2 phases?
If I would buy 2 more voltage sensors I would have to solder another jack so I can plug in to the input channels? Or can I buy voltage sensors with the correct jack?

Yes, the power indicated in the other two phases will be about 1/2.

I believe so.

A difference in voltage would cause an error, but the real problem is that the reference voltage is out of phase with the current.

You cannot plug a VT directly into the IoTaWatt except on channel zero where there is a 5.5mm jack. If you were to change the jack, you would damage the IoTaWatt. You would see a little smoke come out.

I am developing an adapter that can be used to connect the additional VTs. My intention is to have them available around the end of January.

I’d like to reiterate my response to your post referenced above:

This is over my head, so I don’t want to say if it would do what you need. The iotawatt can measure the power of multiple phases, with three reference transformers, but I think you would need to have an electrician look at your setup and determine where and how to measure the things you need.

Sorry I can’t be of more help.

My concern is that this is only the beginning. You asked about a lot of things that I don’t feel competent to help you with. When the VT adapters come available, you could order one (one services two VTs) and two additional VTs. By then, there will be a wiki page explaining how to set up a basic three phase IoTaWatt system.

I’m sorry that I can’t be of more help, but there are others on this forum who may be more knowledgeable about the other requirements that you have and might be willing to get involved.

I suspect that it takes a hardware intervention, so you can use this menu item. With your adapter it will then go without hardware intervention.

Every house in Switzerland is connected to a three-phase system. If I want to measure the voltage with a VT for each phase, this is very difficult to do. One would have to install a separate socket for each phase. The IotaWatt could not be installed so easily.
For me it would be acceptable to do without a voltmeter. I could live well with the accuracy of plus minus 5%. I only need the measurement for comparison or control and to find big consumers, for example. I do not need absolute and exact numbers.
Would it be possible to create a virtual VT while configuring the VT? This means that I can enter a voltage that is the same on all three phases and is a fix voltage, not a measured.
Unfortunately, I understand the connections at IotaWatt between hardware, firmware and software not yet. Who would be responsible for such a program change?

You seem to be looking for what this person has done.Three Phase with one VT Please read the associated thread. This is a method that now seems to work, but the user interface needs to be simplified. I have put that on the list. In the meantime, you could try to do as he describes, or converse with him about what he has done. I believe there is a ten hour time difference, so be patient.

There is a lot of interest in three-phase from Switzerland, Germany, Australia and New Zealand. I expect this will get worked out over the next few months.