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boblemaire / IoTaWatt

IoTaWatt Open WiFi Electric Energy Monitor
https://iotawatt.com
GNU General Public License v3.0
639 stars 177 forks source link

compact DIN version #345

Closed gkasprow closed 1 year ago

gkasprow commented 1 year ago

I purchased 3 original IoTaWatt units to monitor all my circuits and hardly managed to fit them into my cabinet. The audio jacks and 3 VTs took so much space. It's standard situation in Europe. 2023-07-09 18 38 18 I need to add a few more DIN rail devices, i.e. individual RCBs so had to optimise the energy monitoring dimensions. So, I designed compact 3-phase version with embedded voltage transformers and power supply. I also discovered that in my device the LM358 with 10uF load is oscillating so I fixed that issue by adding compensation network. image I also used miniature CTs from Talema (AZ-1000) with embedded resistors. The design is in Altium but one can easily convert it to Kicad when necessary. image

The PCB fits nicely low cost D6MG enclosure from GAINTA. No cutouts are needed. The image shows enclosure with front panel removed. image

The schematic and production files are here

The sources are here

I'm not sure about licensing model. I usually release all my designs using CERN OHL, can you guide me what license shall I use? Do you think I can use IoTaWatt_DIN name for my design? I think you should add this version to your offer, Europe will love it.

6fta commented 1 year ago

I also started to make a pcb for the rail from ZMPT107-1 transformers, but due to lack of time I did not complete the project. IotaWatt-poiect

gkasprow commented 1 year ago

I see you added anti-aliasing capacitors at the inputs ?

6fta commented 1 year ago

Capacitors are optional, I took into account the article in the following link. Low current measurement performance of the SCT013

gkasprow commented 1 year ago

I think they are the must. To properly measure signals, one must meet the Nyquist criterium of sampling. For the moment the bandwidth is limited only by CT and VT. For pure sine is fine, but we have broad spectrum of interferences in mains.

gkasprow commented 1 year ago

One more thing. The ADC when sampling, is charging internal capacitor. So it needs low driving impedance. Usually one uses opamp or RC filter where C serves as a reservoir of charge for sampling. In case of CTs, that's not a problem, we have 20Ohms. The VTs have 1k of resistance (divider) and this causes measurement error (systematic fortunately). Adding 1nF will do two things - limit the BW and meet Nyquist criteria and provide low impedance for ADC.

boblemaire commented 1 year ago

I'm not a very good electrical engineer, but my reasoning regarding anti-aliasing filters is that the OEM hardware referenced has very low frequency sampling, so aliasing of first and second order harmonics can introduce significant variability and error. IoTaWatt samples the signals at about 38 kHz so those harmonics are actually measured.

I'll take a look at the op-amp filtering when I return from vacation, Charging the sampling capacitor has not been an issue with the op-amp bias. Older designs with simple voltage divider did require a longer charge interval.

gkasprow commented 1 year ago

I meant harmonics and EM interferences generated by loads running on frequencies higher than mains, for example, brushed motors, DC/DC converters etc.

perigoso commented 9 months ago

Here I was thinking about designing a compact DIN rail version, because my cabinet is quite tight as is... Good work @gkasprow! I might fabricate one of yours, have you encountered any issues (that I should try to fix before making my own)?

gkasprow commented 9 months ago

Somebody built it and so far there is only one non-critical issue https://github.com/gkasprow/IoTaWatt_DIN/issues/1 I still didn't find time to assemble my PCBs. Existing IotaWatt is working well. Perfect is the enemy of good