Contactor and outlet surge trigger the Iotawatt to reset

Hardware IoTaWatt
1

Hello,

I’ve constructed my own Iotawatt using the open-source data provided by the developer, and it has worked well in various scenarios. Recently, I attempted to use Iotawatt with an industrial welding machine equipped with a three-phase contactor in its input. I connected the Iotawatt voltage ports directly to this contactor and attached a current transformer (1:2500) to one of the input phases of the welding machine to measure its current.

Initially, I used a switching power supply for the Iotawatt, but it proved to be susceptible to noise generated by the contactor. The Iotawatt reset almost every time the contactor switched, as indicated by “external reset” entries in the log file.

To mitigate this issue, I switched to a linear power supply, which reduced the vulnerability to contactor activity. While the number of resets decreased, there were still occasional resets occurring when the contactor switched—about one reset event for every 10 contactor switching activities.

After extensive troubleshooting, I observed that when the current transformer (CT) was connected to the Iotawatt, resets occurred due to the contactor switching. Surprisingly, when the CT was not connected to the Iotawatt, there were almost no reset events.

I also noticed similar reset events in home applications. For example, if a device plugged into the same outlet as the Iotawatt was unplugged, the Iotawatt would reset, possibly due to a surge caused by unplugging the device.

It appears that the resets are associated with short, strong pulses that travel through the cable and trigger the Iotawatt to reset. Despite using noise and EMI filters in the input port of the Iotawatt, the issue persists.
At this point, I suspect the problem isn’t originating from the input voltage source. It’s possible that the noise is reaching the ADC ports through the CT (current transformer) and causing the ESP8266 to reset. Considering this, using isolation between the CT and ADCs might be a helpful solution.

Has anyone experienced a similar problem? Any insights or assistance would be greatly appreciated.

2

I believe few people here use that device, and certainly not on a 2.5 kA feed. When switching up to 2.5 kA, you expect some disturbance to the mains electricity supply (what voltage is it?) and that a spike is getting in an causing a reset is probably due to the configuration of the input circuits. Have you been able to measure the inrush current of the welding machine? Knowledge of this is your starting point, and it is this which will dictate the c.t. rating, not the running current. My guess is the internal clamping diodes in the ADC are conducting and causing the 3.3 V or 5 V supply to the ADC to see a spike. I have no knowledge of the detail design of that piece of equipment, so as you appear to have done all the preliminary things to alleviate the problem, I suggest you try to contact the designer for a solution.

3

Hello dear Robert.

Thank you for your prompt response.

I used the device on 220V line not 2.5Kva. The utilized CT is 1:2500 which converts a maximum line current of 50 Ampere into 20mA. The nominal current of the welding machine in each phase is around 20 Ampere. So, we have a maximum current of 10 mA in the secondary of the CT.

There is a push button on the handle of the welding machine. When the worker pushes this button, the contactor switches, and the 3-phase voltage is applied to the welding machine and a 20A current flows through each phase. We connected our iotawatt to the input side of the connector.

you said that “w people here use that device”. Do you mean Iotawatt or welding machine?

Also, you mentioned that I should contact the designer. The designer of Iotawatt?

4

Make your mind up: you originally wrote a 2500:1 c.t. which means 2500 A rated primary current and a 1 A secondary winding. This is a normal rating for a large current transformer. You should have written - if this is indeed what you have - 50 A : 20 mA.

I don’t believe your current of 20 A per phase - at least initially. There will be a big 3-phase transformer, quite possibly with an air-gapped core so that it works at least in part as a current-limiting device, so I expect a very high current on the first few cycles after the contactor closes, maybe 60 - 80 A on the first cycle. I think it’s here that your problem lies,

Both. I can think of maybe only 5 or 6 installations that we know are industrial - OEM installations are almost exclusively domestic. As far as I know, Megni no longer has any commercial relationship with Iotawatt.

Yes. I suggest you try https://community.iotawatt.com/

5

Thank you very much.

I am going to contact iotawatt community.

sincerely.