Current monitoring with RPi

Hi guys,

I have a RPi running an instance of node red which controls a timber kiln, via 4 solid state relays for heat, vents, compressor, and circulation fans. All running very well thanks to help from this group in the past! The whole setup has been bullet proof so far.

I know want to add some safety/redundancy functionality to it, most of it I have my head around but I would like to monitor the current being drawn by the circulation fans. Two of the fans on that circuit are responsible for circulating air over the compressors coils and also over the heaters, I worry if one were to fail the heater would over heat, causing heat damage to the unit or possibly even a fire. It does have a Tstat on the circuit but I'm not certain it is working and it is difficult to get at, for the likes of testing/adjusting. It would also be possible to prevent damage by disabling heater in event of circulation failure, rather than responding to damaging conditions like the Tstat does.

I know RPi doesn't have an analogue input so wondering about ideas to achieve this, by way of external component or some clever circuitry. The current draw from the circulation circuit should be consistent and never drift too far (6 fans always running on their own breaker - one bus to monitor). If one dropped a bearing and stalled or its field coil failed open, both cases should be detectable by way of current change. So I don't necessarily need to know the current in amps, but a change from normal current.

Thanks in advance as always!

Do the fans have a separate connection into the mains supply? If so then you could use one of the smart plugs with built in power monitoring. I use SmartThings zigbee smart plugs.

You can get various modules (IoT Current Measurement) which use Current Transformers (CT) to measure the current and send the information over MQTT.

So depending on the size of the fans, as Colin says, a Smart Switch may suffice, or if higher current (>13A), a measuring module with a CT of whichever size fitted would give the ability to measure the current used. The advantage of this is that you don't have to have a break in the wire feeding the fan, it just goes through the CT.

On my incoming domestic mains supply, I measure the current using a PZEM-004T with a 100A CT. On the Motorhome, there is an inline shunt (not CT) on the feed from the batteries, but the module measures dc current not ac. There are many modules out there.

Not exactly the same but IoTaWatt may be of interest.

Sorry I'm late back to this, too many open boxes.

I would be looking up hill at a learning curve to go with anything involving mqtt as I've not used that before.

Is there any reason using a CT sensor, an ADS1x15 I2C module, and this Node wouldn't work? As I said I don't really care what the current is in amps, only if it deviates.

Is a CT sensor likely to be affected by other circuits running close by - but not through the centre of the windings?


You can't just use an ADC as the current is AC. You would need to look at the spec of the CT and see how it is supposed to be interfaced.

TBH, I held off looking at MQTT for exactly the reasons you stated, the learning curve. In fact it was probably one of the easiest things I did since using Node-RED.

Filled with trepidation about it, I loaded Mosquitto MQTT onto the same Pi as I was running Node-RED on, enabled MQTT on a couple of Sonoffs with Tasmota running on them, pointed the Node-RED MQTT nodes at the server address:port and it just ran! Using MQTT explorer to see exactly what was going on, I have not looked looked back since!


This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.