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Detect if a pump is running?

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I have a project where I would like to detect whether a pump is running in order display where hot water is being transferred from (eg. solar thermal, log burner). There will also be a couple of temperature sensors on the flow pipes which will show me the temperature of the water but not whether it is moving or not!

It would be nice to be able to use the emonth for this with a couple of ds18b20 sensors connected externally. I currently have two ideas:

  1. Use a CT clamp to detect current consumption wired to a spare analog pin in the emonth - is there one available?
  2. Install a relay in the pump circuit and use the secondary coil to trigger a digital input on the emonth.

Has anyone done this before, any thoughts on which way would be best?

There have been a few posts in the past about detecting the presence of a current, or whether something is running. Try a search for the details - including the old forums, but the general idea is to use your CT feeding into a rectifier and smoothing circuit, and put that into a digital input (emonTH V1.5: D3 is the obvious choice), so saving on processing power (i.e. you don’t need to run for a long time, 40 ms or so to be confident you’ve detected a cycle peak, you can poll the input and go to sleep again immediately).

Or you could wire a neon across the pump and look for that with an LDR and a digital input with the right choice of series resistor (but remember neons flicker, and that’ll only tell you the pump has volts, not that it’s drawing current).

The circuit diagram (via the Wiki) will tell you which pins are available on your emonTH.

Secondary coil? I think you’re getting a bit mixed up here :worried:

[Edit] A Thread or three:
Problem with current sensor, or me!
Building a Yes/No current detector

curiuos instead of using a ct or relay just use a flow switch magnetic or paddle or go crazy and install flow meter and one temp sensor on the hot side and on on the cold side then you can calculate the actuall amount of heat produced by either your solar and/or wood boiler… after the digital thermal sensor all you need is a digital port - it be more secure than just a simple relay as it will also tell whether or not your pump failed too