[colug-432] Monitoring an analog, external device's power usage?

[Rick Hornsby]

On Jan 26, 2013, at 15:53 , Peter Kukla <fruviad at yahoo.com> wrote:

> I'm a new home owner, and I have a sump pump in the basement that I would like to monitor electronically.
> 
> Best case scenario...my complete solution provides me with electronic log data in a way that I can access any time via a network connection.
> 
> My objectives are twofold.  
> 
> 1.  Monitor the amount of water pumped from the basement to get a "baseline" value that I can compare against when trying to improve the property's drainage
> 2.  Setup an early-warning alarm system that would alert me if the sump pump failed to work for some reason.
> 
> The sump pump currently plugs into a power outlet.  The only way I can see to monitor this sump pump is to monitor the power usage.

I can't speak too much to sending data off to another device.  I think the idea of measuring to see if you're improving the property drainage is cool.  I can think of two ways to measure the flow, either the volume through the outlet pipe (essentially, directly), or by noting the frequency with which the sump drains (indirectly).  You know the pump comes on at a certain volume, and you know it shuts off at a certain volume, and that immediately after it shuts off ground water flows in until it settles down, somewhere below the activation volume.  If you can measure the difference between the "full" volume and the "empty" volume, you can approximate how much water the sump is moving.  Count that volume each time the sump runs.  *Lots* of factors will affect the total volume beyond just your drainage strategy as I'm sure you know.

However, you might be over thinking the alert system a little bit.  A buddy electrical engineer, very smart, is a guy who definitely gets KISS.  He has a (9V?) battery hooked up to a piezo, in an open circuit with stripped ends of wire hanging down near the top edge of the sump well.  When the water gets too high, it touches the wires closing the circuit and sounding an alarm.  He also has a battery backup for his sump.

Just thinking out loud here, you could even use this method with something like a zigby, arundo, raspberrypi, etc type device - run sensor leads way down into the sump well (just above the "empty" point) and make the device send a message each time the circuit opens.  It should be pretty easy, and you're not horsing around with the 120V 15A circuitry of the pump system itself.

There are also float sensors for tanks (ie gas tanks) that send an analog value (voltage) to indicate the liquid level. 

> Does anyone out there have any Linux-friendly solutions for monitoring power use by an analog external device?  If I could grab that information, then I could use some Linux-based device to process the information and dump it to the network.  I'm just not sure how to go about monitoring the power usage of the sump pump.

You might be able to find something to measure the power usage here: http://www.p3international.com/products/index.html.  However, caution may be advised against purchasing something to do this that is real expensive.  There is a large current draw when the pump motor starts (think your lights dimming when the fridge or a circular saw starts going).  The kill-a-watt I have (an isolated, stand-alone device) is only rated for 15A.  I've never tried to hook it up to my fridge (I think those are normally 20A) or another motor-driven appliance to see what it would do.  My guess is that it could burn out the electronics after a while.  I doubt it would stop the appliance from running, but it would make my yardstick pretty useless.

I'd definitely be interested to hear what you come up with in the end.