I have been using an iotawatt successfully for months, but due to the difficulty of finding a second unit in Australia I’m looking at what I can cobble together with parts at hand.
I’m wondering if I could piggyback on the CT clamps my zappi uses to monitor power flow (directing solar exports into my car). It’s a bit of a long story, but this would save me from needing a second iotawatt.
The clamps don’t have a connector, they’re just wires, but if connect them up with a stereo jack will the iotawatt be able to monitor it?
Here’s the spec sheet:
The catch is I’d still need the myenergi device to read the signal, and fork off a pair of wires to the stereo jack for the iotawatt. Is that a crazy idea? Would one monitoring system impact the signal read for the other?
I’ve realised that I can avoid the need for this probably dodgy patch by combining circuits into one CT instead (the thing I’m trying to do is fit all clamps into the cat6 extension). I’m leaving the question up out of curiosity.
I’m no expert but since nobody else has chimed in, here’s my understanding:
They’ll probably work fine as generic 2500 turns and phase lead of 2 (at a guess). I couldn’t easily find the phase offset so I’d probably manually calibrate it to read PF 1.0 with a pure resistive load.
In short, that won’t work. Both devices expect to sink all the current from the CT clamp across their own burden resistor.
As a thought experiment, you might be able to get somewhat reasonable numbers from IoTaWatt by adjusting the turn count to compensate for the other device’s burden resistor. I’m guessing you can’t fake things on the other device that way though which would kill this idea. If both devices have the same burden resistance, you could half the number of turns in the config and get pretty close numbers. You’ve potentially got other issues to deal with though like sharing a ground between both devices which, if power supplies outputs are not floating, could result in smoke escaping. I would stay away from the idea of sharing a single CT between multiple devices.
Ah. I was wondering why you were trying to share a CT clamp instead of giving both devices their own clamps.
A less dodgy idea would be to share a ground between all CTs going to a single device. You should be able to easily tone out which wires are in common on each pair and free up cores for more CTs. This is less than ideal though because the extension will be more susceptible to noise by not keeping each CT to their own twisted pair but it’d probably be fine on shortish runs if sufficiently separated from other cables. Your mileage could significantly vary though.
If you can’t easily run more cable to your IoTaWatt then this is probably the best way to go.
That was the main thing I wanted to know, as I begin to understand how fundamentally similar all these things are.
Makes sense. Thank you for clarifying; I think I knew this already but I am a long way from an expert here so I wanted to make sure.
Yeah. I ran cat6 recently for monitoring, while we had a trench open, but with 3-phase power I’m glad I asked for a second cable intended as a dark backup. I’m going to have to use 3 pairs from each leaving only capacity for 2 other CTs.
That’s a very interesting idea. However it’s not a short run, and after further thought I’m actually limited by iotawatt’s 14 inputs; with 3-phase power and soon 3-phase solar that only leaves 8 of the 14 for detailed monitoring so limiting myself to 2 on the extension cable is beneficial.
This is why I’d like a second unit, but there’s no indication of when (or even if) that might be available. I’m formulating a plan where I can combine some circuits (e.g. lights) and use output calculators for the rest. The beauty of 3-phase is I have 3 opportunities to calculate grid total (or export usage) minus known CTs on that phase.
An aside: You may find your solar inverter and associated smart meter (required for the 5 kW per phase grid export limit) gives you enough detail to not have to monitor the mains and solar with IoTaWatt, leaving you heaps of capacity for other circuits. I am using the stock Fronius integration with Home Assistant and its output closely matches what I see from my IoTaWatt. The only downside is the Home Assistant integration only refreshes once per minute but it also provides watt-hours in addition to watts so the 1 minute resolution doesn’t matter for long term stats and Home Assistant’s Energy dashboard.
Additionally, if you end up with home batteries at some point, you’ll probably have to rely on data from your inverter/battery system for charging/discharging data anyway.
I am lucky enough to fit everything into the 14 channels of a single unit and definitely prefer having mains and solar data via IoTaWatt (sending to InfluxDB and viewed in Grafana). I also feed data from my inverter into InfluxDB using Home Assistant along with some other power metrics (e.g. smart plugs) but don’t tend to look at that much.
Something to consider if you find yourself wanting more channels and are unable to source another IoTaWatt.
Good to know! I’m going with solar edge, and in Tasmania our limit is 10kW per phase so I won’t have any limiter.
I also feed my iotawatt uploads into influxdb, with grafana attached, but I haven’t spent the time to learn how to set up dashboards etc. I’m realising I should probably just get into home assistant and feed all of my data into that.