Some beginners questions

Hi All,

I’ve got a few basic questions :slight_smile: so bare with me. My setup is an emonpi and I’m pushing current W and KwH to homesssiant and influxdb / grafana

  1. is there a way to calculate “standby” power ie the amount of power the house always consumes and doesn’t drop below? What would be the best way to calculate this and to set this up? (I have an emonpi installed by an electrician with one clamp)

  2. is there a way to capture “events” and the cost of these. Let’s say the kettle boils, electricity usage goes up significantly and above a threshold then capture and record this “event” spike with the cost and electricity usage of that event with time/date stamp. Idea being to capture the most costly “events”

And some more generic questions:

  1. how do people monitor individual appliances typically ? I have lots of smart plugs which record Electricity usage but how about larger appliances such as washing machines etc ? How do I determine what is safe load for smart plugs ? For example I have a small network cabinet(switch, firewall, modem, various home automation hubs, server, pis) … plug in the UPS in to a smart plug and then in to the wall would give me measurements but is this a safe setup ?

(UPS is a cyberpower )

  1. is there a way to figure out how much my smart lighting is drawing ? These are on separate lighting circuits (in ceiling lights) but could I for example work out the standby draw and “on” draw via a lamp on a smart plug and then calculate an estimate usage across the house based on these being on/off ? Or not as simple as this ? (Typically these are all hue bulbs)

Thanks in advance !


When using units, think that if the unit is a name (i.e. James Watt) then the unit will be a capital i.e. kWh.

Just turn everything extra off and see what the consumption is. It will never be constant as fridges etc turn on for a while then off again.

Not really, you can just look at the graphs for that specific period of time.

Smart plugs are the only viable route really. beware though most are not very accurate without calibration.

You could connect a second CT to the emonPi and if there is enough slack clip it round the lighting circuit supply or return.

You’re absolutely right.

Here (yet again):
The rules are fairly simple, and in this order of precedence:

  1. Units named after people have an UPPER CASE letter (Ampere, Gauss, Newton, Hertz, Kelvin, Faraday, Celsius, Joule, Volta, Watt, etc.)
  2. Multipliers greater than one have an UPPER CASE letter. (Mega, Giga, but kilo is beaten by rule 1 - K for absolute temperature after Lord Kelvin)
  3. Units not named after people, and multipliers less than one, have a lower case letter. (metre, second, gram, milli, micro(µ), nano, pico.)
    So two very common errors: Mhz is always wrong by rule 1, mhz is always wrong by rule 1 and most probably wrong by rule 2.
    Some commonly confused are: Siemens & second, Kelvin & kilo, Newton & nano. Unfortunately, there’s the exception that proves the rule: Tesla (after Nikola Tesla) & Tera - both share an upper case letter.

But I think, using the conditional processes on the emonCMS inputs page, Daniel could create one or more feeds with the “top slice” of power or energy, i.e that when the power exceeds the set value. That’s not what he’s asking for, but it might help his understanding of the proportions in which energy is used.

I have no idea whether Grafana is capable of any of the things that are being asked for. @Bill.Thomson knows Grafana reasonably well I think, maybe he can offer some advice.

@Daniel_Edge - you don’t say where you are in the world. Knowing that helps us because standards and practices vary greatly from country to country, and we often need to tailor our advice based on where you are.

Read the instructions for the smart plug - those or the rating label should give the maximum current, and the rating label for each appliance that’s fed by it, and do the sums. Bear in mind that for many things, the current may well be greater that the ratio power ÷ voltage indicates, for some types of load considerably more. Can you not use the plug itself on each item in turn to measure the current? Generally, it’s only things like timers on microwaves, ovens, etc that take a current that’s considerably (i.e. many times) larger than the power indicates; in most cases, the current should be between one and two times that which the calculation would indicate. So without detailed information or measurements, you should be OK up to about half the plug’s rating. Above that, and in the absence of measurements, I’d advise caution.

I have no idea whether Grafana is capable of any of the things that are being asked for.

Grafana has threshold detection and alerting built in.
That said, I’ve not had the need to use either of them, so am unfamilair with their set up and use.

Unfortunately, the rules aren’t quite that simple. Whilst kilo indeed has a small letter, Tera has a capital. The SI prefix abbreviation for a multiplier of 1,000,000,000,000 is T, not t. Also, BTW Nikola is spelled thus - he was a man, not a girl.

See SI units - NPL or Metric (SI) Prefixes

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