Sorry this is extremely basic, but one wrong assumption will have me drawing incorrect conclusions and I know approximately zip about this sort of thing.
My electric bill is too high, so I’m going around with a very ancient watt meter testing things out to see if they’re drawing more power than I think. For example, I have a grow lamp that’s on 24/7, and the meter says it’s drawing between 11 and 12 watts continuously. So I figure thusly:
12 watts x 24 hours x 30 days = 8640 watt-hours per month, or 8.64KwH per month. Cost per KwH on my electric bill is in tiers, but the highest tier is about 8 cents, so: 8.64KwH x $0.08 = $0.69/month cost to have that lamp on.
Does that sound correct?
(By the way I get that some things will have vastly variable power draw, like the fridge, so I need to learn how to use the meter to measure KwH over a period of time. All I know to do there is reset the KwH button then come back and look 24 hours later or one week or whatever, and recalculate monthly cost as appropriate.)
How nice for you if electricity is really that cheap…
Smart socket running Tasmota (or whatever) to measure current as well as accumulated energy use is the easiest. You can also measure current using a clamp meter.
Sounds like you’re doing the math right, but I’ll point out that 12W for a grow lamp (I assume LED) is very low. That is pretty much the equivalent of one regular LED bulb, so I’m a little suspicious of your watt meter.
This may be a stupid question, but how does it work? Some I’ve seen are like pincers that clip around the cable. I’m not sure how accurate that is at top and bottom of the scale.
Does 12 watts match the bulb type, if that info is available? Seems reasonable for LED.
I recall something about AC and RMS calculations (root mean square). AC is not the same as steady current.
Also, what you may need to do for things like fridges and freezers and furnace fans is figure the duty cycle - what percentage of the time is it off and on? Assuming your house is a relatively steady temperature, the heat loss should be a constant so the fridge cycle should be pretty flat. (Except if you have no AC in the summer)
You need access to the wire to be able to clamp a loop around it. Which is why I suggested a smart socket may be much easier with a plug-in appliance.
That’s what I mean, but in that case if you set it to zero, then come back later and read how many kW⋅h were used, does that not match the appliance’s energy usage? If you need second-by-second power readings, then you need a meter which records and/or broadcasts that info, and then there are apps where you can look at the data and compare what happens over individual hours, days, weeks, months.
Correct, and…you would want to capture the power usage at the mains to verify that the usage is in line with what you are paing for. This would certainly require the expertise of an electrician. Your plug-in tool will only get you so far. The heavier loads will be difficult to capture with anything other than a proper recording meter.
That is a case where the plug-in meter will not help you, but you do not have to be an electrician or fuck with the mains, just get a clamp probe around each phase; there is no direct electrical contact. The energy monitor can then record it or transmit the data every few seconds to a separate unit for display/analysis.
I would never recommend that to anyone who isn’t very comfortable with electricity!
Clamping a current probe around the mains puts you very close to dangerous uninsulated conductors.
I suppose I have to concur. Even if you do not have to open up the distribution box where the exposed conductors are, you are still working pretty close to it and must do so safely, and in any case you have to know what are all the different coloured wires. So better safe than sorry if anyone is not comfortable with electrical wiring.
I just got one of these home energy monitoring systems (HEMS):
The hardware cost $165 and it took my electrician less than an hour to install. (I watched him, and although I had been uncertain enough about opening the breaker panel to do it myself, after seeing what he did, I could have handled it just fine. And I have reassigned sensors to other circuits myself since then.)
The base unit connects to your wifi and sends data to an app on your phone or tablet, with graphs on power use by each monitored circuit by week, day, hour minute, and even second, if you want it. The unit in the link has sensors for 16 circuits, and you can get packages with eight or just two to monitor the whole house consumption. If you want more, you need a second base.
If, as we do, you have solar panels on your roof, it will also show how much power they are producing.
There are other competing brands, but this was the least expensive, well-reviewed, and AFAICT, is just as good as the pricier ones.
It’s also possible to replace your whole breaker box with a smart panel that has monitoring and control built in. But that’s around $5-6,000.
I’d like the OP to return and tell us how he decided his electric bill is “too high”.
What KW-H cost and consumption numbers do you have now versus some prior baseline? What’s different in your facilities and your family? What time of year was your baseline?
I noted I’m dumb in this area, and I don’t really understand how to use the KwH button on the meter except to reset it, come back exactly 24 hours later, and multiply that figure by 30 for a month’s estimate. I think there’s supposed to be a timer that I can’t get to work. So instead of doing that, I’ve just been measuring wattage as a moment in time, assuming it remains constant (I know it doesn’t really) then doing the multiplication laid out in the OP. That’s what I needed to verify, in case even that was egregiously wrong. Looks like it’s a subpar method, but not actually wrong: if my lightbulb is a steady, exact 100 watts, I wanted to make sure I knew how to translate that into what it looks like on my electric bill.
@LSLGuy: yeah, I knew it’s not really lightbulbs, but I did want to start checking to see if any plug-in devices are using more juice than I think. There’s a hundred things that are on standby 24/7, and the LED grow lamp is new so I did honestly worry about that (no longer).
Why I think the bill is “high”: the electric consumption in January was about 20% higher than that in January last year, with slightly warmer temps and no other changes I can think of, except one: in November, I had the attic re-insulated and expected an improvement, not a worsening. Maybe something went wrong there, or maybe something’s wrong with the heat pump, that’s my guess. The water heater’s gas, thank God.
ETA there was one other significant change, and I bet this really is the cause: I had always-on bathroom fans put in at the same time as the insulation. They don’t draw any significant power themselves, but they are probably pulling a lot of cold air into the house.
For small loads, a modern wattmeter is the way to go. They use an ADC to simultaneously sample the voltage and current a few thousand times per second, multiply each pair, and then display the average over time. The newer ones will also tell you the average power used over one day or a week.
The power for larger loads that don’t plug in to standard 120 VAC receptacles (air conditioner, range, etc.) is more difficult to measure. The simplest method is to measure current using a regular clamp-around meter, and then multiply by the voltage. But this only works well for resistive loads like heaters. If the load has appreciable reactance or has a weird current waveform, you need more advanced methods. One method is to measure the true RMS of the current, and then multiply by the cosine of the I-V phase angle. But that’s a pain. The system shown by commasense is probably the best solution.
Though that only works for loads that are somewhere on the spectrum of pure inductive and pure resistive, which isn’t always the case (like with many dimmer switches).
I’ve been running the Emporia system for a couple of years now and it works well:
Main downside is that it’s not very open. I wish I could directly access the data, but it’s all app/cloud based. It is cheap, though.
