MNSBR: $11 AC Power Monitor, PZEM-061 - MNSBR

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$11 AC Power Monitor, PZEM-061

#1 User is offline   Jim Hubert Icon

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Posted 01 May 2018 - 01:15 PM

I'll be reporting on this project as it may help guys at the track with tire warmers, etc.


View Postripperd, on 01 May 2018 - 09:40 AM, said:

IIRC new computers must have PFC (power factor correction). But you are right, older PC power supplies didn't give a rip about power factor and were often pretty poor.

That's good information. I suspect my computer's power factor is probably better than the 0.65 value I quoted (which likely included a UPS backup and monitor). The CPU loading probably has some effect as well.
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#2 User is offline   Jim Hubert Icon

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Posted 01 May 2018 - 01:20 PM

I'm a bit of an efficiency nut. According to Xcel, my home routinely uses significantly less energy than my efficient neighbors. Some of that comes from making choices based on monitoring electricity consumption of appliances. One of the instruments I use for that purpose cost me $1000 in 1995. The thing I'll be showing here cost $11 directly out of China and does a lot of the same work. I think you can buy them for around $16 on Amazon from US stock. It is model number PZEM-061 which can measure AC power up to 260 volts and 100 amps. There is also a 20-amp version that costs 50 cents less.

Attached Image: PEZM-061.JPG
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#3 User is offline   Jim Hubert Icon

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Posted 02 May 2018 - 06:19 AM

Even though I had no intention of monitoring more than 20 amps, I purchased the 100-amp version. The thought of passing 20 amps directly through the unit's cheap connection terminals made me very uneasy. The 100A version comes with a current transformer (CT) which alleviates that concern.

Below are pics of my finished unit (but I probably should label the controls).

Attached Image: PZEM-061 front.JPG Attached Image: PZEM-061 inside.JPG

The knob adjusts the auto-transformer (aka Variac) which allows me to power a small load from 0 to 140 volts. The toggle switch bypasses the Variac to power the load from standard line voltage up to 15 amps. Although the small Variac is not extremely useful (2.25 A max), I had it laying around and it does add a nice heft to the box! In fact, other than the power meter itself, I had all the parts on hand. I also had to make a brass extension for the toggle switch and a Nylon insert for the CT to secure and center the current carrying wire.

Power measurements are quite accurate for computers, incandescent bulbs, fluorescent lamps, and LED bulbs. But it's only within about 10% for my bench grinder. I suspect most motors will give it trouble. The worst accuracy I've found is a heat gun at half power. To make half power, the heat gun uses a series diode that blocks one half-cycle of the AC sine wave. The PEZM-061 claims it is 86 watts when in reality it is 580 watts!

Attached Image: Heat Gun Half-Power.JPG

Although the unit is specified for a minimum input of 80 volts, mine runs down to about 42 volts. I appreciate that it is parasitically powered (so no batteries are required). My unit exhibits a small offset error of 0.05A and 0.5 W when no load is connected. When I short the terminals where the current transformer attaches, the offset does not disappear. Perhaps the designers intended it to represent the power consumed by PZEM-061 itself? More likely, it's just error since the unit is intended to measure up to 100A.

More to come.
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#4 User is offline   ripperd Icon

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Posted 02 May 2018 - 08:35 AM

Here is some other cool info on home power monitoring as well. If I had about 10 more hours of free time each day I'd probably make something geeky and fancy haha

http://marc.merlins....rMonitoring.pdf
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#5 User is offline   Jim Hubert Icon

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Posted 03 May 2018 - 06:09 AM

View Postripperd, on 02 May 2018 - 08:35 AM, said:


That "KILL A WATT" is probably the easiest way for the average person to access useful data on appliance power consumption. But I read a couple Amazon reviews -- seems like the output of a non-sine wave generator might kill the KILL A WATT!

I wonder if it's more or less accurate than the PZEM-061? If anyone has one, I'd be willing to compare it against my $1000 Fluke.
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#6 User is offline   Jim Hubert Icon

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Posted 03 May 2018 - 06:33 AM

My biggest gripe about the PEZM-061 is that the plastic tabs intended to retain the unit in a panel are worthless. They appear to be designed for a panel only about 1mm thick. Mine broke off while I was still test fitting it in the enclosure. I used hot-melt glue to secure my meter. Epoxy would be "better" but I did not want something that permanent in case the unit died or I wanted to make changes.

I love the fact that the meter will totalize energy consumption. That's not something my $1000 Fluke meter will do, and I have another instrument just for that job. Why is that important? Let's say you want to know the energy consumption of something that does not have a constant power draw (like a refrigerator or washing machine). In fact, your tire warmers are not constant either, and even the energy used by your computer depends on what the CPU is doing from moment to moment. Unfortunately, the button to reset the totalizer is very poor quality (it would be nice to be able to attach an external one). And, that single button is multi-function. It will toggle the backlight, and there's also some type of warning you can program for a power limit. So using that single button is a bit complicated.

The energy value is non-volatile, so if there is a power failure (or just the next time you use it) the last value is saved.

Attached is a scan from the instruction sheet.

Attached Image: PEZM-061 datasheet.jpg
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#7 User is offline   ripperd Icon

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Posted 03 May 2018 - 07:54 AM

I have a kill-a-watt, although I don't know a great way to get a remote comparison.

The kill-a-watt does do accumulation (as you likely know), although it is not stored in non-volatile memory. I used it to figure out how much my garage heater ran (and subsequent natural gas bill increase) by measuring the idle power usage, and then the heat-on power usage. The kill-a-watt would give me a total kwh used, and a total time. I knew that completely idle, the heater (really, the 24v control transformer) used around 5w. When the heat was on, it used about 500w (combustion fan, blower fan, gas galve).

This is pretty much middle school math probably, but I haven't had to solve equation pairs like this in a loooong time.

A = time heater idle at 5w
B = time heater heating at 500w
T = total cumulative time = 60h
W = total cumulative Wh = 4000Wh

A+B=T
(A*5)+ (B*500) = W


A+B=60
5A+500B=4000

A=60-B

5(60-B) + 500B = 4000
300-5B + 500B = 4000
-5B+500B= 3700
495B=3700
B= 7.47

So the heater ran for 7.47 cumulative hours out of the 60 hours monitored. At 45kbtu input, and an average price of 75 cents a therm, that is about 45,000 (btu/hr heater) * 7.47 (hours) / 100,000 (btu/therm) * 0.75 = $2.50 in natural gas for those 60 hours. Extrapolate that usage to a full month an you are at $2.50/60 * 744 = $31/month.

Who ever thought you could estimate gas usage by using an electricity monitor! (tying back to main subject haha)
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#8 User is offline   Jim Hubert Icon

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Posted 03 May 2018 - 08:47 AM

View Postripperd, on 03 May 2018 - 07:54 AM, said:

I have a kill-a-watt, although I don't know a great way to get a remote comparison.


Put a diode in series with a heating element and see if it reads half-power or some crazy value like the PZEM-061.
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#9 User is offline   mike4king Icon

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Posted 03 May 2018 - 09:00 AM

How does this stuff compare to the Sense product? I don't have the electrical knowledge to keep up with some of the conversation in this thread, but I've considered buying Sense for a while to monitor what my house is doing.
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#10 User is offline   Jim Hubert Icon

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Posted 03 May 2018 - 10:44 AM

Just from a quick read, Sense looks like a fun nerdy toy -- but also kinda gimmicky. I question how accurate it could be in discerning individual appliances.

Try to get hold of the instruction manual. If it's all done by "machine learning", and you don't have the "teach it" what the power signature of your [ name of appliance here ] looks like when it's running, I'd be fairly skeptical.

The average user would have no way to verify its accuracy. It also begs the question, what would you do with the information it provides?
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#11 User is offline   mike4king Icon

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Posted 03 May 2018 - 10:58 AM

View PostJim Hubert, on 03 May 2018 - 10:44 AM, said:

Just from a quick read, Sense looks like a fun nerdy toy -- but also kinda gimmicky.


A friend has it and said the information it provided was interesting, although like you said, I'm not sure how useful it is. You do have to train it, so turn on the dryer and you'll see a new "power source" pop up that you can then label as a dryer. I don't think it can fully identify appliances based on their power draw. I think it would be helpful for optional things like seeing how much power a garage heater or a heated floor pulls in, and using that information when deciding when to use them and how high to turn them. My electricity bills are really high at home, and my only guess is that it's because of the 18 year old 105 gallon electric water heater that we have. I've considered replacing it with a newer/smaller one just to save some money on electricity.
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#12 User is offline   Jim Hubert Icon

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Posted 03 May 2018 - 11:04 AM

View Postmike4king, on 03 May 2018 - 10:58 AM, said:

My electricity bills are really high at home, and my only guess is that it's because of the 18 year old 105 gallon electric water heater that we have. I've considered replacing it with a newer/smaller one just to save some money on electricity.


Electricity costs roughly 3x that of thermal energy (natural gas). If you have to use an electric water heater, Marathon is a good choice due to its insulation. https://www.rheem.co...-water-heaters/

Some electric utilities offer off-peak rates, which makes the above even better.
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#13 User is offline   Jim Hubert Icon

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Posted 04 May 2018 - 08:31 AM

A couple things to add before I forget... The PZEM-061 can be used to manually calculate power factor. Simply divide indicated power by indicated voltage times indicated current. The result will be a number between 0 and 1. This is Watts divided by Volt-Amps, which is one definition of power factor.

You can learn some surprising things with a power monitor. For example, I inherited a Westinghouse fan from my father that was manufactured in about 1960. Best, most high-quality, fan I've ever owned. They literally don't make them like that anymore. It has two speeds. Although the low setting is quieter and provides a gentler breeze, it consumes slightly more power than the high setting – I never would have guessed that.

Also wanted to mention that another device called a clamp-on AC ammeter is useful for investigating current consumption of appliances that are hardwired, or operate on 240V, or anything you can't plug into a device like the Kill-a-Watt.

Here's one example: https://www.amazon.com/dp/B077FWR3CT/

I don't have any experience with that particular unit, but it certainly is inexpensive and has gotten good reviews.
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