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Old 12-25-15, 08:51 AM   #1
Ron342
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Default $9 Multifunction voltage, current. power meter, alarm etc?

http://pages.ebay.com/link/?nav=item...13300&alt=web*

Above is an eBay link for a small multifunction board displaying power, voltage, run time, current, programmable. overload alarm, even apparently saves data on shutdown and more all for $9 delivered.

Really would be great to hang on a hacked unit if it works.

Anyone tried one? Sometimes these things come with no or unreadable data sheets.
I saw the ad under the $15 ebay power meter link someone kindly posted here earlier. This seems to have a lot more functions and is even cheaper.

Merry Christmas everyone!

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Old 12-25-15, 10:59 AM   #2
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I have run one for several months. At some point, I'll probably permanently mount it somewhere, I just haven't decided precisely which location I'd like to use it in. If I could mount a pair on my generator, that would allow me to see live load conditions, and keep track of run time.

Getting the CT wires out of a home panel, along with 120V to run it while still reasonably staying within NEC rules is a little bit challenging. If you have the means to cut a rectangular hole in an electrical panel cover, you can probably get close to staying within NEC rules, except for the fact that the device isn't UL listed. I wish someone would make these widgets the size of a Decora cutout where they would snap into easily obtained covers.

If you mounted it in a reasonably large enclosure, you could put a 240V in/out setup on it and use it like a big brother to a Kill-A-Watt. It will only measure L1 or L2, not both.

It won't replace my TED 1001, or TED 5003-C, but it's good to have options in my toolbox to choose from.
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Old 12-25-15, 02:10 PM   #3
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I like this one in its different forms:

Led panel, 100 amp:

http://www.amazon.com/80-260V-BAYITE.../dp/B00YYA01AW

Embedded, TTL serial interface:


PZEM-004T Maximum 100A AC Multifunction Power Monitoring Communications Module Monitor Module Sale - Banggood Mobile

They can both be rigged to a remote device to provide data logging via serial port. Various approaches have been employed to achieve this goal, and there is a wiki page about it. Datasheets, program code, and hardware details are all there.
https://wiki.cuvoodoo.info/doku.php?id=spark_counter

One can get the devices quickly from a domestic source, or slower and cheap from China.

There are oodles of implementations of this stamp by various manufacturers in lots of colors and sizes to fit size or personal taste. Black, white, silver, gray, etc. LED or backlit LCD, low voltage low amp to high voltage high amp. Or, like the above pic, no display at all.

Last edited by jeff5may; 12-25-15 at 02:48 PM..
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Old 01-05-16, 11:28 AM   #4
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Default now on wifi with an app for $40??

Thanks guys, the wireless option was really interesting but beyond my programming skill!
But found a a wifi power meter/controller/alarm/sort of logger with an app for your phone. Called an Edimax, on ebay for $40, 120v only tho, 15 amp max, sort of a killerwatt meter on steroids. Maybe use it on 240v by measuring one phase to ground?
Think about this tho - looks like you start your test system up , go do something else, and it logs power and buzzes your butt if if spikes?
Anyone tried it?

Maybe this thread needs mirroring in tools?
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Old 01-05-16, 12:13 PM   #5
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Default link for Edimax wifi meter etc

Here's a link

Edimax Wi Fi Smart Plug Switch w Power Meter Intelligent Engery Management | eBay
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Old 02-04-16, 10:23 AM   #6
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I have one like the originally posted link, connected in the garage to the 240 volt circuit feeding my charging connection for our Nissan Leaf electric car, so that I know what the car is using. It works fine and does what I expected and the price was great. It is mounted on a 4x4 electrical box with extension so there is room for the #6 wire and the connections and the current transformer--the meter is mounted on a knock-out on top of the box. I'm thinking of getting a couple more to monitor energy usage of my mini-split heat pumps, if I can figure a good place to mount them.
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Old 02-04-16, 10:16 PM   #7
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So you're reading one hot leg of the 240v to ground?
If so , isn't it going to read half of your real usage?
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Old 02-05-16, 01:15 AM   #8
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Quote:
Originally Posted by Ron342 View Post
So you're reading one hot leg of the 240v to ground?
If so , isn't it going to read half of your real usage?
With many devices that run on 240, the neutral wire isn't present. They have 3 terminals: line 1, line 2, and chassis ground. What goes through line 1 equals what comes through line 2. The ground connection is isolated for shock protection. Large window shakers and baseboard heaters rig up like this.

Some units have a 4 wire connection, and have a neutral terminal. A number of unit makers cheat and use the neutral and one line leg for some low-power components. Electric dryers and ovens do this with lights, clocks and mechanical timers. Even in these "cheater" units, the stuff that only uses 120 volts account for very little of the operating power. Unless, of course, you use your oven for a night light or something.

In theory, you could rig 2 kill-a-watt units to a 240 volt circuit so they each read a line leg with reference to the neutral, then connected to a 240 volt device, and you could add the two readings to get the total power draw. You could subtract one reading from the other to tell if there was an imbalance somewhere. In reality, a rig like this would violate more than a few rules in the electrical code. That's why they sell 240 volt kill-a-watt meters.
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Old 02-05-16, 07:33 AM   #9
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Measuring power in some circuits and appliances is confusing. Consider an electric water heater and a resistance type (not gas) electric clothes dryer.

First the water heater. This is a device with two active leads, L1 and L2 together with a chassis ground. The chassis ground never has any current on it and is only there as a true safety so that if one of the L1 or L2 leads shorts to the metal exterior, then that dangerous current is shunted to ground. You can disconnect this ground (stupid) and the electric water heater will work fine.

In the water heater, L1 and L2 are connected to a large resistor - the heating element. What goes through L1 is the same as L2. In this case, the total power is the amount in any leg multiplied by the voltage. If you put a current meter on L1 and get 20 amps, then the total power to the water heater is 4800 watts (240 v x 20 amps) or 4.8 kW when it is on. When it is off the power is 0 watts.

The electric dryer is a 240 V appliance with at least three leads, L1, L2, neutral, (and sometimes ground). It will have a plug with either three or four leads.

The large resistance element in the dryer is between L1 and L2 - just like the water heater (lets assume 20 amps). But there is typically also a 120 V electric motor on one of the legs that spins the drum. There is also a small 120 V electric bulb and a circuit board that runs off off 120. This circuit is between one of the legs (lets call it L2) and neutral. The neutral must be there for the 120 V circuit to work. This 120 V circuit alone draws 1 amp.

The ground (4th dryer wire) is there for safety and is attached to the metal of the dryer frame. It is there to prevent voltage on the metal dryer exterior if a fault occurred with L1 or L2 shorting to the metal skin of the dryer. Just like the water heater - safety.

As Jeff mentioned above, some dryers "cheat" and use the neutral and ground as the same wire (a three wire plug).

If you only have L1 and L2, the resistance element will have power, but there is no power for the drum 120 V motor as the return neutral for the 120 V circuit is absent.

With the electric dryer, the total current for the resistance element is the same as with the water heater. But there is also the extra current to run the 120 V electric motor (and also electric bulb and circuit board). In this case, the current through L1 might be 20 amps, but through L2 it is 21 amps. The extra current of 1 amp going through L2 is to power the dryer electric 120 V motor (and bulb and circuit board).

The total power of the dryer is 20 amps x 240 V (heating the resistance element) plus the 1 amp x 120 V (for the electric drum motor and bulb/circuit board).

Total power is 4800 watts for the resistance element plus 120 watts for the 120 V motor and bulb/circuit board or 4920 watts (4.92 kW).

A dryer is interesting. Much of the time, both the 240 V resistance element AND the 120 V drum motor are on. But there are times when the drum is spinning and the 240 V heater is off. This is an intermediate power load. So you need to average the power over the entire drying load to get the average power to do a load of laundry.

With the water heater, it is just off or on and there is no intermediate power load.

What I do is to measure current in both legs of a 240 V circuit. I take the current number that is highest and then multiply by the voltage. This is an approximation for a spot check. But to get accurate loads, you truly need to measure power on each 240 V leg for some period of time and know how much duration is on each.

Hope this helps.


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Old 02-05-16, 07:58 AM   #10
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It does help - i knew dryers used one leg to neutral to get 120 for the motor - i think the code changed in the 80s to require a 4 wire plug with the neutral so you didn't have a current carrying ground.
But the little ebay panel meter uses 1 current sensing coil and it looks like the other connection is to ground.
So instead of phase to phase for 240v, its seeing (and reporting?) One phase to ground?

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