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Wall meter to measure power usage?

amitmishra4

Member
Apr 9, 2018
116
129
Bayonne, NJ
Can I connect a power usage meter like kill-a-watt or something to measure power consumed at the plug point and provide an easy readout? I will be charging at my parents house occasionally and would like them to keep track of how much power I’m using off their utilities so I can compensate them accordingly and put them at peace that the car is not gong to cost a ton of $$$ to charge every time I visit. Is it ok to plug the UMC through such a contraption every now and then?
 

doubleatheman

Member
Feb 24, 2016
126
154
Sacramento, CA
The Kill-o-watt meter on 120v outlets works fine, I've used it before. The Kill-o-watt itself is raited for 15 amps. If your looking to monitor usage on a 220v outlet your going to need something like the dryer buddy, which I use the meter on it to keep track of the power I use to subtract from what my roommates portion is.
 

ai4px

Wes
May 2, 2018
448
481
Sumter SC USA
The Kill-o-watt meter on 120v outlets works fine, I've used it before. The Kill-o-watt itself is raited for 15 amps. If your looking to monitor usage on a 220v outlet your going to need something like the dryer buddy, which I use the meter on it to keep track of the power I use to subtract from what my roommates portion is.

If I’m not mistake, the dryer buddy uses the same meter I just recommended. YMMV.... :)
 

doubleatheman

Member
Feb 24, 2016
126
154
Sacramento, CA
If I’m not mistake, the dryer buddy uses the same meter I just recommended. YMMV.... :)
You are correct, the non upgraded meter is the exact one you linked on eBay. It works great, just requires some wiring and effort, which wouldn't be that hard. For the op would go that route if he is not also in my situation of only having a single Nema 10-30 outlet for my dryer and car. $17 is much better than ~$250.
 

tga

Supporting Member
Apr 8, 2014
3,952
2,794
New Hampshire
I wouldn't charge through a Kill-A-Watt. I don't think they are built to handle 15A continuously for hours on end.

You can also track it the old fashioned way - pen and paper. 3 hours * 240V * 24A * 0.15/kWh * 1 kW/1000W = $2.59.

That assumes they trust your math. I installed a meter like @ai4px described for someone who's roommate wasn't confident in the calculations, and wanted to see a meter with a running total.

You can also get a refurbished utility meter from hialeahmeter.com and put it in line with the outlet (as long as nothing else plugs in). A meter and base will cost you around $50.
 

CWFLY

Member
May 9, 2018
65
55
San Diego
I didn't see where the OP said what type of plug.

120 Volts???

Here's a simple 120v meter that shows how much energy has been used. (BTW, kWh is a measure of energy, not power :)) P3 International Kill A Watt EZ Meter-P4460 - The Home Depot
Meter.jpg


Two things:
  1. If your parents have TOU (time of use) plan for their electric, the rates vary by time of day.
  2. If you offer money to your mother, she will probably refuse to accept it.
 
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SDRick

Active Member
Jun 25, 2015
1,446
1,005
SD CA United States
I ordered this from eBay AC Digital LED Power Meter Monitor Voltage KWh Time Watt Energy Volt Ammeter | eBay . You need to select the option for the 100amp current transformer, its $17 total. Works well. I got a dual gang box at Lowes and a dual gang blank plate. A little love with a Dremel tool and the meter is neatly mounted in my garage wall.

I use the same meter, Works great! I don't think you can beat it for the money. With this type of meter you do not need to charge through the meter but rather use a CT around one of the conductors.
 

amitmishra4

Member
Apr 9, 2018
116
129
Bayonne, NJ
I didn't see where the OP said what type of plug.

120 Volts???

Here's a simple 120v meter that shows how much energy has been used. (BTW, kWh is a measure of energy, not power :)) P3 International Kill A Watt EZ Meter-P4460 - The Home Depot
View attachment 309268

Two things:
  1. If your parents have TOU (time of use) plan for their electric, the rates vary by time of day.
  2. If you offer money to your mother, she will probably refuse to accept it.

Yup I’m just using a standard 120V outlet and charging at snails pace (12A) but it seems to work sufficiently for when I visit. I resorted ultimately to using the old pen and paper method after all. I just take the number of miles I use and calculate my usage with some added margin for the lower efficiency. You are right that mother wants nothing to do with my money but at least they are assured that there is nothing else causing any vampire drain in the house. :D

Point taken about power vs energy terminologies in your example - I find myself using those terms interchangeably since it is also (usually) referred to as power supply or a power receptacle.
 
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eprosenx

Active Member
May 30, 2018
2,073
2,513
Beaverton, OR
You can also get a refurbished utility meter from hialeahmeter.com and put it in line with the outlet (as long as nothing else plugs in). A meter and base will cost you around $50.

Yeah, I was going to second the refurbished meter thing. It is vast overkill (probably rated for 200 amps) but the refurbished meters are stupid cheap because all the utilities have swapped them with smart meters so there is virtually an unlimited supply. My solar guy said they were like $10 (they state energy credit required one on my solar). Meter bases are also stupid cheap since they are produced in insane volume. Naturally it handles 240v and is "revenue grade" (i.e. accurate).

But with that being said, something with just a CT over the wire and a monitor display would work fine as well (just probably not UL rated).

On the Kill-A-Watt - my first thought was that I would be highly suspect with running that much continuous current through it, however, it probably just has a CT in there anyway and so it is not hard to have a piece of metal of sufficient ampacity to pass the power through from the plug to the receptacle. Regardless, I probably still would not trust it (and as others have pointed out, it won't work on 240v).
 

davewill

Active Member
Feb 5, 2014
1,828
1,979
San Diego, CA, US
Here's my meter install. When I did the install, I was part of a power company TOU pilot that required a submeter. When I got solar, I had to leave the program, so I bought a refurb meter and slapped it in. As you can see, I've logged almost 30MWh of EV charging since then, and that doesn't even include my wife's Prius Plug-in which charges off a 5-15 outlet that isn't on the submeter.

IMG_20180613_143630.jpg


P.S. I've seen photos on the LEAF forum of Kill-A-Watts that melted from people using them to track EV charging...but that was a long time ago.
 
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CWFLY

Member
May 9, 2018
65
55
San Diego
Yup I’m just using a standard 120V outlet ...
I resorted ultimately to using the old pen and paper method after all. I just take the number of miles I use and calculate my usage with some added margin for the lower efficiency....


I charged my car with a meter attached. For my Model 3, it took 18 kWh from the house to add 55 miles of range to the battery.

So roughly, 3 miles of battery range requires 1 kWh.


Note: For those who sometimes skim too quickly (I'm guilty of that too), this is the ratio for putting charge into the car... has nothing to do with driving economy.
 
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GregRF

Squirrel Power
Jul 22, 2014
521
1,044
CA
Does anyone have a meter that also uses TeslaFi? I'm curious how accurate the reporting from the car is.

It was reporting about 70% efficiency for 120V charging and about 90% for 240V, so it seems to be in the right ball park.
 

CWFLY

Member
May 9, 2018
65
55
San Diego
P.S. I've seen photos on the LEAF forum of Kill-A-Watts that melted from people using them to track EV charging...but that was a long time ago.


I agree. Some (or all) are made in China, and have some fancy sticker, but are not UL.
15A is a lot of power... don't take chances with it.
 

David99

Active Member
Jan 31, 2014
4,850
7,026
Brea, Orange County
Does anyone have a meter that also uses TeslaFi? I'm curious how accurate the reporting from the car is.

It was reporting about 70% efficiency for 120V charging and about 90% for 240V, so it seems to be in the right ball park.

I'm using Teslafi and I also have a meter on my 14-50 outlet. Teslafi and my meter tend to agree with each other. The car is just tricking you. When your car is done charging it shows how many kWh were added. That's on the battery side, though. It ignores the losses in the chargers. While you are charging it does show the Volt and Amp from the grid and that wht Teslafi looks and uses to do it's own calculation. By comparing this with the kWh the car reports you can calculate the efficiency. So Teslafi can replace your power meter. It also has the advantage that is adds up power anywhere you charge your car, not just at home. In fact it keeps track of how much energy you charged at each location separately.
 
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