SDRick
Active Member
These little meters are great for the money and not difficult to install. The hardest part is finding a clean, cheap, simple and efficient way to mount or house the meter. Has anyone had any luck in this regard?
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
gkalexdc
Member
Perfect !
That's what I'm talkn about.... Now I get it. You attached the two voltage wires to the two Hot leads on the socket.
This is very easy and will be lotsa fun in my Plain old JuiceBox 30 I use for my smartED.
Thanks again,
Dr Alex
Houston
That's what I'm talkn about.... Now I get it. You attached the two voltage wires to the two Hot leads on the socket.
This is very easy and will be lotsa fun in my Plain old JuiceBox 30 I use for my smartED.
Thanks again,
Dr Alex
Houston
Last edited:
gkalexdc
Member
I will!!
I have another question:
I want to know why only one hot lead is through the donut transducer, instead of both leads, since it is 240v, 125v each lead. Does this one lead show all the current? Or, do you have to multiply the current reading X2 to get the total.....
Just wondering.
Dr Alex
Houston
SDRick
Active Member
gkalexdc
Member
I can assure you that your meter will read total power, and you don't need a second meter for the other leg. I say this based on experience - my own experience. I have 5 of these meters installed. One on my refrigerator in my kitchen, one in the living room for the TVs and DVRs, one in my garage for my Tesla, one in my garage for my Volt, and the one I posted this thread about which is attached to the EVSE I keep in my Volt and use at work. They all read total power. For example, the Volt (mine is a 2011 model) only allows 10kwh of its battery (which is a 16 kwh battery) to be used. When I get to work the whole 10kwh has been used as my drive is about 36 miles one-way, and that's mostly at 70 mph. So, after I charge up, the meter shows 10 kwh used. So I know its reading total power. My home meters on the Volt and Tesla also use kwh that agree with what I know the battery capacity to be.
gkalexdc
Member
Ok!!
Good to hear !! I can't wait for my meter to come , and do a DIY!!
This is pretty cool....
Great pics BTW
Thanks a million!
Dr Alex
Houston
Good to hear !! I can't wait for my meter to come , and do a DIY!!
This is pretty cool....
Great pics BTW
Thanks a million!
Dr Alex
Houston
SDRick
Active Member
I have 2 meters set up on my generator, one for each hot leg of the 240 V. My meter shows each leg at 120 V. Are you saying your meter shows 240 V with only one CT around only one of the legs?
Yes, please look at the original post and the second one - you can see the voltage readout in the meter display. The CT is a "current transducer" - and it does not measure voltage. It measures current. The current it measures would be the same, regardless of which "hot" you put through it. The current in one "hot"is the same as the other - it is flowing in on one "hot" and out on the other "hot". No need to measure the same current twice!
Also, I am not commenting on your generator setup. I read a little about this and it seems that depending on the loads you put on the outlet sometimes the neutral can carry current. But in our case, with just the EVSE on the outlet, the neutral doesn't carry current. I may be wrong, but I believe this is correct.
SDRick
Active Member
I believe the discrepancy in my set up and yours may be the neutral wire.
With my 120\240V generator it is desirable to load each leg somewhat equally. Depending on what 120 V circuits I have running there can be a great discrepancy between the two 120 V legs. Having 2 meters shows this discrepancy. Also, when I installed the home solar system, we also installed 2 bus bar CTs (one for each leg) to monitor the net electrical demand.
I am sure an electrical engineer or electrician could explain the discrepancy in our respective applications or experience.
Dithermaster
Member
My EVSE has it's own power company meter. I was part of our city's DOE-funded EV power use study since I bought my volt 4 years ago. The study is over and they are taking the meter out in the next month or so. Other than the reports they shared with me I never logged any data, although the meter has a whole slew of data it can show on the front panel. The main take-away from our first 3 years was that I would save about $100/year if we switched to Time-of-Use metering. I had the Volt set to charge at night, but with the larger capacity of the Model S I have it set to charge as soon as I plug in, so we probably won't switch to TOU unless they offer it only for the EV charging (something apparently being discussed).
@SDRick - Your question pertains to Electric Metering and the proper 'Form Type' meter to use for your electrical service. Your generator and your house are using what is called a single phase, three-wire service. Unfortunately, for a lay person, there are multiple 'Form Type' meters that can be used to properly meter the service, but all require different wiring of the meter.
On a Typical home, a Form 2, self-contained meter is used and all of the current from the electrical service runs through the meter. If the meter is pulled from the socket, the power to the house is killed. However, there are a number of applications where it is unsafe or not desired to have all of the service amperage run through the meter. Thus, the Instrument Rated meter was created. An Instrument Rated meter utilizes 'Current Transducer' (CT) to sense the current running through the conductor by measuring the 'flux field' generated by the current flow around the primary conductor. The CT measures the current flow in a known proportion. The output of the CT is connected to a meter, where the meter is programmed with the Ratio of the CT so that the meter can display the value in the actual Primary Value. CTs can be 'Current to Current' or 'Current to Voltage' transformers. In the utility world, most all CTs are Current to Current transformers. In the commercial world like TEDs or EMONs, the CTs are usually Current to Voltage transducers. This is neither here nor there for answering your question, but I state all this because electric metering is complex.
So, to your point or question as to why two meters show a discrepancy on your generator. On a single-phase, three wire service, L1-N is 180 degrees out of phase with L2-N. Your 120VAC load will be measured correctly on each phase. But, when you connect a 240VAC load, you are connecting between L1 and L2 and there is now neutral current flow. So, the current is flowing through both the CT you have on L1 and the CT that is on L2. However, the current flow on one of the CTs is 'backwards' from the L-N current flow that the meter is set up for.
Problem #1 - If you have 10A of P-P current flow, CT1 is showing +10A and CT2 is showing -10A.
Then there is the problem of Voltage
Problem #2 - Each meter is setup to measure only the 120VAC leg - P-N. Neither are actually measuring the P-P voltage.
Then there is the problem of Wattage
Problem #3 - Wattage will never be correct on either when 240VAC load is used because each meter simply multiplies the Voltage it measures time the current it measures. In the case of each meter when 240VAC load is connected, one meter will have 1/2 Voltage times the actual current flow while the other meter will have 1/2 voltage time the negative amount of the actual current flow. Most meters will not record reverse power flow, so the meter with the negative current flow will not record any wattage.
I know this has been a long and maybe confusing answer, but you won't be able to use two 120V, two wire meters to properly measure both 120VAC load and 240VAC load unless you get some serious technical advice from a metering pro.
My advice is to invest in the proper CT meter that is designed for 120/240VAC single-phase, three-wire electrical service.
PM me if you want more detailed information.
On a Typical home, a Form 2, self-contained meter is used and all of the current from the electrical service runs through the meter. If the meter is pulled from the socket, the power to the house is killed. However, there are a number of applications where it is unsafe or not desired to have all of the service amperage run through the meter. Thus, the Instrument Rated meter was created. An Instrument Rated meter utilizes 'Current Transducer' (CT) to sense the current running through the conductor by measuring the 'flux field' generated by the current flow around the primary conductor. The CT measures the current flow in a known proportion. The output of the CT is connected to a meter, where the meter is programmed with the Ratio of the CT so that the meter can display the value in the actual Primary Value. CTs can be 'Current to Current' or 'Current to Voltage' transformers. In the utility world, most all CTs are Current to Current transformers. In the commercial world like TEDs or EMONs, the CTs are usually Current to Voltage transducers. This is neither here nor there for answering your question, but I state all this because electric metering is complex.
So, to your point or question as to why two meters show a discrepancy on your generator. On a single-phase, three wire service, L1-N is 180 degrees out of phase with L2-N. Your 120VAC load will be measured correctly on each phase. But, when you connect a 240VAC load, you are connecting between L1 and L2 and there is now neutral current flow. So, the current is flowing through both the CT you have on L1 and the CT that is on L2. However, the current flow on one of the CTs is 'backwards' from the L-N current flow that the meter is set up for.
Problem #1 - If you have 10A of P-P current flow, CT1 is showing +10A and CT2 is showing -10A.
Then there is the problem of Voltage
Problem #2 - Each meter is setup to measure only the 120VAC leg - P-N. Neither are actually measuring the P-P voltage.
Then there is the problem of Wattage
Problem #3 - Wattage will never be correct on either when 240VAC load is used because each meter simply multiplies the Voltage it measures time the current it measures. In the case of each meter when 240VAC load is connected, one meter will have 1/2 Voltage times the actual current flow while the other meter will have 1/2 voltage time the negative amount of the actual current flow. Most meters will not record reverse power flow, so the meter with the negative current flow will not record any wattage.
I know this has been a long and maybe confusing answer, but you won't be able to use two 120V, two wire meters to properly measure both 120VAC load and 240VAC load unless you get some serious technical advice from a metering pro.
My advice is to invest in the proper CT meter that is designed for 120/240VAC single-phase, three-wire electrical service.
PM me if you want more detailed information.
Last edited:
I think you're exactly right. I use my meters for my EVSEs, or for simple loads like TVs and refrigerators which hang on one 120V supply, and the meter is not measuring anything but the entire load on the single circuit. You have a more complicated case. Did an electrician install your meters? I'd like to see a picture of them if you have any.
SDRick
Active Member
The 2 meters I installed were on a portable generator. The CTs for my house were installed in the main panel by an electrician and feeds into the demand side of the solar company provided monitoring system. Not much to really show in a picture.
SDRick
Active Member
I just picked up my model S and hooked up a spare meter I had lying around. My wall charger is connected with 2 120v legs and a ground. The meter is using one CT with one 120 V conductor passing through it. It looks like the meter is only reading exactly one half of the energy that is going into the car. (The wall charge is set for 48 amps).
Is there another way to wire the CT or do I need another meter, or do I just need to get used to multiplying by two?
Is there another way to wire the CT or do I need another meter, or do I just need to get used to multiplying by two?
@SDRick Is the meter capable of accepting 240VAC input? If so, connect your voltage leads to L1 and L2, so the meter measures the 240VAC.
SDRick
Active Member
Mike, I guess that would make sense. Thanks.
I am not sure how to safely provide 240 V to the meter. Currently, I have a 120 outlet just below the meter with 18 gauge lamp cord plugged into the 120 V receptacle providing power. (I also have a 30 dryer receptacle next to it). Do I bring the L1 and L2 voltage conductors to the ammeter from the panel or the 30 amp receptacle? In either case, what wire gauge is used since the meter draws such little amperage on its own and would it need its own circuit and circuit breaker?
Here is how I installed mine. I had provided a link to the actual enclosure I used later on in the thread.
Similar threads
- Question
