Current transformer

[alphacat]

Thanks again Hero.

You have an idea how much current an house might draw?

This CT is 50A rated, you think that an house might draw more than that?

 

[Reloadron]

Looks like you are in France so I would venture 220 Volt mains. Unless it is a very large house with multiple high current appliances running, I would venture less than 50 Amps. Considerably less. (50 Amps x 220 Volts = 1100 Watts) which would be quite a bit for a residence at any given time.

Do you have a link or anything as to information where you bought this from?

Ron

 

[Hero999]

Last time I measured the current my house was using it was less than 10A but there will times when it's much higher than that such as when the electric oven is being warmed.

I suggest you look at the highest power rating device and add a bit more but I think 50A sounds reasonable for a worst case scenario.

 

[alphacat]

Hey guys.
The largest appliance I got here is a 12A air conditioner.
I guess that 50A are indeed enough, moreover it is said in the specifications sheet of the CT that the max current is 75A so its more than enough.

I made contact with a Chinese salesman which sent me the specifications of this CT.
Why do you ask Ron?
Isnt it a common way to purchase Chinese staff?

 

[Reloadron]

I made contact with a Chinese salesman which sent me the specifications of this CT.
Why do you ask Ron?
Isnt it a common way to purchase Chinese staff?

The reason I asked was in the hopes that more information was available out there on the unit. Just more a curiosity thing. I was hoping for a more informative data sheet, however, the specifications you listed were pretty adequate.

Once things are setup you have to return and post the results you get. This is something I have always wanted to get around to and never did manage to get around to. Maybe someday.

I do know that I could run the house on a 4,000 Watt generator less the wife running the electric drier and excessive microwave use. Lights and small electronics (TV, Cable, etc.) ran fine on 4 KW. I have since placed a larger automatic generator in the yard.

Ron

 

[MrAl]

Hi again,


You can calculate the turns ratio by using that data sheet, which i think you already did.

One way is to start with the value of 100 ohms and noting on the data sheet it says 2 volts at 60 amps primary current.
Assuming one turn on the primary, 2v with 100 ohms is simply 2/100 amps, which is 0.020 amps on the secondary,
and with 60 amps on the primary that means the turns ratio is 60/0.02 which comes out to 3000 as you found.

If you want to use this device to measure power factor you will note that phase angle becomes an important quantity
that you need to measure. Since the device may have some inherent phase shift already (large turns ratio) it is
probably a good idea to test it for that before you use it for making measurements. To do this you can apply a known
voltage and known resistive load and look for any phase shift and take this phase shift into account when you make the
final measurements.
As others have said, you should be able to calculate the power factor once you measure the current and voltage and take
the phase angle between current and voltage into account.

In the USA, 100 amp main breaker panels used to be common, but over the past 20 years or so they increased the common
panel up to about 200 amps i think. That's for 120vac though, so at 220vac 100 amps is probably common, or at least it
should be That means 100 amps will probably be the max for a house but i would be surprised to see a house draw that
much really unless of course you have electric heating and the heating is running.

 

[alphacat]

@Ron
I will post up the results once I get it, count on that

@MrAl
Thanks for these great advices.

100A is indeed a huge current for an house to draw.
I mean, most air conditioners dont draw more than 16A, so you must have there 6 such devices in order to get near the 100A level.

In order to measure the power factor error, I need to connect a primary load with a known power factor, say a power factor of 0.7, and a resistive secondary load, say 100ohm, and expect the phase between the primary voltage (mains) and the secondary current to generate a power factor of 0.7?

**broken link removed**

 

[MrAl]

Hi again,


Yes you can do it that way, but isnt it easier to use a pure resistive load as the primary load? That way any phase shift is easy to spot right?
If you have a load where you know the phase shift then you can test it again using that load and see if your calculation is correct.

BTW with homes with electric ranges and an electric oven and also electric heating i would guess that the current draw could be very high. Ranges are usually around 1100 watts and that's for the small ones, so if all four ranges are going that's 4400 watts just for that, and then the oven and the heating could add really a lot to that number. A lot of homes in PA have electric heat and ranges too.

 

[alphacat]

Hi MrAl.

Yes you can do it that way, but isnt it easier to use a pure resistive load as the primary load? That way any phase shift is easy to spot right?
If you have a load where you know the phase shift then you can test it again using that load and see if your calculation is correct.

The problem is to find an high resistive load.
If I connect a simple 100Kohm resistor, the primary current will be very small, and the secondary current, which is 3000 times smaller, will not be measurable. You see?

BTW with homes with electric ranges and an electric oven and also electric heating i would guess that the current draw could be very high. Ranges are usually around 1100 watts and that's for the small ones, so if all four ranges are going that's 4400 watts just for that, and then the oven and the heating could add really a lot to that number. A lot of homes in PA have electric heat and ranges too.

Would you recommend on a CT with higher current rating? say 100A rated?

 

[MrAl]

Hi again,


Oh no i wasnt implying that you should look for a higher current device as your house probably doesnt draw that much current unless you really are using a lot of electric stuff like i mentioned.

Yes it may be a problem finding a good load for the testing, but that's life i guess. You might try one of those small electric hot plates or maybe get some heater cones. The heater cones are available in 1000 watt units so you can get a few and some good lamp sockets, if you care too I dont know what they cost each anymore though. Maybe a couple toasters and some baseboard heaters? he he.

Did you consider the hall effect devices yet? You could check the spec's on them and if they look good enough you can use them to calibrate your CT even if you dont want to use the HED permanently.

 

[alphacat]

Yeah, I'll take some heaters which draw all together around 16A.
Using a 20Ω resistor at the secondary circuit, the IC should be measuring ~0.106V on that resistor (16A / 3000 * 20Ω ≈ 0.106Vrms).
The IC cannot measure more than 250Vpeak, so I dont want the resistor's voltage to exceed that level.

 

[alphacat]

Hi.

I was trying to look for other CTs in mouser and got the following list of Transformers.
Could you tell me please which one should I pick?

Thanks!

**broken link removed**

 

[MrAl]

Hi,


I could not find any on Mouser that were less than about 40 dollars. Perhaps someone else can find one.

 

[Reloadron]

If you just want a simple 50:5 or 100:5 current transformer like these I would be happy to send you one. I have a bucket of them. We replaced literally hundreds of them with HAL Effect 4-20 mA transducers so being a dumpster diver (Garbage Picker) I spared them from a landfill.

The link is to Allied Electronics and I have no clue if they ship to France. Problem is I have no clue how to sent a CT to France either. I mean if I can simply take the thing to the Post Office and send it to France then no problem but if it involves customs on your end then I am clueless. What do I put on the post mailer? Used CT value $10.00 USD? I don't want anything for it, I just don't know how to get it from point A to point B?

Ron

 

[kinarfi]

In looking for CTs, don't forget to check your local electrical wholesaler. That who probably sell the most, and should have the best supply and prices.
Kiarfi

 

[alphacat]

Hi guys.

Thank you so much Ron for your kind offer.
Thats ok, I'll be receiving the Chinese CTs in less than 2 weeks.

Thanks for the good advices!

 

[MrAl]

Hi again,


You know you can 'roll your own' too right?
You take an old wall wart, rip the secondary turns off, replace it with 1 turn of heavier wire or multiple wires, and there you go.
The original primary becomes the secondary, the primary is that one turn.
The only drawback is you dont know what turns ratio you are getting unless you test it.

I used a converted wall wart as a current transformer for about a year or so as a current monitor for a kitchen appliance.
I also used a home made brass shunt for a while too.