Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Using current sensors (transformers) for input to microcontroller

Status
Not open for further replies.
Please read my blog #18.
Instead of using 2 CTs in chain you can look for CT with turns ratio of 1:5000 or 1:1000 and 25A primary. They are available.
Alternatively if you take a 5VA transformer of lets say 120v to 12v the primary will have about 2000 turns. wind around the primary or secondary one turn of 25A wire and you have your home made CT. Because you don't know the number of turns you will have to put known current through the 1 turn, and measure the voltage on 100 ohm resistor across the primary (the 120V terminals, the 12V terminals aren't used at all) . The number of turns is the ratio of the current through the 1 turn to the current through the resistor.

2 CTs in a chain? You lost me.

I know there are other turn ratios available. I was trying the computation with the 50:5 that Ron had on hand. As this is a home project it is about low cost and using what I have or can get easily. (for work it is another story, the customer pays all the bills...usually)

P.S. What blog? I don't see any entries.
 
Sorry, I meant post #18 on page one. It explains that in industry inside instruments there is a CT of 5A primary and 5mA secondary. The burden resistor is on the 5mA winding. Instead of buying a CT of 5A to 5mA and getting another one 50:5 get one that gives 5mA for 25A. You can also make one like I described before. CT is a very easy to use component.
This is how it's used in industry: Sometimes there are several CTs in a chain.
t2.GIF
 
Our trains just passed each other. I was speaking of wrapping the source wire (carrying 25A) through the CT a second time.

On another note, I'm not following your words, but I do follow the math. The picture shows 50:5 and 5:1000, so 25A source reduces to 2.5A, then 2.5A is reduced by 5:1000 from 2.5A to 12.5mA. The description says "getting another 50:5", by which the 2.5A would be reduced by 50:5 from 2.5A to 0.25A.

That is unless I'm not following something.

In regards to post #18, if I was silly enough to use the 50:5 CT directly, are the method and values correct?
 
Last edited:
......................
You got me curious? So why use a burden resistor chased by a precision rectifier?
Now that you ask the question, I can think of no good reason. ;)
 
Our train just passed each other. I was speaking of wrapping the source wire (carrying 25A) through the CT a second time.

On another note, I'm not following your words, but I do follow the math. The picture shows 50:5 and 5:1000, so 25A source reduces to 2.5A, then 2.5A is reduced by 5:1000 from 2.5A to 12.5mA. The description says "getting another 50:5", by which the 2.5A would be reduced by 50:5 from 2.5A to 0.25A.

That is unless I'm not following something.
I made a mistake on the drawing the CT should be 1:1000 instead of 5:1000 . If you use CT of 5:50 then you have also to buy and to use 1:1000 that will give you total ratio of 1:10000 or 25A to 2.5mA .
The alternative is to buy a CT of 1:1000 or 1:3000 which is for 25A like this one:
https://uk.farnell.com/magnelab/sct-0400-025/current-transformer-splitcore/dp/1797759
or another one that is cheaper and easy to get. If you search on the net you will see what is on offer in your area.
 
In regards to posts 18/19 and 22/23, how is my math and method doing? You know what they say, if it seems too easy it is probably wrong.

I have a lead on a 1:2000 CT for $10.
 
If it can take 25A then it is good for you.
Albert Einstein said that the "equation of everything" must be simple like the one E=MC2
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top