Dial-Up said:
I was reading another topic,
http://groups.google.ca/group/sci.e...db?q=make+an+ammeter&rnum=37#010987b260d96bdb
and was wondering: How exactly do you make the CT described?
I understand that there'll be your two coils, one that the wire you
want the measure the current of goes through, and then the other which,
I'm assuming, goes to your load. What I don't understand is what to do
with the leads of the first coil. Do I just connect them together?
You make a CT by winding a large number of turns of wire onto a core,
usually a toroid. But in your case, to make things simple, a small filament
transformer would do just fine.
Remove the secondary winding from the transformer. The transformer's
primary winding becomes the secondary of the CT.
In the space left by the winding that you removed, wind a single turn of
wire. This becomes the CT's primary.
Connect a resistor of 10 - 100 ohms across the CT secondary.
Connect one end of the CT primary to one side of the AC source.
Connect the other end of the CT primary to the load. This load will be the
device that you want to measure the current that is passing through it.
Connect the other end of the load to the other side of the AC source.
When you apply power from the AC source and turn the load device on, the
current that is passing through the load will be transformed by the CT to a
voltage impressed across the 10 - 100 ohm resistor in the proportion of E =
(I(load) / N) * R
where
N = turns ratio of the CT, which will be the number of turns on the
transformer's secondary (the original primary), assuming a single primary
turn
R = specific value of the resistor across the CT secondary
The circuit will look like this (viewed with a fixed pitch font such as
Courier):
CT
AC --------+ +--------+--------+
Source ) || ( | |
) || ( / |
) || ( \ |
1 turn ) || ( N / R AC Voltmeter
) || ( turns \ |
) || ( | |
+---+ +--------+--------+
|
|
|
Load
|
|
|
AC -----+
Source
--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)
Never take a laxative and a sleeping pill at the same time!!