I was reading another topic,
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?
For a small CT, one could remove the secondary from a filament transformer from RS - leaving some space for an insulated one turn high current sensing primary. The 110V winding left on becomes the secondary and needs to be loaded; ideally shorted. The secondary current times the turns ratio (secondary turns divided by primary turns) equals the primary (input) current.
Heh, now I'm slightly more confused... I want to measure the current drawn by the load, but what I gather from your explaination, I'm supposed to put the coil in series with it?
Perhaps there's more than one kind of CT? The kind I am familiar with is what I use at work: they look like black doughnuts with a pair of twisted wires and a ground coming off of them. Through the hole, we put our big 4/0 wire. The wires coming off of the CT are only 14 gauge, so I'm assuming it's relatively low current. It goes off to a low-voltage panel to monitor something-or-other. I don't know much about the low-voltage panel, and its doings.
So in my idea of a CT, it's not powered.
If I'm thinking of the wrong thing, then perhaps, could you draw a small diagram?
One day Dial-Up got dressed and committed to text
Think a bit :-) How can the current being measured pass through two wire that are joined together ?? Mebbe you should connect one of the heavy wires to the supply and the other end to the load ?? DONT ever forget to short the output winding if the ammeter or whatever is removed, since very high and lethal voltages can be developed if that winding is open circuit.
-- Regards ..... Rheilly Phoull
-- Regards ..... Rheilly Phoull
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!!
Read the thread
from April 22 on. We had a decent discussion there on it. THen we can fill in any details you don't understand.
John Perry
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