RODALCO

I have successfully used an old 220 / 5 or 8 volt TX and wound a couple of turns of 1.5 mm² wire around the core.

The 8 volt or the 220 volt output can be used for the measuring circuit. In case of the 220 volt winding, put a resistor 100 or 470 ohm ½ watt across the terminals. A CT does not like open circuit voltages across it's terminals.

I used above system to check my outside security lights. lamp ON, LED ON. circuit working OK.
The LED is directly driven from the CT - TX. with an antiparrallel diode (1N914).

I made up 4 of these CT's to measure all 4 outside lights.

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Electricity, Electric clocks, Meters and Trains are great.

jbarnaby2000

Thats awesome, do these measure current or just an AC presense?? I really want to measure an AC current so I can determine how much power that circuit is using. I guess I am looking for something a little more consistant in the actual measurement. If I were just needing to detect an AC current(to just detect if something is on or not) I am sure your idea would be a wonderful one.

Thx again...

Boncuk

There are toroidal core inductors used in many dimmer circuits. You might want to look up those and make a primary winding using isolated electric cable. (of course the cross section fitting your needs)

The ratio should be about primary:secondary=1:10.

Hans

RODALCO

I use my circuit to detect a current flow in an AC circuit.

Current flow, lamp working, CT secondary drives LED on indicator panel in my hall.

In commercial metering proper CT's are used.
These are mounted at a link section in the main busbars of a switchboard.

Ratios may vary from 50/5 to 2000/5 Amps.
Generally these CT's have a seconday of 5 Ampères which will drive the kWh or kVArh metering via a testblock. The voltage potential is directly taken from the busbars via potential fuses.

On high tension sites also voltage transformers are used and the metering potentials generally run on 57½/100 or 63/110 Volts.
These values ascertain safe voltages on the metering equipment and create easy multipliers on 10 and 11 kV systems or multiples thereoff.
The yellow phase is usually earthed at the secondary of the VT.

__________________
There are more ways to get to Rome.

Electricity, Electric clocks, Meters and Trains are great.

tyru

JBaraby,

Did you ever get the circuit figured out? I'd be very interested.

I have a similar interest. Want to use a CT to measure current (0-5 A) on a motor to detect a jam condition using an a/d on a pic micro controller. I need a circuit to convert the AC volt to DC Volt (0- 5 VDC) for the pic input.

found this at the CR micro site.

http://www.crmagnetics.com/pdf/ancrct-4.pdf

Any help would be appreciated

jbarnaby2000

tyru,
It looks like that is a great solution to the current measuring solution I was looking for...the only thing, the application note above does not give you is any information on the zener diodes....any one have any ideas or suggestions on which zener's to use in that circuit??

Thx

crutschow

The zeners are to protect the op amp input so 4-6V zeners should be fine.

It should be noted that the circuit in the ap note generates a DC voltage equal to the peak of the AC waveform which is not a particularly accurate way to monitor power. Any noise or distortion (such as from dimmers) will give an inaccurate reading. To get the average (not as good as RMS but better than the peak), move the output resistor from ground and connect in series with the output filter capacitor. Note that this resistor should be at least 10 times larger than the sum of R4 and R5.

Ubergeek63

Any reason not to use this convenient $3 part?

http://www.allegromicro.com/en/Produ.../0713/0713.pdf

crutschow

Well, it's for DC current and he wants to measure AC.

tyru

The techs at CR Magnetics have been helping me with the values in the circuit. The CR8410 saturates at greater that 2 V. Recommended R1=20 ohm for a voltage of about 100 mV at a primary current of 5A. (Note that the 8410 has a compensated turn ration of 1012). R2=R3=10K. R4=10K R5=500K I was thinking of using a 470K with a 100K mutliturn trim resistor in series for R5 so that I can adjust the gain. Final reistor and capacitor act as a filter. They recommended a 10K with a 4.7 microfarad cap.

see diagram at: http://www.crmagnetics.com/pdf/ancrct-4.pdf