I have 4 motion sensor lights at my house (one at each corner of the building), and would like to have an audible indication when one of them is activated. I have found a circuit at Bowden's Hobby Circuits for an "AC Line Current Detector". A coil of 800 turns of magnet wire on a U-bolt is used as an inductive pick up. The description of the circuit mentions detecting 50 watts or more. With a pair of 75 to 150 watt floodlights in the motion sensor light, I will be presenting 150 to 300 watts to be detected passing the coil. Might this be a problem, and can I modify the number of turns on the coil to avoid any problem.
Also, rather then wind four of these coils by hand, (one for each of my motion sensor lights) I found a low frequency current monitoring transformer at Jameco Electronics. Can I substitute this for the inductive pick up?
Here is the info on the AC Line Current Detector and the low frequency current monitoring transformer.
Thanks for any insight you might offer.
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AC Line Current Detector
(schematic attached as AC Detector.gif)
This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 - #35 magnet wire. The pickup could be made from other iron type rings or transformer cores that allows enough space to pass one of the AC lines through the center. Only one of the current carrying lines, either the line or the neutral should be put through the center of the pickup to avoid the fields canceling. I tested the circuit using a 2 wire extension cord which I had separated the twin wires a small distance with an exacto knife to allow the U-bolt to encircle only one wire.
The magnetic pickup (U-bolt) produces about 4 millivolts peak for a AC line current of 250 ma, or AC load of around 30 watts. The signal from the pickup is raised about 200 times at the output of the op-amp pin 1 which is then peak detected by the capacitor and diode connected to pin 1. The second op-amp is used as a comparator which detects a voltage rise greater than the diode drop. The minimum signal needed to cause the comparator stage output to switch positive is around 800 mV peak which corresponds to about a 30 watt load on the AC line. The output 1458 op-amp will only swing within a couple volts of ground so a voltage divider (1K/470) is used to reduce the no-signal voltage to about 0.7 volts. An additional diode is added in series with the transistor base to ensure it turns off when the op-amp voltage is 2 volts. You may get a little bit of relay chatter if the AC load is close to the switching point so a larger load of 50 watts or more is recommended. The sensitivity could be increased by adding more turns to the pickup.
Circuit found at Bowden's Hobby Circuits
(**broken link removed**)
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LOW FREQUENCY CSE187L
Jameco Electronics (www.jameco.com)
Description:
Designed to monitor current in low frequency applications. This Triad Magnetics part may be used to monitor current from .1 to 30 amperes at frequencies from 50 Hz to 400 Hz.
Technical Notes:
1. Turns ration: Primary to sense 1:500.
2. Suggested burden resistor: 60 ohms.
3. Typical output: 110 mV/Amp.
4. Primary DCR: 250µOhms max.
5. Sense DCR: 21 ohms max.
6. Constructed with UL recognized materials (Class B, 130¡C).
7. Hi-pot: 500 volts.
Also, rather then wind four of these coils by hand, (one for each of my motion sensor lights) I found a low frequency current monitoring transformer at Jameco Electronics. Can I substitute this for the inductive pick up?
Here is the info on the AC Line Current Detector and the low frequency current monitoring transformer.
Thanks for any insight you might offer.
--------------------------------------
AC Line Current Detector
(schematic attached as AC Detector.gif)
This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 - #35 magnet wire. The pickup could be made from other iron type rings or transformer cores that allows enough space to pass one of the AC lines through the center. Only one of the current carrying lines, either the line or the neutral should be put through the center of the pickup to avoid the fields canceling. I tested the circuit using a 2 wire extension cord which I had separated the twin wires a small distance with an exacto knife to allow the U-bolt to encircle only one wire.
The magnetic pickup (U-bolt) produces about 4 millivolts peak for a AC line current of 250 ma, or AC load of around 30 watts. The signal from the pickup is raised about 200 times at the output of the op-amp pin 1 which is then peak detected by the capacitor and diode connected to pin 1. The second op-amp is used as a comparator which detects a voltage rise greater than the diode drop. The minimum signal needed to cause the comparator stage output to switch positive is around 800 mV peak which corresponds to about a 30 watt load on the AC line. The output 1458 op-amp will only swing within a couple volts of ground so a voltage divider (1K/470) is used to reduce the no-signal voltage to about 0.7 volts. An additional diode is added in series with the transistor base to ensure it turns off when the op-amp voltage is 2 volts. You may get a little bit of relay chatter if the AC load is close to the switching point so a larger load of 50 watts or more is recommended. The sensitivity could be increased by adding more turns to the pickup.
Circuit found at Bowden's Hobby Circuits
(**broken link removed**)
--------------------------------
LOW FREQUENCY CSE187L
Jameco Electronics (www.jameco.com)
Description:
Designed to monitor current in low frequency applications. This Triad Magnetics part may be used to monitor current from .1 to 30 amperes at frequencies from 50 Hz to 400 Hz.
Technical Notes:
1. Turns ration: Primary to sense 1:500.
2. Suggested burden resistor: 60 ohms.
3. Typical output: 110 mV/Amp.
4. Primary DCR: 250µOhms max.
5. Sense DCR: 21 ohms max.
6. Constructed with UL recognized materials (Class B, 130¡C).
7. Hi-pot: 500 volts.