How Does This Current Sensor Close its switch?

[ThomsCircuit]

I don't understand your comment.
The track just looked like it could be routed more efficently and kept away from the AC end of the board.

Sorry friend. I was just being funny. I implemented the suggestion right away. Thank you.

 

[ThomsCircuit]

You can mount all components on the same side of the board if you want to.

Ok. Just taking all of the members posts regarding safety with L Voltage seriously. Thank you.

 

[ThomsCircuit]

Since most of the parts are through-hole, there is no added isolation from placing parts on both sides.

I know its not a perfect separation but I wanted to make every attempt possible to make this as safe as possible. And I do appreciate your input. this all helps me understand the project. Its my acknowledgement to the group that I am aware of the dangers and doing everything I can to be a responsible individual. Ive rethought where I'm going to place this circuit. I am going to move all but the CT back to the other side of the board. When I fabricate the enclosure that joins all the modules (AC & DC) ill post the results on this thread.

 

[ThomsCircuit]

The simulation shows the LED turns off when the AC line current falls below ~8.5 Amps.
But this is only a simulation. You'll need to test,tune, repeat, until the desired results are obtained.

That earlier post was a jab at a basketball game. I have the highest reguard for you and every member.
This post about simulation caught my attention but i was not ready to question it but id like to know how you simulated the circuit? The results of the simulation did not make sence to me. How did the results translate to 8.5 amps. Were thoes results obtained with the potentiometer at its lowest setting?

 

[ThomsCircuit]

With SMD subbed out for 2N7000 I routed the GND tracks. Here is the updated PCB with the copper pour.
Ive placed the CT and the 3Pin connector on the bottom of the board. This is so it can function when it is placed with the other modules and it can be adjusted if necessary.

 

[ThomsCircuit]

 

[eTech]

That earlier post was a jab at a basketball game. I have the highest reguard for you and every member.

good to be appreciated.

This post about simulation caught my attention but i was not ready to question it but id like to know how you simulated the circuit? The results of the simulation did not make sence to me. How did the results translate to 8.5 amps. Were thoes results obtained with the potentiometer at its lowest setting?

LTspice is using IRLAC (the CT primary current thru the load resistor RL) to obtain the equivalent AC (RMS) load current value.
I "step" the value of RL to change the load current, and for each step, IRLAC is recalculated. There are 5 steps and the results are shown in #114.
I(LED) is the current thru the LED. For step 3 it is about 21mA, indicating its "on". For step 4 IRLAC drops below 8.5 amps and the same step for the I(LED) shows a tiny amount of current flowing, meaning the LED has turned "Off". I'm gonna stop here because this will get complicated. Before this makes complete sense you'll need to study Ohms law for DC and AC circuits. Then learn the LTspice simulator.

When it comes time to test the circuit, you'll need to do a trial and error test to find the desired Pot setting for the target load current.
You'll need a way to safely measure the AC Line current.

 

[ThomsCircuit]

When it comes time to test the circuit, you'll need to do a trial and error test to find the desired Pot setting for the target load current.

Thank you for the explanation. Ill do some reading on ohms law. im sure there's a "book for dummies" out there.

 

[Pommie]

GlAD i CAME TO THIS DISCUSIOn late. Yup, caps lock won.

 

[ThomsCircuit]

Ive received the parts. Made a BB model and performed a test. It does work.
I don't think i have the equipment to provide data but with the POT at 0-75% and an 15 amp power tool the CT trips the mini relay and illuminates an led. Would love to know how to read the voltage and or current coming out of the relay

 

[eTech]

Would love to know how to read the voltage and or current coming out of the relay

Hi

Use a multimeter (?)
Not sure what you mean....

 

[ThomsCircuit]

Not sure what you mean....

well id like to read the voltage like you did in your simulation.
What would i set my meter at and where do i put the probes?
Ive got two leds in the circuit. one on each pole of the relays switch. They both have 470 ohm resistors. the NO pole is pretty dim while the NC is bright. Wondering if i need the same resistance for each.
I mean i adjust the Trim pot 0, 1/4, 1/2, 3/4, full. There is no change unless it is at 100% (led remains off) would like to read the mA

 

[eTech]

well id like to read the voltage like you did in your simulation.
What would i set my meter at and where do i put the probes?
Ive got two leds in the circuit. one on each pole of the relays switch. They both have 470 ohm resistors. the NO pole is pretty dim while the NC is bright. Wondering if i need the same resistance for each.
I mean i adjust the Trim pot 0, 1/4, 1/2, 3/4, full. There is no change unless it is at 100% (led remains off) would like to read the mA

Use a battery operated multi-meter so its internal power will be inherently isolated from live voltages.

The mosfet has a gate "threshold" voltage, vgs(th). When vth at the gate pin is higher than the spec'd vgs(th) of the mosfet, the mosfet will turn on and energize the relay. The mosfet vgs(th) is typically about 2.1 vdc, but varies slightly for different manufacturer's. The pot varies the voltage at the gate. Remember...it is designed to turn on the mosfet at 8A. Your load is 15A which is probably why its mostly on.

Before we troubleshoot, please post a schematic of the breadboard circuit so we're not guessing.

 

[ThomsCircuit]

Before we troubleshoot, please post a schematic of the breadboard circuit so we're not guessing.

 

[eTech]

I've marked your schematic with letters representing test points.

What voltages will be on pins:

SW1-1=GND
SW1-2=GND
SW1-3=12v

GND=Battery negative (or DC power -(minus))

I will update the attached when you provide info.

Edit: updated schematic per post #156 eek:)

 

[ThomsCircuit]

SW1-1=(-)

SW1-2= (-)
SW1-3=12v

GND=negative (-)

The image shows where sw1.1 & 1.2 lead to.

 

[eTech]

OK.

Assumption:
1. This is a standalone test. The breadboard circuit is not connected to any other circuits or PC boards.

Comments:
1. How are you measuring the AC load current?
2. What type of LEDs: forward current=?, forward voltage=?
If the LEDs are the same then the current limit resistors should both be the same value. LEDs are typically vf=2.0, If=20ma (but not always).
If they are typical LEDs, each limit resistor value should be about 510 ohms. A little larger (1K) is ok.
3. How do you want this to work? When should the LED turn on?
4. 8A of AC load current should produce a Pk voltage of about 4-5 volts.
The Pk voltage would be measured with your +probe at TP B, and your -probe at TP GND.
(With 15A AC load current, the Pk voltage is probably up around 8-9v)

Measure the Pk voltage (+probe at TP B, and your -probe at TP GND) with a known AC load current and report back.

 

[ThomsCircuit]

Assumption:
1. This is a standalone test. The breadboard circuit is not connected to any other circuits or PC boards.

Comments:
1. How are you measuring the AC load current?

Correct. standalone.
A bit embarrassing but i just guessed the amps would be 15 because its written on the tool.

I am reading tutorials on ohms law and recently the N-Channel Enhanced mosfet.
ill get the values to you tomorrow.
My wife is an on-call Ultrasound specialist for our local hospital and her 2020 car battery just died. Ive got to deal with it.

 

[ThomsCircuit]

2. What type of LEDs: forward current=?, forward voltage=?
If the LEDs are the same then the current limit resistors should both be the same value. LEDs are typically vf=2.0, If=20ma (but not always).
If they are typical LEDs, each limit resistor value should be about 510 ohms. A little larger (1K) is ok.

im using 3mm 20mA leds. green and blue. they have similar forward voltages of 2.5

3. How do you want this to work? When should the LED turn on?

i like how it works now but i know what you mean. Coming on at 8 amps is a good value. that would work with any tool i connect to it.
The blue LED represents the CT is ready
The green LED represents the CT is producing current, mosfet is draining, relay coil has been energized.

I have set the BB so the test points are all in one location. from left to right ABCD.
i found this volt meter i could hook up too. If im not mistaken red and black power the thing and i would connect the white wire to TEST Point B to display the current voltage.

 

[ThomsCircuit]

1. How are you measuring the AC load current?

Ive ordered a clamp meter. Seems to be the only way to measure AC amp draw.