How Does This Current Sensor Close its switch?

Status
Not open for further replies.
eTech said:
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.
Click to expand...
Sorry friend. I was just being funny. I implemented the suggestion right away. Thank you.
 
ChrisP58 said:
Since most of the parts are through-hole, there is no added isolation from placing parts on both sides.
Click to expand...
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.
 
eTech said:
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.
Click to expand...
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?
 
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 said:
That earlier post was a jab at a basketball game. I have the highest reguard for you and every member.
Click to expand...

good to be appreciated.


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.
 
Last edited:
eTech said:
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.
Click to expand...
Thank you for the explanation. Ill do some reading on ohms law. im sure there's a "book for dummies" out there.
 
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
 

Attachments

  • 20210813_121003.jpg
    1.6 MB · Views: 269
eTech said:
Not sure what you mean....
Click to expand...
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.
 
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:)
 
Last edited:
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.
 
eTech said:
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?
Click to expand...
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.
 
im using 3mm 20mA leds. green and blue. they have similar forward voltages of 2.5

eTech said:
3. How do you want this to work? When should the LED turn on?
Click to expand...
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.
 
Status
Not open for further replies.

Similar threads

G
  • Question
Replace Hall sensor with switch in Tuya door/window sensor
Replies
9
Views
3K
rjenkinsgb
U
  • Question
What type of sensor is this?
Replies
2
Views
1K
JimB
A
  • Question
Finally got my heat sensor / controller / heating element working.. now, how can I add an on/off switch?
Replies
1
Views
1K
ZipZapOuch
  • Question
How to Create a 12V Breathing/Fading LED Circuit with My Current Components?
2
Replies
33
Views
3K
Lightium
T
  • Question
switch circuit
Replies
13
Views
2K
ZipZapOuch
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…