How Does This Current Sensor Close its switch?

[eTech]

appears to be simple and straight forward. a diode and a cap. So this would act as a switch?

That is the peak detector - diode, cap,resistor. It basically stores the value of the peak voltage from the CT load terminals and is constantly refreshed as the voltage varies. The peak value varies based on the current flowing thru the CT---lower current--lower voltage, visa versa. I haven't tried this circuit arrangement but seems you could connect the gate of a mosfet to the detector output and set the voltage to the gate "as a threshold value" to turn the mosfet on/off. The mosfet drain could then drive a relay.

 

[ThomsCircuit]

Found this which shows how to implement the SCT-013. its difficult for me to follow but it does look like it needs no power source to output the voltage. If im right about this im liking it. Here is the URL

 

[rjenkinsgb]

That's just outputting an AC voltage at some level, then using the analog to digital converter in the Arduino to measure it.

It's not a self-contained "switch"

 

[ThomsCircuit]

I haven't tried this circuit arrangement but seems you could connect the gate of a mosfet to the detector output and set the voltage to the gate "as a threshold value" to turn the mosfet on/off. The mosfet drain could then drive a relay.

I like that as well. if you have time could you draw a sketch or modify the original?

 

[ThomsCircuit]

It's not a self-contained "switch"

would the SCT-013 combined with the modifications on post #78 work? Would it close the switch on my current circuit?

 

[eTech]

would the SCT-013 combined with the modifications on post #78 work? Would it close the switch on my current circuit?

Keep in mind that the current passing thru the CT cannot exceed the service power feeding it.
Most home outlets are 15Amp and some 20Amp max before circuit breakers pop.

So no point in buying a 50A current transformer for a 20 Amp service....use a 25A or 30A (just to provide some overhead)...it'll cost less.

 

[ThomsCircuit]

So no point in buying a 50A current transformer for a 20 Amp service....use a 25A or 30A (just to provide some overhead)...it'll cost less.

i agree. i selected the 30amp model

 

[ronsimpson]

would the SCT-013 combined with the modifications on post #78 work? Would it close the switch on my current circuit?

Yes. The nut that posted #78 has been wrong several time recently. Ask my wife.

The circuit from #72 is easy to turn on. A transistor will do that.

 

[ThomsCircuit]

Here the CT is directly driving a transistor.

So which CT is in this schematic. The SCT-013 has 3 pins and the CTVitec Current Sense Transformers ...1832 have 2pins

 

[ThomsCircuit]

Yes. The nut that posted #78 has been wrong several time recently. Ask my wife.

so the CT on your sketch #78 is SCT-013-030. can you explain which pins are used? there are 3
NOTE: that member E-Tech helped me with the construction of that project. i meant no disrespect.

 

[ronsimpson]

SCT-013-030

One of the wires in the connector is not connected. "Vacancy" You can check with a meter. The middle connection is open and the "tip" to "barrel" will have less than 10 ohms.

 

[eTech]

I like that as well. if you have time could you draw a sketch or modify the original?

Here's what I had in mind.
Its not very accurate but could be set within about 1/2 AMP of trigger point. The output is normally high and would go low when the desired CT threshhold is met. Of course, the mosfet load could be replaced with a relay. Haven't tested this because I don't have a CT, but I think it will work.

 

[ronsimpson]

but I think it will work.

eTech,
We are having a problem getting CTs that output more than one volt. (low cost small transformers) So we removed the full wave bridge and even removed the opto isolator that needs 1.5V. I see what you wan to do but the drop in D1 + Vgs_on of M1 is too high. A transistor will turn on at 0.6V and that should solve the low voltage problem.

If R1 is what the manufacture wants, then we get 1V at 30A but only 0.3V at 3A. By not using a resistor or a very high value we are allowing all the secondary current into the B-E of the transistor. Even at a very light load the voltage on the CT will pop up to 0.6V and turn on the transistor.

We are approaching 100 posts and it is impossible to know what has been tried way back in the thread.
RonS

 

[Diver300]

I've previously made a current transformer from a low power mains transformer. I used the mains-voltage winding as the secondary. For the primary, I removed the low-voltage winding, and put a single turn in its place as the primary.

I've used a current transformer like that to light an LED via a bridge rectifier. The voltage must have been around 3 - 3.5 V.

 

[eTech]

eTech,
We are having a problem getting CTs that output more than one volt. (low cost small transformers) So we removed the full wave bridge and even removed the opto isolator that needs 1.5V. I see what you wan to do but the drop in D1 + Vgs_on of M1 is too high.

At 25A the CT outputs a little more than 5V. I used the pot to be able to adjust the gate voltage above or below VGS(th).
At 8A the gate voltage is around 3.6v, so the mosfet should turn on.

I used a mosfet because I didn't want to draw current from the peak detector, but I also didn't want to go the Opamp route either.

A transistor will turn on at 0.6V and that should solve the low voltage problem.

If R1 is what the manufacture wants, then we get 1V at 30A but only 0.3V at 3A. By not using a resistor or a very high value we are allowing all the secondary current into the B-E of the transistor. Even at a very light load the voltage on the CT will pop up to 0.6V and turn on the transistor.

I showed a different CT than the one you describe.
But understood.....

 

[ThomsCircuit]

Here's what I had in mind.

Awesome.
Can i operate this at12v?
I see that your design has a hi/low output where my circuit needs to close to function. how would i integrate your design to work with mine?

 

[ThomsCircuit]

One of the wires in the connector is not connected. "Vacancy"

aahaaa. thank you

 

[ThomsCircuit]

We are approaching 100 posts and it is impossible to know what has been tried way back in the thread.

if i was searching for how to use a CT in a circuit i would read all 100 posts. There is a lot to learn here.
When i was a software developer I ran into a series of complex VB class files that allowed a user to upload files to a server. This was in 2001.
It was pages and pages of code to understand. it took me 2 months to make it work but i did it. Made good money selling it too.

 

[eTech]

Awesome.
Can i operate this at12v?
I see that your design has a hi/low output where my circuit needs to close to function. how would i integrate your design to work with mine?

What exactly is the "sensor switch"? Is it two wire holes?

 

[ThomsCircuit]

just need to know how to complete the switch E-Tech. this setup is cost effective too.