How Does This Current Sensor Close its switch?

Diver300 · Jul 24, 2021

rjenkinsgb said:
Diver300 said:

The CT-57PR1832 appears to have a maximum current rating of 60 A. You should not exceed that, so if your maximum load is 14 A, you could wind the transformer with up to 4 turns.

The maximum voltage on the CT-57PR1832 is 3.498 V, so that should work.

Click to expand...

NO! Not for this application, anyway.

It is 1000:1 regardless of maximum rating. More primary turns will reduce the ratio, giving more secondary current for a given primary current.

Four turns would mean 60mA out for 15mA load, far too much for the opto isolator.

Stick with one pass of the primary wire through the transformer.

I think you mean that four turns would give 60 mA out with a 15 A load.

The 4N32M has a maximum forward current of 80 mA, so 60 mA should be OK and not destroy the 4N32M.

The current will also be reduced by the resistors in parallel, and there may be a zener to bypass the current.

rjenkinsgb · Jul 24, 2021

Diver300 said:
I think you mean that four turns would give 60 mA out with a 15 A load.

Indeed, typo.

There were mentions of other devices with lower maximum ratings, also I seem to remember it having a minimum current threshold requirement as well, which would be made rather lower by multiple primary turns.

ThomsCircuit · Jul 24, 2021

ronsimpson said:
I was assuming we wanted a relay output and I could not find a "ac" SS Realy. I really wanted to drive a "ac" isolator directly. No diodes. This has a problem that most isolators are fast and will turn off during the time when current crosses zero. If we can live with a transistor output then loading its output with a capacitor will slow down the part so it will not pulse twice every cycle of the power line.

The information is very helpful and the testing you have done.
does it matter if the project uses a relay or a transistor? as long as it closes the switch then to me (expertise limited) im ok with adding a few additional components to govern the 4N32
The TLP182 needs DC voltage to function. i was wanting to avoid having to power the circuit. Unless that is the goals of this project are becoming challenging due to the expense and/or components currently used id be ok with redesign.

ThomsCircuit · Jul 24, 2021

rjenkinsgb said:
There were mentions of other devices with lower maximum ratings, also I seem to remember it having a minimum current threshold requirement as well, which would be made rather lower by multiple primary turns.

The knolwedge i have gained just on the discussion is a lesson by itself. Since you provided the original schematic I will defer to your judgment on what is added / replaced. Its been advised to replace the CT with the 50AMP part

ThomsCircuit · Jul 24, 2021

ronsimpson said:
Some data on this one. Designed for 1V at max current.

SCT-013-050 is relatively inexpensive. how would i implement this?

ThomsCircuit · Jul 24, 2021

SCT-013 datasheet

ThomsCircuit · Jul 24, 2021

eTech said:
What about the CT driving a simple RC peak detector?

Im going to look this up

ThomsCircuit · Jul 24, 2021

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

eTech said:
simple RC peak detector

ThomsCircuit · Jul 24, 2021

I want to know if the design with the more powerful CT (50AMP) with a single pass (no loops) the additional resistors added, and 1A diodes for rectifier (1N5817 1A 20V). There are some concerns that the CT-57PR1832 is designed for 100khz switching power supplies and will not work at 60/50hz.

The SCT-013 sounds like a viable option if it solves any problems. id need to know how to utilize the output so it acts like a switch.
I found this breakout board that identifies the pinouts.

ronsimpson · Jul 24, 2021

ThomsCircuit said:
does it matter if the project uses a relay or a transistor?

I think we need to talk about this.
A relay had metal contacts. Much like a light switch. They are ratings for how much voltage and current it can switch. Also rated for motors differently than light bulbs.
A Solid State relay is almost the same but ...... The ones I pointed to are low voltage and low current. 30V 1A I don't remember. There are higher voltage and current versions. I don't know what you want to do with the output.
A Transistor does not know what to do with AC. It should only work with DC and what you are looking at are less than 30V and 0.1A or less. (read the data sheet)

We need to understand the end thing. A 110Vaclight bulb, 1hp motor, door bell, LED?

ronsimpson · Jul 24, 2021

ThomsCircuit said:
I found this breakout board that identifies the pinouts.

The CT has two pins. The breakout board was designed to be used by a little computer. A very different project.

ThomsCircuit · Jul 24, 2021

ronsimpson said:
We need to understand the end thing. A 110Vaclight bulb, 1hp motor, door bell, LED?

the end thing would be that it triggers this switch in this circuit

ThomsCircuit · Jul 24, 2021

ronsimpson said:
The breakout board was designed to be used by a little computer. A very different project.

i really dont want to use it. i really like the current design.

ThomsCircuit · Jul 24, 2021

ronsimpson said:
We need to understand the end thing. A 110Vaclight bulb, 1hp motor, door bell, LED?

sorry i pressed enter and it submitted
The workshop circuit is closed it engages a switching relay (12v) which triggers a larger relay which completes the AC circuit.

ronsimpson · Jul 24, 2021

ThomsCircuit said:
The SCT-013 sounds like a viable option

If you get the parts with the build in resistor they will output a voltage from 0 to 1V with a current of 0 to (rated current).
If you get the one with no resistor then you have some options. "100A=50MA" so it appears to be 2000:1 It was designed to output 1V and needs 20 ohms to turn 50mA into 1V. But if you used a 10 ohm resistor then the output would do 0-0.5V. Or a 5 ohm --> 0 to 0.25V. If you put a 40 ohm resistor it would go from 0 to 2V but at some point it will saturate. Probably it will not output more than 1.5V. I don't know. The data sheet "1V".... we do not know if that is peak or rms or what. If it is average then the peak will be 1.4V.

ronsimpson · Jul 24, 2021

ThomsCircuit said:
the end thing would be that it triggers this switch in this circuit

A transistor output is just fine.
New idea soon.

ThomsCircuit · Jul 24, 2021

ronsimpson said:
If you get the parts with the build in resistor...

All but one have a built in sampling resistor

ronsimpson · Jul 24, 2021

Here the CT is directly driving a transistor. Almost any small transistor. D4 is to protect the transistor. The transistor will be on for the positive half of the power line and will not see the negative half. (on for less than 50% of the time) but C2 will hold the output low for a while. I have not had time to think this out but lets think on no isolator. The transistor will turn on if it gets over 0.65 volts and needs almost no current. I like this because most CTs can make 1V and we don't care about 1.5V or above. The SCT-013 will work with or with out a resistor.

ThomsCircuit · Jul 24, 2021

ronsimpson said:
A transistor output is just fine.
New idea soon.

ok. thank you.

ThomsCircuit · Jul 24, 2021

ronsimpson said:
The SCT-013 will work with or with out a resistor.

so which SCT-013 would you recommend? or can i use the CT in the original schematic? 57PR1831 (25A) or 57PR1832 (50A)

How Does This Current Sensor Close its switch?

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