How Does This Current Sensor Close its switch?

[Diver300]

The G3VM-41 has a maximum forward voltage of 1.48 V. If you use Schottky diodes in the bridge rectifier, they will add around 0.4 V each, so two of those.

That means that you will need at least 2.28 V as the voltage across the current transformer.

You could just put two of the 57PR1831 transformers in series.

Alternatively, you could use one of the higher-rated transformers, and put more than one turn of the wire that you are trying to sense. The higher rated ones are larger, and have a larger voltage that they will supply.

If you use the 57P1833, it is rated to 150 A. If you wind 10 turns of the input wire around that, the 8 A input current will only have a 100:1 ratio, so the output will be 80 mA. The transformer is rated to have a 43.3 Ohm load, which gives a voltage of 3.464 V as a maximum. That should give you enough voltage to operate the G3VM-41, after any losses in the the Schottky diodes and a resistor.

 

[ChrisP58]

Here is a sorted list of some possible parts from DigiKey.
https://www.digikey.com/en/products...tm_source=google&utm_term=current transformer

 

[ThomsCircuit]

The G3VM-41 has a maximum forward voltage

I'm not using that. The project uses 4N32M
Don't know if that changes anything but I can get CT-57PR1832 (50amp) i could wind that a few times (10)
You say Schottky but which ones?
And thank you for the help

 

[ThomsCircuit]

Here is a sorted list

I thank you for that. They PCB styles that im looking at here in this list range from 5-30amp. Im going to use 57PR1832. Its rated for 50 amps. Nothing in my shop uses 50 amps. But all this has me considering adding a fuse to protect the circuit. If you could help me with that I'd appreciate it

 

[ThomsCircuit]

If you use Schottky diodes

Would these do.
1N5818 Diode Schottky 1A 30V
Or this one
1N5821 Rectifier Schottky Diode

 

[Diver300]

I'm not using that. The project uses 4N32M

The 4N32M has a maximum forward voltage of 1.5 V, so there is no significant difference.

 

[ThomsCircuit]

no significant difference.

Ok. Great. So which diode? 5818,5821

 

[Diver300]

Don't know if that changes anything but I can get CT-57PR1832 (50amp) i could wind that a few times (10)

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.

 

[Diver300]

Ok. Great. So which diode? 5818,5821

It really doesn't matter. You don't need anywhere near 1 A. You could use diodes rated at 100 mA if they are cheaper or smaller, but 1 A rated ones are not large or expensive

 

[ThomsCircuit]

It really doesn't matter.

Ok. So ill get that done and ill up the CT to 50amps then that should make this circuit complete. Should I protect the circuit with a fuse? Where would I add this?

 

[ronsimpson]

I have a collection of small CTs. I could not get them to light a red LED directly. The max voltage was well below 1.4V. When I moved to larger CTs I could get enough voltage to drive low voltage logic.

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.

 

[ronsimpson]

Should I protect the circuit with a fuse?

No you have 1/1000 of the line current. So we are talking mA.

 

[ronsimpson]

Do not order Current Transformers until you see the data sheet. I am looking at the 57PR1832 on ebay and they do not have a data sheet there. It appears the CT is designed for 100khz switching power supplies and will not work at 60/50hz. You need a "power line 50/60hz" transformer. The CTs come in two types, high frequency and power line frequency.

 

[ThomsCircuit]

Do not order Current Transformers

Ok. Ill wait. And thank you so much for assisting me

 

[ThomsCircuit]

The CTs come in two types, high frequency and power line frequency.

So I need the power line frequency?

 

[ronsimpson]

100A=100mA @ 4.2 volts
I can not find my data sheet on this one. Have used with micro controllers. I think I was getting 1 to 2 volts.
Data on this one is confusing. Might work.
I have a box of these but do not remember how they worked

 

[ThomsCircuit]

Data on this one is confusing. Might work.
I have a box of these but do not remember how they worked

Now your talking my language

 

[ronsimpson]

Another part and some interesting reading.

Some data on this one. Designed for 1V at max current. You may have noticed some CTs come with a resistor built in and some leave it for you. This data talks about using the part with out a resistor and then adding your 33 ohm resistor which appears to have a peak voltage near 2V. They want to measure a pretty sine waveform and you just wan to know if there is current. I think you can drive a "ac" opto isolator directly and maybe not have a resistor. The wave form will look distorted but who cares. The voltage will look almost square wave but the current in the LED will be a sine wave.

Note many of the CTs show 50 to 1khz or 10 to 2khz or 50/60hz. Do not use 100lhz to 300khz.

 

[eTech]

Hello

What about the CT driving a simple RC peak detector?
The peak detector input would be connected across the CT load resistor. The peak detector output would drive a mosfet switch with its gate connect to the wiper of a pot to adjust the trigger threshold. The mosfet switch output would be normally high then go low when the current exceeds the threshold setting, or drive a relay.

 

[rjenkinsgb]

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.

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.