How to "sense" 1.5 Amp's of current?

[Diver300]

A current transformer works very well with AC like that.

The thing to remember is that it is a CURRENT transformer not a voltage transformer, so you must not leave it open circuit. The output current is set by the input current and the turns ratio. There is a maximum output voltage that you can take. The transformer specification should say that.

It is quite easy to wire the output to a bridge rectifier, then a capacitor and a resistor.

You get much less power in the resistor for the same voltage drop, and it is much safer.

 

[Krumlink]

@Khristie: How would I do that? I have never used current sensing before.

 

[Mikebits]

Her is a nice little Current sense. They work just like a transformer.
https://www.electro-tech-online.com/custompdfs/2008/07/P524.pdf

I think Digikey has some as well.

 

[Krumlink]

Mike that looks interesting, how could I use it?

 

[Mikebits]

Well, you have your AC line, which is primary and essentially 1turn going through the xformer which is the secondary say the secondary is 50 turns. So if 1 amp is running through the primary 1/50 current will run through secondary. Have a resistor load on secondary and using ohms law Vsense = Isense x Rload (E=IR). For given voltage across Rload you know what I primary is. Check out this link on transformer equations. May help explain.
Transformer Formulas

Keep in mind the voltage would still be AC.

 

[kchriste]

I'll try and reply before this thread gets locked.

@Khristie: How would I do that? I have never used current sensing before.

This datasheet shows how it is basically done at the bottom:
https://www.electro-tech-online.com/custompdfs/2008/07/3110.pdf
The I is the one wire of the AC lamp cord you pass through the core. It is also the amperage though that wire. They include a formula for you. So, if you put a 1K resistor on the output of the current transformer, you would get apx 0.48 volts RMS AC across the resistor for a current of 1.5Amps which agrees with the chart they provide you:
1.5A x 1000hm: / 3100 = 0.48V
You could amplify this voltage with an OpAmp (Or try a 10K resistor) and then rectify it to detect the 1.5A threshold.

 

[audioguru]

The tiny transformer is made for high frequency SMPS and might not work at the mains frequency.

 

[ecerfoglio]

The tiny transformer is made for high frequency SMPS and might not work at the mains frequency.

No, its made for 50 / 60 Hz (look at the data sheet at https://www.electro-tech-online.com/custompdfs/2008/07/3110-1.pdf

Its a CURRENT TRANSFORMER. It needs a resistor in parallel with the secondary (or else an ammeter) so it doesn't develop a high secondary voltage.

 

[Mikebits]

I think he was speaking about the one I suggested and I think he might be right. I should have looked more closely at the data sheet.