Current Transformer

[wekers]

Dear all, i can use current transformer for make a AC Short circuit breaker? or is a not good idea

 

[dr pepper]

Yep you can, and devices that use them often have such a function.

Your question is still a bit vague, more details please.

 

[wekers]

I want use in my workbench, in line AC jack with a short circuit protection, but i dont want use one power resistor in series to take voltage control for detect the short, now i see that have this teroid current transformer, but i never see before this dude.

 

[ChrisP58]

Yes, you can use a current transformer to make an isolated measurement of the current to your workbench.

The output of the current transformer needs to be terminated in a resistor to make a voltage. Rectify that voltage and feed it to a voltage comparator whose reference voltage represents your trip point. Use the comparator output to drive a relay that interrupts the bench AC power.

You will probably want to add a little delay because many devices have inrush current far greater than their operating current.

 

[wekers]

what you suggest for delay time, i say usec, milliseconds or seconds

 

[dr pepper]

There are ratings or curves for 'breakers, however 10 mains cycles would be a good start, 200mS

 

[MrAl]

Hi,

My suggestion would be for a progressive rating.
For example:
1 amp, 100ms
10 amps, 10ms

or if you have to use it with motors that have to start up (or something like that) you may want to make it faster for low currents and slower for higher currents.

 

[JimB]

At the risk of stating the blindingly obvious, why not just use a commercially produced MCB (miniature circuit breaker)?

Something like these:
https://uk.rs-online.com/web/c/fuses-sockets-circuit-breakers/circuit-breakers/residential-mcbs/
Readily available for the cost of just a few £, $, Euro, etc.

JimB

 

[wekers]

i will not exclude MCB and RCD too, but they i put on main workbench line, the all AC line jack will be individual with digital on-off push button power.

 

[dr pepper]

An rcd is a good idea for a workbench.

 

[wekers]

Well, i take one and begin tests, i see that samples, logic that are AC sample, then i ask, to convert DC, cant use diode because so small voltage, so i should be use one OP Amp or i look for AD736. What guys suggest

 

[ChrisP58]

Yes, you can use an op-amp configured as a precision rectifier to make DC from a small AC voltage.