electronic circuit-breaker for workbench

[redwire]

What are you guys using to limit explosions when fixing mains powered stuff? Fuses are a hassle

I was thinking of making an electronic circuit-breaker, something you can dial in trip amps, with a latching relay. For 120VAC mains.
The LM1851 is obsolete but I found it some old GFCI's. I'd gut an old GFCI and put a line-current CT in it with a potentiometer.

[cpt.charlie]

Re: electronic circuit-breaker for workbench

Use the light bulb trick.

[Longbow]

Re: electronic circuit-breaker for workbench

You always use an isolation transformer on off-line switching power supplies or other devices that require you to poke around in the mains section. This precaution is for your safety and to save the test equipment, which by code is required to be grounded w/r to the mains. Getting power from a GFI isn't a bad idea either since it monitors current in the ground wire. If no Variac is available, the 100 watt light bulb can limit current while testing something with a major short circuit. The light bulb however has nothing to do with safety. Do it right an get an isolation transformer.

[capwizard]

Re: electronic circuit-breaker for workbench

Ressettable Electronic Fuse (Circuit Breaker) Circuit for Securing General Power Supply
http://www.deeptronic.com/ressettabl...-power-supply/
Use R3 current resistor to turn on PNP (0.6v) then turn on the protection relay, is A pretty simple design. If you can change to NPN , MOSFET, IGBT will be better.


Transistor as a Switch
http://www.electronics-tutorials.ws/...or/tran_4.html

AC_CIRCUIT_BREAKER
http://www.seekic.com/circuit_diagra...T_BREAKER.html

Ultra Fast Acting Electronic Circuit Breaker Engineering Projects
https://www.youtube.com/watch?v=GQa9W6rxeEs

Ultra Fast Acting Electronic Circuit Breaker

[redwire]

Re: electronic circuit-breaker for workbench

The series lightbulb trick works for me if only if you have a primary-side dead short. For other problems, I have damaged gear using it.
100W lamp measures 10ohms so 12A inrush current and anything in between down to the 0.83A hot after 500msec or so. Lightbulb does limit current but how much you can't really tell and it's sluggish with negative resistance too.

Lightbulb trick can also make a mess for troubleshooting.
SMPS IC's have a complex state-machine in them. Example NCP1234 which gets lost in soft-start, undervoltage lockout and over-current cycles when you have a lightbulb in series.

For better current-limiting, I'm going to make an electronic circuit-breaker like capwizard's post - a small CT and op-amp/comparator, and maybe add in a ground-fault CT- although that is a useless feature with an isolation transformer which is a second need for bench work.

I need to connect my scope to the -ve DC bus in SMPS as it's the only way to look at waveforms.
*** I find some PFC circuits go unstable if you swap in too low an ESR capacitor.

An isolation transformer is a must to do that, or maybe a decent differential scope-probe but that is expensive. I've been using two scope channels and subtracting them but it's so awkward.