Electronics > Beginners
240vac Electronic Fuse
DarkZero:
Hello all!
every now and then i repair some sort of smps psu and so far i have been using incandescent light bulb as my current limiting when I'm testing it but lot of times i change from one light bulb to another which breaks the seal between the glass and metal part so they explode at times sometimes ruining thing i was working on.
is there any reliable AC electronic fuse circuit something like 10mA to 1A ? i had a look in those big 300W variable resistors but their price is just to much for what I'm doing.
kripton2035:
something like this : http://nutsvolts.texterity.com/nutsvolts/200909?folio=42&pg=42#pg42
kripton2035:
and the code is here : https://www.nutsvolts.com/uploads/magazine_downloads/refuseable.zip
Gyro:
The useful thing about using a bulb is its positive temperature coefficient. It will pass more current initially before increasing its resistance as required (hence 'dim bulb tester'). You want a current limiter, not a 'fuse'.
I would suggest two or three bulb holders and ordinary light switches. That way, you don't need to keep unscrewing bulbs. Probably quicker, easier and safer to implement too. 30 minutes tops.
T3sl4co1l:
Mind that the above article is a trip relay; quite useful by itself, but it won't limit current, and relays aren't fast enough to save fast-blow fuses, let alone transistors. (Diodes and thyristors are probably okay, assuming they are fused appropriately.) It would work well in combination with a light bulb (or other load resistance) bank.
To do better, you need a current limiter. I'd like to make one myself, actually; a resettable, current limiting fuse, that is. I've already made a smaller version, 30V 20A, which works very nicely, fits in a handy enclosure, and is battery powered.
The challenge is, to withstand mains power, the circuit must dissipate many kW at a time, and it may occasionally be subject to overvoltage swells and surges. (Wouldn't want your project suddenly kicking on full throttle just because someone turned on/off their air conditioning nearby, or because it's stormy outside!) Semiconductors can't handle this for long at all. There aren't many other things you can dump that energy into (big resistor, stack of MOVs?), and none of them are very compact or reliable. It would probably cost a few hundred dollars, though.
Tim
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