Short mains voltage without tripping the breaker?

[DJduck]

A weird question here: I want to burn some old motherboards with mains voltage but i don't want to trip the breaker. Can i use an old PFC transformer? I can use any step-down transformer, but they don't do much damage. So, can i use it? I have shitloads of them, going to use a 4 wire one.

[mariushm]

Re: Short mains voltage without tripping the breaker?

Get two transformers and tie the secondaries together .. as in 220-240v to 12-48v , then from 12-48v to 220-240v

Or just find some capacitors rated for 400-450v , charge them through a bridge rectifier then discharge them on mb

[kaboom]

Re: Short mains voltage without tripping the breaker?

Get a 220u, 330V AC oil cap. Connect one side to the line. From the other side of the cap to neutral goes the "device under test."

Short circuit current will be limited to ~15A.

[cheapie]

Re: Short mains voltage without tripping the breaker?

I always have fun with my 12V 200A battery charger. It happily melts screws and sets footlong lengths of 20AWG wire on fire in seconds. I take it you want sparks though, not just burning... for that, wire some heaters in series with the load as a ballast. Assuming that space heaters are 1500W there too, you'll want one for ~7A, or two in parallel for ~15A. You can also do multiple heaters in series for lower current.

[DJduck]

Re: Short mains voltage without tripping the breaker?

So a PFC will not work? Also, i think the 220-12-220 won't work, since the step up should get fucking hot when shorted? But, isn't a PFC just a 220-220 transformer? And i will not make any load by heaters I just want to quickly blow some shit up, and mains should do. So, 220 from wall to pfc input and pfc output to the device being "tested" Mariushm, your idea is good, but i should find some 400-500v caps first, since i don't want to scrap any good psus. Also, when charging them, how long should i charge them for? And can i use multiple 200-250v caps? Another idea: Get two mains step-down transformers, take the primary off from one of them, and then from the other, remove the secondary. Then wrap the Primary to the other ones secondary.

[DJduck]

Re: Short mains voltage without tripping the breaker?

Ok, i think i have found a candidate. I think i found a mains isolation transformer from an Enhance ENP-0730. It says PFC on the case, but the fucker is wired straight to the 220-115v switch and has four thick wires. Should i connect it to the wall outlet and see what AC voltage comes out? Then short it, and see what happens. Any ideas?
Edit: It's marked as: RD-IF008 B XP 0304. 0304 should be a date code.

[budm]

Re: Short mains voltage without tripping the breaker?

What do mean by PFC? Power Factor Correction?

[kaboom]

Re: Short mains voltage without tripping the breaker?

Ok, i think i have found a candidate. I think i found a mains isolation transformer from an Enhance ENP-0730. It says PFC on the case, but the fucker is wired straight to the 220-115v switch and has four thick wires. Should i connect it to the wall outlet and see what AC voltage comes out? Then short it, and see what happens. Any ideas?
Edit: It's marked as: RD-IF008 B XP 0304. 0304 should be a date code.

Sounds like a combination autotransformer(sets 12/240) / line frequency PFC inductor. Or even just a tapped inductor. You may think you'll get what you want, but you're gonna blow it up if you do what you posted. It only has a rating of a few amps.

I wouldn't go ahead and "see what happens."

You should also realize that if you take an isolation tx and short it out, it too will eventually overheat.

[DJduck]

Re: Short mains voltage without tripping the breaker?

I know it will overheat. I'm going to see, maybe i can get a high voltage / high amp psu from my friend.

[DJduck]

Re: Short mains voltage without tripping the breaker?

How about i use an old LCD inverter? Also, i could just bring the boards to BaseMetal, they pay 5eur ~7 bucks per kg.

[ben7]

Re: Short mains voltage without tripping the breaker?

Easier way: use an electric heater to limit the current. The electric heaters typically use around 1500 watt of power, and that will be the maximum you could draw, draws the breaker won't trip. Think of it like as a resistor, that limits the current for an LED.

[momaka]

Re: Short mains voltage without tripping the breaker?

Easier way: use an electric heater to limit the current. The electric heaters typically use around 1500 watt of power, and that will be the maximum you could draw, draws the breaker won't trip. Think of it like as a resistor, that limits the current for an LED.

+1

I do this all the time when I need to test a device that will require lots of power (too much for the "dim bulb" trick anyways), but still won't trip my breakers if something goes wrong.

Also can use this to "weld" thin wires together. I just used a space heater today set on low (I think only 700W at 120 VAC) to weld some type K Chromel/Alumel thermocouple wires. Worked great.

[tom66]

Re: Short mains voltage without tripping the breaker?

You sound inexperienced.

A PFC circuit on a power supply is connected to the mains, so any short circuit on its output goes back to the mains.

You need to be careful when trying "random" things out because you could electrocute yourself or start a fire. Especially when you're talking about mains electricity, which is no joke.

An electric heater will actually set the maximum power at 750W not 1500W (read up on maximum power theorem, two equal resistances gives the maximum power), but into an actual short circuit the power will only be a couple of watts... good for testing, bad for what you want.

A variac is also fun, and can be used to limit the current by means of limiting the voltage (but take care not to damage the variac on overload.) I've used one before when powering up a dead-short power supply, but not destructively, just to find a short.

If you want a "safer" destructive method, you can do this on a concrete surface (fire hazard, be careful): Wire a computer SMPS so the 5V and 12V are switched. This kills the motherboard rather quickly. If you want to nuke the chipset, wire 3.3V to 12V, too. For bonus points wire the 12V in reverse polarity to the VRM to watch those MOSFETs and caps cook, if the supply can take it.

[momaka]

Re: Short mains voltage without tripping the breaker?

An electric heater will actually set the maximum power at 750W not 1500W (read up on maximum power theorem, two equal resistances gives the maximum power), but into an actual short circuit the power will only be a couple of watts... good for testing, bad for what you want.

True.

Although, if the short circuit is not able to pass all the current, then it will heat up and eventually burn.

Like I mentioned, it's perfect for welding TC wire together. Technically when I run the wire in series with he heater, it's a short circuit at first but quickly heats up and glows. Some of the thinner TC wire straight up explodes and throws sparks with heavier loads.

If you run the mains across thin traces on the motherboard, expect to see lots of smoke.