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Is it safe to hook this transformer up directly to the AC mains? Answered

I bought an old high voltage transformer from the internet a while back. It seems to work well at AC frequencies (anything higher and it doesn't work at all), and can make some pretty good arcs. When hooked up to a power outlet with 360 ohms of resistance in series with it, it produces a 1.3 cm blue arc. When using a 30 ohm resistor, it makes crazy arcs with a bit of orange (I'm using four 5 watt 120Ohm resistors in parallel, and they still overheat). None of these tests caused the transformer to heat up at all, though. Would it be a good idea to directly hook up the transformer into a power outlet? Would it burn up the transformer and/or my house?

A couple other things about the transformer:
The primary has around 2 ohms of resistance, but I don't know anything about its inductance.
The whole thing is pretty hefty and has a fat iron core.
If you brush a wire from a 12 volt power supply across the primaries, you can get a nice spark c:

Any help would be appreciated. 



Best Answer 8 years ago

You can wire it in series with a 60 watt incandescent light bulb. That way if there is not enough resistance or there is a short the light bulb will still protect you from a direct short. The light bulb will only reduce the voltage a small bit.

You still have to protect yourself from the mains voltage.


8 years ago

What is safe ??
Iv seen that xfmr before,
Are we talking 60hz 120 VAC scary
or 50hz 220 VAC death wish

This type of xfmr will probably short internal turns and char itself .



Answer 8 years ago

120 VAC scary. Wouldn't the inductance of the primary stop the transformer from drawing too much current? If not, is there any convenient way of reducing current draw?


Answer 8 years ago

No, the leakage inductance will limit it to some extent, but a good transformer has very little. And besides, if you operate the secondary into a short circuit, the transformer is going to do its darndest to pump energy from the primary to the secondary anyway.


Answer 8 years ago

Inductive reactance does limit current flow, if you try, do use Re-design's
good light fuse concept and work up in bulb wattage when it works.
I don't spend words failures.

My reservation is the primary is center tapped meaning it was designed
for lower voltage inverter drive.  It may be well built and survive for a
few minutes.



Answer 8 years ago

Yeah, I agree with you - looks low voltage primary to me too.