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/diy/ - Do It Yourself

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161144 No.161144 [Reply] [Original]

I noticed a curious side-effect from my homemade MOT welder (from a 1.45KW microwave). Normally, when I test it I make sure to unplug everything in the room, all PCs, Stereo, etc. Now, my house is wired so that in one room there are 3 breakers. 1 for the lighting and 2 for the wall outlets. The outlet are arranged to one break leap-frogs the other one. Like A, B, A, B, A, B around the room.

This is for when a breaker is tripped I can simply unplug from that outlet and plug it into a still working outlet. It's a great system. I keep all my PCs on break A and tools and testing on breaker B.

Now, everything has been smooth sailing because I unplug every thing for the MOT testing. HOWEVER, one single time, I left one PC hooked up and on. When I fired up the MOT, it knocked out the PC. Luckily, it didn't harm it that much, it only stopped it from working. However, it one of the 2 video cards is now non-functional.

The distance from the PC to the MOT was about 5 feet. Now, is this EMP damage (the PC doesn't have a cover) or some sort of line interference even though they are both on different circuit breakers?

pic not mine, but related

>> No.161156

probably the current surge killed it.

>> No.161158

Just because two devices are on separate breakers doesn't mean they are electrically isolated. You probably created a surge through your house wires that was either too fast or not powerful enough to trip the breaker before damaging the computer.

>> No.161189

It's not EMP. It would be a surge or possibly a very localized brown out. In your breaker panel you have 240v coming in off 2 wires with a center tapped neutral. The center tap allows you to split the 240v into two 120 volt AC rails. That's exactly what your breaker box is doing. Every other breaker is on a different side of the 240v mains.

Right now your welder probably has no capacitor attached. When you use it it draws a relatively (for your house) massive amount of current off just one side of the drop. Depending on that current it could cause the neutral to saturate or when you turned it off a spike on one side of the transformer.

My guess is that the power supply in your computer is working close to capacity and the momentary (~10-100us) blip in current either by neutral saturation or the current spike caused it to shutdown.

Buy some capacitors for your welder to keep the spikes down.

>> No.161248

>>161189
How many microfarads would such a capacitor need to have? Not OP, but curious for my own project.