Instructables

Attention Electrical Engineers and Physicists! Light bulb as current regulator?

A light bulb can work as a current regulator right?

If I understand correctly, an incandescent light bulb conducts with negligible resistance until it reaches a critical point at which point it resists any more… More what? More current? More voltage?

The situation is this: I have made an AC arc welder out of microwave oven transformers but I have no control system. This welder works great for about an inch of weld then starts blowing the breaker until it cools off. (You’d think it would be the opposite with resistance increasing and current decreasing as the coils warm up, but it’s not… Why?)

So what if I put three 500 watt light bulbs in parallel with each other but in series with the welder? Could this work as a 1500 watt current regulator?

And if I did this, where should I put the bulbs? Should they be in series with the 110v side of the transformers or on the ~40v side of the transformer? I figure they should be on the 110v side but then they’d be on all the time, heating up the primary windings, right? Or should they be in series with the secondary windings? This way they’d only be in when I’m actually welding but they’d have to conduct a lot more amperage.

What would jyou do?

iceng1 year ago
Super welder ible, I really enjoyed reading through it.
BTW your mit.edu is not found..

The lamps in the primary are a simple active resistor.

Put them in the secondary and they will allow a high current start and provide a reduced current once the arc is established.

Though the secondary voltage even in two with two coils in series
may be too low to match the bulbs.
It wont hurt to try.

. A
testlight.png
If it were that cheap and simple, your average buzz box would have light bulbs on the top.
UK I don't know but

The USA in it's infinite wisdom has started putting the stops to incandescents !
us too. But the buzz box has been around for years. They're regulated by using a very leaky transformer.
rickharris1 year ago
Have you tried to measure the resistance of a light bulb - this may answer many of your questions.

Look up another term that may be useful for you "duty cycle"
Can you see another comment from me in here, or has it been censored ?
This you mean?

No, a light bulb is a non-linear resistor, but its not got discontinuities in it. Take a look at a real welder transformer and you'll see how its done. The transformer is deliberately "cr? ppy", and acts as its own current regulator.

The change in temperature of a light bulb is typically room (20C) to incandescent (~1300C) - if your transformer windings did that you would have a major fire on your hands in a fraction of a second.
There's one without the question mark in "cr?ppy". The censors strike again.
No, a light bulb is a non-linear resistor, but its not got discontinuities in it. Take a look at a real welder transformer and you'll see how its done. The transformer is deliberately "cr? ppy", and acts as its own current regulator.

The change in temperature of a light bulb is typically room (20C) to incandescent (~1300C) - if your transformer windings did that you would have a major fire on your hands in a fraction of a second.
No, a light bulb is a non-linear resistor, but its not got discontinuities in it. Take a look at a real welder transformer and you'll see how its done. The transformer is deliberately "crappy", and acts as its own current regulator.

The change in temperature of a light bulb is typically room (20C) to incandescent (~1300C) - if your transformer windings did that you would have a major fire on your hands in a fraction of a second.