Now Sarge:

Ya gotta give the guy some credit.....he actually got the bulb lit!

This is the sort of thing that plasma physics labs are made of.

Eric

I see that you are a former broadcast engineer, and that you teach electronics. I have asked why my transformer draws too much current. Either you do not know, or else you are not going to say. Which is it?

 

Except on the internet, and when they are a moderator of this site. Most of these guys have the experience and advanced degrees. I've kind of regretted not using a pseudonym, there are a lot of crazies out there.

I would suspect a lot of the heat is your laminations are loose, way too loose. They should be insulated from each other (so they don't become a circuit in and of themselves), but in very close physical contact, and mechanically tight. This is why varnish is usually used on professionally built models. Same thing on the wire.

Generally thickness in insulation translates into inefficiency, which translates into heat. On pole transformers they use sheets of aluminum separated by oil soaked paper, at least that what they showed on How It's Made. Having a kid has benefits sometimes.

Still, I liked it.

 

Are all of the turns connected together with a tap being on the 40th of 110 turns? Or, is there isolation between two sets of turns? Can you post a simple diagram of the system to the forum?

This transformer consists of a single coil, with a single tap. There are one-hundred-and-ten turns altogether. The tap is at the forty-turn point. Assuming one-hundred-and-ten volts at the wall socket, this means that I should be able to tap either forty volts or seventy volts. I am tapping forty volts. The extension cord fastens to the ends of the coil, and the lamp fastens to the tap, and to the end of the coil which gives me forty volts. Do you know why this circuit blows a fuse?

 

I once made an electro magnet by winding over 100 turns of #24 enameled wire around a 16 penny nail driven into a block of wood. I connected it to a 120 volt outlet and man was that magnet strong!

How long did it take to melt the wire?

 

In that configuration you have created a very large power resistor that has a very low resistance. Can you measure the resistance of the wire? From that you can calculate the current that it will draw through the wall socket, i = V / R. My guess is that the current is larger than your fuse rating.

A transformer is created by using isolated coils, i.e. you have one coil for the primary, or wall socket side, and any number (in your case 1) of secondary coils, or lamp side. These coils are not electrically connected together but use the magnetic material, the chunk of iron or steel, to couple the magnetic fields generated by the wall current together.

 

In that configuration you have created a very large power resistor that has a very low resistance. Can you measure the resistance of the wire? From that you can calculate the current that it will draw through the wall socket, i = V / R. My guess is that the current is larger than your fuse rating.

A transformer is created by using isolated coils, i.e. you have one coil for the primary, or wall socket side, and any number (in your case 1) of secondary coils, or lamp side. These coils are not electrically connected together but use the magnetic material, the chunk of iron or steel, to couple the magnetic fields generated by the wall current together.

Okay, here we go:
Autotransformer

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An autotransformer (sometimes called autoformer)[1] is an electrical transformer with only one winding. The winding has at least three electrical connection points called taps. The voltage source and the load are each connected to two taps. One tap at the end of the winding is a common connection to both circuits (source and load). Each tap corresponds to a different source or load voltage. In an autotransformer a portion of the same winding acts as part of both the primary and secondary winding.

Okay, so this guy wants to call the ends of the coil taps also. Whatever.

 

Something to be aware of with autotransformers. They do not isolate the user from the line (galvanic isolation), so they always present a lethal shock hazard. Unless fed through a 1:1 isolation transformer, they cannot be made safe to use. Every part of the autotransformer must be considered to be at line potential.

You are literally risking your life using this thing.

 

Mike, please read the following, and pay special attention to item #1: http://forum.allaboutcircuits.com/announcement.php?f=6&a=3

It was you who came to us for help, not the other way around. This thread will be locked if contentious behavior continues.

 

Some rough calculations on the current question.

 

Mike,

I am just trying to help. I was not familiar with that term. Everyone here is still learning the trade at some level.

OK, I agree that you can use the autotransformer to change the voltage, as is done in many power applications. It is also very similar, in simple terms, to a resistor divider with low resistance. And, you have shown that your setup definitely works by getting the lamp to temporarily light.

It still does not change the fact that your resistance to 60 Hz signal is too low for your rated fuse. You need to identify how much current you are pulling through the transformer. Your options are change the fuse or the coil resistance.

A little reading about transformer design might help here as well.

And, be careful. Even though you do not necessarily believe those that say it is dangerous, it is best to error on the side of caution. There is a great deal of knowledge and experience that the people here possess. And, given little information about the people they are making recommendation to, they tend to error on the side of caution as well.

S@HE out

 

Something to be aware of with autotransformers. They do not isolate the user from the line (galvanic isolation), so they always present a lethal shock hazard. Unless fed through a 1:1 isolation transformer, they cannot be made safe to use. Every part of the autotransformer must be considered to be at line potential.

You are literally risking your life using this thing.

Been, I strongly suggest that you convert your household electrical system over to twelve volts. Your irrational fear of common household current, although sweet, is beginning to get a tad bit annoying. Tesla won the battle of the currents a long time ago. Get used to it.

 

Mike, please read the following, and pay special attention to item #1: http://forum.allaboutcircuits.com/announcement.php?f=6&a=3

It was you who came to us for help, not the other way around. This thread will be locked if contentious behavior continues.

Please point out to me which post or posts you have found to be contentious, so that a correction can be made.

 

How long did it take to melt the wire?

I never gave it enough time. But I think it would work continuously. This was back in 1976 and my memory is not trustworthy.

But, I gotta tell you, I admire your work. I think we must be kindred spirits because I am alway breaking the rules of convention myself!

 

I never gave it enough time. But I think it would work continuously. This was back in 1976 and my memory is not trustworthy.

But, I gotta tell you, I admire your work. I think we must be kindred spirits because I am alway breaking the rules of convention myself!

Good for you for not letting it burn out. I used to have a pretty good arc welder, but, like most of the arc welders that I have seen, it was never designed for a one-hundred-percent duty cycle. A heat sensor on that magnet would have been an interesting add-on.

 

hmm, mike. Reading trough this thread one cant fail to notice that you have a dozen of very experienced people telling you why you should discontinue with your current plan. In all due respect you seem to be very ignorant of the fact that it could easily turn into a disaster when your insulation fails (which it is likely to do since heat dissipation is propably enough to slowly melt the tape). The iron alone has very big eddy current losses which increases core losses greatly.

The reason your transformer is drawing too much current is most likely because your core has gone into saturation (read up on hysterisis loops). When that happens it pretty much shorts right trough itself if i remember correctly.
Have you looked up the maximum magnetic flux the iron material can handle. Being an unpure iron core i doubt the Bmax value (for the iron material) is very high. Meaning you'll likely need ALOT of extra turns on the primary to be sure that the maximum voltage per turn is not exceeded.

Aka, the material sucks because it has high losses and saturates easily. So in almost every way from core material, wire type to insulation this transformer is ineffecient and dangerous.

If you really want to be stubborn you can try adding more turns on the primary but that will propably just mean more heat building up inside the bulk of tape insulated windings.

I recommend you look up transformer calculations in books on transformer theory to get the correct primary winding count relative to the dimentions of the transformer and the core material used.

 

Sorry that -

Your irrational fear of common household current, although sweet, is beginning to get a tad bit annoying.

- so I guess we wil have to stop bothering you.