Why did my transformer give out?


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Old 08-17-15, 07:07 PM
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Why did my transformer give out?

I recently saw a video online of a guy cutting a glass jar with wire connected to a transformer. I wanted to cut the top of a wine bottle off to make a bottle neck guitar slide so i gave this method a try. I'll explain my setup from here. I bought a 120v to 24v transformer at the local electrical store. I cut the end off a standard power cable and connected one wire of it to the 120v wire of the transformer and the other to the 60hz black wire of the transformer. I tested the out put wires of the transformer and has 24v. Next, i attached a piece of copper wire (stripped from a standard coaxial cable. I know this is not pure copper.) to the output of the transformer. When i plugged it in i saw a flash on the output side of the transformer and from there on out it would not put out voltage. Can you tell me what went wrong here?
Thanks,
Ian
 
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Old 08-17-15, 07:13 PM
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The copper wire you connected to the transformer secondary drew so much current so as to burn out the transformer.

Or due to an incorrect connection or wires touching that should not touch, you caused a short circuit that drew so much current so as to burn out the transformer.
 

Last edited by AllanJ; 08-17-15 at 07:28 PM.
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Old 08-17-15, 07:16 PM
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hmm i see thank you. What wire would draw less current?
 
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Old 08-17-15, 07:24 PM
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You will need to do some homework (electrical engineering) to figure out how much heat is needed to make the bottle crack and then how many watts are needed to heat up a wire that much. You would need to select a wire of a material that did not itself melt when reaching that temperature. Then select a transformer that can deliver the needed wattage.
 
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Old 08-17-15, 07:30 PM
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You need something like nichrome wire (like what is in toasters), which has higher resistance and can operate at very high temperatures without failing. As AllanJ said, you need to figure out needed temperature first, then you can select the correct type of nichrome wire and figure out how much voltage and current is required to achieve the needed temperature.
 
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Old 08-17-15, 07:31 PM
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stripped from a standard coaxial cable. I know this is not pure copper
It is pretty dang close to pure. You created a dead short on the secondary of the transformer and that is why it burned up. Any wire will do that as the resistance of the wire is much too low and causes too much current to flow, as Allen posted.

You need some resistance heating wire that is designed for the voltage you are applying to it, and the transformer needs to be able to handle the load applied to it. Also, you might want to consider adding a fuse to the secondary side so you only take out the fuse and not the entire transformer.
 
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Old 08-17-15, 07:42 PM
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Back in the days when they rebuilt picture tube I watched a guy cut the neck off with a white hot platinum wire. As I recall he was using 120 volts AC no transformer but I may be wrong and certainly wouldn't recommend it.

The common way of cutting bottles when I was growing up was to tie a string soaked in lighter fluid around the bottle, light the string, then when it burned out apply water around the string.

There also use to be a crafts project kit for kids that had a cradle with a glass cutter in it. You then rotated the bottle in the cutter to score it, then broke it by tapping the inside at the score.

At a glass company I worked for the glass cutter use the cut coke bottles just with a hand held glass cutter.

There are many DIY solutions such as this one: http://www.instructables.com/id/easy...-common-parts/
 
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Old 08-17-15, 07:49 PM
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The transformer needed to do what you are trying to do would be 10-30vac at around 10amps.

P 8695 Stancor 115V Volt 24 V 10A 1500V 50 60Hz RMS Transformer | eBay

LP 520 24 VCT 10A Transformer | eBay
 
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Old 08-17-15, 07:49 PM
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Ok I'm going to have to do some homework on this one. A glass cutter or even the fire string would probably be okay for what I'm trying to do but i want to do it this way mainly because I'm trying to teach my self about electricity. First things first I'm going try to put a fuse on the secondary side as Tolyn said. I don't have any idea how to do this but ill do some research and come back with questions.
Thanks all.
 
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Old 08-17-15, 07:52 PM
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Don't buy the same type of transformer again. You need a larger amperage transformer that can deliver the current needed to heat a wire up.

You also need to pick up a piece of nichrome wire. It can be removed from an old toaster.
 
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Old 08-17-15, 07:54 PM
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I posted a site that has a DIY bottle cutting rig while you were posting. Check my edited previous post.
 
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Old 08-17-15, 08:00 PM
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The melting point of glass is 1400 C to 1600C but copper melts at 1,085C so as you can see copper isn't going to cut it (no pun intended). My quick look showed they were not really cutting the glass. Instead they were heating it like the string and lighter fluid then quenching it in water so the thermal shock snapped it. Nichrome with a melting point of 1400 and higher resistance would be a better choice than copper wire. To cut through with heat you pretty much need platinum at 1,768C.
 
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Old 08-17-15, 08:08 PM
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Cool site you linked to with the bottle cutting jig. In that article was an interesting video too....
you tube/watch?v=E4yovEi7j7E/cracking off
 
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Old 08-17-15, 08:16 PM
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Great video Pete. .
 
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Old 08-18-15, 06:46 AM
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I have made a bottle cutter similar to what Ray posted. Worked fairly well, but then a friend of mine found an old antique one. Now, I just use mine for the candle to heat the score line a little and then pour cold water on it.

Cutting off the neck of a bottle might be a bit tougher as the glass will be much thicker.
 
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Old 08-18-15, 04:41 PM
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Back in the days when I did such things I found that unless you were able to first lay a deep scratch in the glass the success rate was less than fifty percent. Using the heat would add to the stress from the scratch and snap the bottle (or glass tubing) better than ninety percent of the time.

I have used various tools to make the scratch from a standard glass cutter to a triangular file and my favorite, a diamond grinding wheel dresser.

Anyone remember the Fleming Bottle and Jug Cutter? Doing a Google returned lots of hits and it seems that equivalents are easily found.

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Old 08-19-15, 03:29 PM
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Ok so i got a new transformer with 100VA ass opposed to 40VA from the last one. I am unsure how to wire the new one to be 120v primary and 24v secondary.

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From what i take away from that i attach my cables from my power outlet to the two outside terminals of the primary side and i attach the secondary side cables to the out side terminals also?
Is this correct? What do the circles in the schematic around the terminals mean?

Secondly i couldn't find any good information on how i would put a fuse on the secondary side. Does anyone have any links or information on this? I really don't want to blow this transformer out too.

Also i acquired some nichrone wire from a hair dryer. i don't know the exact gauge of the wires but I'm going to use the thickest one i found in hopes that it has a high enough resistance. I believe i need a resistance of 6 or higher to keep the amps below 4.1:
100/24=4.1
I=24/r
24/6= 4.
 
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Old 08-19-15, 04:13 PM
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Only issue I see is that wire from the hair dryer is made for 120 volts. It will likely not get very hot on 24 volts. This may be good or bad. Best thing to do is to take an Ohm meter and see what the resistance is on the wire. Then take that number and plug it into your Ohm's law equation as "r"

For the transformer X1 and X2 are the secondary 24 volts
The primary appears to connect one line of 120v to H1 and H3
The other line to H2 and H4

To protect the transformer just buy an in line fuse holder like this: http://www.amazon.com/Parts-Express-...ne+fuse+holder or this: http://www.amazon.com/RoadPro-RPPS-2...ne+fuse+holder

You can find these at some home centers, most auto parts stores, and that "radio" store, as well as fuses.
 

Last edited by Tolyn Ironhand; 08-19-15 at 05:16 PM.
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Old 08-19-15, 08:32 PM
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Used nichrome wire can be hard to read resistance on. There are two elements in most blow dryers. The whole element is designed to be run on 120v so you'll need a shorter piece.

You can try measuring the resistance or start with a longer piece and work your way shorter. As it gets shorter the resistance will go down and the current will go up. It would be good if you had a current meter (Amprobe) to monitor the draw. You can probably run the transformer up to 5 or so amps for a brief period. You can also use a voltmeter. When the voltage gets down to around 20v the transformer is pretty much maxxed out. If the transformer gets really warm then you are loading it too heavy.

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