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| Cold Fusion |
 Posted: Wed Jul 16, 2008 3:10 am Post subject: Transformer usage |
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Can you reverse a transformer? As in, could you take a 120v to 12v and input the 12v to the secondary to get 120v? Essentially turn a downstep into an upstep transformer.
Are transformers based only on a ratio? Could I take a 12v to 120v transformer and input 1000v in order to get 10,000v?
What happens if you exceed the amperage limit?
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| Harold14370 |
| Posted: Wed Jul 16, 2008 4:16 am Post subject: |
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Yes, they are reversible. But if you are talking about a 120v to 12v ac adapter they also include a rectifier to go from a-c to d-c so you can't feed backwards from a 12 volt battery. For that you need an inverter.
If you exceed the voltage limit, the insulation will break down and the wires will short out. If you exceed the rated current, you will generate a lot of heat and melt the wires or the insulation or both. |
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| Pumblechook |
| Posted: Wed Jul 16, 2008 11:25 am Post subject: |
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Transformers are actually quite complicated because the windings have resistance depending on the thickness of the wire in the primary and secondary. The high voltage one will use thinner wire than the low voltage one. There will also be stray capacitance and also loss in the core which will increase the effective resistance of the windings and other effects such as core saturation, flux leakage and hysteresis which make a real transformer behave quite differently to the simple 'ideal' step-up/step-down one governed by the turns ratio.
A typical 120 to 12 V transformer will produce 16 - 18 Volts with no load. You will get 12 Volts when you load it at its stated rating ..usually in VA or kVA.. Volt-Amps and not Watts... VA ratings are used when the V and A are not in phase (in step).
Say it was a 120 to 12 V, 12 VA transformer. It would deliver 12 V with a 1 Amp current flowing. The turns ratio will be that which would give say 16 V (light or no load) output so would be more like 7.5:1 rather than 10:1.
You shouldn't exceed the power, voltage or current ratings as the last poster has said.
The equivalent circuit of a real transformer is far more complicated that an ideal transformer with just two coupled windings....
Scroll down 'Equivalent Circuit'...
http://en.wikipedia.org/wiki/Transformer |
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| Harold14370 |
| Posted: Wed Jul 16, 2008 1:59 pm Post subject: |
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Everything that Pumblechook says is true but still the short answer is yes, it can be done. In fact, it is routinely done at power plants to backfeed from the main transformer to the unit station service transformers when the main generator is out of service. It does require changes to the tap settings on the USST to adjust the voltage.
If you have a home generator and do not have the proper disconnect switch, then during a power outage your emergency generator system could backfeed though your pole transformer and possibly kill a lineman working on the supposedly dead power lines. |
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| Cold Fusion |
| Posted: Fri Jul 18, 2008 1:34 am Post subject: |
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In an audio forum that I was in a while ago people posted their amplifier schematics (they built them). In them the transformer did not have any additional components, besides the bridge rectifier, drainage resistor, and filtering capacitors. Maybe the extra components are not necessary with all electronics?
Is it possible to ice the transformer (with it insulated with plastic rap) in order to push it higher? 
I need around 10k volts if not more for an experiment that I want to perform. What is the best way to get there? I can't find a transformer (non industrial...as in the ones that cost $10,000 +) that can bring 12v (with an oscillator), or 120v that high. The power output will be around .0001 amps.
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| Cold Fusion |
| Posted: Fri Jul 18, 2008 3:11 am Post subject: |
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| Harold14370 |
| Posted: Fri Jul 18, 2008 3:26 am Post subject: |
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| Pumblechook |
| Posted: Fri Jul 18, 2008 3:34 am Post subject: |
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That is a one Watt output.
I would run it off batteries (sealed lead-acid or Ni-MH).
You need a 15.625 kHz (UK) or 15.750 (US) (although exact frequency is not important) oscillator and the line output transformer (flyback..not to be confused with other sorts of 'line output') + rectifier from an old TV.
http://en.wikipedia.org/wiki/Flyback_transformer |
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| Cold Fusion |
| Posted: Fri Jul 18, 2008 3:46 am Post subject: |
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ahhh, neon transformers. Do you need to input a high frequency to them, or will they run 60hz wall? I'm assuming the output is also at a high frequency; do you need a special type of diode to rectify high frequencies?
Say I wanted to use batteries as a source for portability, where can i get/how can I make a 60hz oscillator? I have seen a few schematics......but am unsure whether they can power a transformer like that.
If I end up getting a 100kv transformer, would it be a bad idea to make a voltage multiplier to bring it to 1Mv? (Does Mv stand for million or mili?)
_________________
Forget all that you know, achievements can only be accomplished by starting from nothing and selectively applying facts that are purely objective and absolutely necessary.
"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."
"Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"
-Einstein
http://boinc.berkeley.edu/download.php
Use your computing strength for science! |
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| Harold14370 |
| Posted: Fri Jul 18, 2008 4:06 am Post subject: |
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The neon sign transformer just works off normal house current, 120 or 240 vac, 60 hz.
The device you want to convert 12 vdc to 120 vac is called an inverter. You can buy a UPS for your computer that will generated 120 vac from battery power. I guess one of those would run your jacob's ladder for a while. |
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| Cold Fusion |
| Posted: Fri Jul 18, 2008 5:37 am Post subject: |
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ok......I will order the parts soon. 10Kv should be good to start.
I'll try to post a vid on youtube if the results are particularly favorable.
_________________
Forget all that you know, achievements can only be accomplished by starting from nothing and selectively applying facts that are purely objective and absolutely necessary.
"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."
"Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"
-Einstein
http://boinc.berkeley.edu/download.php
Use your computing strength for science! |
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| Cold Fusion |
| Posted: Tue Jul 29, 2008 1:25 am Post subject: |
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Forum Ph.D.
Joined: 10 Apr 2007
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Could you make a variable transformer (they are kind of expensive) by putting one variable resistor on either end of the transformer set at say, 10 ohms. By turning down the first one to zero at the V+ end you would eliminate the 1/2 voltage drop at that end and allow full original voltage through until the second resistor which would create the second voltage drop. Turning the second resistor all of the way down down while the first one is at full would turn the voltage down to zero. Turning both down would result in the same outcome as the first one, allowing full voltage through. Would this work? Wouldn't using a 10ohm resistor at the primary end limit the maximum output current at the secondary end accordingly? I would use smaller resistors, although then I would not have full limiting capabilities since the resistance of the transformer itself would play too large of a role.
_________________
Forget all that you know, achievements can only be accomplished by starting from nothing and selectively applying facts that are purely objective and absolutely necessary.
"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."
"Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"
-Einstein
http://boinc.berkeley.edu/download.php
Use your computing strength for science! |
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| Harold14370 |
| Posted: Tue Jul 29, 2008 1:42 am Post subject: |
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I'm not sure I understand your idea. You can drop the output voltage with a resistor, but you will dissipate heat, and the voltage drop will depend on the load current. So it could work if you had a consistent load current, and didn't care about wasting the power.
What would be the point of an adjustable resistor set at zero? It would be equivalent to no resistor at all, wouldn't it? |
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| Cold Fusion |
| Posted: Tue Jul 29, 2008 1:53 am Post subject: |
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I could take it out, but that would be laborious. If I only had a variable resistor at the negative end I could not adjust the voltage. The resistor would take the vast majority of the voltage drop at any level; it would have to be extremely precise, although I have never used one that is that precise.
I used either on or off to demonstrate the main idea, but I would vary either one to acquire the needed voltage.
I cannot find a variable transformer under $90, and those do not really do want I would like them to do. I found a DIY a while ago about how to make a variable HV power supply. They used a variable transformer that brought 120v to 6,000v and then resorted to a voltage multiplier to bring it to around 50,000v. I cannot find one like this, and it would likely cost way too much anyways.
_________________
Forget all that you know, achievements can only be accomplished by starting from nothing and selectively applying facts that are purely objective and absolutely necessary.
"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."
"Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"
-Einstein
http://boinc.berkeley.edu/download.php
Use your computing strength for science! |
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| Cold Fusion |
| Posted: Tue Jul 29, 2008 2:31 am Post subject: |
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Joined: 10 Apr 2007
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It turns out that I also need a 1:1 transformer for a project I am working on. It will need to take the full 10-15,000 volts that I plan on outputting to it. Does a transformer like this exist that does not cost hundreds of dollars? If not, how should I make one?
http://www.allaboutcircuits.com/vol_6/chpt_4/3.html
How many turns are necessary? If possible I want to do as little as possible for obvious reasons. What will make it 15,000v compatible without melting itself? I will only run around 20ma through it.
_________________
Forget all that you know, achievements can only be accomplished by starting from nothing and selectively applying facts that are purely objective and absolutely necessary.
"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."
"Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"
-Einstein
http://boinc.berkeley.edu/download.php
Use your computing strength for science! |
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