Appliance power supply
05-19-02, 11:53 AM
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Appliance power supply
What do you guys reccomend for DC to AC conversion? There's only a few things I need to run, and my new electrical system will be able to handle quite a load, so I'll be all right as far as actually *providing* power. However, I need convert some of it to AC 120 power. I'm not running blenders, hairdryers, and microwaves out of my FC, but I will be mounting a 350watt computer. When I'm not using it, it will go into suspended sleep and use less power, anyway. (Hopefully, it will be able to be on all the time with my solar cell when I'm not running the car.) My cousin has one of those $80 DC to AC converters from Radio Shack--should I buy it off him for fifty? Or should I get something else?
05-19-02, 12:06 PM
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DC-AC converter - the "modified sine wave" stuff is cheap, but try not to use it too long with them; the modified sine wave crap is extra stress on power supplies due to it's inferior output power wave.  A "true sine wave" DC-AC converter is BIG BUCKS (close to a grand), so I doubt you can afford this anyways.  You need to figure out maximum current draw and convert to wattage requirements; most DC-AC converters are rated per wattage draw.  You can easily convert wattage requirement by looking for current draw on the electrical "appliance" and multiplying that by 120 to equivalent wattage use.
-Ted
-Ted
05-19-02, 12:21 PM
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You're wasting your time buddy. What kind of voltage does your computer need? 12 volts and 5 volts, right? Do some math, use a transformer, and make your own power supply. You won't even need the power inverter, and you wont NEARLY drain as much power.
If you're still confused, talk to Aaron Cake. That kid is a genius. He has a computer in his 7 to play his mp3s that he integrated very very well in his car. Programmed and everything. Funny as well as practical. But i've seen his setup, and the power supply is excellent.
If you're still confused, talk to Aaron Cake. That kid is a genius. He has a computer in his 7 to play his mp3s that he integrated very very well in his car. Programmed and everything. Funny as well as practical. But i've seen his setup, and the power supply is excellent.
05-19-02, 12:49 PM
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Use your cars power for your 12 volt that works fine. Thats what im using. Ditch the powersupply in your computer and use your cars. Why would you want to switch from dc to ac and then back to dc. I beleive sonicrat knows how to make a dc transformer. Or go to radio shack and ask how to make one im sure they can help.
05-19-02, 03:10 PM
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There is no such thing as a "DC Transformer".
Transformers only work with alternating current.
Computers need both positive and negative supplies, which would require a somewhat complex regulator circuit with PNP and NPN transistor bridges to handle the current.
Do yourself a favor and either get a power inverter (DC to AC) or get a laptop. You can use the car's power directly with a laptop. Most laptop batteries are around 14 volts.
You can then connect it just like an amp.
Transformers only work with alternating current.
Computers need both positive and negative supplies, which would require a somewhat complex regulator circuit with PNP and NPN transistor bridges to handle the current.
Do yourself a favor and either get a power inverter (DC to AC) or get a laptop. You can use the car's power directly with a laptop. Most laptop batteries are around 14 volts.
You can then connect it just like an amp.
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05-19-02, 03:55 PM
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Yea thats what im doing there are like a million websites on how to do it without using a converter. You can start at mp3.com. or do a search on google. If you have any ? on what OS and stuff works the best i would be more then happy to help. just fire me a email
scooter@uplogon.com
scooter@uplogon.com
05-19-02, 06:24 PM
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Originally posted by Josh
There is no such thing as a "DC Transformer".
Transformers only work with alternating current.
There is no such thing as a "DC Transformer".
Transformers only work with alternating current.
http://www.mos.org/sln/toe/glossary.html
This definition does not limit the term "transformer" to AC circuits.  Does this mean this reference is wrong?
-Ted
05-20-02, 12:20 PM
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I disagree with you, josh. I've made several DC-DC transformers in physics class. They either step up the current by decreasing the voltage, or increase the voltage by degreasing the current. They do in fact exist. If you don't believe me, buy an o-shaped magnet, and wrap two lengths of wire around it. Run current through one set of the wires, and put a voltmeter on the other set. Now add or reduce a few turns on the wire with the live power, and you just varied the current and voltage of your transformer.
05-20-02, 06:01 PM
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There is no such thing as a DC transformer. All transformers require an AC signal. A DC-DC converter is probably what you mean. They take an input DC voltage and either invert it to AC and run it through a transformer, or just use a regulator to bring it down to the required level....
If I were you, I'd check out http://www.mp3car.com
If I were you, I'd check out http://www.mp3car.com
05-20-02, 06:49 PM
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Long response, maybe difficult to understand.
I am not implying the reader can't comprehend what follows, I am saying I can't explain it clearly. Certainly some of our E.E. folks can do much better.
To say there is no such thing as a DC transformer is a little "too correct". In the sense that there are no DC "transformers" that will maintain a constant voltage and current output using DC voltage is correct. There are DC transformers that are in use on every car using spark plugs. Think of the ignition coil. It takes 12 volts DC and converts it to 18,000VDC or in some cases many thousands of volts more. It is not capable of doing this on a constant current flow however.
An AC transformer works because the magnetic flux generated by the rise and fall of the voltage is in a constant state of building up and then collapsing. It is the AC cycle that actually provides the means for an AC transformer to work. When the voltage polarity changes, the magnetic field collapses and the energy is absorbed by the secondary winding. The points in a car ignition system are kind of a ghetto way to "fool" the coil into thinking it is getting fed AC voltage (remember the rise and fall of the magnetic flux in an AC transformer).
If you apply a constant DC voltage to a transformer, the magnetic flux will saturate the core and build up a reverse force (impedance) to the flow of current. If the voltage is suddenly removed, the flux will collapse and cause both a tremendous increase in reverse electromotive force in the primary winding and a corresponding output voltage in the secondary winding. Without the collapse the secondary winding will have no more that a few times the primary winding voltage on it and virtually no current flow. This is why the old style points type ignition systems had a "condensor" in the circuit. The "condensor" name is an archaic term for a capacitor. This component acts as an electrical "shock absorber. At the moment the points open or the primary voltage is removed from an ignition coil, the flux collapses and on a 12 volt coil a reverse EMF of about 400 volts is generated. This collapse then causes the output voltage in the secondary to spike to the 20K needed to jump the spark plug gap. The plugs actually fire when the points open. This phenomenon is why the "dwell time" or the time the points are closed and current flowing is so critical. Too much dwell and the coil overheats. Too little and the magnetic field doesn't get a chance to saturate the core which reduces the output voltage. This reverse EMF will rapidly fry the points (by arcing the gap) unless the capacitor is there to absorb the voltage spike. It is this collapse of magnetic flux that generates the high voltage on the secondary side. Reverse Electromotive Force is why you do not see brush type (AKA universal) motors of large size. Since the motor acts as a generator at the same time it is acting as a motor, a reverse flow of current is being created that opposes the flow of current into it. A diesel electric locomotive has an extremely complicated series of relays and shunts to overcome this EMF by varying how the traction motors are connected to the generator as the speed of the locomotive increases.
Take a six foot long piece of wire. Connect each of the ends to the terminals of a car battery. Almost instantly the wire will burn the insulation off and eventually melt the conductor. Wrap this same wire around a ferrous metal core and the magnetic flux will saturate the core and "impede" the flow of more current. The core will continue to absorb energy and get very hot, but the principle will be obvious.
A soldering pistol (120VAC) is a classic example of a high current step down transformer. The voltage at the tip is quite low, but the current flow (amperage) is very high. Take a foot long piece of 12 gauge solid wire and bend it in a large diameter circle. Hook it up to the soldering pistol terminals. While the wire will get hot, it will not melt solder. It is the very sharp turn in the tip that concentrates the current flow at that point causing a traffic jam of electrons and the subsequent heat build-up. Kink that same wire anywhere along its length and see how hot it gets there.
In most EE degree programs a lot of the time in class and lab is spent understanding the principles of impedance in AC circuits. Measure the resistance of a light bulb filament. It is so low that without some higher resistance it would smoke the wire supplying it. The impedance (and simple resistance) of the filament after it gets hot increases, thereby increasing the effective resistance to current flow.
I know there is a large degree of license taken in this post. I am merely trying to help those who would like to know understand what makes a transformer work.
Please don't flame too much for any inaccuracies. I am after all just a dumb old cop.
To say there is no such thing as a DC transformer is a little "too correct". In the sense that there are no DC "transformers" that will maintain a constant voltage and current output using DC voltage is correct. There are DC transformers that are in use on every car using spark plugs. Think of the ignition coil. It takes 12 volts DC and converts it to 18,000VDC or in some cases many thousands of volts more. It is not capable of doing this on a constant current flow however.
An AC transformer works because the magnetic flux generated by the rise and fall of the voltage is in a constant state of building up and then collapsing. It is the AC cycle that actually provides the means for an AC transformer to work. When the voltage polarity changes, the magnetic field collapses and the energy is absorbed by the secondary winding. The points in a car ignition system are kind of a ghetto way to "fool" the coil into thinking it is getting fed AC voltage (remember the rise and fall of the magnetic flux in an AC transformer).
If you apply a constant DC voltage to a transformer, the magnetic flux will saturate the core and build up a reverse force (impedance) to the flow of current. If the voltage is suddenly removed, the flux will collapse and cause both a tremendous increase in reverse electromotive force in the primary winding and a corresponding output voltage in the secondary winding. Without the collapse the secondary winding will have no more that a few times the primary winding voltage on it and virtually no current flow. This is why the old style points type ignition systems had a "condensor" in the circuit. The "condensor" name is an archaic term for a capacitor. This component acts as an electrical "shock absorber. At the moment the points open or the primary voltage is removed from an ignition coil, the flux collapses and on a 12 volt coil a reverse EMF of about 400 volts is generated. This collapse then causes the output voltage in the secondary to spike to the 20K needed to jump the spark plug gap. The plugs actually fire when the points open. This phenomenon is why the "dwell time" or the time the points are closed and current flowing is so critical. Too much dwell and the coil overheats. Too little and the magnetic field doesn't get a chance to saturate the core which reduces the output voltage. This reverse EMF will rapidly fry the points (by arcing the gap) unless the capacitor is there to absorb the voltage spike. It is this collapse of magnetic flux that generates the high voltage on the secondary side. Reverse Electromotive Force is why you do not see brush type (AKA universal) motors of large size. Since the motor acts as a generator at the same time it is acting as a motor, a reverse flow of current is being created that opposes the flow of current into it. A diesel electric locomotive has an extremely complicated series of relays and shunts to overcome this EMF by varying how the traction motors are connected to the generator as the speed of the locomotive increases.
Take a six foot long piece of wire. Connect each of the ends to the terminals of a car battery. Almost instantly the wire will burn the insulation off and eventually melt the conductor. Wrap this same wire around a ferrous metal core and the magnetic flux will saturate the core and "impede" the flow of more current. The core will continue to absorb energy and get very hot, but the principle will be obvious.
A soldering pistol (120VAC) is a classic example of a high current step down transformer. The voltage at the tip is quite low, but the current flow (amperage) is very high. Take a foot long piece of 12 gauge solid wire and bend it in a large diameter circle. Hook it up to the soldering pistol terminals. While the wire will get hot, it will not melt solder. It is the very sharp turn in the tip that concentrates the current flow at that point causing a traffic jam of electrons and the subsequent heat build-up. Kink that same wire anywhere along its length and see how hot it gets there.
In most EE degree programs a lot of the time in class and lab is spent understanding the principles of impedance in AC circuits. Measure the resistance of a light bulb filament. It is so low that without some higher resistance it would smoke the wire supplying it. The impedance (and simple resistance) of the filament after it gets hot increases, thereby increasing the effective resistance to current flow.
I know there is a large degree of license taken in this post. I am merely trying to help those who would like to know understand what makes a transformer work.
Please don't flame too much for any inaccuracies. I am after all just a dumb old cop.
Last edited by copandengr; 05-20-02 at 06:53 PM.
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