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    Need help converting ac to dc

    What you're looking for is a rectifier. Remember that the Vdc out of the rectifier will be a function of the ac input. It's usually easier to transform the ac going into the rectifier to a value that will give you the desired dc output than to convert the output dc into another value.
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    Three Phase Power Concerns

    Averagesupernova is 100% correct, my mistake. If you draw out 3 sin waves 120 degrees apart you will see that they would maintain a stable rotation in a motor with poles 120 degrees apart as well. connecting 3 phases to a node would be Wye operation, you would be well served to study Delta...
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    Timer switch questions

    Allen Bradley makes excellent timer relays that you can do this with. They have many functions and even an adjustable dial with adjustable time units so you can set the timer anywhere from under a second to a couple of days. They are bulletproof. I have retro fitted many of them into use for...
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    Three Phase Power Concerns

    Of course 3 phase is important, basically every large motor in any building is a 3 phase motor. Elevators, HVAC, etc. If you have a good foundation on AC, all you need to know is the phases lead/lag each other by 90 degrees. Are you asking how a 3 phase motor works? Motors are the main reason...
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    Two Phase Power For Contactor Coil?

    Is the thing running? I don't see how. AB contactors are good, but if you're coil is 120v you're going to ruin it if you try to operate it with 208v. (For the record AB has contactors with 208v coils, so maybe that's what you have. It should be printed on the side of the contactor) As for wiring...
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    Questions regarding something in Feynman's lectures.

    Interestingly this is why we abandoned the original Edison DC grid for the more efficient and easier to propagate Tesla AC system. To achieve similar results a DC system would need gigantic conductors and copper is expensive. Tesla = Genius
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    3d glasses.

    I'm thinking you could have more depth gradients than the two you would see on what you describe.
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    Need help for my project

    Same thing with a Peltier. Think of it as a solid state sterling engine if you want, it will only generate voltage if there is a temperature differential between the top and bottom sinks. I did a similar project making an Ipod charger that used a candle on one side of a Peltier and a CPU heat...
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    House Power Out of Phase?

    I use phase protection relay's all the time in my line of work. (Elevator mechanic). Everybody is correct that your manual would be better written if it said "in proper phase relation" rather than "in phase". If my elevator motors lose a phase they begin to sound like a sci-fi movie UFO sound...
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    Self exiting dynamo question

    Sounds like you're re-inventing the transformer. :smile:
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    Power issues with power drill physics help needed please

    The inrush current on a motor is huge compared to up to speed current draw. This is why large motors are started with a wye-delta setup (or soft starters mostly now). It is also why your lights dim when you first turn on a hair dryer or vacuum cleaner. I would bet short circuit amperage is very...
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    Wave freq vs freq of its oscillating source

    I could see why a beginners book would say that, but you have to realize this is not accounting for frictional/heat losses which you would always have in the real world. A non perfect wave transmitting medium (everything) would not act as expected. Imagine laying a floor speaker on its back and...
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    Is It Possible To Shape An Electric/Plasma Arc?

    I don't think your speaker would sound too hot in an argon tube.
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    3 phase rectifier with cap filter w/overheating wire.

    Are you saying you want to run this rectifier at less than 300 amps or that you want your circuit to handle the high amp output? To lower your amperage you could modify your SCR driver. (You could use the SCR's to rectify less of the AC waveform). Otherwise it seems you simply undersized your...
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    ARRRH I'm gonna explode. This is my pet hate!

    What a joke... So many people will eat this up too. Way to go Michiu Kaku.... (I think that was his voice, right?)
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    How to calculate r.m.s radius of a N-body system?

    I don't know how you would collect the data for something like that, but if you did the formula's are here: The first one would be if you took a bunch of points, the second if you map the waveform. The first one would not be too accurate, or only...
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    Baffled with experiment

    lol, I missed this before I replied.
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    Baffled with experiment

    A meter set to measure amps has to be inserted into the circuit in SERIES, if you took a meter set to amps and touched the probes to the motor leads, you have effectively shorted the motor and you are lucky if you didn't wreck your meter. You can either get a clamp on meter or series your meter...
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    Why does grounded imply V = 0 ?

    Here's another simple way to look at it. Imagine 2 unknown points in a circuit. Say you take a meter set to measure voltage and touch the probes to these two points and you read 5 volts. This does not mean one point is 5 volts and the other is 0 volts. One point could be 600 volts and the other...
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    Why is a changing magnetic field and changing electric field perpendicular?

    This is basically the explanation of Lorentz force. A good way to visualize it is the right hand rule. You make a thumbs up position with your right hand and grab a (hopefully insulated) wire carrying current. If your thumb is pointing in the direction of current flow, your other 4 fingers...
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    Properties Of Gravity

    The problem with that statement is that physics has yet to model the flow of time. Your future is not the same as mine, relativity will explain this. Entropy was later investigated as a benchmark for the flow of time, but it turns out entropy increases when we look to the past or the future of a...
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    Weight difference between an empty and a full memory stick

    I just read a book called "Decoding the Universe" by Seife. It is an intro to information theory and I enjoyed it. Here's a few things I would say: The mass would not change in your memory stick because a string of 8gb of 0's is just as much information as 8gb of text. That's why we have...
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    Who knows the proper name for this experiment

    I'm not sure of the name of the experiment in question, but I would have to assume any difference in restart amperage would be due to residual magnetism. Possibly the coefficient of friction of warm bearings vs. cold ones too. I'd be interested in the actual experimental results if you ever find...
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    Preventing Arcing Across Relay Contacts

    A time honored technique to prevent arcing across relay contacts is to series the arcing contact to another pair of contacts (as long as they are not too close to the arcing one). This will basically double your air gap and help prevent arcing.
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    [HELP] Exhaust valve!

    Are you sure about that? Are the first two strokes on a four stroke identical to the last two? As far as the valvetrain positions that is. does a cam run 1/2x faster than the crankshaft or 2x? Not trying to be a wiseguy, I really dont know. I'm just thinking it can't be just any downstroke, but...
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    [HELP] Exhaust valve!

    You could just rewire the starter to "park" the motor in exactly the right position after the ignition is turned off (like windshield wipers) for the "single spark start", and than just hook up a pump to the chosen cylinder to compress it to the right ratio. :biggrin: ....I wrote this as a...
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    Some questions regarding Electromagnetism

    I think what you're looking for is a potentiometer, not a transformer. (imagine a dimmer switch on a light). It's basically an adjustable resistor that you could use to smoothly control the current to the load. Most transformers only come with preset "taps" of certain voltages. Sure you can rig...
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    The true nature of length contraction

    Good, I'm sure you'll enjoy the book regardless. In my edition it's chapter 14 : The Universal Correction, where all this is discussed. This is what I have a problem with too. To me it's as if he's dismissing length contraction. Maybe this guy is a friggin genius and wants the reader to...
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    The true nature of length contraction

    Unfortunately that is the only mention of length contraction in Calder's book. (I still have a couple chapters left but at a glance it doesn't look promising.) I don't know why he would leave the subject out but it appears he did. I'm even thinking he's just plain wrong, primarily due to his use...
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    The true nature of length contraction

    Thanks for the reply. You're very clear and I understand what you're saying, but doesn't that contradict the last sentance in the quote from Calder's book? From what I gather he's saying the contraction is ONLY a product of the angle the ship is seen from, not the measurable length. I guess both...