Just wondering, most of all equipment at home have components/circuitry inside to transform high voltage (AC) into lower voltage (mostly DC), also all modern LED lambs. Modern products become more and more efficient and operates at low voltages. Still we have only very high voltage sockets at home.  Also nowadays many manufacturers provide adapters with their consumer products. The amount of adapters is enormous, I think I have at least 40 adapters lying around the house. All of them are near or below 24 volts. For example my laptop adapter output 19 volts.  Would it be more efficient to have a (isolated) 24v AC socket instead of 240v? The transformation is done at the fuse box (what is the name in English, cupboard with energy meter). To step down isolated 24v AC is much easier (requires less components and no transformer i guess) for each product. Or is there any downside doing this? It will reduce the amount of repeating components required for many products, cables, transformers etc.  I know why AC is used instead of DC to transport electricity so that is why I suggest 24v AC. Or do we need a higher voltage?  What could be the reason why we don't have this green environment socket? Any downsides or is there no reason at all?
121994
I'm wondering why, in a standard house, instead of using many low power AC-DC rectifier, there isn't a big (like 12V 20~50A) AC-DC rectifier which supplies some wall socket with a DC voltage? In the long run this should be less expensive, given the fact that AC to DC in one big apparatus is done better than in many low-quality transformers, right?  Also, modern chip DC voltage regulators have efficiency of >90%, so smaller (or even larger) voltages are still efficient and possible.  So we could use a 12V socket to charge a phone, desktop computer, laptop, radio etc... and still have an AC socket to move washing machine engine and other things that work better with an AC supply.  Why isn't this done?  edit: real question is: is it convenient, given a standard family (2 laptop, 1 desktop, 4 smarthpone, 1 big tv and some minor electonic) to do so?
57558
I'm having trouble understanding something in one of my text books:     Let’s have a look at the implications of each circuit configuration.   Figure 3.13 shows the Conventional representation of a parallel   circuit. If you assume that the resistance of the wires can be   neglected, then the voltage drop across each bulb is equal to the   e.m.f. of the source, the dynamo. The Current flowing from the source   is divided between each bulb depending on its resistance (remember I =   E/R), Removing one of the bulbs would not affect the voltage drop   across the other bulb and would therefore not affect the Current in   it, although the overall Current from the dynamo would drop as the   demand has been reduced.   Specifically, the line about removing one of the bulbs not affecting the voltage drop. My understanding is that the sum of voltage drops in a circuit must be equal to the output of the emf, but the way I'm reading the text suggests that if you have three bulbs in a parallel circuit and you remove one of them, the voltage drop remains the same - this is what I don't understand, though. If you a lamp is removed, then that's one less lamp consuming emf. Does it not get redistributed to the other two lamps?  Likewise, the text mentions the overall current from the dynamo dropping because demand has been reduced.  My initial understanding was that current from an emf is only affected by the emf - not the demands of components further along the circuit, as in this case. What have I misunderstood?
21243
I'm looking for a high current DC switch (able to switch something like 5V@30A) and I've encountered several DPDT that might do what I need, however they are only rated for AC applications (3A@250VAC or 6A@125VAC). Are these rating convertible to DC? or is that something that only the facturarer would know?
95111
I have a need for a switch that can handle 28Vdc at about ~1A.  The switches I would like to use have a rating of 24Vdc at 5A.  I would think that the limit of switch is the power, so if we take a switch at 24V and 5A, then it can handle 120W. My reasoning is that a switch can run at higher or lower voltage currents, so long as its less than the 120W (in this case). A 24V 5A switch can be used for a 28V 1A application.  Is the reasoning behind that correct ? Am I absolutely limited to 24V 5A spec'd by the datasheet ?
50735
I'm trying to purchase several switches for a DC system with moderately low current (a few amps at 12V). When browsing for switches in parts catalogs (e.g.  and ) there are always separate voltage ratings for AC and DC applications. I understand that AC switches are less expensive because the switching time does not need to be as fast and arcing is less of a concern. There is only one current rating listed and I am not sure if it applies to AC switching, DC switching, or both.  Does this current rating apply to both the rated AC and DC voltages? Is there a good rule-of-thumb for converting between AC and DC voltage/current ratings? What is the highest current I could reasonably expect from a DC switch before moving to a relay?
37275
Possible Duplicate:             Let's say I have my laptop charger that uses 19.5V and 3.9A and I want to use it in other laptop that has no charger but it needs just 19V and 3.16A, I've studied a little of electtronics and I know that the amperage doesn't affect because the computer will use just the necessary, but I'm not really sure about the voltage.  I read  post and I know the polarity is the same and the connector fits, but it doesn't say anything about voltage, I also know if the voltage of the charger were lower than the specification it'll not be a problem, but what about this little almost insignificant difference??
1228
Power supplies are available in a wide range of voltage and current ratings.  If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify?  What if I don't know the device's specs, but am replacing a previous power supply with particular ratings?  Is it OK to go lower voltage, or should it always be higher?  What about current?  I don't want a 10 A supply to damage my 1 A device.
56761
Many of us have lots of devices that uses AC mains (110V/220V) to DC (typically 12VDC, 9VDC and sometimes 15VDC) adapters. There's my Wi-Fi router, my powered speakers, printer, scanner, etc.  So I would like to combine all these into a single device; do the AC/DC conversion once and have everyone tap the DC line, instead of each doing the conversion themselves.  Regarding to this, I have two questions:   is there any commercial solution out there to do this? (bench power supply for example)? suppose I have one of these beauties powering my stuff and this power supply can deliver 100W of power. Will the device always be consuming 100W of power or will the consume increase as I hang more devices?    thanks.
41149
I've lost my original power adapter, and I can't find the proper one in any of the stores currently available.  I've HP Compaq 6730b, and as per  it outputs 18.5V 3.5A. However, I've found an older power adapter I have which outputs 19.5V 4.62 A.  So, my question is: how much of a difference between those two it really is, and more importantly, how much of a risk would it be if I tried the power adapter I already have.  P.S. I know pretty much nothing about electricity/electronics.
54888
I'm having trouble understanding why the earth is a viable fault path for electricity brought into my home. Isn't there really high resistance? I mean, it's dirt?   Also, let's say I connect the hot wire coming into my house directly to the ground wire. What is the path that the electricity takes to get back and "complete the circuit?"
113032
I have a electric 220 dryer hook up in my kitchen now I want to convert it over to use for a higher grade power supply for my microwave blender and toaster without converting Any wires or touching the  fuse box, is this possible ?
17975
(Apologies upfront if this question seems too vague, I'm trying to formulate the problem statement as I ask this)  I'm thinking about circuit assembly in a high component variability / low MOQ environment, from the standpoint of passive components. Assuming identical footprints, I'd like to be able to substitute:  Resistors   tighter % tolerance for looser higher wattage for lower   Capacitors   Higher voltage for lower   What I'm getting at is - if I'm prototyping lots of different designs, parts inventory management becomes a substantial issue. If I could aggregate by component value, and use the same parts where possible, inventory requirements go down, likely enough to offset the potentially higher cost of the individual items.  Does an approach like this work, or would I break designs by doing this? If this works, what other components can I try to standardize?
93662
I have been using and making LED flashlights for years now and I am VERY familiar with all of the circuitry and technology inside of them, but I just got my first LED house light bulb that runs off of 110v AC electricity.  It is very similar to a flashlight - it has a large heatsink, and 1 or more LEDs inside of it (brand and specs of emitters, I do not know).  The part that I am most curious about is how the electricity from the socket gets to the emitter.  In a flashlight the power comes from a DC battery through a current regulator (LED driver) and into the LED itself.  This is not difficult because the voltage of common LED emitters is about the same voltage as Lithium batteries (3.7v, 7.4v, etc) which makes the current limiting relatively simple coming from a one or two cell light.  How does this work for a high voltage AC bulb?  Is there a transformer and rectifier inside of EVERY bulb (I sure hope not), or are the emitters manufactured to run off of 110v AC power and just use half of the wave cycle?
77814
I'm attempting to build an LED bed lamp that will be powered by 240V mains. The LEDs are  which if I use with a 12V supply and have calculated correctly will draw 0.24W each. I plan to use 5 or 6 of them in the lamp so will consume a maximum of 1.5W.  Initially I thought I'd use a transformer and bridge rectifier to get the required 12V DC but the transformer weighs a ton and is too bulky. The next option was to use a  but I'm wondering is there is a better way?  I think it would be possible to power the LEDs directly from mains using only a rectifier without mains and stepping down the voltage but then it's not safe. Are there any smallish components that can both isolate the mains and supply a DC voltage?
49600
I'm not sure if there's a better place to ask this or not.   Why, at least here in America, is the standard electrical system set up for alternating current (AC) rather than direct current (DC)? I'm just completing a long-distance move and realizing how many DC adapters I have and how many of my devices require DC power:   All of my guitar pedals. My alarm clock. My external hard disks. My USB car HDD dock.   ... and the list goes on. If we're almost constantly having to use DC adapters to convert AC into DC, why isn't the standard DC, other than because people resist change?
62984
I understand that this is a really basic question, but, I've been unable to really understand electrical terminology for some reason. What exactly is an amp? How does it correspond to a watt?  And: How does a watt correspond to a volt? What does the frequency of electricity refer to? (Hz, 50/60)  Please be as specific, and laymeny as possible :).  Thank you!  Edit: Since I didn't get anyone yelling at me for talking about adding a few more questions, here goes:  What is a volt? My understanding of it is the difference between the neutral and phase, but, this doesn't make it any clearer. If anyone can help out with more information, with an analogy or two, plus some technical information, I'd appreciate it very much!  What does the "earth"/ground portion of the circuit do? How does it help safety? If it helps safety, why aren't all plugs 3-pin instead of 2-pin?  Hypothetical:  If I plugged in two wires to a socket, and put the other end into something conductive (for instance, a bucket of water), assuming the breaker doesn't go off (if it would, why would it?) after I remove said wires(or turn off the socket), does the water "hold" the charge? Is it in any way unsafe?  For what it's worth, I'm assuming no. The current flows from phase-neutral, the water simply facilitates this. Right? If I'm right, I assume this means that I am in some way "using" the electricity? How does this differ if I for instance put the wires up against a block of wood? How does it differ if I stick the wires on myself?  I apologize if some of these questions show a fundamental mis-understanding of electricity. If they do, smack me across the head and point me to a resource that will educate me and help me answer such questions myself. These questions have plagued the back of my mind for a while, but I've never found the right place to ask.  I have more such questions, both hypothetical, and real (how does a stabilizer work, why is it required? Why do motors require 2x as much electricity to start up vs to run? Why can't this be optimized/why hasn't it been fixed yet?). I'm hoping I'll be able to answer the hypothetical ones myself once I gain more of an understanding, with your help.  I hope questions at these level (and their answers) are useful to at least one other person!  Again, Thanks to whoever helps me out!
57508
I recently bought a laptop. While connecting it to the AC mains for charging it up for the first time, I wondered what would happen if a power surge occurred while my laptop was connected to the AC mains.  I asked a few of my friends who told me not to worry.. the adapter I use would protect my laptop. Still the doubt lingers in my brain..  So here's my question: should I use some form of stabilizer for my laptop? My question might be simple and downright stupid, but I thought I'd ask it anyway, as my electronics knowledge is literally zero.  Note: I live in India, in case you need that knowledge.