releted to  I wonder what the use of the number of mA printed on an AC-DC adapter/converter means.  I am charging a Bluetooth headset, which came with a AC-DC adapter, over USB using a "DIY-hybrid-cable" and it is working. The original AC-DC plug (which I've cut) has 450mA printed on it and the USB standard AC-DC plug, to which my "hybrid-cable" is connected, has 1.0A printed on it.     Does the mA number has any relevance? Why? I feel I am missing important knowledge.
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.
19453
When measuring the AC voltage across a DC battery (CR2032), and I am getting 6v. The DC voltage across it is 3.01 volts. I also tested on a 9 volt battery; again the same thing. I am reading about 20 v AC and 10v DC. I am using MASTECH MAS830L multi meter. I also used another multimeter, and I get the same result.  When I am putting the multimeter probes in the same polarity with the battery, I am getting the AC voltage, but none if I put the probes in reverse polarity.  Why is this happening?
84072
I have HP 1514 printer. I noticed that the usb type A plug coming from printer has as buzzing feeling when touching skin. I connected one multimeter probe to the USB plug and the other one to ground pin in my power outlet as shown in the sketch below. The multimeter shows 18V. Shows 0 when measuring current with same setup.    I believe that this is not okay? What could be the cause? Could I damage my Macbook by using this printer (I have used it for a year with no problems, though)
86412
I have powerbank that provides 5v (presumably regulated) power, as typical of most usb interface powerbanks. I have been trying out my powerbank with different phones. It works on all except one. I have tried it with various USB cables, making sure I didn't overlook anything foolish. Then, I looked at the AC adapter of the phone that it didn't seem to be compatible with. The adapter read: 5.4v DC output. The device's official website or manual doesn't tell me what the input voltage should be. So I have the following questions   Is the fact that the device's AC adapter creates a DC 5.4v output enough to assume that, this is the correct voltage for my cell phone? If 5.4v is the input voltage, then when I attempt to power it with a 5v power bank, am I hurting it? Thus far, it just seems to be non-responsive when I try this. It seems another explanation is polarity mismatch. I'm aware that laptops have a polarity correction feature, which could explain why I can charge this phone via my laptop. Is there any other way to tell if polarity is an issue, given that I don't have access to detailed product information (unless the official website is updated, or something)   So that's the gist of it, I'm not sure why my powerbank isn't charging my phone. And I'm having difficulty troubleshooting the underlying problem by myself. Any tips big or small will be appreciated.
24924
I've got 15 devices each with a current of 20mA and I am interested in running them all for 10 seconds. How would I go about working out the amount of mAh a battery would need to provide for this?   I understand that to find the mAh to run something for an hour you take the current and multiply it by 1000 and so my understanding of his problem was that you could get minutes by multiplying by 100 and then seconds by 10. So What I thought I needed to do was something like this:  15 x 20mA = 300mA/0.3A   0.3 x 10 = 3  3 x 10(seconds of runtime) = 30mAh   However I am not sure if this is right, so I would be grateful if someone could look it over and point out my mistakes.
77583
I asked this question on Physics StackExchange but was advised to ask it here. When I charge me cell phone or notebook or whatever device what should I plug in first? Should I at first plug in usb charger to the AC wall outlet and only then to the cell phone or vice versa? What are the precise physical arguments for this? And are there any differencies at all? I think it is safer to plug in wall outlet first because of peak charge. Can someone give me a technical explanation? Thanks in advance.
64789
So I'm wondering if anyone has any information about the Dell power supplies which have 3 contacts on the barrel.    I know the 3 are power, ground, and some sort of communication link. Does anyone know what the communication line is for and/or what kind of protocol it uses?  Thanks  EDIT The reason I ask is I'm considering trying to build my own semi-advanced charger (not for a laptop but something else... it's a long story) and while I'm sure I could figure out a charging circuit given the internet as a resource, I was wondering what they use the communication line for and if it's necessary for my purposes. It seems the answer is no since I will be the only one using my device and thus don't need to worry about people plugging in not kosher chargers...
53183
I have some USB 3.0 ports on my motherboard which can deliver up to 900 mA of current I believe.  If I plug in a USB 2.0 cable, I can still get up to 900 mA right? I have some devices that uses USB charging and outputs from 1A to 2A but I'm not sure if the cable provided is a factor or not since I'm just using a generic USB cable for this.
111626
I am wondering how to read the numbers on electrical wiring separated by slashes such as 12/2. What do the numbers refer to? What other numbers should I watch out for when purchasing wires to be run within the walls and sockets of a home? P Thanks.
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.
96386
I am trying to include a DC jack on one of my PCBs. I am just setting up the footprints now, and I am not quite sure which pin is which. What do the symbols on the drawing mean?  I have included a snap of the schematic below, it has been taken directly from the .
14892
This is a philosophical question. Over the last few years, many of the household devices, particularly those that are more mobile and etc are DC devices. Are we at some point where a DC household may become a possibility and Edisons dream might come true??  The array of DC devices    Internet stuff - routers, modems Most complex computer electronics - Desktops, laptops, NAS, phones, tablets, gaming consoles, etc Lighting - LED More that I cant think of or perhaps know which also convert AC -> DC   Problems with AC     Each device needs its own power supply ( AC-> DC power brick). This is a) Unpleasant to look at and deal with, and b) a costly point of failure.  Each power brick may or may not be optimized, as far as power conversion goes.   Alternative - A central (or a few ) high capacity power adapter which converts the AC into a DC power grid for the house which can then be tapped directly by the various devices. This eliminates the need for the power brick, and hopefully the central power adapter is of state of the art, and can be upgraded seperately from the devices, as needed.  Need standardization of:   Device voltage. Currently devices use 5/ 9 / 12 or others I may not be aware of, for this idea to work they need to work with one particular one, unless switching between voltages is cheap enough, or multiple DC lines are provided. Power socket input. Each device appears to have its own input socket type, this should standardize if the power supply cable should be comoditized, perhaps USB - C will play a part here.
15444
I've heard about laptops such as the new Chromebooks that are charged via a wall charger that connects to a USB-C port. I'm quite happy that this will supposedly standardize laptop chargers but I'm a little unclear about how this works.   Existing USB ports provide a 5 volt source, but the laptop chargers provide up to 20 volts. is there some kind of higher voltage line or are the USB-C powered laptops running on a lower voltage?  All this information I've seen gives a fairly vague idea of providing more power, providing up to 100 watts rather than 10 watts. Even so, my laptop is not the most powerful machine and the charger still outputs fairly near 100 watts, I can imagine more chargers for power laptops providing much more than 100 watts. Could a general purpose USB-C charger really power all these machines?
50365
this time I'd like to ask a few questions about capacitors, all noob questions again;   What's a better idea, having one capacitor at 5x farads or five capacitors at x farads each? I want to get a certain amount of voltage and want to discharge the direct current as fast as possible. I'm trying to build an amateur railgun, and intend to shoot projectiles that weigh about 10 grams. Using the formula that someone helped me with in my other question, in order to give that a speed of 100m/s at a total of 20.000 uF assuming 2% efficiency I'd need a little less than 112V's. The question is, is this amount of voltage I need my capacitor or series of capacitors to provide for the duration of the shooting? What determines how much voltage a capacitor can hold? This may come off stupid as I am aware that there is a voltage rating when you buy them, but better safe than sorry. I was only assuming 2% efficiency, and depending on my rail length it could be higher. The question is, what determines how fast the capacitor will discharge and how it can be prevented from going above the rated voltage?
68958
OK, the one answer I got was way off target, and another commenter couldn't figure out what I was asking, so I'm restating the question...  Are 15A 3-prong grounded outlets actually rated to 20A, allowing them to be used on 20A circuits? And if so, why, when the outlet can never be asked to supply more than 15A by anything that would be plugged into it?  More info:   had a comment that 15A outlets were actually rated to 20A. However, by design, there is nothing that will plug into a 15A outlet that will draw more than 15A. An appliance that draws more than 15 amps would have a "T-blade" plug that wouldn't go into a standard 15A outlet.   In addition, outlets are always wired in parallel, meaning that a 15A outlet would never have to transmit the amperage draw of a "downstream" outlet; you never "daisy-chain" outlets by connecting hot to neutral, for a number of reasons.  So, there is AFAIK no situation in which a 15A receptacle would ever have to handle more than 15A, even if installed on a 12AWG, 20A-breaker circuit.  If all the above is true, why would a 15A receptacle even have to be rated to 20A?
25013
Is there any IC which converts 230V AC to 5V DC? As lossless as possible. I want to connect my microcontroller to an ordinary electrical socket and I don't have enough space available. Thanks.
84243
I've just bought a portable battery, but the portable battery don't comes with an adapter for the house current; it only comes with a USB cable so I can charge it with my laptop. My mobile phone came with a charger, and I want to know if is safe to use that charger with the battery without problems, even though the output has a higher amperage. These are the specifications:  Battery input: 5V, 1A Charger output: 5V, 2A  Will the output only give the quantity that the input is requesting, or will the input overheat because it cannot handle all the current it receives?