I have a power adapter that, according to the label, is rated for...  Input : AC 220v Output : DC 10-12v 2000MA  It has dual outputs allowing me to power two devices at once.  I am plugging it into a UK mains outlet and on measuring the power tips they both read 20v.  I have opened the unit up and the only components inside are a transformer, 4 rectifier diodes and a capacitor.  With such a small component count, which of these components could be causing the incorrect voltage to be output?
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.
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?
85097
Every time I plug my MagSafe 2 power supply into an power outlet, this Mac's aluminum body gives me a mild vibrating sensation and sometimes an electric shock. After searching for info about my problem on many forums, they believe there's some problem with my grounding.  My country's electricity is about 220v. If I plug it into a 110v power outlet should it solve the problem?  I'm not an electrician so I don't really know what to do.
30238
Note: I am very new to the more advanced side of electricity. I do not have a firm grasp on the exact mechanics.  Lets say I have an example circuit:  5V Power Supply -&gt; LED -&gt; Resistor -&gt; Ground  Now the LED is receiving 20ma and 5V. If I were to switch the LED and the resistor however, the LED should receive less voltage but the same current, so wouldn't it be dimmer? Or would it receive the same voltage?  I've looked at these two threads and their answer doesn't help.
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??
110230
The AC adapter supplied with my laptop is designed to accept voltage in the range of 100-240VAC at 50-60Hz, but the AC cable that plugs into the adapter unit itself is only rated to 125VAC 7.5A 2.5A.  I know the adapter can accept 220V power, but is it safe to use this cable with the AC adapter to plug into a 220V socket?  Edit: The part in question is a 90W HP Smart AC Adapter.  The laptop does not cause the AC adapter to draw more than about 80 watts from the socket (as measured with a Kill A Watt meter).  Edit 2: The amperage rating of the cable as marked on the attached label is 2.5A, not 7.5A.
56600
I've search for a solution to my problem both on this site and on Google but I did not find a complete and adequate response.  I need a circuit that switches two 12v sources (one that comes from a lead-acid battery powered by a solar panel and the other source comes from the output of a 220-12v switching power supply) without the final power output being interrupted during switching (this is very important!).  Notes:  - The final power output will be used to power 12v devices (30 Ampere maximum).  - The sources voltage range is 11-14.7v  How can I switch between two 12V sources?
58774
I am trying to build a 18w amplifier based on  however my  doesn't have a center tap on the secondary winding  Is it possible to use this power transformer for this project?  I also tried it using a solid state rectifier (the one with 4 pins: - AC AC +) connecting the ac to the transformer the (-) to ground and the (+) to the standby switch (please see the schema), although I could measure the correct voltage on the (+), there was no current going on the grids of the tubes, not even on the filtering capacitors.  or maybe the problem is somewhere else in the circuit? appreciate your help
104843
Question says it all really. Based in the UK so mains is 240v and 20 amps. It's a lighting circuit.
30063
Manuals of several various electronic devices I came across recommend connecting their AC adaptor first into the device, then into mains. I always thought the reverse order is safer because I thought that connecting into mains can send a voltage spike into already connected device. Are power supplies (adaptors of laptops or other electronics) designed in a way that there is no risk of harm to their device when connecting? Are both connecting orders equally safe in these terms?
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?
43544
I was trying to figure out how much power I actually use when I am charging my phone. Here are the specifications of my charger:   Input: 100/240 V, 50–60 Hz, 0.15 A Output: 5 V, 0.7 A   I've heard that in order to calculate this, you need to pay attention to the input.  $$P = V\cdot A = 240\ \mathrm V\cdot 0.15\ \mathrm A = 36\ \mathrm W$$  I charge my phone for 4 hours a day at most. In that case, I use 144 watt-hours a day, and 51840 Wh a year, or 51.84 kWh. And that seems awfully lot, considering that all the articles I've read about the power consumption of chargers stated that they used about 2 kWh a year. I know I charge my phone too much (I really need a new battery), but it still doesn't add up. Are my calculations wrong? And if they are, what is the correct number?
42592
I am looking at  (dual low-voltage power amplifier). On the fourth page, there is a sample circuit; right at the V+ input there is a symbol that looks like a capacitor. However, it looks like it is shaded in. What is that?
55034
I'm designing a project that controls 110VAC (plug in, socket out), and also has a microprocessor inside.  I'd really like this project to not need a wall wart to get it's 5V, so I want to include a small DC power supply inside.    Apple's USB power adapter looks like a great small design that I can fit inside my case.  I'm guessing this is a switching power supply but I can't find any teardowns or schematics anywhere.  Does anyone know how this thing works?  I know I could make my own 110V->5VDC supply from a bridge rectifier and some caps, but I'd like to also be super safe.  What's in the Apple brick?
96763
Thanks to the help of a few of the other guys I have my AC to DC rectifier working, and the rest of the power supply working.  Now while testing the power supply, my 18V AC transformer gets rectified and put into my circuit below   And I end up with 1.3-26V DC output selectable via the pot R2.  Now while running this @12V with a LED strip light, running about 600mA my heat sink got quite hot. Not hot enough to cause the thermal protection in the LM317 to cut in but hot enough to get me thinking.  Power dissipated = (Vin - Vout)*Il = (26 - 12)*0.6 = 8.4W  My heat sink is rated at 11 C/W and I pasted the LM317(TO-220) on.  Max C/W is = (MaxRunningTemp - ambientTemp) / power = (60-25)/8.4 = 4.2 C/W  Does that sound right, never done any heat sink calculations before. So I would need a heat sink rated at &lt;4.2 C/W  I would not see my self running this over 500mA again but running this circuit at 5V would change a lot? The power dissipated would be 42W if 5V @ 500mA. What can I do to prevent needing a HUGE heatsink? and are my calculations above correct?
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?
113860
Can I use a 12 V power supply as the source of electricity for this circuit? And where do I connect the positive/negative of my power supply?  I'm a bit new to this so please understand, thank you.