I know questions similar to these have been asked  before. However, I could not deduce the answer to this question, because they only did tell me what I should do, but not why I should do that.  I have a laptop which needs 19V DC power, but I do not know whether I have the original adapter. I have some old adapters which seem to fit, but, you could've already guessed it, they give different output voltages.  Now I have multiple options:   I plug an adapter with 17 V / 1200 mA into the device. I plug an adapter with 18 V / 1250 mA into the device. I buy a new adapter which outputs 19 V, and plug that into the device.   Now I have the following questions:   What will (most likely) happen with the laptop if I plug in abovementioned adapters? Is it okay, is it bad, does it harm the device? Does Amp. matter? This might be basic physics; can anyone post a link where this is perfectly explained?
26704
I have a laptop that says it needs a 19V 3.42A power supply. I have a Dell 20V 4.51A power supply.  Can I use this power supply with my laptop, or will it destroy the machine?
86692
When I plug A 12V DC 8" LED strip into my car, it gets too hot to touch, but when I plug it into A 110V AC to 12V DC 120mA transformer, it works great; "cool to the touch".   So do I go buy a resister and put it in line? If so, what resister do I ask for and which band goes to the LED side?
47215
I have the following ammeter:   The seller recommends 75mV 100A shunt be placed with it. I want to know what will happen if I change the voltage going through the shunt. Should I be changing the shunt as well to read amps correctly?   I want to build a 1-40V (or maybe 50V) adjustable DC power supply and use this ammeter to measure current. What the right value of shunt that I should use to get the right measurement? Changing shunts in a lab bench power supply is impractical, of course.  EDIT: I am planning to measure only up to 5A or so. Sorry I forgot to mention this previously.
120917
I am using the original power adapter with the Dell Inspiron 6400 laptop and now when it boots up I get the following error message.  The AC power adapter type cannot be determined. You system will operate slower and the battery will not charge. Please connect a Dell 65 W AC adapter or higher for best system operation. To resolve this issue, try to reseat the power adapter.&quot;  I don't have another power supply or laptop to try. Is there a way to test the power supply, or whatever the computer uses to determine the power supply size?
15729
Possible Duplicate:        I have the opposite problem outlined in   My AC adapter (19&nbsp;V, 3.95&nbsp;A, 75&nbsp;W, 3-pin) Part No. PA3468E-1AC3 for Toshiba Laptop L40 18Z is now useless. I am currently risking using an IBM Thinkpad adaptor (my old laptop) after checking the specification. The centre pin polarity is the same, I cannot currently find any references to Wattage output for the IBM adaptor - but the only difference I can find is in current and voltage.  The defunct Toshiba adapter is rated 19&nbsp;V and 3.95&nbsp;A. The IBM adapter is rated 16&nbsp;V and 4.5&nbsp;A.  I've used the IBM for several hours with no ill effect - risky I know! The lower voltage means that the battery isn't charging - but my concern is the higher current - 0.55 more.   Could this damage the sensitive internal electrics in the longer term - or is it unlikely to make a difference. If it works, which it does - could I confidently continue to use this until I've sourced a proper replacement?
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.
96108
I want to know if it is possible to design a power supply for a circuit that can operate from DC and AC using the same input terminals.   Thus, the output should be xxV DC (5-24 or whatever is decided on), and on the input side the consumer can connect whatever he has available - 120V AC, 230V AC or 24V DC.  A transformerless AC to DC power supply can work for at least the AC side, but the ideal one looks to be the capacitive type which would not allow DC to get through, am I correct?  There is also an resitive transformerless design, not ideal at all since it is very ineffecient.     Any ideas? Thanks!
12020
I have a 13&quot; Macbook Pro that came with a 60W power adapter and a 15&quot; Macbook Pro that came with a 85W power adapter. There seems to be disagreement . Can I use either adapter with any portable Mac?
88934
The general question is: When installing low voltage RAM in a board that outputs a higher voltage to the memory module, will this fry the RAM or will it be like overclocking it?  My specific case is: I have the Alienware m17xR3 laptop with a 2630QM Sandy Bridge board. Currently, I have the stock 1.5 V modules and when I check the overclocking options in my bios, the RAM voltage option ranges from 1.5 - 1.65 V. Is this simply because the bios recognizes that these are the values which my current RAM support and thus they will change when I install 1.35 V RAM or will I have to run the 1.35 V sticks at minimum 1.5 V?  If the case is the latter, would I fry my 1.35 V sticks? Or would they become automatically overclocked and get tighter timings with a higher voltage? Or both? Or neither? I'm a bit lost :p
121975
Note that this is a theoretical question - there is no schematic I can show. I will show some schematic, but it will be a very simplified version of an actual circuit, only for illustration purposes.  Assume I have a voltage converter that takes as an input my main voltage (from a power supply) and outputs a certain voltage, for example 1.8V. It would look something like this:         &ndash; Schematic created using   When connecting my circuit to the P.S, I notice it draws too much current (the P.S shows that).  Since I have multiple voltage converters in my circuit (not shown here), I check resistance between each output of each converter to ground. I see that the resistance between 1.8V to ground is almost 0 Ohms. Now I know the fault is either in the voltage converter or one (or more) of the other components drawing power from that 1.8V.  I desolder the resistor shown in the image to disconnect the converter from the other components and see that the converter is fine, but checking resistance from the point connected to all those components still shows 0 Ohms.  My question is - how would you check which component is the faulty one, without desoldering each suspicious component? As you can see in the image, the 1.8V supply is connected directly to the components, without a resistor/bead.  For the sake of this question, assume I have access to whatever equipment needed (no matter how pricey). I wouldn't want solutions to be limited due to availability of equipment.  Thank you!
3411
I have many different AC adapters and power supplies for a variety of devices, ranging from small 5V/1A USB chargers to laptop power adapters and desktop PSUs. However, I often hear a whining noise from  some of these power supplies. This happens most often when they are not connected to a device or otherwise in use, and stop making noise when I connect a load to it such as by plugging in a device that is not fully charged.  Why do some AC adapters and power supplies make this whining noise? Why do some not make this noise? Is there anything I can do to suppress it?
60687
I have recently been working on a custom sound system in my living room. For the subwoofer, I am using a 1000W amplifier. This is currently running off of a 12V computer power supply that outputs around 650W (The power supply shuts off at a certain volume because of lack of power). I have another power supply (not a computer power supply) that is 500W but has a voltage of 13.5V, not 12. I've read that this voltage is actually better for running car audio equipment and I am using another 13.5V power supply for the head unit to power the highs and mids.  I am wondering if it would be possible for me to connect these two power supplies in parallel to increase the power to this amplifier since they are both safe voltages. Would this be possible? Would I need to use a resistor to match voltages? Or is this just not a good idea altogether?  Update: This is car audio equipment so high power ratings should not be a shock.
63074
One concept of electronics I have a hard time understanding is if things like motors, actuators, solenoids etc. use as much power as they need or what you give them.   If a motor needs 12 volts and 500ma and I supply it with 12 volts and 3000ma will it only consume 500ma? Also, if I supply it with 15volts and 500ma what will happen?   It seems logical that an LED and a DC motor are way different when it comes to requiring/using electric where as an led has to be completely regulated and (I assume) a DC motor doesn't.   Is my understanding wrong?
37633
Basically, I'm looking for some do's and don'ts. Is it bad to keep my laptop plugged in when I'm not using it (majority of the time)? Is it bad to plug it in once I've finished using it (with it having something like 30% or 70% life left)?     This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details.
16505
My laptop's cable broke and sadly it seems like I need to buy a new power supply.  What I wonder is, I've found that universal power supplies are much cheaper than the official HP ones. Are they really worth it?  Another question: the original supply has these specs: 65W, 18.5V, 3.5A. However the universal supplies are more powerful (90W, 100W) and come in integer voltages (17V, 18V, 19V, etc). Are they compatible? Should I set them to 18V or 19V?
117600
I'm using a repurposed ATX power supply for my hobby projects since it's got 3.3/±5/±12 outputs, all of which are really convenient. But one thing I didn't really think about until I slipped my probes across the pins of an opamp, since I've always dealt with commercial/proper lab power supplies in my school labs, was that an ATX power supply will gladly deliver lots of current if that 12V line (or any other) is shorted to ground. The poor LM318 didn't stand a chance. My meter and supply survived, but in the interest of not killing anything in the future, myself included, I was wondering what the best option was for short/overcurrent protection?  I was thinking of sticking some high wattage resistors at the output of the supply before connecting them to the rails of my project breadboard (I use a separate breadboard with terminal blocks for power, which the ATX supply connects to). The problem is if I'm drawing a lot of current (LEDs etc) this will sag the voltage on the line. And, for example, if I use a 1W 200ohm resistor on the 12V line, it limits my current to only 60mA - if I want more, I need some really beefy wattage resistors. I can probably work around the voltage sagging by using a voltage regulator (eg at 10V), but this all doesn't seem like the best way to go about doing things.   I'd appreciate some input from someone more experienced than I am.
585
I realize connecting two different voltage sources in parallel is a contradiction (in an ideal circuit). But if I were to connect this in practice and measure the voltage across points A and B, what value of voltage would it show? And how much current would be sunk by the 5V battery? (Non ideal conditions)