I have an USB charger with 5V DC output.  I want to use this charger to power a 1.2V DC motor.  I think about adding an extra load, like a DC bulb, to this circuit, maybe it could reduce the voltage to my requirements.  Could you help me?
8513
I have been looking around for an easy way to convert 12V to 5V. I have seen some people saying that a simple resistor is all that is needed.  $$ Volts = Ohms \cdot Amps $$ $$ Amps  = \frac{Volts}{Ohms} $$ $$Ohms  = \frac{Volts}{Amps}$$  So applying a resistor will diminish the voltage of the circuit. That should mean that an appropriately sized resistor could simply be placed in the path of a 12V circuit, converting it to 5v.   If this is the case how would one reduce amps? Would series vs parallel make a difference in this area?   I have seen designs that include a regulator IC and some capacitors, but if a simple resistor/fuse/diode setup will do the trick, I would really prefer that.
94695
I have a powerbank with a 20,000 mAh capacity, from which I can power different devices.   The devices include an LED strip and a Raspberry Pi Zero W (RPI Zero W).   The LED strip consists of 60*5 LEDS = 300 LEDS, and will roughly draw 4.5 A with 50% PWM.   The Raspberry Pi requires about 170 mA.   The powerbank has 3 output ports, one capable of drawing 2 A, and the other two capable of drawing 1 A.   Would it be possible to somehow extend the current draw from these USB ports?  I could put them in series, such that I would have one port with 4 A, but how would that affect voltage? I need to power both my Raspberry Pi, and the LED strip.   Would the USB port be able to handle such a high current draw?
87416
I just started studying about batteries and battery chargers. I have this simple query so please help me out.  I am trying to charge my 3000mah li-ion battery. The battery voltage is around 3.6v and the charger regulates the 5v from the source to 4.2v. I connect the battery to the charger. Now what is the voltage at the output should I expect? Shouldn't the output voltage be at 4.2v so that the battery gradually charges to 4.2v ? I ask this because I am using Bq2057 IC and once I connect to the battery to the charger the output voltage is dropping to 3.63v.  My assumptions were, 1. I considered the charger as voltage source 2. Battery also as a voltage source  I experimented this buy connecting two DC voltage sources(5 and 3.3v) in parallel and measured the voltage at the node and it was 5v. So I was expecting the charger output to be 4.2v even when I connected my battery to it.    Thanks
40509
Designing the power supply for an radiation detector, need to supply up to 1500V at 2 mA from mains (170 Vdc).  I've largely considered a flyback converter, but cannot find a flyback transformer with a gain of N=~16 (for a gain of 8 at 50% duty cycle) rated for 1500V at the output winding.  Looked into charge pumps/voltage multipliers some but not in depth yet.  Also just recently learned about CCFL inverter transformers, but still need some time to understand them better.  This project requires a small size and weight, so using a large transformer is not preferred.  What are other ways to step up voltage which I may look into?
32554
When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my  supplied board when using this adapter?  Edit: This regulator accepts up to 12V inputs. So that will be no problem. A second "9V" adapter yields 15V to the multimeter. Will this one burn my circuit?
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Below is a picture of a battery shell for a NiMH circuit for a power assist wheelchair battery.  I'm taking a guess that each of the 20 batteries is 1.2V because the entire circuit is 24V.  These are rechargeable.  I'd like to convert this circuit to the same voltage (24V) and same capacity (3Ah).    First, is this possible given the space you see in this wheelchair battery shell, and the circuit board in the pictures?  Second, what are the material requirements to be able to convert this circuit from NiMH to Li-Ion and the type of charger as well?  What materials will I need to solder/weld the materials together, etc.. for the actual labor?  I'm an electrical novice, so please ask me more questions (as comments) and I'll do my best to answer.  Note: right click image and open in a new window to make it larger!
60243
I saw a battery charger that converts 220V AC to 6V DC without a transformer.   Now I am wondering why many (if not all) power adapters are using a transformer, is it about efficiency or about drifting over time?  Update: This circuit is inside of this torch
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.
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If I have a 5v capacitor and a 3v power source, and I connect the power source to the capacitor will it charge up to 3v then stop, or will the voltage rise above 3v?
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I've implemented above circuit and it was successful.  The given circuit needs 12VDC to run properly.  I want to run this circuit on 5-6VDC or 9VDC whichever is possible. I know I have to change resistors but not confirmed which to use.  Also if I use 9V battery only to activate 6V relay for 8hrs daily, for how many days will that battery work?
93331
I have a 12V battery connected to a circuit driving an ignition coil. The circuit requires 2A to run. The ignition coil produces 40,000V and the spark is measured at 50mA. By simple calculations the input power is 24W the output power is 2000W, how?   If I could harness the output power and my battery is 200Wh does this mean I can run a 2000W device for 8.3 hours, as the input is only 24W from the battery?   This does not seem right, what am I missing?   Or am I actually drawing 2000W power from the battery (over time) to charge the capacitors in the circuit etc, meaning that it will only last 6 minutes?  Thanks for the help.
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I'm making a small project which will take +5v from USB, What should I do with the D+ and D-, keep it open or short them to ground or do I have to add some components?  I want to run ATMEGA168 and 16x2 LCD with back light.
22633
Can I charge computers by inducing 5-volt into their USB connectors? Is this possible? I noticed that when my EeePC 900 is off but plugged in charger, there is power coming out of the USB port. Can this be a sustainable way of charging a PC, or a flaw in design?
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?
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I understand that many of my consumer devices charged by USB ports can charge at higher rates than 0.5A.  However, in testing, I've found they don't consume more than this. Test Setup  I have a power supply that outputs between 0 and 30 volts, and 0 to 20 amps. I set the voltage to 5 volts, then connected up a female USB to the wires correctly. When I plug in a Samsung Galaxy S4 Mini, it pulls around 0.44 amps. It is the same with a Samsung Galaxy Tab Pro. However, when I connect an iPad Air with an official lightning cable, it only pulls around 0.11 amps. Also, I tried connecting a ZGPAX S28 smartwatch and it was still about 0.44-0.45 amps.  The power supply is more than capable of outputting the maximum 2.1 amps, so why doesn't it to at least the tablets? What do I need to do in my test setup to convince the devices to consume their maximum charging current?
20192
I would like to connect an electric toothbrush motor (Braun Oral-B Type 4729) directly to external power supply. So far I have been trying at least 3 different DC power supply unit with appropriate voltage (1-5 V) but nothing happened. However motor works perfectly fine when connected just to a regular battery (AA, 1.5V)...what is happening? The only guess I have is some impedance mismatch between the source and the motor...can anyone confirm this and/or provide any solution how to connect this motor to regular DC power unit? Thank you very much!
51102
I am in hold of an Arduino board and 12V DC motor.  I need to be able to control the motor speed gradually, my intention is to output a PWM current in range of between 0 and the maximum 5V of the board to the motor.  My question is what do I need to have in order to multiply the output from the range of 0 - 5V to 0 - 12V to fit the motor?