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Questions tagged [power]

Where power is a primary concern for the design under discussion. Use the "low-power" tag when that applies.

5
votes
4answers
4k views

Advice on cleaning up 5VDC from a wall-wart

Assumption: I think it's generally true that commercially available AC/DC wall-worts can be expected to be pretty noisy (e.g. you can't count on much better than 5% stability). Background: I'm ...
4
votes
3answers
997 views

What's needed to get 100 mA from a USB port?

I'm trying to build a stereo speaker system for use on a laptop. I want to keep it as simple as possible, so I'm thinking of using laptop's audio output to for the audio signal and a USB port for ...
10
votes
17answers
35k views

Can you harvest electrical energy from the air?

I found a website recently about harvesting energy from the air, and I am wondering if someone could tell me why the following wouldn't work? Their "generator" is supposed to make electricity from ...
7
votes
2answers
5k views

What's the difference between a “Switching Regulator” and a “UBEC”

I want to regulate the voltage from a battery down to 5v to power an Arduino and a Wi-Fi webcam. I’m not too keen on a linear regulator as a lot of power is wasted, so that’s led me to look at ...
6
votes
3answers
354 views

What type of battery to use?

I Am currently looking for battery suggestions for use in one of my projects. My projects current consumption (calculated) is 360mA for the main rotor 2.5A stall Link (my exact part RK370SD-4045) ...
8
votes
5answers
4k views

Constant-Current for a 20W LED

Can someone explain "constant-current" circuits? When are they necessary? What happens without one? What's the simplest version of such a circuit? I bought some 20W LEDs off ebay intending to make a ...
2
votes
1answer
2k views

What Happens When You Exceed a Solid State Relay's Max Amps?

Had a quick question. I am using a Crouzet GA8-6D05 SSR to relay xmas lights for the holidays. I basically hacked an extension cord (120VAC US <1Amp) to do this. I am currently using a spliced ...
2
votes
2answers
447 views

Netduino powerd by USB wall charger

I have a IPhone wall charger. Can I plug my netduino into it to power it via USB?
1
vote
2answers
178 views

Does socket orientation have an effect on sound?

Is it possible that the socket orientation (in Europe: one pin 230V, the other ground) can have an effect (albeit very small) on the amplifier behavior of a very old stereo sound system? What is, if ...
23
votes
6answers
8k views

Why do high voltage power lines hiss when it's raining?

I noticed when walking home the other day that the high voltage (200kv I believe) lines running through here were hissing in the rain. What is causing them to hiss?
3
votes
4answers
8k views

USB without Vcc

I want to remove the Vcc pin from a USB cable and connect my computer to a device. My goal is to allow the device to communicate with the computer while not charging the device. Does some section of ...
13
votes
3answers
5k views

How far apart should PCB traces be for mains isolation?

As a hobby project I'm building a power line monitor to detect when a load is switched on and turns on some additional loads. I have 120 V 220 V running through my board and was curious what the ...
29
votes
5answers
28k views

Why is it important for mains power supplies to be isolated?

In all the computer power supplies and other power supplies I've taken apart, I've noticed they are fully isolated from the mains. Galvanic isolation through transformers, and often optical isolation ...
4
votes
5answers
669 views

Need comments and ideas for LED flashlight project

I'm thinking about making a simple LED flashlight. After doing some research, I think I'm going to use some 5 mm 12 Cd white LEDs with 3.6 V drop which can pass 20 mA. I'm not yet sure how much ...
7
votes
3answers
13k views

How to measure the maximum power of a solar panel

What is the best way to measure the maximum power generated by a solar panel?
5
votes
6answers
2k views

Is it okay to briefly exceed a resistor's power rating in a high-reliability product?

I am dealing with a 0.01R 500mW resistor. It is a current sense resistor and measures the current flowing through a MOSFET and inductor. According to simulations, when the supply starts up, the RMS ...
26
votes
5answers
7k views

How much power is really wasted by a wall wart?

The title pretty much sums it up... Hyperbole aside, how much actual power is consumed by a typical wall wart when the device it's attached to isn't powered on? And are there designs for wall warts ...
2
votes
2answers
248 views

Is there a hobbiest's source for Akros Silicon PoE evaluation boards?

I am interested in experimenting with PoE for a variety of small embedded controller projects. Is there a hobbiest's source for any of the Akros Silicon PoE evaluation boards? Or is there another bit ...
3
votes
4answers
401 views

Male Apple Dock Connector => USB (power only)

I have an old external battery for Apple devices (has 30 pin Apple Dock Connector), and I want to repurpose it to be an external battery for all my USB devices. Anyway, I don't have much experience ...
7
votes
4answers
9k views

Does it make sense to use MWh/h as unit of measure?

Since MW is actually the rate of energy is being used, why would we use MWh/h as in Fingrid's electricity market Load and Generation forecast page? Wouldn't MWh/h be the same as MW???
3
votes
3answers
1k views

How can I handle a low power condition with PIC?

I am working on a project that uses a PIC24F mcu. The power to my pic is backed by a very large capacitor (1F). When there is a main power loss, I can sense that immediately via a port pin but the PIC ...
8
votes
4answers
3k views

Why does Oscilloscope cause short?

I want to measure how much power my PIC is using. At the output of my 3.3V regulator I put a 1 ohm resistor in series with the rest of the circuit. I was going to measure the voltage drop across that ...
4
votes
2answers
13k views

Is there any way to determine power rating of a potentiometer?

I salvaged a 1kΩ potentiometer from a broken circuit. Is there any way to determine how much power can it take without destroying it? EDIT Picture of the potentiometer: The distance between left-...
14
votes
5answers
5k views

detecting zero cross in ac?

I need to detect zero crossing for a soft starter. A long while ago, I have done it using a 1 Mega ohm resistor directly connected to micro controller at one side and live power at another side. I was ...
3
votes
1answer
1k views

3 phase ac induction motor speed control

I need to speed control small ( 0.25 HP ) 3 phase 2800 rpm motor to achieve speed in the range of 6000-7000 rpm. I know basic stuffs. ( have created soft starter etc ... which is good enough for ...
4
votes
1answer
97 views

Are the specs for the “Ears of the World” challenge reasonable?

I saw a post today on the Make blog about a challenge to create an extremely cheap FM/SW radio kit for developing nations. The organization sponsoring the challenge distributes donated wind-up powered ...
17
votes
5answers
38k views

Are watts usually measured in watt-hours?

Pardon me, I'm a total newb to electronics. My question is, when a device is measured in watts, such as a 60-watt light bulb, is this ALWAYS supposed to be assumed to be watt-hours, i.e. 60 watts per ...
6
votes
2answers
2k views

How to go about sensing AC power in existing wiring

Is there a practical way to sense 60Hz AC power in a pair of wires? Measuring the exact power or even current isn't necessary; it would be sufficient to know whether the load is pulling more than, say ...
8
votes
2answers
1k views

Is it true that the power line frequency is kept accurate by atomic clocks?

I've heard rumors that the power line frequency is kept stable and accurate by syncing it with atomic clocks. Is this true? What kind of accuracy does it have? Is this true everywhere?
5
votes
2answers
2k views

Arduino how to get more Power

I have an arduino project that is almost finished. Now it controls a series of ShiftBrites(ShiftBrties being 10bit RGB LED's) now they use a simple 4 wire configuration(Data, Logic, Clock, Enable) ...
6
votes
2answers
7k views

Connecting arduino and separate power supply grounds

I am working on an arduino project that uses transistor switches to power on high power leds that are powered by a separate 24 volt power supply. My issue is that I have two different grounds, making ...
6
votes
2answers
11k views

Power line communication principles

What are the principles of implementing Ethernet over power lines ? Is it reasonable/possible to create an Arduino shield which will provide both power & network ? (properly isolate the "dangerous ...
16
votes
7answers
4k views

What if I overload a cheap AC adaptor?

I'm experimenting with PIC microcontrollers and various related circuits both on plugboards and simple homemade PCBS. I'd like to use various old AC power adaptors I have lying around to power my ...
4
votes
3answers
1k views

Plugging a UPS into an inverter

First off, I am aware that plugging an UPS into an inverter is a bit redundant. The only situation I can think of it being useful is in a car when you want full amps for cranking over the motor but ...
16
votes
5answers
31k views

How do I connect two identical batteries to increase the consumer lifetime?

If I've got a device that uses a single battery, and with that single battery, the device lasts an hour, and I want the device to last for two hours, I'm assuming I can wire two batteries up and it ...
4
votes
5answers
5k views

How to Determine a PCB's Power Requirements?

Disclaimer: I have very little (almost none, really) electronics experience. I purchased a set of IR illuminator boards off of eBay. The only information that the seller provided was that the board ...
-1
votes
2answers
799 views

Help me find an adapter USA --> Israel [closed]

I just bought a cat feeder from the united states, and brought it to Israel. Israel has 220V power sockets, and the device (that came with the timer below) doesn't fit, obviously. The problem is I ...
13
votes
4answers
19k views

Deciphering a DC jack schematic

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 ...
7
votes
3answers
2k views

What is the coolest way (using passive cooling only) to step 12V DC down to 5V DC

I'm building a project that needs both 5V and 12V rails which will draw about 1A on the 12V and 0.5A on the 5V. I was thinking of using a 7805 to produce the required 5V but this could generate some ...
55
votes
8answers
45k views

Decoupling capacitors: what size and how many?

Lots of chips nowadays require smoothing capacitors between VCC and GND for proper function. Given that my projects run at all sorts of different voltage and current levels, I was wondering if anyone ...
3
votes
2answers
9k views

Mains Hum Filter

Are there any chips or simple circuits available for removing the 50/60Hz mains hum from a regular power supply unit? So I've got a few bits of audio equipment that have bad PSUs and they have a bit ...
6
votes
3answers
447 views

best quick&cheap power supply inverter

I have a +5V power supply and need to invert to a -5V supply sourcing about 25mA. I've got an LMC7660 running now. It's ok for the short term, it outputs -4.4V with 100mV p-p switching noise, but that'...
11
votes
2answers
4k views

How can I stop a solid state relay from latching up?

I'm trying to use a power relay (PR26MF) to turn on and off a device. The device takes a 9v supply and typically draws ~250mA. I'm finding that the relay turns on just fine, but when I try to turn it ...
6
votes
5answers
442 views

LED producing heat and best power supply

I was wanting to get a bulk lot of small LED lights similar to Basic LED - 5mm Yellow. I want to put them in balloons so that the balloons appear to glow in a dark environment, so I have a few ...
5
votes
4answers
3k views

how to get more power out of a astable multivibrator?

Hey I have a circuit like this, I am powering this circuit with a 6v alkaline battery, the circuit works just fine with 100uf capacitors. But the problem is I want to replace the LED with a dpdt ...
3
votes
2answers
2k views

Inductor for LM2575

Can anyone suggest a 330uH inductor and associated Eagle .lbr for use with an LM2575? I've been looking all day for this! Any suggestions would be appreciated.
17
votes
2answers
3k views

How might you use a LiPo battery as backup for mains power loss?

Many people seem to run their projects off the mains (e.g. with a wall wart) or from a battery, but there doesn't seem to be too much discussion about how to run a device off the mains, charging a ...
31
votes
2answers
12k views

How to calculate battery life

How do I calculate how long a battery operated product will run? Here's what I've got: 2 AA, 1.5V, 2700mAH batteries Voltage Regulator with a Iq of 25 uA Voltage Regulator Eff = 80% Active Current = ...
4
votes
1answer
371 views

ArduinoBT UART Communications

Is there any way to monitor what is being sent to the WT-11 module via UART? I'm trying to implement deep sleep on the WT-11 and can run the iWRAP "TEST DEEPSLEEP" command successfully but the deep ...