Question, How can I turn On an LED powered by 2 AA Batteries Switched on from a low voltage .15v from a small Genorator? When the wind blows The small Generator has a propeller and I would like to send a signal to turn on the The LED that is powered by 2AA batteries. The generator Is not powerful enough to light the LED on it's own for this application. It is a model of a wind turbine for demonstration purpous so it will not produce enough power on its own to light up anything.  Thank you for your help
123652
How to activate a  pn2222 transistor with very low voltage  0.15 volts or 150 mV   from a small dc can motor Generator. I would like the Transistor to turn on as soon as the generator starts producing current.  the problem I had is the Power source is running back through the Transistor and spinning the Motor/Generator. I want the Generator to give power to the base of the Transistor to activate some LEDs.  This is a small 6 volt can motor as a wind generator. I also tried a 3A Solid state Relay  but it needs conrtol voltage at least 3 v. Would it be reasonable to try a Ge transistor instead of the Si one .   Thanks
88042
I have a bright white LED from a flashlight. Aproximatley How long will it light up with a 150 farad 2.5 volt capacitor. Do I need a resistor? And if so how many Ω? The capacitor is a maxwell 150 farad 2.7 volt boostcap .
75428
What I would like to do is have an LED turn off 1 minute after the power is turned off. The LED would be on all the time when power is on. Thus:  Turn power on: LED comes on immediately. Turn power off: LED stays on for 1 minute and then turns off.  This is to signal when someones eyes have adequately adjusted to the dark in a darkroom.  Thanks in advance.
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
94117
I have a question that may seem silly, but I am only new at this type of thing:    Is there a sensor that I could connect to an LED (via an integrated circuit of some description, I assume) that would allow the LED to light up when the sensor came into range of a certain frequency?  I would like to run this setup from a 9v battery, if possible.  If this is possible, could I get a parts listing for what I would need for this setup?  Added:  What i was trying to achieve was a small device that incorporated an led that lit up when it detected a certain frequency/radio wave from another device (possibly a vehicle). Maybe an antenna instead of a sensor might be the go? Not sure yet and I am still very green with this. It was just an idea I had that may be useful for my work environment.
34051
What is a suitable frequency for 15V/3A DC motor? Is there any effect on the motor when the frequency is changing? I am confused with this until now and the Internet shows a lot of theory that confuses me.
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?
78706
I'm new to electrical engineering, and probably asking the wrong question. Not sure how else to phrase it.  For the question, I'm going to use an example layout of simply a 9v battery attached to a toy DC motor.  From my understanding of my , the voltage coming from the battery through the motor will be around 9v. The current will be from 0amps to however much the battery can supply without frying. What decides how much current goes through the motor?
102279
[![enter image description here][1]][1]I am trying to build a simple circuit to power a load with two different power supplies (5 V and 0.7 V).    When one is active the other one is not and it's disconnected from the load. I know that this would be straightforward with a manual switch but I need this application to be automatic, maybe using a MOSFET as a switch controlled by a uC but it's not clear to me how I can achieve that. I wouldn't use a relay since I have constraints on cost and size of the footprint.  Thanks. Claudio
62508
For the purpose of a project I wish to power an arduino using a supercapacitor charged to 5V. The supercapacitor will be fed straight into the power Vin and GND terminals on the Arduino. No power plug or USB connected to a computer will be connected, so all power is to be drawn from the supercapacitor. Previously I have powered the board using a 0-12V variable voltage supply, and the arduino draws between 20 and 35 milliamps.  My question is this, if I connect the supercapacitor straight to the arduino board, will the arduino govern how much current to draw from the supercapacitor? Or will I need to place a resistor in series with the supercapacitor discharging in order to regulate current and stop the supercapacitor rapidly discharging and frying the board?  Lastly is this feasible at all? I am aware that as the 5V from the supercapacitor will drop off the period during which the arduino will run is limited.  Any advice is appreciated as I  do not wish to fry my Arduino board attempting this.
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.
39949
I want to supply constant voltage to my LED's but the supply varies from 3.7V to 4.2V (Li-ion battery). I cannot use 3.3V voltage regulator as it will need at least 4.3V voltage at the input but my battery can supply only 4.2V max. so is there any other way I can supply regulated 3.3V to my LED.   RGB LED = 3.3V, 60mA Battery = 3.7V - 4.2V, 3000mA Number of LEDs = 24 The LED's are connected in parallel
10886
When I was young and learning about electricity, a fabulous tool for understanding voltage/current/resistance was an incandescent lightbulb (in my case it was a small 3V bulb). When you doubled the voltage by putting two batteries in series, it glowed 4x as bright, but heated up more and was more prone to burning out. When you put two lightbulbs in series, they glowed 1/4 as bright. When you put them in parallel, they glowed normally, but drained the battery twice as fast. Etc.  This day and age however incandescent bulbs are on the way out, and LEDs are replacing them for a good reason (like not burning out every few months or so). But LEDs are different and follow different rules, which I don't understand myself very well.  I was wondering - can LEDs be used in the same way? I know that for a LED to be usable in a similar way as a classical lightbulb, you need to put it in series with a resistor, otherwise it draws too much current and burns out. I think you can even buy LEDs with built-in resistors. But would they work in the same fashion? Would changes in voltage be accompanied with corresponding changes in brightness?
105960
I see every day high voltage, high current; high voltage, low current. I rarely see low voltage, high current; why?  I know that I can take a high voltage, high current signal, send it through a step-down transformer and theoretically get a low voltage high current (with the same power output, of course), but I never see this done.  Can someone give me a reason as to why I wouldn't want a low-voltage high-current scenario?
21750
For the sake of not incorrectly connecting my power supply and damaging my board I'm going to ask a relatively dumb question. Is ground on my board the negative terminal on my battery? Explicitly should I connect the ground to the negative terminal of the battery?
10727
What would be the least expensive way to boost a DC voltage?   The aim is to convert 1.2&nbsp;V/1.5&nbsp;V (from an AA/AAA cell) to 3.3&nbsp;V to power a small 8-bit microprocessor, like Atmel ATtiny45 or ATtiny2313, and also (if possible) 6&nbsp;V to power a buzzer.  Also, what would be the maximum current one could draw safely from an alkaline battery, after boosting it to 3.3&nbsp;V/6&nbsp;V?  Finally, how I could compute the duration for which the alkaline battery would last, given a certain consumption?
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)