Go Down

Topic: 4 Legged capacitor?! (Read 12315 times) previous topic - next topic

fungus


Hmmm.  I would have thought "connected in parallel" not series.



A white LED won't even make it to 20mA at 2.7V.
Advanced Arduino

dc42


If it can do 86 amps for 5 seconds then it can do 20mA for about six hours...but that's to discharge to half voltage so your LED would be dim. If you run at 10mA you might be OK but it would take two connected in series to keep your LED at 20mA all night.


For a capacitor, the fundamental equation is Q = C*V where C is the capacitance, V is the change in voltage, and Q is charge. If the current is constant, then Q can be replace by I*t, where I is current and t is time. So if you charge your 400F capacitor to some known voltage and then discharge it at a constant 20mA, it will take (400 * 1)/0.02 = 20000 seconds (about 5h30min) for the voltage to drop by 1v.

In practice, to drive any LED other than a red one, you would need to use a boost converter.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

fungus


In practice, to drive any LED other than a red one, you would need to use a boost converter.


Or two of them in series.
Advanced Arduino

dc42



In practice, to drive any LED other than a red one, you would need to use a boost converter.


Or two of them in series.



Yes, but then you would have the problem of making sure that they charge equally. A switch mode converter would also make use of the energy more efficient than a series resistor or linear current regulator.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

fungus


Yes, but then you would have the problem of making sure that they charge equally.


Making a switch mode converter work well down to 1V isn't much easier...
Advanced Arduino

dc42

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

fungus

Advanced Arduino

cmiyc


I found this 1 legged transistor with arms.

You got me busted in a meeting when I started laughing out loud...
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

7brian4



I found this 1 legged transistor with arms.

You got me busted in a meeting when I started laughing out loud...


Oops, sorry..... I hope you don't work in the funeral business or something.

Henry_Best


I found this 1 legged transistor with arms.
The arms are used to control WAVE forms...

bigred1212

Okay, I ordered one of these and it showed up today. 400 farad.

I'm going to make this circuit:

http://www.digikey.com/schemeit/#g0h

If I have that correct, L1 should go dim once the cap is charged with S1 in the initial position.  Throw the switch and L2 should light until the cap is drained.  Voltage on the cap is 2.7.  With a standard red LED, I'm not even going to bother with a resistor next to it.

Step right up, ladies and gents!  Place your bets on how long the cap lights the LED!

MAS3

Not for very long.
You're throwing a lot of energy at that LED.
Wear safety goggles.

I can guess what kind of discussion this will turn to now, i'm not going in to that.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

bigred1212

What kind of discussion do you think it will turn into?  I'm curious.

nickgammon

Please, not that again.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

bigred1212

This has the smell of some sort of holy war of which I'm not aware.

Maybe I'll back slowly away. 

Go Up