How much precious leccy juice does an LED use ??

clyst

clyst

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On my switch / trip panels beside each switch is a small dim LED about 2mm dia which indicates when the switch is on . Very usefull for nav lights etc but the cabin lights and other equipment that is generally left on most of the time like VHF ,instruments etc are also indicated by these LEDs. Now all you eletrical guys how much do they consume ?? Approx as there are no marking at all on them . If there were I doubt if my poor ol' peepers would be able to read it as they are soooo small .

cheers

Terry
 
The panel mounted ones listed by Maplin are all 30mA maximum. But I have found others on the RS site as low as 2mA
 
They consume so little .. Just switching a 12v light on and off would use enough power to keep one of these going all night .. 33 hours = 1 amp .. 100 amp battery 3300 hours .. /forums/images/graemlins/laugh.gif
 
I have used 5 mm led's with a 1 K dropper resistor so each led will consume about 10 mA.

The normal for 5 mm is 20mA but I have used a bigger resistor ohm value and the glow of the LED is still OK.

If your LED's are smaller the current consumption may be even lower.
 
It was a million years ago when I learned my electrical/electronic theory but I seem to remember that putting a resisitor in series with a LED, or other power consuming component, simply means that the voltage drop across the LED goes down while the voltage developed across the newly introduced resisitor goes up with the total power consumption across the two increasing. (I=VR)
The only way to reduce the total power consumption is to use lower power components.
W=IR^2
W=VI
I=VR
If voltage remains constant and R goes up then I must go up. Or have I forgotten something.
 
Sorry ... major flaw in your algebra. The formula is V=IR so I =V/R which means for a given voltage the current goes down as resistance is increased.
Morgan
 
The series resistance of an LED that is fully turned on is very low, so the forward current is controlled by a series resistor, often termed a current limiting resistor as it has to limit the current to below a maximum rated value, which for small indicator LEDs is often around 20-25mA.

Connecting an LED across a battery without a series resistor could short circuit the battery and cause damage to the battery (and LED - but they are cheap). LEDs in an manufactured panel will have some form of current limiting built into them, or the panel. But if you are building or modifying one, its worth bearing in mind.

As everyone has said, it is likely that the current consumption of an LED on a switch panel is very low, probably less than 10mA.
 
[ QUOTE ]
Or have I forgotten something.

[/ QUOTE ] As morganandlm says V=IR also W=I²R or V²/R.

So putting a resistor in series will reduce the current, and the power consumption. The volts across the LED will be reduced. The higher the resistace the lower the current and the dimmer the LED, until you get to the point where the LED does not light at all.
That is what you do to run a standard LED from 12 volts. The Maplin catalogue even explains how to calculate the resistor value. (Useful when it's a million years ago since you learnt the theory /forums/images/graemlins/laugh.gif)
 
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