LED multipack / multimeter question

[daviddoria]

I bought this big bag of LEDs, all different kinds... so i figured with my multimeter i could figure out current draw, voltage drop, the kinds of things one usually likes to know about LEDs, however, i am not seeing any function that will do that....

do i need to actually hook a battery up to them and see what is going on? i am only hesitant to do that cause i dont want to burn them all up seeing what they are!

any suggestions would be great!

also, while we're on multimeters.... mine has 5 functions...
1. V
----
- - -
this is DC voltage, correct?

2. V
(wavy thing)
this is AC voltage, correct?

3. (OHM symbol, how to draw this on a computer?)
yay, i know how to use this one!

4. looks like a sound wave getting louder.... understand what i'm saying.... then it has a slash, the it has a diode... i'm guessing this is a diode tester... can this help with my LED question?

5. 1.5V battery symbol
???


any info on those would be great, or if you have an informative multimeter page that'd be sweet too!


thanks
david

 

[kinjalgp]

The fourth range is Continuity Tester/ Diode Checker. Rest all are correct.
For testing the operating voltage and current through an LED use the following circuit.

 

[daviddoria]

ahh i see.

also, the 5th thing on my list was "1.5v battery". what do i use that for? it doesn't seem to be a battery.... lol

anothing thing, the 1-5 on my first list was everything my multimeter has. does that mean that i need to get a new meter in order to measure amperage? seems like that should be a standard function...

david

 

[kinjalgp]

Yes I think you'll have to get a new meter for measuring current. But it seems very starnge to me that your meter does not have any current range. :roll:

 

[Dean Huster]

Well .....

Kinjal's second schematic for measuring the LED current is only telling you how much current YOU are letting the LED draw, it being limited by that 1K resistor to a value of (9-Vled)/1K

The current you want is the maximum current that the LED can handle without being destroyed, and that is not a measurable value. Takes a data sheet for that one. However, most LEDs will handle a maximum of at least 20ma.

You don't need an ammeter for measuring the current. Just use the same circuit that Kinjal provided on the left, but instead, connect the DC voltmeter across the 1K resistor. The reading you get on the meter is directly equivalent to the number of milliamps flowing in the circuit. Assuming that the resistor is reasonably accurate, this is a more accurate method of measuring current anyway. Ammeters usually insert enough resistance into a circuit that they change the actual value of current, lowering it somewhat.

Be careful of REVERSE voltage across an LED. Where most diodes can handle anything frm 40 to 2000 volts reverse, depending upon the diode type, most LEDs have a maximum reverse voltage rating of anywhere from 3 to 5 volts. More than that at higher current levels can damage the LED.

Dean

 

[Pilot]

Hi Dean,

Keep posting educational answers like that and you'll soon (re)gain the rank of 'Oh Exhalted One'.

I only wish I knew half as much.

Wicked sense of humour!

Ron

:lol: :lol:

 

[kinjalgp]

Yes, Dean the second schematic will show only the current R1 is allowing. That was an example of showing how to measure current through an LED. This is definately not going to show its max. current capacity because if you allow an LED to go upto this limit it will never return back. For experimenting purpose there is no harm in connecting LED with a potentiometer and slowly decreasing the pot. resistance until LED burns out. That current will be its max. limit.