How do you test your led's?

[VegasF6]

I was checking a q5 on a star tonight by touching bare leads to the board and I tripped the protection circuit on not 1 but 2 junky ultrafire 18650's. I can't imagine it was pulling that kind of current in the milisecond before they blew. So I stacked 3 C cell alk's together with magnets and the emitter was still fine. The 18650's both tested 0.0 volts aftwards, but after going into the charger at least one of them has come back, remains to be seen on the other.

How do you guys normally do it?

 

[Zero_Enigma]

I normally use a 9v battery clip with leads on it and clip a special 4xAAA battery holder which both sides have 9v clips on. One side is 2xAA power and the other is 4xAAA power. I normally use the 2xAA just to be safe first. I clip the 9v cap on with the leads to the 2xAA side then touch the +tive to the LED +tive and the -tive to the LED -tive. If it does not light up then I try the other side of the LED. If that does not work then I change the clip to the 4xAAA side then repeat. If nothing lights up then I check if the LED's polarity on the pads are reversed by putting the +tive on the -tive. If that still does not work then I just test the +tive to +tive on the actual LED emitter (not the star) itself. If the LED lights up then probably ther eis some coating or something preventing me from lighting up the LED on the star pads.

That has happened to me before on one of my P4 SSC's. I resolved that problem by soldering to the emitter directly while having the star still mounting for extra heat transfer but later I got some 'solder paste' which cleaned out the whatever problem was preventing me from touching the pads.

Hope that helps some.

 

[VidPro]

cheap bench power supply (ya can gets one for less than 100$)
lithium cell
li-ion cell and 1.4ohm (or more) resister
cheap voltage regulator tied to a cheap power supply (max current ~1a)
plug them into the wall socket (really but only ACrichie 110v leds)
3 large or 4 small alkalines
whatever is handy

 

[Markcm]

I also use a bench top variable voltage and current power supply. If you're looking for an example, I'm happy with the price and performance of this 18v 3amp unit from kitsusa.net

 

[VegasF6]

I also use a bench top variable voltage and current power supply. If you're looking for an example, I'm happy with the price and performance of this 18v 3amp unit from kitsusa.net

Wow that is a pretty nice looking power supply. It will give 3 amps at any of those voltages? Seems like a fun way to power 5 crees in series.

It won't give higher amperage at lower voltage?

 

[Markcm]

Wow that is a pretty nice looking power supply. It will give 3 amps at any of those voltages? Seems like a fun way to power 5 crees in series.

It won't give higher amperage at lower voltage?

Unfortunately, no. The max amperage is 3 amps on this unit regardless of the voltage setting. (amperage and current are the same thing)

The amperage and voltage dials on power supplies like these are "maximum" limit values which are user adjustable meaning that the power supply will do its best to achieve the set values with in the limits of either 18 volts or 3 amps. It can push 3A at 18 volts but you cannot get more amperage by decreasing the voltage.

For anyone new at this who wants to give it a try, here is a bit more in-depth info:

Think of setting the knobs in order: Starting with both knobs at zero (fully counter-clockwise) set Voltage first, then Amperage second.

The power supply will try to achieve the set voltage by pushing as much current as you allow by setting the amperage dial but will not push more current than is required to achieve the set voltage through what ever load you may have attached. Remember that the two LCD displays for voltage and current on the PS are only meters indicating what is going on at the output leads.

For an example of powering an LED, you can start with voltage and amperage turned all the way down and nothing attached. First turn the voltage up to the desired voltage of approximately 3.7v, then attach the LED. Now you can slowly turn up the amperage while watching the amperage display on the PS; the LED will start to light as the amperage knob value increases. Because you have set the voltage limit to a reasonable value of 3.7, the current will rise up to about 1 amp and then stabilize, it will not continue to drive up to 3 amps even if you crank the current knob all the way to max because you have reached your set voltage level setting.

If you do increase the voltage and amperage levels, the PS will drive harder until you blow the emitter or it reaches its limits.

You could also start by setting both values to zero, then crank up the voltage all the way, then connect the LED (nothing will happen yet because the current is all the way down) now slowly turn up the amperage until the current readout on the PS reaches the desired value (say approximately 700-900mA for an average emitter like today's CREE's). Now the voltage will not continue to climb because you have limited the current so the PS can not achieve the peak voltage across your load; the voltage displayed is the Forward driving voltage (Vf) of the LED at the current you have set.

When testing an LED, keep in mind that the "forward voltage" which is the measured voltage on the LED while it is working will be lower that the applied set voltage of the PS. For example, you may set the PS to 3.8v and turn the current knob up until you are pushing about 700mA and you will notice that the voltage has dropped to about 3.3v; this is normal

Of course there are many variations of LEDs, so these numbers are just approximate but hopefully will give an idea how to get started experimenting with a PS without blowing the first LED you hook up to it

Anyone else, please chime in if I stated this incorrectly or was not clear.

Hope that helps.

-Markcm

 

[VidPro]

Think of setting the knobs in order: Voltage first, Amperage second.

Anyone else, please chime in if I stated this incorrectly or was not clear.

Hope that helps.

-Markcm

OK, right before
"Think of setting the knobs in order: Voltage first, Amperage second. "
say Turn both ALL the way down :thumbsup:

but you already said that later.

i am laughin, because what you just said, is the first thing i learned, when using it. It was confusing for a few minutes to figure out HOW each of the items would function, when you cant have current without voltage, and you cant have voltage without current. but you splained it well.

when working with leds, always turn the current down, from when you were charging car batteries i gotta keep remembering that.

 

[TigerhawkT3]

Some DMMs (like mine) have a diode/continuity check. If you have the polarity correct, the DMM will send a tiny bit of current through, making the LED glow faintly.