how to test whether the led is working or not

[AskerOfGeeks]

this flashlight's battery died

**broken link removed**

so i thought i can power the LED inside it with 1.2v from a DC source and use it as a lamp.
but wen i connected a DC source (with right polarity) to the LED, it blinks and turns off immediately (every time wen i connect it blinks for the first time)
so my assumption is that the LED is not fully dead

i tried frm 1.2v to 5v

the original charger's Output is 4.5V 250MA

i used an adapter which supports 500ma

is this LED dead ??

if not then what should i do to light up this LED ??

by the by this LED looks like having some electronic components attached to it ( i think )
it looks some what like these pics

http://www.wired.com/geekdad/wp-content/uploads/2013/01/02_drop_in_660px.jpg
http://igirder.com/lights/xml-dropin/800/ledcompare.jpg
http://www.lightmalls.com/media/cat...fd36334f811d559143a7d5786aff/_/d/_dsc5650.jpg

 

[ronsimpson]

I have looked at many LED flashlights. I did a big study of flashlights.

Most the batteries point toward the LED. I have seen some that must have the batteries facing 'backwards'. The case is at +4.5 volts not 0 volts. Please double check the batteries/LED to see if you have it hooked up correctly.

Some of the LED flashlights do not have a normal switch to turn the light on/off. Many; the switch curs off the power like normal. Some the switch is not in the current flow but off to the side. The switch allows for bright/ dim/ very dim/ off. So I am thinking that maybe the LED is looking for the switch to tell it to turn on.

Some LED flashlight switches are not switches at all. You push the button once for bright, twice for dim, three times for flashing,.....There may be something complicated here that we don't understand. When the LED is out of the case this 'complicated' thing does not work.

These three cases are not common but.......I have 100s of these flashlights in a box in the barn. Most are simple but some are not....

 

[large_ghostman]

I have looked at many LED flashlights. I did a big study of flashlights.

Most the batteries point toward the LED. I have seen some that must have the batteries facing 'backwards'. The case is at +4.5 volts not 0 volts. Please double check the batteries/LED to see if you have it hooked up correctly.

Some of the LED flashlights do not have a normal switch to turn the light on/off. Many; the switch curs off the power like normal. Some the switch is not in the current flow but off to the side. The switch allows for bright/ dim/ very dim/ off. So I am thinking that maybe the LED is looking for the switch to tell it to turn on.

Some LED flashlight switches are not switches at all. You push the button once for bright, twice for dim, three times for flashing,.....There may be something complicated here that we don't understand. When the LED is out of the case this 'complicated' thing does not work.

These three cases are not common but.......I have 100s of these flashlights in a box in the barn. Most are simple but some are not....

can i ask why? you did a study of Led flashlights? and i dont mean it in the "why would anyone want to do that" kind of way, i mean it in a someone like you wouldnt collect a load of Led flashlights to stick in a box in the barn. you were obviously trying to find something out and i am intrigued what it was.

 

[ronsimpson]

I worked as a consultant for several companies that make flashlights. US and China

 

[large_ghostman]

I worked as a consultant for several companies that make flashlights. US and China

see i knew there would be a reason ok part of me wanted it to because you were working for a secret government agency and were tasked with developing a death ray Led flashlight! but thats probaly because i have watched alot of james bond in the last few weeks and everyone starts looking like M or is it Q?? its one of the alphabet anywayok back to reality and my board layout

 

[audioguru]

The LEDs are all "white" because they are a 3.5V blue LED with a yellowish phosphor on top to make "white".
Some of the LEDs have some separate strips of LEDs in series so maybe they need about 17.5V.

The metal piece probably cools the voltage stepup circuit inside it. It probably also regulates the current.

 

[AskerOfGeeks]

I have looked at many LED flashlights. I did a big study of flashlights.

Most the batteries point toward the LED. I have seen some that must have the batteries facing 'backwards'. The case is at +4.5 volts not 0 volts. Please double check the batteries/LED to see if you have it hooked up correctly.

Some of the LED flashlights do not have a normal switch to turn the light on/off. Many; the switch curs off the power like normal. Some the switch is not in the current flow but off to the side. The switch allows for bright/ dim/ very dim/ off. So I am thinking that maybe the LED is looking for the switch to tell it to turn on.

Some LED flashlight switches are not switches at all. You push the button once for bright, twice for dim, three times for flashing,.....There may be something complicated here that we don't understand. When the LED is out of the case this 'complicated' thing does not work.

These three cases are not common but.......I have 100s of these flashlights in a box in the barn. Most are simple but some are not....

oh ok thanks for ur info

 

[AskerOfGeeks]

The LEDs are all "white" because they are a 3.5V blue LED with a yellowish phosphor on top to make "white".
Some of the LEDs have some separate strips of LEDs in series so maybe they need about 17.5V.

The metal piece probably cools the voltage stepup circuit inside it. It probably also regulates the current.

so wats ur point bro ?? should i give 17.5v to make it work ??

 

[large_ghostman]

so wats ur point bro ?? should i give 17.5v to make it work ??

i think the point is that you might have to try a higher voltage yes

 

[ronsimpson]

i think the point is that you might have to try a higher voltage yes

No.....If you are playing with the "LED bulb" then only use the voltage that is the same as the battery. If you are playing with the LEDs that you removed from the bulb then that's another story.

A LED flashlight bulb is not a simple LED.
(OK I have seen some 2-AAA flashlights that only had battery---switch---LED with no resistor. But what do you expect from the bottom end of the flashlight business.)
The LED bulbs that I have worked on have a PWM switching power supply that takes the battery voltage and changes it (boost or buck) to make the correct current for the LEDs. The higher end bulbs have a temperature control so the LED does not get too hot. I have some bulbs that have a 6 pin or 8 pin microcontroller built in that allows for several modes of operation. Some have a time-out timer that shuts off the light. Some even include the battery charger.

The picture is of a bulb packed with electronics.

 

[audioguru]

You NEVER feed a voltage to an LED because an LED is a special diode, not an accurate length of heater wire like an incandescent light bulb. The diode needs a voltage somewhere from 3V to 4V for a single white LED and the voltage is different for each one. If the voltage is slightly too high for the LED then its current will be very high and it will instantly burn out.

Instead of a voltage, you feed a certain current to an LED, or to some LEDs in series. Then the voltage must be enough for the current regulator to function.

Look at the website for Cree LEDs. Many powerful white LED modules can be seen to have 12 LED chips in series inside and are rated for a voltage of about 36V. Then each LED chip has a voltage of 36V/12= 3.0V. The same LED is available with a voltage of about 6V then 6 LED chips are in parallel and the other 6 LED chips in parallel are in series with the first bunch.

 

[ronsimpson]

AudioGuru,
I AGREE WITH YOU if he was talking about a LED. What he has is a LED light bulb from a flashlight that is not just a LED. This bulb is built to run directly from a voltage source.

 

[audioguru]

I have a Chinese flashlight with one very powerful white LED inside. The LED appears to have a few LED chips inside the lens.
It is powered from one 1.2V Ni-MH cell so it MUST have a voltage stepup/current regulator circuit inside the flashlight.

I have another Chinese LED flashlight with 24 white LEDs that are ordinary 5mm in diameter. It is powered from 3 AAA "super heavy duty" battery cells.
Then the LEDs are probably all in parallel and the internal resistance of the battery limits the current.

 

[ronsimpson]

First picture is of three LED flashlight bulbs. Each has a switching power supply inside. The bulb with three LEDs; yes the LEDs are in parallel. There are tightly sorted! The black dot is the inductor for the switcher. They come in white, red, green, yellow etc. The advantage of a current switching power supply is that the Vf of the LED is not important.

The last picture is a bulb that works from 2 volts to 10 volts. My memory says that they work to 20 volts but they were never sold that way. The PCB shows the IC and transistor. The other side the board has a resistor, inductor and cap. This bulb is pretty simple. I have some very complicated bulbs. The one bulb has no case so could work on it.

 

[panic mode]

what is polarity of bulb? is it standardized?

 

[AskerOfGeeks]

here are the pics of the exact flashlight that i am talking about

https://i44.tinypic.com/30ka9lc.jpg
https://i39.tinypic.com/23s9m42.jpg
https://i39.tinypic.com/rmiszk.jpg

the battery inside was 3 x 1.2 ni-cd = 3.6v total. the original charger's Output is 4.5V 250MA
so i know the led module works in between 3.2v & 4.5v

i examined every part of the flashlight and found that there is no electronic parts or circuits inside the flashlight body.
the body contains only a switch (not electronic, an actual switch) which is used to complete the circuit between the battery and the led module.

my assumption is that there is some kind of protection circuit in side the led module which is shutting off the power to led wen i am connecting the dc source. but why it is doing this ??

now just tell me how to wire this led module to make it light up. i delivered different voltages frm 1.2v to 5 v to this led module but it is not lighting up continuously just flashing for a second at the time of connection.

 

[AskerOfGeeks]

what is polarity of bulb?

inside circle is positive and outer body is negative
https://i39.tinypic.com/23s9m42.jpg

is it standardized?

whats standardization ??

 

[AskerOfGeeks]

i think the point is that you might have to try a higher voltage yes

no i dont think so

 

[audioguru]

Does the flashlight still work when it has three charged Ni-Cad cells in it?

 

[4pyros]

There may be something else hiding in there someware.
You may have to put the neg. on the alum body where the threads are.