LED torch adaption

Hi guys,

I need to adapt a little LED torch from a standard LED light to an Infra-red LED. It's all very simple, but I don't know what sort of IR LED to get. The current LED just has one pin touching the batteries and the other bent back to make contact with the switch when it's on. The batteries are 2 x CR2032 3V Lithium batteries. Can anyone tell me what sort of rating IR LED I would need to get as a replacement I can't see any writing on the current LEDs to get a clue?

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regards, James Luff
Gamertag: Lufferov
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Reply to
James Luff
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There generally isn't any writing to be found.

If the driver is controlling current, just get the polarity of the new LED correct, and pretty much any IR LED should work - if scavenging, the optical encoders in mechanical computer mice provide two good IR LEDs - or just buy any suitable one. With a current driver, ANY LED should be fine.

If it's controlling voltage, and the present LED is white, you could be in for trouble - but voltage control is a lousy way to drive LEDs anyway, as they are not well-specified in voltage, but very well specified in current.

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Cats, coffee, chocolate...vices to live by
Reply to
Ecnerwal

Thank, but I'm new to all this so:

Reply to
James Luff
[snip]

If you're absolutely certain there are no other components in the circuit, the 'driver' he's referring to may be built into the LED itself.

If that's the case, you may have to experiment with an IR LED and some resistors to find something that will work in your torch...

HTH

Reply to
Randy Day

Yep, the circuit couldn't be simpler, so the driver (still don't know what a driver actually is) may be built into the LED I guess. Is there a way to check? Think I'll just pop down to Maplins, buy an IR LED and just see what happens, the worst I can do is bugger up the LED which will cost me next to nothing anyway.

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regards, James Luff
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Reply to
James Luff

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Reply to
JeffM

A circuit to control the current or voltage being fed from the battery to the LED.

..and what, if anything, is on the other side of the switch? If it's wired directly to the other side of the battery, then there is no driver as such (or it's remotely possible that there's something built into the base of the LED - but then the LED would look a bit different than the standard LED.) That would be a simple, failure-prone, but cheap (consumer goods like cheap, especially if the maker is well-insulated from customers) method of voltage control, dependent on the voltage of the batteries being low enough that the LED won't draw too much current.

If the switch is connected to the other side of the battery by a resistor, that's a simple, though inefficient, form of current limiting, still somewhat dependent on the operating voltage of the LED.

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A White LED tends to operate at a relatively high voltage - in either of these cases you might burn out a IR led swapped in - but as you say, they are cheap, so give it a try. Might try it with only one battery at first, which would cut the voltage in half.

The longer lead of a new LED should be the lead that is connected to the positive side of the battery.

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If there's some sort of slightly more complex looking lump (often enclosed in epoxy or plastic) there might be a more sophisticated driver controlling the current - or not. Never can tell with consumer goods until you dissect them.

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Cats, coffee, chocolate...vices to live by
Reply to
Ecnerwal

I think go for infrared LEDs based on output and having a beam width or beam angle that appears good (or is about the same as that of the visible LEDs if any secondary optics exist), and having overall dimensions about the same as those of the existing visible LEDs. I give a fair to high chance that if you pop out the visible LEDs and pop in the infrared ones, things work out at least largely A-OK.

Battery life will probably decrease, since IR LEDs generally have a lower voltage drop than visible ones and if current is unregulated they will draw more current. They can also take more current, due to lower voltage drop (and also accordingly thicker bonding wires since a given wattage requires more current due to lower voltage drop).

Sorry, warranty is limited to refund of what I got paid by unsatisfied readers (showing a receipt or cancelled check) to post this! :) :)

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

Yes, that seems to be how these el-cheapo 1-to-1.5" LED flashlights are being made. I remember measuring a few i-v points on one of these a year or so ago, it resembled a bare LED with no current limiting. The internal resistance of the batteries is the only current limit here.

Yes, I'd say definitely start with just one battery and see what happens.

James, do you have any way of telling if an IR LED would be, in fact, producing a "sufficient" IR beam in your setup? If not, you could experiment with a visible red LED, and if things work out then try the IR LED.

Regards,

Mark

Reply to
redbelly

This is common with those 2032 based LED lights, just the battery and the LED. It uses the internal resistance of the battery (approx 20 ohms when fresh per cell) to provide the current limiting. Add a resistor in series with any IR LED you put in there, to limit the current some more. 100 ohms would be a safe value.

Dave.

Reply to
David L. Jones

My experience is that IR LEDs are rated for 50 milliamps or more. Typical voltage drop at that current is roughly 2.2 volts less than typical voltage drop of white LEDs at their maximum rated current.

2.2 / .05 is close enough to 47 ohms.

More appropriate may be to draw 80 mA from fresh "coin cells" or 50 mA from ones in "average condition and at end of a 30 second usage period" and measure the voltage at that point. Subtract 1.4 volts from higher of these, and didvide that by the amount of current that the LEDs can take for a little while (I suspect generally 75 mA for IR ones) and that is the minimum appropriate resistor. Not that I actually tried this, but I give some chance of this indicating 39 or 33 ohms (maybe even less) if using "coin cells" that are typically used in "keychain LED flashlights".

For that matter, I have heard of IR LEDs with 100 mA rating. Also, I have yet to blow an LED with current 5/3 times its "absolute maximum" rating, though its life expectancy could well be reduced quite a bit (from

100,000 hours for most other than white, UV, violet, purple and pink).

Just keep in mind that with an IR LED, the greater current draw means shorter battery life. And most LED "keychain flashlights" won't give full-blast performance for long. You may want two AAA or AA cells and a

33 ohm (conservative) or 22 ohm (a little aggressive) resistor.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

The problem is the little keylight style torch case has no space for a resistor. Let alone changing the batteries as another poster suggested.

--
regards, James Luff
Gamertag: Lufferov
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Reply to
James Luff

Then you can do without the resistor. The worst that can happen is you blow your IR LED, which is probably unlikely anyway. Or take out one battery, you only need one for an IR LED, there is no need for the 6V provided by the two batteries.

Dave.

Reply to
David L. Jones

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