How well do LED's respond to over-volting?

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V

Viper GTS

Lifer
Oct 13, 1999
38,107
433
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A week ago I was wondering if it would be possible to produce a LED "bulb" to replace the bulb in my 4 cell Mag-Lite. The other possibility I considered was an entire head replacement (to allow for more LED's).

I found this on ebay... Only three LED's, but it would give me something to play with & see how I liked it.

The only problem I see is that the seller claims it works on 3 cell mags (4.5V) - Mine is 4 (6V).

I don't mind a reduced life (say it only lasts as long as the regular bulb), I'm presuming they would be significantly brighter at 6V than at 4.5V? Is it going to burn out in 20 minutes?

Viper GTS
 
V

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
Originally posted by: notfred
I'm pretty sure "over-volting" isn't a word...
Click to expand...

If you have any suggestions as to a better way to get my point across, let me know. I suppose I could have said "excessive voltage," but over-volting was easier to type.

Confused

Hmm, that doesn't look good. I did find this site which confirms pretty much the same thing - I have to find a bulb specifically intended for my flashlight.

Viper GTS
 
Jeff7

Jeff7

Lifer
Jan 4, 2001
41,596
19
81
Originally posted by: notfred
I'm pretty sure "over-volting" isn't a word...
Click to expand...

Well neither is "notfred" but we still say it sometimes.:p
The link that Confused posted sums it up pretty well. LED's have a rated voltage. Don't exceed it unless you want to burn stuff.
To answer your original post though:
I don't mind a reduced life (say it only lasts as long as the regular bulb), I'm presuming they would be significantly brighter at 6V than at 4.5V? Is it going to burn out in 20 minutes?
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Yes, they probably would be considerably brighter at 6V than at 4.5V. The life would be more like 20 deciseconds though, not minutes.;)
 
Z

zsouthboy

Platinum Member
Aug 14, 2001
2,264
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It will work for a few minutes, then.. the light will go out, and it will smell like gunpowder :)
 
M

Monel Funkawitz

Diamond Member
Oct 12, 1999
5,105
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LED's aren't bothered by voltage as bad as over-current.

Use Ohms law to figure out the resistor value you need, and install it somewhere in the LED thingy or flashlight.
 
V

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
Well, I found EXACTLY what I want - Drop in mod designed for a 6D cell mag, should work perfectly on my 4 (and I plan to replace it with a 6).

Helios

Problem is it's $200.

But it would definitely get people's attention.

:D

Viper GTS
 
Evadman

Evadman

Administrator Emeritus<br>Elite Member
Feb 18, 2001
30,990
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Originally posted by: Viper GTS
Well, I found EXACTLY what I want - Drop in mod designed for a 6D cell mag, should work perfectly on my 4 (and I plan to replace it with a 6).

Helios

Problem is it's $200.

But it would definitely get people's attention.

:D

Viper GTS
Click to expand...

930k mcd? owie.

 
W

WinkOsmosis

Banned
Sep 18, 2002
13,990
1
0
Hmm I'd like to make some LED driving lights for my car. Much cooler than Xenon... No gas of any kind, pure white.
 
S

SSP

Lifer
Oct 11, 1999
17,727
0
0
Originally posted by: Viper GTS
Well, I found EXACTLY what I want - Drop in mod designed for a 6D cell mag, should work perfectly on my 4 (and I plan to replace it with a 6).

Helios

Problem is it's $200.

But it would definitely get people's attention.

:D

Viper GTS
Click to expand...

Okay correct me if I'm wrong... but couldnt you just create an object (say a small metal rod) the size of a battery that can conduct electricity to replace the 4th batter so you have 4.5 volts from the remaining 3 batteries?
 
V

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
Originally posted by: SSP
Originally posted by: Viper GTS
Well, I found EXACTLY what I want - Drop in mod designed for a 6D cell mag, should work perfectly on my 4 (and I plan to replace it with a 6).

Helios

Problem is it's $200.

But it would definitely get people's attention.

:D

Viper GTS
Click to expand...

Okay correct me if I'm wrong... but couldnt you just create an object (say a small metal rod) the size of a battery that can conduct electricity to replace the 4th batter so you have 4.5 volts from the remaining 3 batteries?
Click to expand...

Sure, but regular mag-lite's are cheap. Might as well just get another one.

Viper GTS
 
A

arcas

Platinum Member
Apr 10, 2001
2,155
2
0
The voltage-current curves for LEDs are non-linear. Once the LED begins to conduct, small increases in voltage result in huge increases in current (ie. the resistance across the LED drops rapidly as voltage increases). If you're not careful, you can melt the LED.

This thing is rated at 4.5V. Most white LEDs are rated for 3.5-4V so this guy probably already has a current-limiting resistor built-in and the LEDs are probably wired in parallel. If so, it's just a matter of changing the resistor to accomodate a 6V input instead of 4.5V. If not, you'll need to add a resistor. Typically, an LED draws 20-30mA so you can add a 60 ohm resistor (to yield 25mA current at 6V peak battery voltage) before the LEDs.

3 LEDs, though, aren't going to be very bright compared to a normal Maglite bulb. They'll last a long time but don't expect these guys to perform like a spotlight (a Maglite mod consisting of 3 Luxeon LEDs would be an entirely different story!). I've seen some Maglite mods that consist of 36 or more high intensity LEDs and they're not bad but with that many LEDs, your costs go way up and, frankly, your current requirements begin to approach that of a regular light bulb.

 
Colt45

Colt45

Lifer
Apr 18, 2001
19,720
1
0
just do it like this:

[-]------------------[led]-------{diode}-----{diode}-------[+]
...................|-----[led]----|
...................|-----[led]----|


most silicon diodes drop about 0,6v.. so two in series should drop 1,2v; close enough to 4.5v.
just use whatever.. 1N4001's or something, theyre common and cheap as hell.


hopefully my crappy ascii art shows up.. lol
 
flood

flood

Diamond Member
Oct 17, 1999
4,213
0
76
overvolting 4.5v -> 6v should be just fine. LED's are more sensitive to over-current than over-volatage if there is a current limiter (which there appears to be).
Just like processors, LEDs are conservatively rated so you can 'overclock' them a bit.
The life will be reduced, but it will still last much longer than a regular bulb.
I'd say youve got nothing to worry about.

If you want to drop down the voltage, SSP has a very good suggestion. You could just put one completely dead battery in there (aluminum foil shorting the + and - leads).

EDIT:
the reason the led failed in the bit-tech article is because he didnt use a current limiter. You can see from the pictures that he connected the LED directly to his power connector.
 
E

Eli

Super Moderator | Elite Member
Oct 9, 1999
50,419
8
81
Aren't flashlight mods awesome? :D

Here's another good site

I'm surprised I've only heard about the Luxeon Star by one person in this thread.

By all means, if you're looking into LED-izing your flashlight, look into this LED! :)

180k mCd each. :Q

Edit: Just looked at the drop in mod.. That's awesome. 3 5w Luxeon Stars. :Q It's 200$ because these LEDs cost like 44 bucks each. :( The 1W versions are only about 15$.

The batteries only last an hour though.. But it sure is bright. :D
Originally posted by: Garfang
Check out the CandlePower Forums :)

Good stuff there. If you're like me when I found that site, you'll spend the next 14 hours reading about LED flashlights and flashlight mods.
Click to expand...

How sadly true... I'll probably be browsing for another couple of hours, even though I've already been through most of it. ;)

Wow.. this post was attacked by the emoticon monster. :p
 
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