Homemade 9v Disaster

phatalbert · Nov 4, 2005

This was my first real time dinking around with flashlights so I though I'd follow the short instructions available here: http://flashlightreviews.com/mods/9v_mod.htm for making a 9v light. I ended up with a burnt finger and three dead nichia CS's. I'm guessing there's supposed to be a resistor in there or something? This is a sad day for me, my nichia's and the 3 bucks I spent on those dumb radio shack terminals. :mecry:

HarryN · Nov 4, 2005

Well, that is not bad actually. I have blown up plenty of more expensive stuff than that. Now that your first project has failed, you are ready for the long journey toward success.

With 3 LEDs in series, I am a little surprised that they burned out so quickly - I assume that they were white ?

OK, first step - try rigging it up with wire clips first and measure the current going through the string. If it is above the rating of the LED (approx 20ma) then it is time to add a resistor. You can buy some cheap large resistors at R/S for testing, but 1 - 5 ohms should do it.

Are you pretty sure you put the LEDs in the right polarity ?

phatalbert · Nov 4, 2005

Thanks for the response, you guys always make me feel better

Actually, it was two in a series, after one burnt I replaced it and then it burnt along with the other one. I'll definetely look into a resistor next time, though I may save my remaining CS's for "safer" projects.

Doug Owen · Nov 4, 2005

HarryN said:
OK, first step - try rigging it up with wire clips first and measure the current going through the string. If it is above the rating of the LED (approx 20ma) then it is time to add a resistor. You can buy some cheap large resistors at R/S for testing, but 1 - 5 ohms should do it.

QUOTE]

Harry's right, you need some resistance. It'll take more than a few ohms, I'd suggest 150 ohms, that's what the PacLite uses on high (with two LEDs in series with a 9 Volt battery). I'll give you about 16 mA per LED.

And there's a neat way to measure the current in this sort of setup. Just clip one pair of terminals together, say the male battery connector to the female light connector. Leave the battery female and light male open. Then put your current meter leads on those open connectors to complete the circuit (battery female and light male).

Doug Owen

greenLED · Nov 4, 2005

it gets much more expensive when you're dealing with Luxeons and fancy converters from the Shoppe :awman:

paulr · Nov 4, 2005

You definitely need to add some resistance if you're using an alkaline or 8.4 volt nimh battery. With a 7.2 volt battery (these are common) you might be able to get away with direct drive with a high-Vf led, but I still wouldn't recommend it. Choose the resistance to put about 20 mA through the leds.

James S · Nov 4, 2005

I did one similar to this, but with 2 3mm LED's that I shaved down and glued together like this:

For calculating the resistance, there are plenty of calculators on the web, my favorite is here:

http://led.linear1.org/1led.wiz

phatalbert · Nov 5, 2005

Thanks alot for all the helpful info guys! I will definetely consult this forum before attempting anymore mods or homemades.

andrewwynn · Nov 5, 2005

4.5V pretty high for most leds... so 3 in series probably better..

A better solution is the little circuit that will buck the voltage to run 1 led so that it doesn't dim.. it's a very clever circuit you can build with making your own hand-wound inductor.. a very nice 'diy' feeling.

In any event.. 'what he said' about blowing expensive parts.. I went almost 2 yrs w/o blowing any parts doing my testing than i managed to melt THREE u-bin emitters and maybe 4 fatman drivers... it gets 'dicy' on the cutting (bleeding?) edge.

-awr

Homemade 9v Disaster

phatalbert

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HarryN

Flashlight Enthusiast

phatalbert

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Doug Owen

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greenLED

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paulr

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James S

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phatalbert

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andrewwynn

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