See what you have done?

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To the exponents of having no resistors in series with leds:

My son got a camping led lantern that has 24 white leds in it, some of them had stopped working and some of them were intermittent, some flashing. No problems some dry joints of course.

Opened up the box and almost died with a heart attack, 24 white leds, all in parallel, no resistor/current limiting anywhere, all driven by 4xAA batteries or 6V!! :shock:

Resoldering the joints brought back some leds and just killed others. The working leds were SO HOT that would give 6 degrees burns at the touch. Yes it was cheap, brand new in a box and sold at a stall that you will not find the next week. Working leds were almost bluish by the overdrive.

So money down the drain, the "manufacturer" got his money by bad design and the seller got his as a fly by night salesman.

Please DO NOT encourage bad practises here.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I bet the design engineer's initials were JW ;-)

(and not Jan!)

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Any photos of the device in question? So we know what not to buy?

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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I have a one LED flashlight from a US dollar store that have 6 V to led and no res. it has 2 coin celles stacked (very thin) so I bet the design was for one normal coin cell and a 3 V LED.

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A coin cell has a fairly high internal resistance that acts as current limiter. Won't work with other types of batteries.

And paralleling LEDs likely only works if they are from the same wafer and have good thermal coupling.

What would a cheap chinese resistor cost in big quantities? a millicent or so?

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But then you need a PCB, in this flashligth you just "bend" the LED. It's two pices of plastic that snap together with a LED and two coin cell's that all.

Edit: remove the snap and add 4 screws :lol:

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You don't need no stinking PCB for a resistor, just cut one leg of the LED and solder a resistor to it :)

Ideal job for a Chinese sweatshop :)

Those jobs really exist there, where one person places R2 on PCBs that shift along a conveyor belt and another person places R3, the next person C1; personal space is about 2 inches each side.

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The lamp had a proper plastic case, therefore the cost of the moulds, and it looks quite nice. It has 4 1/4 circle PCBs wired up in parallel so to add small SMD resistors would have not been a drama.

I suspect that they wanted the leds very bright, which they were, but the batteries would have not lasted long. Even at say 20mA each led it's 1/5A. I would say that the leds would be drawing a lot more than 20 mA judging by the temperature, so the batteries would be dead very quickly.

Now my daughter in law is determined to have a fully functioning camping led lamp..so I wonder who will be modifying it. :? May get some samples of TI?? led driver chips with built in CC driver and boost/buck converter. That should make the whole thing reliable but the cost of 24 good quality white leds alone will be many times more than what they paid for the whole lamp.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Or use one VERY high powered - like the Luxeon 10W monsters.
http://www.philipslumileds.com/p...

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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Not THIS J.W.!

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Quote:
Not THIS J.W.!
:lol: I think the W sounds like a medicine for blood clots.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Why blame the Jehovah's Witnesses? Except for their poxy Awake and Watchtower mags - the whole armageddon thing gets boring after a while.

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I am not defending the bad design, but at one time I recall seeing LEDs with inbuilt resistors.

... and John, just tell your son to go camping during the daytime and be sure and be home for dinner time like in the old days. :lol:

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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To the OP: but you bought a camping lantern. You're supposed to light fires when camping. This lantern is going to help you do that :lol:

js wrote:
To the exponents of having no resistors in series with leds

I know we're not in the business of naming names here but surely nobody would be that stupid. (sure to make someone bite by saying that!). Excepting coin cells which as jayjay has said have a high IR and will self limit their output current. Not an elegant design but it works. In a bank of AA batteries or whatever you'd have to be dumb as a suitcase full of rocks to design something that badly.

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Quote:
I recall seeing LEDs with inbuilt resistors.
I have used them (Jaycar...get a bank loan first) but these did not have anything judging by the ammount of heat generated and by the fact that they start dying 1x1 with 6V.

Yes, great for lighting camp or bush fires or keeping warm in winter for a few minutes. :lol:

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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You'd better use an ordinary light bulb and get the best of both worlds... heat and light at the same time :)