Joule Thief

[WilbyInebriated]

I noticed a very tiny black thing soldered in line on the pos rail-ring. I believe it is a diode.

I wonder about this diode thing. In those 70 leds I bought last spring, the lights work fine with the ac wall line, but they are very dim with the secondary.
This ring light showed the same behavior.
It was terribly bright with 4 batteries, I shorted across various batteries and 3 AA's dropped the amps to 108mA which is still much too high for a led, but when I dropped it to 2 AA's it only drew 3.8mA which is very dim. It is OK, for area lighting, and more than a nightlight because there are 24 of them, but how did the amps draw diminish so much?

It was when I looked really close because of this question and I saw the very tiny black item with 270 printed on it, that I connected the dots to the string of leds.

These must also be diodes and their purpose must be to limit the amps somewhere, although this does not seem to be what it is doing.

I would love some help with this.
Is there any one who has any idea what is going on here?

small surface mount components like that can be diodes, resistors or caps even. can you meter it with a diode tester to make sure it is?

[jeanna]

small surface mount components like that can be diodes, resistors or caps even. can you meter it with a diode tester to make sure it is?

I do not remember how to do what you suggested.
Here is what I did.
I put the dmm on diode mark... battery and switch are off.
The amount ends up at 28
on the ohms meter it also says 28

But, I only did this procedure once a long time ago, I am not too sure I did the right thing to test it.

Please advise, and thank you.

jeanna

[DreamThinkBuild]

Jeanna,

If the diode is on the positive rail it's most likely just a protection diode just in case the batteries are put in backwards. I've seen this in a couple of my solar lights I have taken apart.

[jeanna]

Hmm,
Thanks DTB, you are the 3rd person who has told me this.

I guess it is in the string for the same reason, but it is interesting how it kills the brightness of the leds.
If digital cameras didn't adjust for the light I could show you. It is a pale grey color from a blazing bright white.
And the same comparison is true for the string of leds which are intended for ac.

OK then,
I will short over the diodes and see what happens with a joule thief.
They are in parallel and I was wanting to make 4 clumps of leds in series, but maybe I will just see how it works as a parallel set of lights being run with a jt.
It only cost $6.88.
I like the shape. The ring does well inside a regular lamp shade and makes a good substitute for a bulb in a lamp. (But not if it only lasts 6 weeks which is what these very bright chinese things do.)
I might need to cut out the switch too.

thanks,

jeanna

[WilbyInebriated]

I do not remember how to do what you suggested.
Here is what I did.
I put the dmm on diode mark... battery and switch are off.
The amount ends up at 28
on the ohms meter it also says 28

But, I only did this procedure once a long time ago, I am not too sure I did the right thing to test it.

Please advise, and thank you.

jeanna

testing in circuit can sometimes be problematic. albeit hard to replace the component if you remove it and change your mind. the thing that bothers me is the 270 on it. doesn't seem right for a diode to me. if it was a resistor, the 270 should mean 27 ohms, which matches your dmm measurement.