Decrypting LED ring Requirements

[Cliff321]

I bought these little 25 LED light rings because I had a yen to make a couple of desk lamps like the Tolomeo Classic Task Lamp by Artemide. I'll make 'em from Siberian Elm I harvested on my property.

Anyway The website where I bought 'em said they are 9 - 14 Volts at 3 Watts
Yah somebody goofed up because there's no way that these things can run on 3W.
There's only two leads and EIGHT (this is EDITED) resistors rated with code 181 which means 180Ω.

I have a little variable PSU that goes up to 12 VDC at 3 Amps ( 3KW). It will not get the rings to light up.
So I'm a little stumped.
Any suggestions?

PIX below
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Sorry this image is upside down
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The package is entirely unhelpful with not one single word about electrical requirements - - unless it's in Cantonese
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[Cliff321]

Not half as many resistors - - there's only 8. sorry

 

[Dick Cappels]

You have eight resistors and (if I counted correctly 24 LEDs, so there are probably three LEDs per string. Figure approximately 3.5 volts x 3 = 10.5 volts, so you would need 12 volts to get the thing to light up, and you would hit 25 milliamps with about 14 volts in. The voltage requirements can vary something like ±15 among manufacturers, so the actual voltage needed might be quite a bit over what your power supply can put out.

 

[ClydeCrashKop]

When I bought an LED fixture with a "Try-Me" package, there was a 23A 12volt Thumbcell battery and a button switch in the package to demonstrate it. Is there a battery in yours? What voltage?

 

[ronsimpson]

Hi Cliff,
Do you have a volt meter?
Maybe the red and black wires are backwards.
By looking at the board it looks like three LEDs and a resistor. This should light by 12 volts. I dough you will see any light at 9 volts.

 

[Cliff321]

My PSU does do 12 VDC at 3 amps I would have though this suvfficient.

I tried reversing the polarity against the possibility of a color blind chinese assembly line

I have an ATX PSU I can hook up and try. I think that has more amps available. I'll take a look.

Thanks for the input

 

[ronsimpson]

More amps is not the problem. With out a meter it is hard to know. I think there is about 0 amps now. The problem is not your power supply.

 

[Cliff321]

I have a multimeter. Can barely use the thing. Should I be testing volt draw?
One day they'll make one with a GUI interface and a key board and I'll finally figure 'em out ;-p

 

[4pyros]

They should run off 12VDC.
Get your meter out and check for 12 volts at the board.
If yes do a diode check on the LEDs.

 

[ronsimpson]

I have a multimeter. Can barely use the thing.

Because of you comment; Don't measure current.

Does the power supply have voltage? Volt meter needs to be set to VOLTAGE DC not AC. Voltage range should be greater than 12V. Many meters have several places to in cert the probes. Use "common" and "voltage" do not use 'current'. Sorry but I have to assume you don't use the meter.

 

[Cliff321]

Because of you comment; Don't measure current.

Does the power supply have voltage? Volt meter needs to be set to VOLTAGE DC not AC. Voltage range should be greater than 12V. Many meters have several places to in cert the probes. Use "common" and "voltage" do not use 'current'. Sorry but I have to assume you don't use the meter.

An assumption that is mostly correct.
I can barely use the thing. It is however a perfectly good multimeter. Not a Fluke, but a serviceable one with two sets of jack inserts and a dial with more things on it than I understand. Yes, I can set it to measure DC volts.
I can measure current draw That's why I bought it in the first place: to check the line voltage and current draw when I was installing machinery in my shop. I didn't want to be under-volting my motors.

Set inline to catch the volts drawn by the LED ring? I am petty sure I remember how to do that.
Or the output of my little PSU?
What am I testing?

This is my multimeter
It's got Jacks for Com Volts MilliAmps and up to ten amp current. It's pretty bullet proof with overload protection.

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[ronsimpson]

"Try Me Light" What a name.
This is like getting a car from "Hope You Make it Home" motors.
"Good Luck Health Care" Doctor, will I live?..... If you are lucky!

Do we assume the light worked at the factory?

Lets do some simple tests.

1) Are the resistors good?
Meter, Red probe in "VΩ". Black probe in "COM". Meter set to Ω. Omega for ohms.
Short the probes together. Meter should read a small number. 1 or 2 or 0 .....
Probes not touching the meter (depends on meter) will read, "open" or "1999" or "∞".
WITH NO POWER APPLIED TO THE LIGHT. Touch the probes to the ends of one of the resistors. (The solder blobs) The meter should read near 180. Because of the other parts on the board........A reading in the area of 150 to 220 is fine.
I think all the resistor will read the same number, with in 5%.

2a)Lets do some more tests and learn about the meter.
WITH NO POWER APPLIED TO THE LIGHT
Touch one wire (red or black) where it connects to the power supply while the other probe touch where that wire is soldered on the LED board. The meter should read near zero ohms.
2b)Set the meter to continuity mode. Next over from Ω. Looks like a little speaker with sound going out. Touch the probes together. You should hear a beep. This is real good for testing wires. Touch the red wire where the power supply is and touch where the red wire hits the LED board. If the wire is good you should hear the beep.

Test 2 is important. I have seen bad connectors many times. Bad test leads. Almost never bad wires but it happens. Several time I have seen where the insulation was not removed from the wire.

More tests next time.

 

[4pyros]

"Try Me Light" What a name.
This is like getting a car from "Hope You Make it Home" motors.
"Good Luck Health Care" Doctor, will I live?..... If you are lucky!

LOL

 

[Cliff321]

"Try Me Light" What a name.

That is pretty funny, but to the credit of the chinese translators - - if you look at the package (right where the last 't' is in the phrase "try me light") there is an otherwise unused circular part of the vacu-formed plastic cover where once there might have been a little battery and button rig to let the potential buyer do exactly that "Try Me." And I bet that the battery was long dead from countless little tiny asian fingers poking the button on store shelves, and these were sold, as is, to some over-stock type house where the battery and switch and were pulled tossed and the ring re-marketed.


ANYWAY, This is humiliating. I had a bad probe wire. Swapped out the leads and Presto Chango (that's peasant latin for "magic stuff happened") and everything worked

Now I gotta either build or buy a bridge rectifier and a three way resistor set up with three way switch to to change voltages from 9 to 12 to 14 and I'll have a three position LED light ring. Actually I'll have three of them. I suspect that if I can purchase most of it, it'll be smaller in size.

Thanks for all the input.

 

[4pyros]

three way resistor set up with three way switch to to change voltages from 9 to 12 to 14

Why would you do that?
What you need is a regulater.

 

[Cliff321]

Why would you do that?
What you need is a regulater.

Well, it seemed to me to be very direct to get a 14 VDC 3Amp PSU like this one
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And build a little step down resistor circuit with a three position switch where one position dropped the voltage to 9Vdc and another to 12VDC and the third position was direct from the transformer?

However a quick search gave me this regulator
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Which, while I can not see where the potentiometer is on the thing, should let me use the above PSU and control the voltage across the whole 0 - 14 V range.

The description confuses me - - it says in the bullet points

• Rated Output Current: 3A
• Max. Output Current: 4A (more than 15W, preferably with a heat sink)

And that strikes me as conflicting. Which is it 3 amps or 4 ? I can't tell. Chinese translators can be squirrely

 

[ronsimpson]

The LED ring was probably made to run from 12V. (battery)
It has 180 ohm resistors to limit the current.
I would look for 12V wall worts. (adapters) If the 3 watt rating is right it will pull 250mA. (1/4 amp). I think it pulls 80mA. 0.08A. Just a guess. I go to the "used junk" store. When a printer dies they throw the power supply in a bin. (cell phone chargers, laptop supply, calculator supply, etc.) A inkjet printer supply might be 12V at 0.5A. I usually pay $1.00 us.

Ha, Cliff, Drive by the house tonight and I will give you one. LOL.

 

[Cliff321]

Ha, Cliff, Drive by the house tonight and I will give you one. LOL.

I'm right outside even now.. Toss it out that corner window will ya?

I have a 9 volt 1 amp wall adapter I'll try and see how wrong I was about the 3 amps. My little PSU does light it up dimly at 9 volts.

 

[Cliff321]

Odd
My adapter worked to illuminate it but the light flickered at a very fast rate - too fast for the eye to see distinct flickering - more like a high freq' buzzing
Must be a crappy adapter.
But that it worked on a lower current makes me wonder if I can control the voltage with a cheap pot.

 

[Cliff321]

So I'm looking at Voltage regulator kits based on the LM317 chip. I haven't seen one that lets me set a maximum out voltage to protect my LED circuit.
Know of one?
If I use a DC power supply with any of the LM317 type kits I've seen I get a voltage drop across the Bridge Rectifier diodes that let you also use a 24 VDC power supply. The goal would be to lock the maximum voltage to 14 what ever PSU I used.