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LED power strip identification

Thread starter #1
Does anyone recognize these LEDs? Are they the 5050 kind? There are 5 sets of 3 leds on one strand. I have 2 strands of these that I want to connect together, but they don't say the voltage or amps anywhere written on them. As far as I can tell by experimenting with 12v power adapters, they must be 12 volts. I have different Amp rating 12v power adapters ranging from 200ma to 1000ma. Would 1000ma be too high for these two strands connected together?
 

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sagor1

Active Member
#2
They seem to have dropping resistors for each LED. 2000 ohms (I'm assuming) with a 12V supply will give each LED approximately 6mA (a bit less depending on LED voltage drop). Not all that much. Without a schematic, hard to say for sure.
These LEDs could be designed for a higher voltage, like 14V (like a running car), or even 24V.
Best to put each one on a variable power supply, and measure the current. Most LEDs don't need more than 10-15mA each for full brightness.
If everything seems ok with 12V, your 200mA power adapter may be fine provided the total load is 200mA or less (40mA maximum per strand for 5 strands). Be aware that many of the cheaper power supplies give off a higher voltage under low loads. Some 12V supplies (wall plug types) may give as high as 18-20V with no load or little load. Measure the voltages of your supply first...
 
Thread starter #3
They seem to have dropping resistors for each LED. 2000 ohms (I'm assuming) with a 12V supply will give each LED approximately 6mA (a bit less depending on LED voltage drop). Not all that much. Without a schematic, hard to say for sure.
These LEDs could be designed for a higher voltage, like 14V (like a running car), or even 24V.
Best to put each one on a variable power supply, and measure the current. Most LEDs don't need more than 10-15mA each for full brightness.
If everything seems ok with 12V, your 200mA power adapter may be fine provided the total load is 200mA or less (40mA maximum per strand for 5 strands). Be aware that many of the cheaper power supplies give off a higher voltage under low loads. Some 12V supplies (wall plug types) may give as high as 18-20V with no load or little load. Measure the voltages of your supply first...
Thank you!
 

JonSea

Well-Known Member
Most Helpful Member
#4
You don't need to worry about the current rating of the power supply as long as it's greater than needed for the load.

The resistors determine how much current the LEDs will draw. Sagor's estimate of 6mA is good. Say we have only one LED. It will draw only 6mA from a 12 volt supply no matter if the supply is rated to provide 200mA, 1000mA or even 50 amps.

It's like a light bulb in your house. It's rated for 60 watts (an incandescent bulb) and that's all it will draw even though the outlet it's plugged into could supply 1800 watts (15 amp breaker in the US) or 2400 watts (20 amp breaker).

Some LED power supplies are designed to provide constant current, to be used with LEDs without current limiting resistors. This type of supply will have a rating like:

315mA, 6 - 30 VDC.

This supply will vary the voltage to maintain a current flow of 315mA thru the load. A supply like this could power a series string of between two and ten 1 watt LED elements. The voltage will depend on the forward voltage of each LED in the string.
 
Thread starter #5
Thanks. I noticed the leds were brighter with the 12v 1000ma power adapter and I was thinking the higher I went in amps it was possibly gonna blow them out. I'm not sure if they are made for a car or for the house, I dont have anything with higher amps to test them on besides the battery of the car, but I can't imagine them getting any brighter without blowing out. I'm gonna run them with the 12v 1000ma power adapter, they look really bright just with that amperage. I couldn't connect the second strand to the end of the first one to make one long strand because they are sealed inside of a hard plastic case, so I connected them at the other end, positive wires from both strands soldered together and both negative wires soldered together.
Would the total strand be less bright if I somehow was able to connect the second strand to the other end of the first one? I'm guessing they would probably have the same brightness with they way I already have them connected.
 

sagor1

Active Member
#6
The LEDs may be brighter with the 1000mA supply because the load is low, and the supply voltage is actually higher than 12V. Most low end supplies are rated their voltage at the "load" current. That is, a 12V 1000mA supply is just that, 12V at 1000mA load. A lower load, like 100mA will allow the voltage to be a lot higher. Your 200mA supply is probably loaded down more with the LEDs, so the voltage gets closer to 12V.
In other words, those supplies are at 12V only when the load equals their current rating. A lower load, both will have a higher voltage, but the 1000mA supply is not heavily loaded, thus has a higher voltage.
Adding more strips to the same load on a poorly regulated supply will cause a bigger load, lower voltage, and all strips will drop a bit in brightness.
Basic test is to simply measure the voltage with the LED strips connected. That will show you what the actual voltage across the LEDs is...
 
Thread starter #7
I will have to cut the wires again, but before I do that, I just realized the power adapter is actually putting out 16 volts and not 12 volts like it says on the lable. I'm gonna have to look through all the spare adapters I have and test them all.
Should I still test the voltage of the leds connected to that power adapter? Or should I wait until I find a power adapter that puts out no more than 12v first?
 

sagor1

Active Member
#8
Test the voltage while connected to the LEDs, providing the voltage is not too high (up to 18-20V with no load should be ok for short tests). Unless you have a regulated power supply (switching or linear regulated), any other "12V" supply that is a "wall wart" type of adapter that measure 12V with no load, will have too low a voltage once you plug in the LED strips. The LED strips can probably survive 14-15V at the LED wires under load, based on those dropping resistors. Use whatever adapter gives reasonable 12-14V under load, and not exceeding the power supply current rating.
Remember, the voltage will drop as you increase the load. Most cheap power adapters all start with a high voltage with no load. As the load increases, the voltage starts to drop. When the rated load is reached (rated mA), the voltage will go down to the level stamped on the power adapter.
 
Thread starter #9
Ok thanks, I have this Yamaha power adapter that's labeled 12 volts 800ma and reads 16 volts without a load, and with the leds connected, it reads 12.58 volts. I think I'm gonna use that one.
 

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