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# Power suppy dilemma

#### ElectroDuck

Feb 28, 2023
11
Hi, I am new here just posted my introduction. I hope this is the correct place to ask this but I am struggling to figure out the best way to supply power to some LED's on a project that I am working on.

So I have four 5v high intensity LED's that need 2.1 amps total (according to my variable power supply). Unfortunately my control board doesn't supply high enough current, So to actually turn the LED's on or off I am going to use a relay or a transitor... probably the relay as I have a spare laying around. My problem is how to supply the power for the LED's. The control board is powered by a 12v source like a car outlet.

I initially thought about using one of my L7805CV transitors to get 5v but they only output 1.5 amps and peak 2.2 amps. Then I though about using a small converter. And that did even worse... I can get 5v but only 0.5 amps out of a 12v source.

I really don't want to have to buy a 5v 2.1 amp power supply if I can help it. Is there a circuit that I can create or some other alternative. Or do I even need to supply the LED's with the full 2.1 amps they drew from my power supply during testing?

#### Externet

Aug 24, 2009
869
Are you sure the LEDs are 5V ? Try first to power the 4 LEDs in series to 12V capable of 2 Amperes, and come back.

12V(+)-------|>|------|>|------|>|------|>|---------(-)

If you want to run all 4 LEDs from a 5V supply, the 5V supply would have to be capable of 11 Amperes, not 2.1A

#### ElectroDuck

Feb 28, 2023
11
If I run your 12 volt test I'll fry 4 LED's.
They are 5 volt that I am sure, I bought them specifically to be 5 volt. They light at about 3.5volts and burn out at about 8-10 volts.

My variable power supply has a constant current mode. If I set my power supply at say 12 volts 1 amp and try to run a 2 amp circuit the supply automatically goes to constant current mode untill I bring the amperage up to what the circuit needs.

So I already did a series test. To find out where my power supply kicks out of constant current mode. With all 4 leds hooked up they draw 2.1 amps from my power supply.

#### Bluejets

Oct 5, 2014
6,195
So I have four 5v high intensity LED's that need 2.1 amps total (according to my variable power supply).
It would be much better to look up a spec sheet for the LEDs in question (edit...AND post it here)......and go from there.

#### ElectroDuck

Feb 28, 2023
11
It would be much better to look up a spec sheet for the LEDs in question (edit...AND post it here)......and go from there.
According to spec sheet each LED is 1 watt and 5 volts. It doesn't list amps so I did the math and it comes out to 0.2 amps

And for the record my variable power supply confirms. The photo is for a single LED.

#### Attachments

• 20230228_162645.jpg
242.3 KB · Views: 10
Last edited:

#### Martaine2005

May 12, 2015
4,535
What LEDs are they?
They are surely COB or LED board?.
But, whatever the wiring system used, the voltage and amperage is what it is and you’ll need a power supply suitable for the project.

Martin

#### ElectroDuck

Feb 28, 2023
11
What LEDs are they?
They are surely COB or LED board?.
But, whatever the wiring system used, the voltage and amperage is what it is and you’ll need a power supply suitable for the project.

Martin
I believe COB, I know I need 5v 2.1amp minimum. I am trying to figure out how to get that from 12v source without needing a separate power source. If that is even possible.

#### Martaine2005

May 12, 2015
4,535
Well, what LEDs are they? Got a link to them?.
Are they 5V 2.1A each??. Or is amp draw total of four?. Wiring in series, the voltage required is higher. in parallel, the current is higher. So you’ll need 20V for four in series!. Two in series and parallel them, then 10V is required.
But without knowing if current limiting is internal, I couldn’t really comment.

Martin

#### ElectroDuck

Feb 28, 2023
11
I feel like I am repeating myself...
I will reply in the morning when I have a clear clear mind.

#### John Canon

Jun 1, 2022
83
I once used a USB supply that plugged into the car cigarette lighter outlet. They are usually rated at 2.1 Amp.

#### Martaine2005

May 12, 2015
4,535
You’re not repeating yourself, each response has been different. If each LED draws 200mA, you only need 800mA. So a 1Amp or higher supply.

Martin

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
I am trying to figure out how to get that from 12v source without needing a separate power source.
Use a step-down converter (for low losses) with a suitable output rating. Example.

#### ElectroDuck

Feb 28, 2023
11
You’re not repeating yourself, each response has been different. If each LED draws 200mA, you only need 800mA. So a 1Amp or higher supply.

Martin
Ok, it's a new day, clear head.

According to the math I did based on the voltage and wattage listed on the data sheet each individual LED is 200mA. So I understand how you get 800mA for all four LED's. Which when I was designing this was my original number.

When I hooked all 4 LED'S up in testing and was using my variable power supply. It was saying I needed 2.1 amps.

So I am slightly confused should I go off my power supply and say I need 5v 2. amp or electrical math which says I need 5v and only 800mA?

#### ElectroDuck

Feb 28, 2023
11
Use a step-down converter (for low losses) with a suitable output rating. Example.
I have one but it doesn't adjust to a suitable output based on the input.

#### Martaine2005

May 12, 2015
4,535
Ok, so your 12V battery is what? A gel type? A car battery?
What is the
Ok, it's a new day, clear head.

According to the math I did based on the voltage and wattage listed on the data sheet each individual LED is 200mA. So I understand how you get 800mA for all four LED's. Which when I was designing this was my original number.

When I hooked all 4 LED'S up in testing and was using my variable power supply. It was saying I needed 2.1 amps.

So I am slightly confused should I go off my power supply and say I need 5v 2. amp or electrical math which says I need 5v and only 800mA
Generally the data sheets are the most important values. However, your PSU shows 200mA with one indicating it’s correct. You must be wiring them incorrectly. Do you understand series and parallel?. Or you have a different COB in one of them? Have you checked them all individually?

Martin

#### ElectroDuck

Feb 28, 2023
11
I understand the 2 and have them wired in a parallel circuit. All the LED's are all the same. And the pre-solderder resistor rating is the same as well. So I don't have any discrepancies there.

#### Martaine2005

May 12, 2015
4,535
In parallel, the 5V is fine but the current is added, so 800mA..
Can you draw a connection schematic and take a pic and post it?. Not saying you’re silly, but mistakes happen. Each at 0.2A is 0.8A in anyone’s book. So where does the 2.1A come in?. Your PSU clearly says 5V too. Have you checked the PSU with a multimeter for clarification?. Both in in voltage and Amps?.

Martin

#### Alec_t

Jul 7, 2015
3,330
Your meter in post #5 is showing 0.275A, not 0.2A. So 4 LEDs should draw 1.1A at 5V.

#### Martaine2005

May 12, 2015
4,535
Your meter in post #5 is showing 0.275A, not 0.2A. So 4 LEDs should draw 1.1A at 5V.
Yeah, we have that base current. But 2.1A is the mystery.

Martin

#### ElectroDuck

Feb 28, 2023
11
In parallel, the 5V is fine but the current is added, so 800mA..
Can you draw a connection schematic and take a pic and post it?. Not saying you’re silly, but mistakes happen. Each at 0.2A is 0.8A in anyone’s book. So where does the 2.1A come in?. Your PSU clearly says 5V too. Have you checked the PSU with a multimeter for clarification?. Both in in voltage and Amps?.

Martin
I am saying I am silly... just solved the mysterious 2.1 amps.

Ok so I did what you said, the schematic will be included down below. But in the process I realized I had 2 bins of my High Intensity LED's. The ones in my project have a 2.4ohm resistor. The one I was testing on my power supply have a 6.8ohm. So for the one LED I do need 5V @ 800mA to run four and I need 5V @2.1amps for four of the other ones... the ones in my project.

So with the other LED's put away so they don't mess with me anymore. The LED'S for my project have a draw of 600mA so based on the math I need 2.4amps to run all four. And my PSU (as you refered to it) says 2.1amps.

Now that we solved that whole issue... I am still left with how to get that current out of a 12volt source, i.e the car outlet.

#### Attachments

• LED's.pdf
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