It's possible for a 4.2A LED panel consume 9.32A instead?

[Fluence]

Meh... when i powered up my LED panel that has 1491 LED, i've connected the multimeter to measure the Amps, and for my surprise the LED panel was consuming 9.32A, instead of 4.2A.

The configuration of my panel is like this:

125 strings of 7 Red LED - 2.2v 20mA each LED - Each string connected with one 470Ohm 1/2W resistor (yeah i could do it better but when i was about to finish the soldering on the panel i've remembered that Red LED are powered with 2.2v and not 3.3v...)

• Together, all resistors dissipate 23500 mW
• Together, the diodes dissipate 38500 mW
• Total power dissipated by the array is 62000 mW
• The array draws current of 2500 mA from the source.

and

88 strings of 7 Green LED - 3.2v 20mA each LED - Each string connected with one 82Ohm 1/4W resistor

• Together, all resistors dissipate 2886.4 mW
• Together, the diodes dissipate 39424 mW
• Total power dissipated by the array is 42310.4 mW
• The array draws current of 1760 mA from the source.

2500mA + 1760mA = 4260mA

I've bought a laptop Power Supply, with 24Vdc 5A 120W to power the panel.

The panel works great and all the lights are at full bright, (it flashes more than a flash grenade ;3), and the power supply doesn't get too hot, BUT, when i connect the multimeter it read 9.32A, i just don't understand... i mean, if it was really consuming 9.32A the power supply would get toasted, but it's all running smoothly and i don't understand why.

Another thing that's bothering me, it's the wires. I've connected the LED with UTP45 cable (the same we use to create networks) and it gets -very- hot near the entrance of the 24V, i'm thinking in separating the LED panel in about 10 parts and use 2 cooper wires with 2.5mm, but i wonder if that will be enough.

 

[ronv]

I get calculated values of 2.29 amps for the reds and 1.72 for the greens. About the same as your values. 2.5 mm should be more than enough. Maybe your meter is bad?

 

[audioguru]

LEDs are not a light bulb with a fixed voltage. An LED has a range of voltages. Each LED has a different voltage.
Your red LEDs might have been 1.8V or 2.0V instead of 2.2V. Your green LEDs might have been 2.8V or 3.0V instead of 3.2V.
Then their current is much higher.

 

[ronv]

He is off by 2X.

 

[audioguru]

He is off by 2X.

Maybe the current meter is off by 2X.
Maybe he measured the max current available from the power supply by shorting it with his current meter insterad of connecting the meter in series with the load.

 

[Reloadron]

Maybe the current meter is off by 2X.
Maybe he measured the max current available from the power supply by shorting it with his current meter insterad of connecting the meter in series with the load.

I would guess the latter.

Ron

 

[Roff]

I would guess the latter.

Ron

Yeah, I was going to suggest the same thing. It's a common mistake for noobs to make.

 

[Fluence]

Well i've connected the Negative from the Power Supply directly to the Negative of the LED Panel, and the Positive from the Power Supply, i've connected it to one probe of the Multimeter, and the other probe i've connected to the Positive of the LED Panel.

I did it wrong?

 

[Reloadron]

Well i've connected the Negative from the Power Supply directly to the Negative of the LED Panel, and the Positive from the Power Supply, i've connected it to one probe of the Multimeter, and the other probe i've connected to the Positive of the LED Panel.

I did it wrong?

When measuring voltage it is measured in parallel with the load. When measuring current is is measured in series with the load. You need to break a load line so the meter can be in series with the load. Similar to the attached where the current to the load passes through the meter.

Ron

 

[audioguru]

Don't all NOOBs connect an ammeter wrong so they blow out its fuse?

 

[Boncuk]

Don't all NOOBs connect an ammeter wrong so they blow out its fuse?

DMMs are equipped with a fuse for the range of max 200mA. The 10A range is unfused.

Boncuk

 

[Fluence]

I didn't blew up the fuse, because it's unfused and it can measure 20A max, i've measured correctly, it's really strange indeed, but i will try tomorrow with another multimeter to see if the same result shows up.

 

[Fluence]

This is MADNESS!!!

O-M-G... i mean... i understand that with UTP wires, the resistance would be high, and it may lead to the panel consume more amps... but i've changed the wires, and used 1,5mm cooper wire, and now it's measuring 9.92A!!!

I'm really blocked at this, how is this possible? I've made all the correct calculations with the resistors and the LED... this can't be happening... even if each LED consumed 25mA in the total the panel would only need 6A... not 9.92A...

I've took a photo of the back side of the panel:

**broken link removed**

This is the "schematic":

**broken link removed**

Do you think the wires are the problem?

 

[Nigel Goodwin]

That looks like the LED's are all wired in parallel?. It would certainly massively increase current consumption.

 

[Fluence]

**broken link removed**

Is this parallel? Right now i'm so confused that i can't analyse the situation properly...

I use a common negative in all LED strings, and a "serial" (i think) positive for each LED string.

I've made a test, and i've connected 1 string with 7 LED directly to the power supply (24v 5A), and for my surprise, appeared SMOKE from the LED... they had light up, but they were burning too!
I've lowered the voltage to 15V (it's a regulated power supply and 15v it's the minimum), and once again it began to appear smoke from the LED...

What can i possibly be doing wrong?

 

[audioguru]

You are connecting each 2.2V and 3.2V LED directly across the 24V power supply (in parallel) which causes the LEDs to burn out.
You must learn how to connect LEDs in series then connect a resistor in series with each string of series LEDs to limit the current.

Seven 2.2V LEDs in series need 7 x 2.2V= 15.4V and the 470 ohm resistor uses the remaining 24V-15.4v= 8.6V so the current is limited to 8.6V/470 ohms= 18.3mA.

I don't see any resistors on your "schematic" and do not see any in your wiring.

 

[Nigel Goodwin]

LED's should be connected positive of one to negative of the next to be in series, you're connecting them all in parallel (there should be no common connections on them).

 

[Fluence]

LED's should be connected positive of one to negative of the next to be in series, you're connecting them all in parallel (there should be no common connections on them).

/\ This.

I've made a mistake that will take me days to correct... i guess we always should test things at a small scale and only then, take it to a full scale to prevent stupid errors like this one... after all, i just have to solder AGAIN 1500 LED...

i need a beer...

 

[audioguru]

I wish you took a video of your 1500 LEDs blowing up!

 

[Fluence]

rofl... they didn't blow up!

Even now they light up without problems at full bright, i don't know why, but they lit normally, at least the green LED. The red LED indeed some of them seem a bit dim, but i'm not sure if it's normal (red have 9000mcd and green 15000mcd) or if it's because they're damaged.

I think the reason that the LED didn't blow up, it's because the resistor, when i powered the panel, the resistors were so hot that i could ear the flux boiling near them...

AW well... bad memories... now i have "some" work to do...