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I recently purchased five LED strips online (these specifically: http://www.ebay.com/itm/331059064977) to hang up along the outline of my room. Each strip is 5m (16.4 ft.) long, requires 12 V DC to power, and dissipates 0.08 W/LED.

Each strip dissipates 48 W, meaning that at the recommended 12 V DC, there would be a current of 4 A.

I planned on soldering the five of them together in series so that I could have one long chain of LEDs that will only require one power source. However, I am slightly confused regarding what adapter I should purchase that will power the chain.

Each strip seems to come with two cables attached to both sides (power and ground); I'm a little confused regarding this, because I know that LEDs should be forward biased, so why would both sides require power and ground?

Also, because I will have five strips, should I be passing 60 V DC through the entire thing if it's recommended to only pass 12 V DC for each strip? I just want to make sure that I don't blow anything up accidentally by exceeding the maximum rated amperage (I probably wouldn't want to go over 4 A if possible).

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  • \$\begingroup\$ That is a lot of current to go through those small traces. Try and measure the trace size, determine the material and use an trace current calculator \$\endgroup\$ – Voltage Spike Apr 12 '17 at 3:30
  • \$\begingroup\$ @laptop2d I'm not that concerned as there should be an equal current drop through each diode, right? \$\endgroup\$ – Jacob G. Apr 12 '17 at 3:37
  • \$\begingroup\$ Usually the LED strips are not strips of LED's wired serially, but IC's in parallel \$\endgroup\$ – Voltage Spike Apr 12 '17 at 3:53
  • \$\begingroup\$ @laptop2d Yeah, another member explained it below. I don't think there should be a problem as long as I make sure to wire them all together before attempting to use the 12 V/25 A power supply that I bought. \$\endgroup\$ – Jacob G. Apr 12 '17 at 3:57
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If you hook them up end to end, you need just 12V, but at 5 times the current.

The strips actually have a circuit something like this (imagine the vertical resistor-led combinations between 12V and GND are repeated, going off for 5m):

schematic

simulate this circuit – Schematic created using CircuitLab

It may actually have multiple LEDs per vertical section (to avoid needing a high power resistor), but the principle is the same.

So, hooking them end-to-end is actually hooking them up in parallel. This arrangement is also how you can cut these strips without breaking them: You're just removing parallel LEDs from the chain.

So, just get a supply that supplies 12V at 20A.

Alternately, if you don't want to hook them up end to end and instead want to hook them up in "parallel", you are actually hooking them up in series and would require a 60V, 4A power supply.

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$ – Dave Tweed Apr 12 '17 at 3:53
  • \$\begingroup\$ No, there are three LEDs in series with one resistor per such group. Also, hooking them up in series would require equal load on each, which is not guaranteed and once LEDs in one start failing, the others will get more voltage and you will have a runaway situation. \$\endgroup\$ – winny Apr 12 '17 at 5:31
  • \$\begingroup\$ I did say "something like" before and "may actually have multiple LEDs per vertical section" after my diagram because I knew that, but had no way to positively verify the particular number of LEDs or resistors from the eBay page alone. The principle is the same in any case. Valid point about the series stuff, though it wouldn't fit the op's use case anyway. Please see the chat. \$\endgroup\$ – Los Frijoles Apr 12 '17 at 5:46
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These strips are composed of multiple parallel segments of three series LEDs plus resistor. When you add multiple strips together they are still in parallels so the voltage does not change. You want a power supply that's exactly what you will already said, 12 volts at 4 amps or higher.

Keep in mind that flexible printed circuits like these LEDs are on have a high resistance so the voltage will drop the farther down the line the LEDs are from the power source. The ones at the end will be less bright. Ideally you would provide power every five meter section, with a parallel connection using regular wires.

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  • \$\begingroup\$ My goal is to avoid powering every 5m strip individually if possible. Another member had recommended I supply 20 A to the entire strip, but I suppose the voltage would still drop, right? \$\endgroup\$ – Jacob G. Apr 12 '17 at 2:34
  • \$\begingroup\$ Yes. Your options are power it in the middle, or both ends or multiple points. You don't need multiple power supplies, you could do it by running a long 18 or 16 AWG pair of wire alongside the led strip. This parallel conductor would reduce the resistance of the circuit. \$\endgroup\$ – Passerby Apr 12 '17 at 2:37
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    \$\begingroup\$ I'm hoping that the combined strips can form a giant circle around the room so that I can connect them together and power it from a single point, thank you though! \$\endgroup\$ – Jacob G. Apr 12 '17 at 2:38
  • \$\begingroup\$ That will help. \$\endgroup\$ – Passerby Apr 12 '17 at 2:56
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Due to the limit of 3 cascaded strips, series cascade operation is not an option and rather separate AWG 16 wiring from power source to a group of 3 or less.

I would suggest 4 strings with 48V to 56V with 5A supply and a PWM dimmer so your eyes are not blinded. 12V strings are usually design to run at 14.2V auto voltages. This way the current does not add.

But if you use an ATX supply rated for 20A then use no more than 3 in parallel cascaded strings as the 1st strip conductors will get warm and drop voltage.

Use "star" central wiring instead to either end.

schematic

DO NOT CASCADE 5x 48W LEDSTRIPS in parallel END-TO-END

Either connect all at same end with heavier or =AWG 14 or use AWG 16 to each LEDSTRIP or use series higher voltage. but any PC ATX 500W ought to work as long as cables are not too long for voltage drop.

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  • \$\begingroup\$ Obviously one person (-1) has no idea what I am talking about but should. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 12 '17 at 2:42
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    \$\begingroup\$ Hooking them up in series would require equal load on each, which is not guaranteed and once LEDs in one start failing, the others will get more voltage and you will have a runaway situation. \$\endgroup\$ – winny Apr 12 '17 at 5:34

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