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Let me start by mentioning that I have little knowledge in this field.

LEDs I have: 12v 1Meter Rigid Double-row 3pin LED strips with 1.8A total draw (0.9A each row). For some reason, they have massive voltage drop. With 12v input they measure 10.5v at the end of 1 meter and the lights seem noticeably dimmer, At 50cm it reads 11.3v. Is it normal? Wire used for testing: 10cm 2.5mm2(13AWG). Power Supply: 12V 15Amps.

I have to use the strips to light up my display cabinet(s), the cabinet has 6 shelves, each shelf is 25cm tall and 40cm long. I want each shelf to have it's individual light strip. So I will cut the strips in 40cm parts.

Now I have to find proper ways to wire the whole cabinet with minimum voltage drop, so the lights would be as even as possible. If you have any clue while considering the strips' huge voltage drop, please help.

I came up with three methods so far:

SEE UPDATE SECTION

PS: I don't know how/where to provide better diagrams.

Update:

I updated the diagram making it more understandable: enter image description here Red leads are positive, Gray ones are negative. And by "1 meter", I mean 1 meter of LED strip, not the wire. The drop is across the strips.

  • Method 1 is a parallel connection, supplying each strip from both ends. Example from web:

enter image description here

Method 2 is a parallel connection, each cable (2 leads) supply two LED strips at one end. Example from web: enter image description here

Method 3 is a parallel connection, supplying each strip at one end, individually and directly from the power supply. Example from web:

enter image description here

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  • \$\begingroup\$ Where possible, try to provide a supply rail directly to both ends of a strip. There will be voltage drops within the strip and this minimizes the problem leaving only the center with slightly less voltage than the rest. (Assuming the strip supports it, of course.) Lots of separate outputs are great if you can afford the space and cost for it. Otherwise, closer strips will receive somewhat higher voltage (better) than strips further away in the wiring itself leading to the strips. But distances matter and there's not enough detail shown on that score. \$\endgroup\$
    – jonk
    Jul 8, 2020 at 2:15
  • \$\begingroup\$ Thank you@jonk. I've updated the whole question, hope it's more clear now. Strips do support powering from both ends. Also please clarify which one of the methods you said has less voltage drop and results in more even lights. The drop is across the strips, not the wire. \$\endgroup\$
    – Kasra Koohi
    Jul 11, 2020 at 23:55
  • \$\begingroup\$ Given the small scale of the project, there's no downsides to method 1. It's simply better so long as the power supply itself is sufficient in its compliance current. Both ends of the LED strip should be connected up when possible. That might be difficult if used as stairway lighting, for example, as you'd need to run the wire all the way up to the other end, as well. But in your case it seems very doable. So I'd do it if there was any doubt. You can always test things and add the remaining wiring later on. \$\endgroup\$
    – jonk
    Jul 12, 2020 at 1:31
  • \$\begingroup\$ I'd also first try method 1, but I'm surprised the trip does not light-up evenly out-of-the-box. Why would the manufacturer severely under-spec the wiring inside the strip? Can you perhaps point to the actual brand/model? \$\endgroup\$
    – P2000
    Jul 12, 2020 at 5:29
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    \$\begingroup\$ @P2000 I can't justify or explain their decisions. But is is true that it is almost universal that one needs to power both ends from the great many reports about problems. I've bought some higher quality ones that don't show as much dimming over 5 m, but even they benefit from powering both ends. These are on flexible PCB material and they after competing with each other for business in a US market that doesn't research and buys on the basis of price. I expect that's part of it. \$\endgroup\$
    – jonk
    Jul 12, 2020 at 17:01

2 Answers 2

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AWG 13 is 6.4 mΩ/m or 12.8 mΩ/m per pair means 12.8mV per Amp.

But a 1m strip with a drop of 1.5V/1.2A =1.25Ω or 625 mΩ/m implies an equiv gauge of ~ AWG 33.

You can cascade all the strips at one end and should get acceptable results for 50 cm. Otherwise if fussy about a slight difference at the far end, cascade both ends with AWG 13 or AWG 16 which is only double R of AWG13.

The 12V white strings are 3x3V repeated 9V strings so the current is limited by 3V at the start and 2.7V after 50cm and this 10% difference is not usually noticeable in brightness unless both ends were side by side. LED tolerance alone often varies in the brightness of more than 10%.

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  • \$\begingroup\$ Could you please explain how is cascade wiring? Is it like "Method 1"? \$\endgroup\$
    – Kasra Koohi
    Jul 12, 2020 at 14:47
  • \$\begingroup\$ yes I meant daisy chain.. either or both sides \$\endgroup\$
    – Tony Stewart EE75
    Jul 12, 2020 at 14:48
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I would bench test the layout first. I assume you can cut a 100 cm strip into three sections of 40 cm, 40 cm, and 20 cm. Wire up one 40 cm strip. Check result. Wire up one 20 cm strip. Check result. When you get a good result add another strip in parallel across 12 V. Check result. This way you would cut the minimum length necessary for a good result and as long as you don't exceed the rated amps on the power supply it should scale to six shelves with good result. This will require whatever amount of wire necessary to run for the geometry of your setup. The amp draw will go up for each strip added in parallel across 12 volts so be careful not to exceed amp rating of your power supply with a margin of safety. A typical multimeter can measure 10 amps on a fused input so I would measure the amp draw if possible when you get good results in a particular strip length.

This reference describes voltage drop on typical 12V LED strip light:

http://lednique.com/technology-basics/flexible-led-strip-light/

This video describes custom LED strips that solve the voltage drop and lack of uniform lighting problem using a smart variable resistor in each LED:

https://youtu.be/FrRJoauDD5A?t=154

This article describes driving LED strips with current versus voltage source:

https://www.ledsupply.com/blog/constant-current-led-drivers-vs-constant-voltage-led-drivers/

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  • \$\begingroup\$ I will test and check the results. About the first reference link, how does it differ powering the strip with 2 conductors from both sides (4 leads), and powering it by the positive wire to ve+ on one end and ve- to the other side (2 leads)? How does voltage drop behave that way? \$\endgroup\$
    – Kasra Koohi
    Jul 12, 2020 at 14:57
  • \$\begingroup\$ Copper wire parameters for most applications are specified as resistance per unit length and ampere capacity aka ampacity. These specifications vary due to structure of wire as diameter (gauge), solid, stranded, and type of insulation on the wire. In general a large diameter wire has lower resistance per unit length and higher ampere rating. A longer length of smaller diameter wire has higher resistance and this causes the voltage drop between the source and load. Applying 12 volt on both sides of LED strip brings the source closer to the loads at each end with lower wire resistance. \$\endgroup\$
    – SystemTheory
    Jul 12, 2020 at 15:11

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