LED Strips Electrical connection guide, SERIES and PARALLEL circuits

Basic LED principles:

A LED (light-emitting diode) is a semiconductor light source that emits light when current flows through it. Light is energy in the form of photons that beam out when electrons in the semiconductor recombine with electron holes. 

The higher the current flow, the brighter the LED becomes. However, the circuit is not perfect and a part of the current is converted into heat instead of light. When current reaches a certain level, the resulted heat is so high that the semiconductor is damaged permanently. Most LED datasheets mention this important threshold as "Absolute maximum current".

Even when the LED is functioning at below the maximum current, heat will slowly damage the LED, its luminous flux (light output) gradually diminishing as a result. The point in time when the LED luminous flux is only 70% of its initial value is generally referred to as "LED lifetime".

In order for LEDs to have a very long lifetime, 50.000h or more, a current level far below the Absolute maximum current is required, referred to as "typical" or "recommended current".       

Constant current source for recommended current

To power an LED with the recommended current an external circuit is required, a constant current source. Without it, the current in the LED will rise exponentially with the applied voltage, as a small change in voltage leads to a large change in current, until the maximum current is reached and the LED burns up. 

The external circuit, constant current source can be a simple resistor for low-power LEDs (max 100mA at 3V) or a standalone device, a LED driver. 

LED drivers are available in many shapes, sizes and power levels and many accept 230 VAC input. Some specialty LED drivers accept VDC input of higher levels than the output (step-down converters) or lower level (step-up converters).

A common characteristic of LED drivers is that they provide a constant current output (CC out) within a voltage interval. This output voltage interval is mentioned in the LED driver datasheet. For example, a LED driver with 350mA CC output at 1-10V is able to safely power one LED under the condition that its voltage required for 350mA is within the 1-10V interval. Examples include a red LED 2V @ 350mA, white LED 3V @ 350mA or COB LED 9V @ 350mA.

Theoretically the optimum setup is to use one LED driver for each LED, an approach that is unpractical from many points of view, for most LED types. Exceptions are the very high power COB LEDs, from 50W up. 

Series and parallel electrical circuits

To power a string or array of LEDs from one LED driver, the LEDs must be connected into an electrical circuit. This can be a series or a parallel circuit. 

We will explain the two types of circuits with examples using our popular LumiBar 56 cm LED strips, with SunLike TRI-R CRI98+ LEDs, Nichia Optisolis CRI99+ LEDs or special Nichia Rsp0a Horticulture LEDs:

Series connection with LumiBar Sunlike CRI98+ LED strips:

One LumiBar 56 cm Toshiba-SSC LED Strip Zhaga Sunlike CRI98 warm white 2700K has the recommended current at 350mA, reached at the voltage of 39.5VDC.

A series circuit with two, three or four LumiBar LED strips is shown below:

The series circuit is laid out by connecting the positive (+) of the first LED strip to the negative (-) of the second LED strip. This pattern is repeated for more LED strips, from the negative (-) of the second strip to the positive (+) of the third strip and so on. At the same time, negative (-) of the first LED strip is wired to  (+) of the second, then (-) of the second to (+) of the third and continuing. 

In a series circuit of LED strips, the current of the string is equal with the current of the first LED strip while the voltage is the sum of voltages for all the LED strips (voltage of the first LED multipled by the number of LED strips). For example:

1 x LumiBar 56 cm Sunlike CRI98+ LED strip: 350mA at 39.5VDC

2 x LumiBar 56 cm Sunlike CRI98+ LED strips in series: 350mA at 79VDC (= 39.5VDC x 2)

3 x LumiBar 56 cm Sunlike CRI98+ LED strips in series: 350mA at 118.5VDC (= 39.5VDC x 3)

4 x LumiBar 56 cm Sunlike CRI98+ LED strips in series: 350mA at 158VDC (= 39.5VDC x 4)

Parallel connection with Nichia Rsp0a Horticulture LED strips:

The parallel circuit is laid out by connecting the positive (+) of the first LED strip to the (+) of the second LED strip. This pattern is repeated for more LED strips, from the (+) of the second strip to (+) of the third strip, and so on.

At the same time, the negative (-) of the first LED strip is wired to  (-) of the second, then (-) of the second to (-) of the third and continuing.

 

In a parallel circuit of LED strips, the current of the string is the sum of all current values of the strips, while the voltage is equal with the one of the first LED strip. For example:

1 x LumiBar 56 cm Nichia Rsp0a Horticulture LED strip: 350mA at 37.5VDC

2 x LumiBar 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 700mA(= 350mA x 2) at 37.5VDC

3 x LumiBar 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 1050mA(= 350mA x 3) at 37.5VDC

4 x LumiBar 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 1400mA(= 350mA x 4) at 37.5VDC

Combined circuit with LumiBar Nichia Optioslis LED strips

Series and parallel circuits can be combined, for example:

We create one group of two LumiBar Nichia Optioslis LED strips in series. Because one LED strip has 350mA at 39.5VDC, the group will have 350mA at 79VDC (= 39.5VDC x 2)

This group we connect in parallel to a second group, identical to the first (350mA at 79VDC). Then values of the string will be: 700mA (=350mA x 2) and 79VDC (=39.5V x 2).

The principles above can also apply for single LEDs. On our LumiFlex3098+ Pro Toshiba-SSC LED Strip Sunlike CRI98, segments of 7 LEDs in series are daisy-chained in parallel for a total length of 5 meters. The total circuit requires a constant voltage driver of 24VDC.

 

Selecting the LED driver for a string of LED strips

Before selecting the LED driver the current and voltage value of the string of LED strips must be known and the type of input: constant current or constant voltage.

Examples:

1 x LumiBar 56 cm Sunlike CRI98+ LED strip: 350mA at 39.5VDC will require the constant current LED driver Mean Well LPC-20-350 with 350mA output at 9 > 48VDC. 

1 x PowerBar V3 LED Module Aluminium UV 365nm 12180mW 700mA at 44.4VDC can use a constant current LED driver Mean Well LCM-40 with 700mA output setting at 2 > 57VDC. 

2 x LumiBar 56 cm Nichia Rsp0a Horticulture LED strips in parallel: 700mA(= 350mA x 2) at 37.5VDC can be connected to a constant current LED driver Mean Well LCM-40 with 700mA output setting at 2 > 57VDC. 

3 x LumiBar 56 cm Sunlike CRI98+ LED strips in parallel: 1050mA(= 350mA x 3) at 39.5VDC require a constant current LED driver Mean Well LCM-60 with 1050mA output setting at 2 > 57VDC. 

4 x LumiBar Nichia Optioslis LED strips in parallel: 1400mA(= 350mA x 4) at 39.5VDC need a constant current LED driver Mean Well LCM-60 with 1400mA output setting at 2 > 42VDC. 

5 meters of LumiFlex3098+ Pro Toshiba-SSC LED Strip Sunlike CRI98 function at 24VDC and have a total power consumption of 96W (=19.2W x 5). In this case we can use one constant voltage LED driver at 24V, such as HLG-150H-24B with 150W maximum output.

10 meters of LumiFlex Samsung LED Strip function at 24VDC and have a total power consumption of 126W (=12.6W x 5) can also work with the HLG-150H-24B.

 

Disclaimer:

This article is for informative purposes only. It is not a installation guide. LED strips our other electrical components should be installed by qualified personnel (such as an electrician).