domingo, 15 de mayo de 2011

Controlling LEDs Part 8 - What is the minimum or maximum number of LED fixtures/lamps that can be connected to one dimmer?

What is the minimum or maximum number of LED fixtures/lamps that can be connected to one dimmer?

A common problem with LED system operation involves overloading the driver. LED drivers are rated for a maximum load (in volts, amps, and/or watts) that must not be exceeded. Similarly, some LED drivers may not perform well if too little load is put on them.

The number of lamps able to be installed on a single phase control dimmer may seem like an easy question to answer. However, it is not as simple as looking at your 600-watt dimmer and dividing 600 by the 15-watt LED lamp you have selected to determine that 60 lamps can be used on a circuit. You may only be able to use 100 watts of the LED load on a dimmer rated for 600 watts. While the LED lamp may only draw 10 watts continuously, it may have a start-up inrush current or repetitive current during every half-cycle that makes it appear much worse. That 15 watt LED lamp will appear to the dimmer as a 100 watt incandescent load, so if you use more than 90 watts of that LED, you will overload the dimmer.

Neglecting this transient current can put significant stress on the dimmer and can cause premature product failure or undesired system performance (such as excessive acoustic noise). This transient electrical stress may limit the maximum number of lamps you can install on one dimmer. The average stress that has been observed is the equivalent of a 100W incandescent, even for LED loads that are less than 20W. 

A minimum number of fixtures may be required to operate a dimmer because of the 25-watt to 40-watt minimum load that most incandescent dimmers require to operate correctly under all conditions. When using incandescent bulbs, the minimum load requirement was easily met with usually only a single bulb. However, with LEDs, four or more loads may be needed on a dimmer in order to meet the required minimum load.