Technical Note: Repetitive peak and inrush currents Prepared by: Rachel Taranta, Lighting Research Center Date: March 2, 2011 Introduction: In designing LED replacement lamps that are compatible with commonly installed household dimmer switches, questions arise regarding safe inrush currents to the lamp and to other items on the line. Inrush current is input current of short duration during initial start‐up that is greater than the operating or steady state current (NEMA 410‐2004). In addition to the inrush current to the lamp when initially plugged in, a lamp operated on a triac‐based dimmer, which switches the lamp at 120 Hz, may also experience inrush current every half line cycle, which is sometimes referred to as “repetitive peak current.” Inrush current is a familiar problem across the electronics industry and is observed with many types of lighting technologies, including fluorescent lamp ballasts. Electronic ballasts for fluorescent lighting require a level of inrush current to charge the input capacitor. This current may exceed 100 times the operating current. This excessive current can cause damage to relays, which are often rated for only 10 times the operating current. High inrush current may cause the relay contacts to fuse, leaving them in permanent “on” position. Appropriate mitigation techniques like zero‐crossing switching and limiting input capacitance are employed with electronic ballasts to prevent damage to relays (WattStopper TB107.1, 2005). Objective: To measure the inrush and repetitive peak current of a small sample of dimmable LED replacement lamps, an incandescent lamp, and a dimmable compact fluorescent lamp, with and without a triac‐based dimmer, in order to gain insight as to the currents seen by these devices. Methodology: Inrush current and repetitive peak current to the lamps were measured for seven integral LED lamps (Lamps 1‐7), a 40 W incandescent lamp, and a compact fluorescent lamp. The lamps were tested on line voltage and with four triac‐based dimmers. Results: Figure 1 shows the current to a dimmable SSL replacement lamp. The figure shows a full line cycle, and shows both the current to the lamp when no dimmer is used, and current to the lamp in a dimmed position at 45% of light level control. Figure 1. Full line cycle current waveform for dimmed and undimmed operation of dimmable solid‐state replacement lamp. http://www.lrc.rpi.edu/assist Experimental data show that the peak inrush current measured at device turn on is indistinguishable from repetitive peak current. Most of the lamps had a repetitive peak current of short (~50 μs) duration under 2 amps, with one outlier around 14 amps. Figure 2. Repetitive peak current for various lamps and dimmers. While Lamp 2’s repetitive peak current is only about 2 amps, this is almost twenty times its normal operating current (i.e., with no dimmer), which is about 100 mA. According to NEMA SSL‐6 (2010), repetitive peak current should be less 9 amps, so lamp 5 fails for all dimmer combinations, while the other SSL lamps pass. Consumers should be aware of the differences between incandescent lamps and LED lamps in specifying the number of lamps that can be safely used with a dimmer. A consumer can expect to calculate the number of incandescent lamps that can be used with a single triac dimmer by dividing dimmer rated power by the lamp wattage. The same cannot be said when using LED replacement lamps, since inrush current may be significantly higher than rated current of the lamp (NEMA LSD 49‐2010). References: NEMA 410‐2004. 2004. Performance Testing for Lighting Controls and Switching Devices with Electronic Fluorescent Ballasts. Rosslyn, VA: National Electrical Manufacturers Association. NEMA LSD 49‐2010. 2010. Solid State Lighting for Incandescent Replacement – Best Practices for Dimming. Rosslyn, VA: National Electrical Manufacturers Association. NEMA SSL‐6. 2010. Solid State Lighting for Incandescent Replacement‐Dimming. Rosslyn, VA: National Electrical Manufacturers Association. WattStopper TB107.1. 2005. Electronic Ballasts and Inrush Current. September 21, 2005. Internet: http://www.wattstopper.com/getdoc/1326/TB107.1%20Inrushfacts.qxd.pdf Contributors: N. Narendran, Terence Klein, Martin Overington, and Jennifer Taylor, Lighting Research Center About ASSIST: ASSIST was established in 2002 by the Lighting Research Center at Rensselaer Polytechnic Institute as a collaboration between researchers, manufacturers, and government organizations. ASSIST’s mission is to facilitate broad adoption of solid‐state lighting by helping to reduce major technical and market barriers. ASSIST members include: Acuity Brands Lighting; Amerlux Global Lighting Solutions; Bridgelux; China Solid State Lighting Alliance; Cree; Everlight Electronics Co., Ltd.; Federal Aviation Administration; GE Lighting Solutions; ITRI, Industrial Technology Research Institute; Intematix Corp.; LG Electronics; LG Innotek; Lighting Science Group; Lite‐On; NeoPac Lighting; New York State Energy Research and Development Authority (NYSERDA); OSRAM SYLVANIA/OSRAM Opto Semiconductors; Permlight; Philips Lighting; Sharp Laboratories of America; Seoul Semiconductor; United States Environmental Protection Agency; WAC Lighting. http://www.lrc.rpi.edu/assist 2