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Creating a homemade 12VDC LED lighting system

21 Nov 2014  | Joseph Julicher

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From the bunk room, we headed east towards the kitchen. This was a detour for the light switches and a break for lunch. Shortly after lunch, we had all lights tested and operating for the bunk room, kitchen and dining room. With some functioning light, we powered the two lights in the dining room and verified 23Ws from the battery. The 23Ws for a well-lit dining room seemed wonderful, so we had a steak dinner and went to bed.

Day 2
On Wednesday morning, we decided that we needed some parts. We had previously made only a crude conduit plan, due to a lack of knowledge of attic conditions. We were using T fittings at a high rate, and needed a weatherproof switch for the porch light. We loaded the truck and headed for the nearest hardware store, 1 hour away. We saw the morning clouds below us and scared up enough turkeys for a thanksgiving feast. There are some benefits to vacationing up here, but convenient trips to the local hardware store are not part of mountain life.

After returning from the hardware store with the remaining parts and some after-work snacks, we got busy finishing the master bedroom, master bathroom and the utility room.

Figure 4 shows the dining room. We left the previous fluorescent lights in place, as they were wired for use with a generator. If you bring gasoline and want the noise of a generator in the woods, you can get a slightly more light with the 80W twin tube fixtures. The two LMH-2s, however, provide almost as much light with a nicer colour at 20W.

 Dining room

Figure 4: Dining room.

Figure 5 shows the utility room, with a single 23W fluorescent and a 10W LMH-2. The LMH-2 produces a little less light and it is, unfortunately, focused downward because I did not have the optional dome diffusers. The light fixtures are a .032" aluminium bent, punched and painted to hold the LMH-2 fixture and provide a little heat- sink area. Thermal management of this system is very easy because there is only 5W of heat in the light source and about 2W in the power supply; plus, the evening temperatures are around 20°C in the summer and 10°C in the winter. (As I write this, it is 9:20 p.m. and 27°C.

 Utility room.

Figure 5: Utility room.

Day 3
Day three started with breakfast and a discussion on sustainable cabin energy. A waste heat converter on the propane water tank was interesting, but hydropower from the spring is continuous energy while it is not frozen. We checked the Watt Meter and learned that night lights, full power for photos, breakfast and talk used 56 Whs of energy. That should be replenished in 3 to 4 hours with my 30W solar blanket even with winter sun. Work for day three consisted of adding the last light in the kitchen, closed up the conduit and writing the usage manual so our relatives could utilise the system.

After a year of planning and three days of intense work, we now have a DC lighting system running off-grid in a remote part of the United States. This system should provide the family with trouble-free, quiet light for the next few generations. This cabin has already seen lighting advance from propane gas mantles to AC incandescent, AC fluorescent and now to DC LED. Each generation of technology has reduced maintenance, improved performance and increased the enjoyment of family vacations.

1. Devices used in this design: PIC16F1787, MCU-Based Power Supply Controller; MRF24J40MA, 2.4GHz RF Module; MCP16322, 3.3v Switching Buck Regulator; MCP1416, Low Side MOSFET driver; MCP87130, N-Channel MOSFET

2. The Microchip MiWi Wireless Networking Protocol Stack is a simple protocol designed for low data rate, short distance, low-cost networks. Fundamentally based on IEEE 802.15.4 for Wireless Personal Area Networks (WPANs), it was later expanded to support Microchip's proprietary RF transceiver.

Note: The Microchip name and logo, and PIC are registered trademarks of Microchip Technology Inc. in the USA and other countries. Cree is a registered trademark of Cree, Inc. All other trademarks mentioned herein are the property of their respective companies.

About the author
Joseph Julicher is engineering manager for MCU8 Division at Microchip Technology Inc.

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