Author Topic: LED Lighting Off Grid  (Read 4911 times)

Aphrael

  • Newbie
  • *
  • Posts: 12
    • View Profile
LED Lighting Off Grid
« on: August 14, 2015, 02:37:36 AM »
Because some others on this forum are probably using their generator sets for off-grid and emergency power, I thought I would share with you some observations about LED lighting.  

Ten years ago, before the automotive 1156 and 1157 socket LED replacement assemblies were available; I built my own 24-volt LED table lamps from inexpensive individual high-output LED's (Light Emitting Diodes) that were becoming available very cheap from China in bulk.  I have our house wired for 24 VDC, in addition to normal 120/240 VAC.  These are totally separate circuits with a 24-volt outlet (or two) in every room.  We have frequent power outages at our remote home site.  These LED lamps are a wonderful improvement over kerosene lamps and candles, eliminating the potentially serious fire hazard.

The situation is even better today with 12-volt automotive replacement bulb assemblies so cheap.  It's even easier now to wire a pair of 12-volt bulbs in series for a 24-volt system, and make a little table lamp out of them.  The situation is also better today because there is more availability of warm-white bulbs, which are more pleasing for room lighting.

The thing I can share with you that might be valuable is that most of the LED bulbs that I have tried are way over-driven in an effort to rank high in the "Lumens-of-output" marketing war.  This means a short effective life for the LED's.   (By this I mean the low-voltage lamps that one might select for emergency or off-grid.  I'm not sure about the 120-volt replacement LED bulbs).

Heat is a major enemy of LED's.  When the LED is driven with a current that is at the very peak of it's rating, or even above peak, the manufacturer does get a LOT of lumens of measurable light output, but there is also a lot of heat generated at the semiconductor junction.  That heat will rapidly degrade the LED, and light output will start to fall off noticeably after a relatively short time.  Interestingly, while the measured lumen output is high, the increase is not easy to discern by eye.  This means the LED can be operated MUCH more conservatively, with only slightly less light apparent output, and with significantly increased life expectancy before light output declines.  

The solution is just to insert an inexpensive voltage dropping resistor in series with the LED bulb assembly.  It can be inserted in negative lead, or the positive lead, it doesn't matter.   Understand that bulb the manufacturers could do this quite easily, but then they couldn't claim such fantastic lumen output figures.

For example, I just finished converting the low-voltage lighting in our camp trailer from 1156 incandescent automotive bulbs to LED's.  I purposely bought a version that has the LED's mounted on a flat circuit board (about 3-inches square) with pigtail leads to an 1156 base that inserts into the existing socket.  This square LED assembly is fastened to the inside of the lamp fixture with double sided tape that comes with the assembly.  The pigtail leads make a convenient place to insert the voltage dropping resistor.  This setup also has the advantage of directing all of the light downward out of the fixture, rather than in all direction as with a round bulb.

The dropping resistor that I soldered in series with each assembly was a 10-ohm, 2-watt resistor.  (The resistors are available on the bay for about $.40 each, including shipping).  This cuts the current through the LED assembly about in half, from almost 500 milliamps to about 250 milliamps.   It does this because the resistor "drops" the supply voltage about 2-1/2 volts.  There is some noticeable reduction in light output, but I bought the largest LED assemblies I could find knowing that I would want to knock the current back.  The lights are still quite bright enough for our needs, and the heat in the fixture is MUCH less that it would be if it was operated without the voltage dropping resistor.  

The optimum resistance value depends upon the current draw (wattage) of the LED assembly, but if you drop the voltage to the LED by about 20% you will probably be close to optimum if you value long LED life with stable light output over time.  Try some resistance values, feel the heat generated by the LED’s, and compare your visual impression of light output.

The resistor does waste some power, but not much.  The incandescent 1156 bulb draws 1.2 amps, which means it’s consuming about 15 watts of power.  The LED assembly, with the dropping resistor, draws 250 milliamps.  This means it’s consuming about 3 watts of power, with 25% of that being dissipated by the resistor as heat.  The resistor is wasting about ¾ of one watt, which is not much at all.   And if the resistor isn’t dissipating the heat, the LED assembly will be, much to the detriment of long life.

The same problem exists with these “super bright” LED flashlights.  They’re nice to have, but don’t operate them on high power for very long.  Light output will fade rapidly, because the LED’s are being over-driven.  Save the “super bright” capacity for times when you really need it, and operate the flashlight on low power setting most of the time.

If you live or plan for off-grid, LED lighting is nearly perfect.  Sitting in the dark is not good for the spirit in a time of stress.

« Last Edit: August 14, 2015, 03:13:59 PM by Aphrael »

dieselgman

  • Hero Member
  • *****
  • Posts: 3189
    • View Profile
    • Lister Parts
Re: LED Lighting Off Grid
« Reply #1 on: August 14, 2015, 03:48:01 AM »
Very interesting... I have converted a portion of our shop lighting to LED fixtures but the overall effectiveness is quite questionable. Power is still relatively cheap in the US Midwest and large dark shops are not a nice place to try and work on a cold winter day. I noticed that our high-bay LED fixtures are overdriven to the point that they require large heat sinks and fans to keep them cool enough. We have tried 75 and 150 watt fixtures... spot lighting is OK, but generally poor unless you are directly under the fixtures. I have no idea what the actual life expectancy will be. We also tried using larger numbers of very small fixtures within our parts shelves aisles and have somewhat better luck with those as far as useable light levels go without being blinded by one large source. As of now, I think the costs of experimenting with this stuff has exceeded any power savings that we might gain... but others in higher cost power situations would have a different experience.

Thanks for sharing your experience!

dieselgman
ALL Things Lister/Petter - Americas
Lyons Kansas warehousing and rebuild operations

Aphrael

  • Newbie
  • *
  • Posts: 12
    • View Profile
Re: LED Lighting Off Grid
« Reply #2 on: August 14, 2015, 04:16:59 AM »
Very interesting... I have converted a portion of our shop lighting to LED fixtures but the overall effectiveness is quite questionable.

I agree fully.  I don't have any LED light in any place where real work light is needed.  Even my 120-volt LED "trouble light" seems pretty dim.  LED only seems like a good solution when power is scarce or expensive.
« Last Edit: August 14, 2015, 04:21:27 AM by Aphrael »

LowGear

  • Casey
  • Hero Member
  • *****
  • Posts: 2132
  • What? My diesel had fries for lunch?
    • View Profile
Re: LED Lighting Off Grid
« Reply #3 on: August 14, 2015, 08:55:39 PM »
I've found that cheaters (cheap eye glasses) really help my LED stuff perform.

Casey
NPR Tipper/Dump Truck
Kubota BX 2230
Witte BD Generator
SunnyBoy 6000 + SolarWorld 245