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Old 02-03-2013, 08:57 PM   #1
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Re-inventing backup lights

I cannot back an Airstream in the dark. The backup lights shine out the back of the trailer and I don't have X-ray vision, despite what I used to tell the girls. I think backup lights on the rear end of an Airstream are 98% useless.

I've been thinking for years how to illuminate the sides of the Airstream when the backup lights are on. Something not too obtrusive, of course. Once I got my Chinese garden lights, I was able to check the illumination brightness and pattern--the LEDs in these lights (ordered separately) will work perfectly.

I've decided to move the taillight assembly reflector down to the small casting below and put the "sidelight backup light" into a hogged out hole in the old reflector location.

The lens for the new light is formed pneumatically (thanks, BARTS) using a small fixture and a 300 degree oven. Details on the tools in a subsequent post. The bubble lens will allow the LED to project significant light almost directly down, as well as a high level of illumination out to the side about 12'. This LED uses 6W (advertised as 10W), so it's the equivalent of a 40W incandescent. Plenty of light around the rear end. I also intend to replace the OEM backup light with this same LED, but with a new semi-bubble lens that will project light 45 degrees to the side. More on that later.

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Old 02-03-2013, 09:19 PM   #2
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That is a very good idea. LEDs are the way to roll. I am interested to see more. Where did you land the lens?
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Old 02-03-2013, 10:04 PM   #3
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Originally Posted by Zeppelinium View Post
I cannot back an Airstream in the dark. The backup lights shine out the back of the trailer and I don't have X-ray vision, despite what I used to tell the girls. I think backup lights on the rear end of an Airstream are 98% useless.
Zep.

Back up camera's these days, are super cheap and do a great job.

Andy
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Old 02-04-2013, 09:52 AM   #4
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Originally Posted by Inland RV Center, In View Post
Back up camera's these days, are super cheap and do a great job.
Great reminder. I had looked at these some time ago and didn't connect them with backing in the dark, I mean really dark. I think they are great for general backing and not hitting stuff, but a lot of places I back into I want the tires +/- 6" of the track--I'm not sure a camera would help with that. Zep
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Old 02-04-2013, 10:26 AM   #5
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Great reminder. I had looked at these some time ago and didn't connect them with backing in the dark, I mean really dark. I think they are great for general backing and not hitting stuff, but a lot of places I back into I want the tires +/- 6" of the track--I'm not sure a camera would help with that. Zep
Zep.

Today's technology has provided some very good back up camera's.

I would suggest that you purchase a good one, and add to it your idea of the LED backup lights, then sit back and give it all a huge WOW.

You innovative enough to give it a good shot.

I tested one at our shop and it did great at 150 feet between the camera and receiver. And, was less than a hundred bucks.

Andy
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Old 02-04-2013, 11:40 AM   #6
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ZEP, my infra-red BU camera sees in the dark very well. That being said, I think corner lights which illuminate beyond the viewing angle of the camera, to the rear "45s" would be a big plus.
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Old 02-04-2013, 01:33 PM   #7
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Originally Posted by Inland RV Center, In View Post
...I tested one at our shop and it did great at 150 feet between the camera and receiver. And, was less than a hundred bucks...
Thanks, Andy. Brand and source, if you have them? Zep
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Old 02-04-2013, 01:53 PM   #8
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Making lenses

I recommend a 4-part tool--backing plate, plastic to be formed, open extrusion die, and stiffener for the die. The backing plate is hogged out so that the expanding part of the plastic isn't touching anything, which allows the front and back face to heat up relatively the same. You need to clamp the assembly sufficiently to slow air leakage, as it does take a bit of pressure to expand the acrylic.

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There seems to be a limit (maybe based on temperature of the plastic) to how much you can deform it. For small items like the teardrop in post #1, it's about 5/8" of extrusion. In order to get this, I had to heat it in an oven (using small C clamps, I could get it in a toaster overn) to get even heating across the face and through the thickness.

For large pieces like this lens (where you're not attempting to make a high extrusion), you can heat it with a heat gun and observe the shape as you apply air. If you don't like it, keep heating it. I had to concentrate the heat around the eges or it would have looked more cone-shaped. This photo gives you an idea of how much expansion I wanted for a taillight lens. The lens is sitting on one of the taillight cans that has been removed from the casting. I'll "frost" the inside surface of the lens to make it look a bit less DIY.

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Things don't always work. I tried the 0.050 non-glare plastic and popped one and made balloons out of the next two, so I went with the 0.093 acrylic for everything. If I had low pressure air and a better valve, maybe the thin stuff would work.

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BTW, I checked the current consumption of the original backup bulb and it's 2 amps (each). Four of these LEDs will use a total of 2 amps, with about 6-7 times the efficiency, so I expect something on the order of 3-4 times as much light in the back, using half the current. Efficiency isn't a big deal, since the tow vehicle provides all the power, but I'm thinking of adding another party switch that can turn these guys on in a dim mode powered by the Airstream battery, maybe 1/4 power. That's still a lot of light and only 1/2 amp.

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Old 02-24-2013, 01:41 PM   #9
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Backup LEDs

The LEDs are installed. I think the light pattern meets my expectations and is going to be a great help in night parking.

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The installation looks good and will be improved when I apply a masking paint scheme to the lenses. I especially want to provide a bit of a mask to the side light so that I don't see the LED directly when backing. One other thing I won't do is sand the lens--sanding/hazing the lens would make the lens itself appear much brighter from the tow vehicle.

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These "high power" LEDs require some care in their mechanical installation, to ensure proper heat dissipation. Don't kid yourself, when you have 10 watts being dissipated by such a small device, it gets HOT. I used 0.050 and 0.062 sheet metal to help conduct the heat away, plus some scrap aluminum extrusion to add fins to the mounting flange. All items are assembled using heat conducting paste (available at Radio Shack).''

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Note that the LEDs are "aimed." The one in the can is canted down 30° and left 45°. The side light is down 30° (you'd think 45° would be better, but aiming it up/out more still provides bright illumination on the ground close to the Airstream). The mounting flange for the side light is narrow where it pokes through the hole in the taillight casting, but is quite a bit wider inside where it's riveted to the casting. This provides good heat tranfer and mechanical stability.

Electrically, these high power LEDs are a pain. The lower power 2-Watt discs are easy to work with, don't need resistors at full brightness, and use common 1/2 Watt resistors in the 80-200 ohm range for dimming. These guys MUST have a suitable series resistor or they will burn out in something like 1 second or less (you know how I know I that, I know).

So here's the challenge--these LEDs, when they come in the spotlights, only consume 6 Watts even thought they are advertised as 10 Watts. I don't know if the vendor derated them on purpose, but at that power level they are bright enough. The spotlights use a current limiting regulator, so all the power (99%) is being dissipated by the LED. I wanted an easy installation, so I elected to use a resistor for current limiting. A 7.5 ohm resistor (R3 in the circuit below) limits the current to 0.50 amps. That's a total of 6 Watts, but about 2 Watts are being dissipated in the resistor and 4 Watts in the LED. This is plenty bright. Four of these LEDs per my install design use 2 amps, half of what the previous two backup incandescents used, and put out 2-3 times the light (usually LEDs are about 7 times as efficient, but I'm losing some in the resistors).

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After I got started with this project, I realized that the backup lights would provide full area lighting around the rear of the Airstream--party time! But they don't have to be full brightness to do that. So a couple of rectifiers, a switch and one additional resistor can power these LEDs from the Airstream battery. The photos above were taken with resistor R1 at 6 ohms, or about 400 milliamps total current to the two LEDs (the curb side isn't installed yet). Using a 16 ohm resistor will reduce that to 200 milliamps and still provide a lot of area illumination.

There are some alternate resistor schemes, but don't try to parallel the LEDs (circuit on the right). They have extremely low internal resistance, on the order of 0.01-0.05 ohms and are not matched. If you parallel them without an external series resistor, the currents through them are widely different, on the order to 3-4 to 1. If you plan your power dissipation to be equal, you will surely burn one out early, which will allow all the current to go to the other one and burn it out even more quickly.

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BTW, I found it pretty difficult to find 3W to 5W power resistors at these low values (4-25 ohms). You can order them from Digi-Key, but the cheapest you will find are $3.00+ for ones with mounting tabs. You may want to use axial lead resistors (like I did) and a terminal block or just secure them with a nylon tie. Use heat shrink insulation liberally!

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Zep
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Old 02-28-2013, 08:00 PM   #10
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Hell, I was just gonna run a dedicated line under the TT and git some work lamps that were a decent shape & quality to switch on when backing. Maybe even cut holes in my fairly flat bumper for those and for fog lamps. The other thought is to integrate strobes for the potential breakdowns on-road.

As usual, Zep finds the cool way to do it!!

.
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Old 02-28-2013, 08:08 PM   #11
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Zep.

Today's technology has provided some very good back up camera's.

I would suggest that you purchase a good one, and add to it your idea of the LED backup lights, then sit back and give it all a huge WOW.
I have to agree with the Inland RV guy! I bought a camera from voyager and it is really something, great night vision. The more light though, the better when backing. I went to a campsite in January and arrived at night. I could see behind in the camera but there was a tree on one side and a power pole on the other. I was unsure in the dark of dimensions, etc. Distance is a difficult thing to judge without looking over everything in person. Your lights AND a camera would be the bomb!
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Old 02-28-2013, 08:52 PM   #12
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Wouldn't a bank of cameras, say three (or more): one straight back, then one on each of the corners on a 45-degree angle. Then of course, three of the little monitors arranged in a left centre right row.

The result should be a nice clear panoramic view of what's behind.

If the night vision of those cameras is as good as touted, and the cost of them is as low as mentioned, it could really be the end of "Fear Of Backing Up".
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Old 02-28-2013, 09:06 PM   #13
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You need to install some of those color changing LEDs in these and mount them on some nice bases, like blocks of mahogany.

Maybe a color organ circuit.



OK, the backup lights are great!
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Old 02-28-2013, 09:21 PM   #14
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This looks really neat, Zep! I've had to back into some very tight (6" clearance) spaces in the dark, and that took a lot of in and out, and prob. 15 minutes of running the whacka,whacka,whacka diesel in the campground at night.

For straight back, just the lights will do it, but for those turn and back in the dark situations, a backup camera would be a perfect addition.

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