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Old 13-02-2011, 09:02   #1
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Light for Compass Binnacle

My old Danforth Constellation has an incandescent bulb (#1487 with a screw-in base). I would like to replace it with an LED. Do any of you know of a direct replacement or am I going to have to fabricate something? Thanks.

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Old 13-02-2011, 09:58   #2
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Not familiar with this part number, but fabricating something in this case is extremely easy. In electronic parts shop ask for a high brightness, wide angle red LED in a diffuser body (i.e not plain clear but 'milky'). Ask for nominal current of this LED (typical parts from signalling range will be rated @ 20mA or 30mA) and a forward voltage of this LED at nominal current (will be around 2.4 V). Knowing this, calculate resistance value to place in series with diode.

Assuming highest voltage on board to be 14.4V and nominal diode voltage 2.4V at 20mA current:

resistance = (14.4V - 2.4V) / 0.02A = 600 Ohm. Nearest standard value is 610 Ohm.

Power dissipated across this resistor will be (14.4-2.4)V * 0.02A = 0.24W. Pick a 0.5W variant for safety margin.

If a single LED will not cut it, connect more in series, modifying resistance accordingly.

If something is not clear, ask. I'll try to explain

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Old 13-02-2011, 12:55   #3
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Yes, and avoid both too bright and too dim ones. By trial and error probably.

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Old 13-02-2011, 13:25   #4
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The 1487 bulbs have an E10 base. Here's one example of a LED replacement.


Here is the incandescent version for comparison.

Much better price here.

google - E10 base LED - and you should be able to find something suitable.
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Old 13-02-2011, 13:55   #5
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Thanks to the helpful salesperson at Jaycar...

Thanks to the helpful salesperson at Jaycar Electronics, Rydalmere I got a real introduction to using LEDs for my compass.

They actually got some red LEDs and wired them up to a motorcycle battery for me. They were way too bright. I could see them taking my eyes out on a dark night.

After much fiddling round we ended up with two LEDs, resistors and an adjustable resistor with the "don't connect here" lug cut off.

It was a bit tricky. You can dim LEDs but they don't really like it. At some very low current they just cut out.

They must have spent at least half an hour, and the end result cost only a few dollars

I haven't put it in the boat yet. I'll see if I can report back when I do.
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Old 13-02-2011, 17:06   #6
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Considering the lack of heat buildup, I wonder if there isn't a simple way to adjust brightness.

Brush a thin coat of white paint on the surface of the bulb. After it dries well take a sharp point and scribe a four lines through the paint to re-expose the surface. Very thin lines of course.

Then test at night and add lines as needed to adjust. Seems reasonable to me.

I had not considered a LED would be too bright myself. Mine has a tiny red incandescent bulb just on two wires, no socket. No way to even tell it's on during the day but glows perfectly at night. Only the lettering appears lit.

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