Bought a gooseneck light from a garage sale for a few dollars. It had a hook on the end to hang it, that was useless, not sure what it was meant for, but it had to go. I converted it from using a small incandescent bulb to 24x 0.5w Cool White LEDs in a 10mm package, 12w total. Wanted to keep it as simple as possible, run it from mains AC and build a more useful way to mount it. I used a surplus clamp style base, a 2x2, a 1/4" bolt and some Shapelock plastic to create a versatile mount.(That was all recycled or scavenged)Powering LEDs from Mains AC:
There is a lot of information out there on how to do this, it gets a bit hard to sort through as there are many different configurations people have used. And none that I found had used these type of 0.5w LEDs.
I found these sites to be quite helpful:http://www.electronics2000.co.uk/calc/reactance-calculator.phphttp://www.marcspages.co.uk/tech/6103.htmhttp://www.ele.uva.es/~pedro/optoele/LEDs/Appnotes/LED_AC_operation.pdf
This circuit uses the reactance of a capacitor to limit the current supplied to the LEDs. This method is a lot more efficient and safer than trying to rectify the AC and then use resistors to limit the current. The 0.5w LEDs require 100ma and 130ma Peak. I wanted to keep it in the safe area as I want this to last, rather than trying to make it brighter.
Through trial and error on a calculator and checking what capacitor values were available to me, I settled on a 1.8uF, 250v, X1 type capacitor, the X1 designates it as a fail-safe capacitor which I required.
Reactance of a 1.8uF at 60hz = 1.474kohm
Peak: 170 vac / 1.474 = 115.33ma
Nominal: 120 vac / 1.474 = 81.41maElectronics:
C1: 1.8uF, 250v, X1 type. Such As This
C2: High uF Capacitor,(I used an 18uf I had around) Smooths the rectified DC, 100v or higher
R1 & R2: 100ohm 1/4w, prevent transient currents and act as a fuse.
R3: 1 Mohm or so, bleeds the capacitor when power gets turned off. Note I used two 3.3 Mohm in parallel to get a 1.65 Mohm
R4: Most designs have this, I did not include it in my device.
Diodebridge: 250v or higher, I made mine out of 1n4007s
LEDs: 10mm, 0.5w(100ma), Cool White LEDs Find Some Here
There are 10mm LEDs out there that are only 20ma or 50ma, check before purchasing.
Take a look at the Image notes for more details.
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