Dimming my Ultrafire WF-501B

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4 February 2015 | by Sverre LA3ZA | Share | | Leave a Comment (1)

I got this red LED flashlight as a Christmas present. But unfortunately the intensity was way too high for what I intended to use it for. A soft red light preserves your night vision, and is ideal for use with a telescope in the dark as was my intention. But if the intensity was as high as before the modification, night vision would suffer.

I then found this YouTube video describing how the controller circuit board could be replaced by one with more functions. As recommended I therefore ordered an AMC7135*8 2800mA 4-Group 5-Mode Circuit Board with 8 AMC7135 current regulators in parallel. The image shows the the original circuit board as connected before the modification in the front in the image and the new one behind it.

The new board gave me the choice of one of 4-groups:

3-mode: Lo (5%) – Hi (100%) – Strobe
3-mode: Lo (5%) – Mid (30%) – Hi (100%)
2-mode: Lo (10%) – Hi (100%)
5-mode: Lo (5%) – Mid (30%) – Hi (100%) – Strobe – SOS

I selected the second one by bridging the corresponding gap on the circuit board. The lamp will take either a single 3.6 Volt battery or two smaller ones in series which is what I had. Before the modification the LED lamp would consume 0.68 Amps from 2×3.6 Volt batteries. Now it consumes 0.14, 0.83, or 2.4 Amps. The controller remembers the last mode if the light stays off for more than 2 seconds. If the flashlight is turned on again faster than that it will change to the next mode.

I am very happy with the Low setting, but I wish I could have avoided the very power hungry High setting. I am not even sure if there is enough cooling for the LED and the controller to take that much current over a longer period of time. Perhaps a board with fewer AMC7135 chips would actually have been better, like this one with 3 rather than 8 chips and max current 1050 mA? Anyway, the whole modification took only 20 minutes or so.

Sverre Holm, LA3ZA, is a regular contributor to AmateurRadio.com and writes from Norway. Contact him at [email protected].

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