Electronics

bsilvers · Joined: 13 Dec 2007 Posts: 2

My wife bought a Christmas decoration which needs some electronic "tweaking". It is a resin moose with both fiber optic lights as well as several LED's. The fiber optics are quite pleasant, but the LED's are so bright they actually hurt our eyes when we try to look at the moose. I took it apart to check the wiring. The plug is a 12 V transformer with an RCA type jack which plugs in the back of the moose. Inside, there are two white wires running from the jack to a small PC board containing three small cylindrical (resistors??), one large cylindrical (capacitor??), and a white (ceramic??) rectangular block. From there, there are four wires running out- two to the fiber optic control and two to the multitude of wires powering the LED's. I cut one of the wires to the LED's, so we can now at least enjoy the fiber optic display. However, ideally I would like to keep the LED's burning, but just make them dimmer. I went to Radio Shack to buy a rheostat, but was overwhelmed with all the electronics terms (volts, ohms, etc.) I took my chances, bought one labelled "25 ohm, 3 watt, 20% tolerance" and tried to hook it up. It did not work.

My questions then are:

1) Can LED's be rheostatically controlled?
2) I did not know when I bought the rheostat that the device was 12 watts. Since the rheostat is only 3 watts, does that mean that the device somehow "overpowered" it? Will I need a matched 12 watt rheostat before it will work?
3) If it is possible to do this project, can someone explain how I need to hook up the wires? I have done a small bit of research on the net, so I have a very general understanding that the two outside terminals are a "straight path" through the control and the center terminal is the wiper. I just need someone to tell me what to do with the two power wires and the three terminals.

Thanks for your time.

neon · Joined: 25 Feb 2006 Posts: 570

LED are diodes or light emiting diodes there is a voltage treshold to be met and current treshold. UN FORTUNATELY THEY ARE NOT LINEAR in response basicaly they are on or off. you may adjust by reducing current trough them since you have no save of that to do the job leave it alone. LED are specified as lumens output and angles and spectrum. so your solution is replace those LED with low output to suite you the range is very big from 500 to 10000 and more. good luck

bsilvers · Joined: 13 Dec 2007 Posts: 2

Thanks for your response. I am still a little confused though. You said they are either "on or off", but then I think you said it could be done by reducing the voltage. Is that correct? I did see some voltage regulators at Radio Shack that required being soldered onto a PC board... is that what you mean? You're right, I don't know how to do it... but at this point I would just like to know how to theoretically make it work.

Any other responses from other forum members would also be appreciated. Thank you.

neon · Joined: 25 Feb 2006 Posts: 570

Well like all diodes they follow an eponentional curve meaning that increasing current they will not dramaticaly increase in voltage. No you do not need any kind of regulator. Those are nice but not neccessary. To decrease the current trough thosE led ALL YOU NEED IS a series resistor to limit the current. Now here is the thing NORMALY a 10ma to 20ma is enough to see the light NORMALY the forward voltage is 2.5v. You may check across to see the voltage is now present. Now for xmas lights means a lot of them probably in series with just one resistor in series to regulate the current[i don't know] Allow me to tell you how one works get any voltage DC and add a resistor to drop the any voltage -2.5v allowing 10-20 ma per LED. remenber polarity while doing so. so 22.5v -2.5=20 20v/20ma=5k that is how it works .good luck seepower supply for fading lights to get some ideas

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