I've got a TERMOSFAR light setup for my room and I'd like to mod it before I put it into functionality. The transformer for the lights is in the big metal ball and converts 120V -> 12V @ 8.75 A. That powers 5 halogen bulbs, each taking 12V and 20W. The bulbs are all in parrallel. Now, what I would like to do is take a bit of that 12V and run it through some LEDs inside the globe, making it glow through the holes when it's on. I'm also going to have it plugged into a wall-outlet that is switch powered so they'll act as the room lights. I was thinking about just Blue LEDs because would look neat coming out of the globe I think. The globe is meant to be wall or ceiling mounted and hard wired into the house, but I'm going to put some rubber feet on the bottom of it and solder a real power cord into it so I can just plug it in and have it on display in the room. Now, with 12V, I would want 4 x 3V LEDs in series and I wouldn't even need resistors? Any other cool idea's I didn't think of or consider?
You should put a fairly low value resistor (~100 ohms) just so the LEDs don't run the risk of drawing too much current (if connected by themselves, there's nothing to limit the amount of current they draw before they die/explode). Go ahead with the idea as long as you don't add any other colored LEDs and play disco, or else there will be consequences (*shakes fist a la Homer Simpson*).
One point, the lights will be running on 12v AC so you need a bridge rectifier after the transformer for the leds. No smoothing you'd have 12v RMS DC, add a bit of smoothing, say a 220uF 25v electrolytic, & you'll get about 15v DC for the led supply. You could safely run 2 strings of leds in inverse parallel off the 12V AC supply but they'll flicker at 60Hz, may or may not bug you.
Of course, I forgot that it's AC.. Hmm, will blinking at 60 Hrz even be visible? I don't think I understand this. You mean 2 strings of 4 LEDs each? What does 'inverse parallel' mean? Is this going to pull too much power from the halogen lights?
My uncle has those lights in his apartment. Not enough for the entire room. Maybe spotlights at best. And IMHO that giant metal ball is naff with the wires that crawl out of it.
Hmm minor thing from experience - I have one of them ... except I got the one with the nifty blue lights on flexible stalks. Same wattage etc, same transformer, different mounts. Got 4 on no problem. Got the 5th on, poof of smoke bye bye transformer. LEDs are really small current draw-ers so they shouldn't cause any problems... but just a warning that they might not be able to handle all 5 - and definately not any more.
60Hz will probably be a bit noticeable. Inverse parallel, if i'm understanding this correctly, means you have two strings of LEDs in series, connected in different polarities, like so: Code: AC - - - - |<| - |<| - |<| - |<| - AC | |>| - |>| - |>| - |>| | That way, you'll always have a string that's on, and if the LEDs are placed correctly, it will look as if there was just one.
8.75 x 12 =105W, so 5 bulbs @ 20W only gives 5% headroom. The transformer's gonna run hot. The leds are only going to add about 0.3W a string, so a few really make SFA difference to the load.
