Dropping voltage on "Christmas Lights..."

[ModRob]

New to this, so...<p>I have an older jukebox that used approx.40-50 small bulbs. It's much too expensive to replace each, but I'd like to substitute "Christmas lights". With my limited electronics knowledge, I believe I'm getting a feed of about 9.6 or so volts to each bulb; each being fed from what is called a "five-bit sequencer" that allows a "flashing pattern" of sorts to occur (which now only stays lit constantly, but that's another project). Since the Christmas lights are 3.5 volts, I have tried a 1 watt, 100 ohm resistor wired between the feed and a leg of the bulb. The brightness seems to match the others now, but the resistor is indeed very hot. There is room for circulation for each replacement; but I'm concerned if a better option, and is this too much heat?
Thanks.

[haklesup]

Purely resistive voltage dropping will create a fair amount of heat considering the amount of voltage you are trying to "waste" as heat. <p>As an alternative to resistors you could wire 2 or 3 bulbs in series or drop the excess voltage using a zener diode and resistor combination or any combination of the above.<p>9.6V Is this AC? (probably filiment voltage from tubes) in that case a normal diode and resistor may be enough to bring the brightness to what you want since a half wave rectified signal has less power than the full wave AC<p>[ January 12, 2003: Message edited by: haklesup ]</p>

[russlk]

It is normal for the resistor to be hot. You are within its rating, so don't worry about it. You could use a 2 watt resistor to reduce the temperature, if that is a problem.

[ModRob]

Hey guys..thanks for the help thus far...let me see if I can elaborate a bit more..
As far as the diode, I'd like a bit more info on that one (added to the resistor), as far as values and such...For the series part, I think that would be more involved, since there is a scheme to the five-bit sequencing..
AC or DC? I think DC, since on my voltmeter, I only get a reading of about 9.6 when DC volts is selected..I get some kind of MV thing, I believe, when switched to the AC volt setting.
Russ, I'll try the 2watt version...
So, from your answers, I'm thinking I'm on the right path. The method I'm using at present is working, but just concerned maybe I was adding the element of too much heat when it wasn't necessary by means of another component or two..
Again, thanks.

[Chris Smith]

A five dollar light dimmer from the hardware store can handle up to 600 watts. No heat, any voltage within reason.

[haklesup]

If you don't actually burn your finger on the resistor, its not too hot and you can't beat the simplicity of a resistor. What you do need to worry about is the heat discolering or warping the plastic or other materials in its vicinity. If you have some air space around the R when you are finished, it will probably be OK. You can mount the resistor anywhere along the wire that is convenient. If you mount it onto a metal panel then you will be well in the safe zone.

[Bernius1]

We took a set of 110V lights, & counted how many died if 1 bulb was pulled. A string of about 16 went dead, so each bulb took about 7V, with 16 in
series, total of 110V. My bro' took all these bulbs, & blue butt conn'ed them 2 each (14V),then in series for automotive use. Try it.

[chessman]

why not add a simple power supply to match the X-Mas light voltage and switch the lights from the sequencer with a BJT?<p>~kyle

[ModRob]

Oops..after all this, I find I made a mistake..the actual voltage going to the original light bulbs is AC...I did try a 47ohm, 2watt resistor on the Christmas light; still hot, but I think tolerable. Nothing close to discolor or harm.
I'm still torn on how to resolve this issue totally though. I found a site that sells original bulbs for .55 cents. (Of course shipping is a bit extreme for such a small product)
The sequencer has stopped letting the bulbs flash in a pattern, but still allows the bulbs to light, although dimmer--hence the 9 volts. (The site with bulbs shows them to be 14 volt bulbs.)
The sequencer is comprised of about 20 or so resistors in all, five I guess "transistors", and one capacitor. I may scrap the whole thing to work in a string of chasing Christmas lights, which would make a better pattern. Only trouble with that is most strings are 100 to 130 lights, and I have use for only 53........
Again, I thank the participants to this question. I've found through avenues like this and some magazines that the electronics community out there is so helpful and loves to share information....

[Timothy Rasch]

Hi, the formula for figuring out resistor is
e[source]-e[lamp]/I[lamp]=r[ohms]. The resistor power is [e[source]-e[lamp]^2]/r[ohms]. Make sure
e is in volts and I is amps. Another thing you can try is a diode [1n4001] which will cut down voltage about 70% wired in series with the lamp. This won't always work with low current lamps like your 3.5v . You can try putting the diode across the resistor. Now you have a parrellel shunt type circuit so the resistor won't get quit as hot[the diode conducts on every half cycle of the sinewave].You might have to put a capacitor [.047uf ceramic] across it to prevent interference buzz to the amp in juckbox. I hope this works out for you. Tim Rasch [email protected]