lights on layout - electrical question

If the power supply is DC then you can. AC supplies do need a rectifier in order to use them.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!

If you already have a six volt supply, why not just put four, five or six 1,5 volt bulbs in series? This will allow you a degree of adjustment of voltage to each series group of bulbs and also give you the option of using other voltage bulbs as well. The higher voltage will allow you to use a smaller wire gauge and you will require no additional electronics which will offset the 3 or 4 bulbs hanging loose under the layout that have yet to be allocated a lighting position ;-)

One point that comes with experience is to make every bulb easily removable. The scheme I like is to mount each bulb on a length of brass tube with a bottom screw bracket inserted through a hole in the baseboard. Run a wire inside the brass tube for the feeds to the bulb.

If you're going to have voltages other than 12/16 volts on the layout I would recommend using a unique coloured wire and perhaps a unique plug/socket connection scheme.

Regards, Greg.P.

Light bulbs don't care if they are feed AC or DC, other than the fact that they last a little longer on AC.

Bill Sprouse wrote:

You may want to consider a few things. The 1.5 Volt bulbs are very small and not very bright. They are useful in the confined spaces inside rolling stock and the simple constant brightness circuit works. On the down side, all the ones I have seen are "solder in" making bulb replacement hard. For various reasons making a good 1.5 volt power supply is hard. Was it me, I'd do some serious looking around for a 6 or 12 volt bulb with a base and socket. I'd want to pick a bulb that's fairly easy to find, and of a type that will stay in production for many years. I'd take a look in your friendly local auto parts store, or Radio Shack for a small 12 v type. To see how widely available the bulb is, drop the part number into Google and see how many hits you get. Sockets are very nice, having to warm up the soldering iron to change a dead bulb is a nuisance. For good bulb life, run them on less than rated voltage. For instance ordinary household 75 Watt bulbs are rated at something like 750 hours. If you ran them on 90 volts instead of 120 they would last much longer. A 12 volt bulb operated on 10 volts, a 6 volt bulb on 5 volts will give excellent life. Bulbs don't care whether they run on AC or DC. For AC power, all that is necessary is a transformer. Radio shack has (or had) 6.3 and 12.8 volt transformers. The somewhat odd voltage ratings are a legacy from vacuum tube days. Transformers for those two voltages are fairly easy to find. Other voltage ratings are scarcer. If you roll your own transformer be sure to put it into a proper enclosure to prevent children's hands from coming in touch with 120 VAC hot terminals and wiring. Even if you don't have of your own children, you may have visitors... I have seen strings of tiny white christmas lights that might be useful. If you wire your bulbs in series remember that when one bulb finally fails, the entire string goes dark. Finding and replacing the single dead bulb in this case can become a chore.

David Starr

'Es not feeding the globes directly, 'es running a voltage regulator supply circuit. That requires DC on the input. I assume a grounded LM-317T or something like that. Putting the globes in series will work, but is not a good idea. If you lose one you have to troubleshoot the whole string to find it. Depending upon many variables, that could be a major PITA. I like the idea of a 2N3055 with a voltage regulator circuit. The 2N3055 has a continuous collector current of 15 Amperes and will dissipate

115 watts with heat sinking. That's a lot of globes at 1.35 volts, 50mA., plus it has the advantage of having virtually no load on the regulator. all it has to do is turn on the 2N3055

Build this one and you can light thirty globes @ 50mA

This one shows you how to include the transistor for a low voltage high current device. Use the transistor specified or the 2N3055.

Cheers...............F>

If you have a 6 volt 1 amp power supply and a voltage regulator circuit you will at best supply 1.5 volts at 700ma = 14 bulbs. If you have a 6 volt 1 amp power supply direct to strings of 4 bulbs at 50ma you can feed

20 strings = 80 bulbs for the same total consumption or with 5 bulb strings at 40ma; 5 x 25 strings = 125 bulbs.

That's about 6 power supplies and 7 voltage regulator circuits you've saved on a small layout against checking 5 light bulbs on the rare occassion that one blows! Add to that the trouble shooting required when one of your lineup of voltage regulators fails to fire up. KISS.

Regards, Greg.P.

Putting the bulbs in series is a bad idea. If you build a power supply with a pass tansistor you eliminate all the problems associated with the current capacity of the LM317 and you have only one power supply. As another rspondent pointed out, using

1.5 volt bulbs is a bad idea, but I am working within the stated parameters. I would use 12 volt bulbs, but I'm not the one doing the project. Running bulbs in series is always a bad idea for troubleshooting and because you might get a bulb of different manufacture next time that has different characteristics. In parallel, it will simply use what it needs. In series it will affect every bulb in the string. KISS has its practical limits. A maintenance intensive system, while possibly simpler, is also a PITA. I don't want to trade a KISS for a PITA.

First, I agree with Froggy that wiring multiple lights in series is a bad idea, unless your idea of fun is tracking down which single bulb in a circuit has to be replaced to get the whole string going again.

For similar reasons, I'd suggest looking at using LEDs where you can in order to eliminate the maintenance needs. LEDs are extremely long lasting (practically speaking, they'll outlast all of us) as long as you properly limit the power. Use them where you really, really, don't want to have to go back in and replace a bulb.

The cheapest route to go is a string of Christmas tree lights, especially if you're just lighting the inside of buildings. Use the power supply that comes with it, since you already know it'll run all the lights on the string. To ease maintenance, I'd rewire them to parallel, unless they're already that way.

Mike Tennent "IronPenguin" Operating Traffic Lights Crossbucks Special Effects Lighting