Setting up power for a christmas village?

[Black Blade]

Well, I found an old PC, so now have a power supply with all kinds of different voltages

• +5 V 25 A
• +12V 10A
• -5V 0.3A
• -12V 0.8A
• +3.3V 14A
• +5VSB 0.8A

Would I need to keep the motherboard in there, to get the power supply to turn on?

 

[Sceadwian]

No.
It's probably an ATX supply (as long as it's not REALLY old) Look for a green wire on the main motherboard connector, when that is shorted to ground all the power outputs will turn on.
One of the 5V lines on the motherboard connector is always on (in your case limited to 800ma) that is only ever 'off' if the power supply is physically disconnected or if it has a REAL power switch on it (many don't now days) The wikipedia link bellow will show you the pinout and color coding of the cabling. It's very standardized.
I'm gonna guess the 12 volt line is the one that should interest you most. Possible the 5 volt one. the 5V one is only 2 volts over the nominal 3 the lights need, and can supply tons of current. Supplies like this pulled from old machines are really handy for the hobbyist.
On thing that you'll need to keep in mind is that these types of power supplies have short circuit/over current detection. And if you have a really heavy load on them at startup it will stop working and you'll hear a buzzing noise coming from the power supply. in order to reset it you have to turn it off and back on. There are ways to prevent this from happening if it does end up occurring, but worry about that later.

For more reference
ATX - Wikipedia, the free encyclopedia

 

[Black Blade]

I measured the current on the various light sets...two sets have three lights on the lamp post have .33 A

Two other sets of lamp posts that have only two lights on the post measured .22 A

Also have a little phone booth which measures 1.05 A, it only has one light inside the booth, so don't know why this one draws so much more current!!

All these units have the same 3V battery pack. Although that phone booth one doesn't have the 1/8" jack, so no option to use an adapter on it as it is.

So since there are different current draws from the different sets of lights, I should not connect all of them in series, cuz if I did, the one that drew the most current would hog most of the available power and the other lights would be very dim or not on?

 

[mneary]

So since there are different current draws from the different sets of lights, I should not connect all of them in series, cuz if I did, the one that drew the most current would hog most of the available power and the other lights would be very dim or not on?

The opposite would be true - the one that (normally would) draw the most current would not be getting the current it needs and will have less voltage across it. The 'other' lights would receive the remaining voltage which is probably too much for them.

You also have 3.3 volts at 14A. That's about 0.8V more than the lights expect. (AA alkaline cells drop to 1.25V or so after a few hours.) If you put one diode in series with a light, it will drop about 0.65V which is as close to perfect as you'll get. This diode needs to be able to handle the current: for simplicity in calculation I suggest one 1N400x (1N4001 thru 4007) in series with each light.

 

[Black Blade]

You also have 3.3 volts at 14A. That's about 0.8V more than the lights expect. (AA alkaline cells drop to 1.25V or so after a few hours.) If you put one diode in series with a light, it will drop about 0.65V which is as close to perfect as you'll get. This diode needs to be able to handle the current: for simplicity in calculation I suggest one 1N400x (1N4001 thru 4007) in series with each light.

But if used the 3.3 volt output, would I only be able to run one of the 3 volt lights? Wanting to be able to string them together...or would this be where you would connect all the lights in paralell? Then each branch would draw its own current it needs (as long as they don't all add up to more than what the supply can give)

 

[kchriste]

would this be where you would connect all the lights in paralell? Then each branch would draw its own current it needs (as long as they don't all add up to more than what the supply can give)

EXACTLY!
I doubt you'd need a diode anyway. 3.3V is only 10% higher than 3V and the extra voltage drop in small gauge wire will eat some of the voltage also.