Setting up power for a christmas village?

[Black Blade]

I am helping my wife to set up a winter/christmas village arrangement and there is many little streetlamps and other items that each have its own little AA battery pack.

Is there a way to construct a power source somewhere on or under the display that I would be able to run all these little lamps to, so I didn't have 50 of these little battery packs all over. The biggest problem is when the battery runs low and needs changing...you have to root around to find the right battery pack that needs attention thus disrupting the winter display.

All help appreciated.

 

[Mike_2545]

How may batteries in each pack?

 

[Sceadwian]

You could wire any of the devices that use the same number of cells together, such as anything that used 2AA's or anything that used 3AA's but anything run on 2AA pack that needed 3 would either be very dim or not light/work and anything run on 3 that was meant for 2 would either be way too bright run too fast or simply burn out. Mind you the batteries are going to drain faster so you'd be better off going to Radio Shack and buying a 2 or 3 D sized cell holder and wiring everything to that, or if you feel adventurous wiring it all to a DC wall supply that can provide the proper voltage you need, no batteries needed then. Wiring them together is simply a matter of removing the positive and negative wires from each battery pack and connecting them to the same pack.

 

[Black Blade]

Just dug them out...each battery pack holds two AA's, and also has a female 1/8" power jack. labeled DC 3V 500mA.

So you could have a wall power adapter for each of these little street lamps, but she has quite a few, so the cost of all them adapters would be horrendous...lol.

I guess that was what I was wondering...how to have one unit that plugs into the wall but would be able to supply all of these little lamps and other things that each requires 3 volts.

Also noticed that some of the street lamps have 2, some have 3 led lights (maybe so they are brighter?) while other strings of 'christmas lights' that are used have as many as 15 small colored LED's...all running off the same type of battery packs.

 

[Mike_2545]

Lets see, 50 little lights @ 3v 500mA = 25 Amps. Finding one power supply for that current will be pricey but if you split them up into "zones", say use a 3 Amp supply to run 6 lights.

 

[Black Blade]

You could wire any of the devices that use the same number of cells together, such as anything that used 2AA's or anything that used 3AA's but anything run on 2AA pack that needed 3 would either be very dim or not light/work and anything run on 3 that was meant for 2 would either be way too bright run too fast or simply burn out. Mind you the batteries are going to drain faster so you'd be better off going to Radio Shack and buying a 2 or 3 D sized cell holder and wiring everything to that, or if you feel adventurous wiring it all to a DC wall supply that can provide the proper voltage you need, no batteries needed then. Wiring them together is simply a matter of removing the positive and negative wires from each battery pack and connecting them to the same pack.

Would connecting all the units together to a single wall adapter overload the wall adapter? I tried something last year for her like that and some lights didn't light up and others did burn out...so I thought I had done something wrong.

 

[Sceadwian]

You'd need a very high current capable 3 volt power supply, gonna be hard to find. The thing is if these are all lights you could run them in series on a higher voltage. If you connect the + and - leads in a chain between each of four devices you end up needding (3 volts times 4 devices) 12 volts to power each 'string' of lights. Then you only need 1 12 volt 500ma power adapter for each four lights.
How far you can take this is really up to exactly how many of these little things you have, if they're only lights or if there are motors involved as well.

 

[Sceadwian]

Black Blade that depends, on exactly how much current those devices actually use. If you connect too many to a generic wall wart they're just going to dim, most common plug in DC transformers won't explode or burst into flames when short circuited (which is what putting too many devices on it would effectively do) so you could try. Generally speaking if you run the setup for a couple of minutes and you can touch the supply without actually burning your hand it should be safe. I would if you can go with a series approach though as 12 volt high current DC supplies are much cheaper and easier to find. You might even be able to use an old laptop supply which is 14-17 volts and generally a couple amps, but it depends on how many you can chain together. Heck if you chain enough of them together you could run it straight off wall power, that's how christmas tree lights work =) (I should say older ones with all the LED models out there now) They're really just a whole string of low voltage bulbs chained together to add up to the 120 volts the outlet puts out.
So why don't you find out how many lights you actually have (just lights) altogether and let us know. You might have options. If they have motors things get a little more complex because you generally shouldn't put a motor inline with a lightbulb.

Also with the setup you tried a few years ago you'd have to tell us what wall adapter you used. a 3 volt wall adapter isn't very common, and likley puts out more than the 3 volts you think it does.

 

[Black Blade]

Right now she has 7 sets of lights, but no doubt will have more as time goes on!

The only wall adapter I have now that actually works is one from a Linksys router I once had..the output is stated 12VDC 1000mA, but when I measure the output, its actually a steady 16 V.

But this would still be not enough to run all the 7 sets with right? You would need 21 volts and also the current is too high as well...

First opportunity I have, I will go and check out some second hand stores to see if there are any power supplies kicking around in bins or something, might luck out and find one of these old laptop power supplies mentioned

 

[Sceadwian]

The current doesn't increase in series, only the voltage does.
3 sets of 3 volt 500ma devices in series will draw 9 volts at 500mas
Current increases in parallel.

 

[Black Blade]

The current doesn't increase in series, only the voltage does.
3 sets of 3 volt 500ma devices in series will draw 9 volts at 500mas
Current increases in parallel.

I was thinking of that adapter I have when I referred to the current being to high...it puts out 1000mA and all the light sets call for 500mA. Would that not be a bad thing?

 

[Sceadwian]

No.
Voltage is the only important thing in that respect. The supply has to be able to source as much current as the load needs or the voltage will drop. If you supply too much voltage the circuits will simply blow up. You can't force it to draw more current without increasing voltage. Basic electrical law. The mA rating on a power supply is only what is CAN supply, the voltage rating is the voltage it will supply at that current draw. If the current draw is lower the voltage will be higher so there is more than one way you could have hooked things up wrong.

 

[Black Blade]

No.
Voltage is the only important thing in that respect. The supply has to be able to source as much current as the load needs or the voltage will drop. If you supply too much voltage the circuits will simply blow up. You can't force it to draw more current without increasing voltage. Basic electrical law. The mA rating on a power supply is only what is CAN supply, the voltage rating is the voltage it will supply at that current draw. If the current draw is lower the voltage will be higher so there is more than one way you could have hooked things up wrong.

Ahh, so thats why my meter was reading 16 volts, the meter wasn't loading down the circuit, so the voltage could get so high.

 

[mneary]

You could try five in series on 16V. If the supply sags to only 12V (as it should) with a load attached then it will drive four in series. Since the power supply is 1A and your lights are 500mA, you can use two strings of four (8 total) on it.

Before hooking them up, measure the current drawn by each light. You should only put lights in series with one another if they all use approximately the same current. For example, if you find four that draw 50mA each (3V), put them in series for 12V. If a light draws 100mA, it needs to be in a series string only with other lights which also measure about 100mA.

 

[Black Blade]

You could try five in series on 16V. If the supply sags to only 12V (as it should) with a load attached then it will drive four in series. Since the power supply is 1A and your lights are 500mA, you can use two strings of four (8 total) on it.

Before hooking them up, measure the current drawn by each light. You should only put lights in series with one another if they all use approximately the same current. For example, if you find four that draw 50mA each (3V), put them in series for 12V. If a light draws 100mA, it needs to be in a series string only with other lights which also measure about 100mA.

How do you measure the current drawn by each light?

 

[kchriste]

You'd need a very high current capable 3 volt power supply, gonna be hard to find.

He may be able to find an ATX computer power supply which has a 3.3V output with enough current. He could even use an old computer case to mount the power distribution system with fuses and terminals for various branches to protect against shorts on the tiny wires. ie: Circuits grouped in 3-5Amp legs would be fairly safe.

 

[Black Blade]

He may be able to find an ATX computer power supply which has a 3.3V output with enough current. He could even use an old computer case to mount the power distribution system with fuses and terminals for various branches to protect against shorts on the tiny wires. ie: Circuits grouped in 3-5Amp legs would be fairly safe.

Sounds like fun...lol, can see the wife rolling her eyes already on this one Would love to build a Tim Taylor Special

BTW many thanks to all for helping me to figger this out, much appreciated!

 

[mneary]

How do you measure the current drawn by each light?

Disconnect it from the 3V source and put a meter in between.

If there are no convenient connectors I make a sandwich of two pieces of aluminum foil on a piece of paper and insert it between two of the batteries. Then touch one of the meter leads to each piece of foil. (Meter is set to measure mA).

 

[Sceadwian]

Use your meter in current measure mode, it should have a separate jack for it. That jack goes through a fuse across a shunt resistor (low value resistor). The meter measures the voltage drop across the known resistance and knows how much current it's drawing. So you just insert the meter leads in series with the existing circuit. Most common meters have a MA mode that goes up to 200-500ma with 1ma resolution, and a 10 or 20amp mode which generally has a resolution of .1 amps

 

[Black Blade]

Well, hooked up four sets of lights to the 12 VDC 1000mA adapter and worked fine until I unhooked it. Connect it all up again and no power output from the adapter...it must have bit the dust