DC to AC wiring formula help please in time for Christmas

Can you help me wire up my miniature trees?
I have 11 miniature DC Christmas trees I want to hook together in series to an AC power supply.
Some use 3 AA batteries (4 of them), some 3 AAA size (7 of them). Obviously the batteries are all 1.5V, and with 3 in each tree thats 4.5V, but I don't have any other electrical parameters for the trees.
Will this work? How do I figure out what watts and amps in an AC power supply to get for this?
Also, I would actually like to vary the power down a little sometimes. As the batteries run down the lighting effect is even better. Is a potentiometer what I need for this?
Any expertise is greatly appreaciated. I do great photoshop work and would be willing to do some for you in return. :)
Jacques
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On Mon, 2 Nov 2009 20:17:57 -0800 (PST), " snipped-for-privacy@gmail.com"

The only way this will work is if each string draws the same current.
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On Nov 2, 8:52 pm, snipped-for-privacy@aol.com wrote:

So does that mean I need separate power supplies for the 4 AA trees, and 7 AAA trees?
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wrote:

Probably, If you have a meter and figure out what current each draws you might get lucky and be able to find a combination that will work. Once you get the effective (volts/current) resistance it becomes one of those resistor ladder puzzles.
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klipsch wrote:

Yes, one will want 6V and the other will want 10.5V. If it were me, I'd use a 6V "wall wart" to run the 6V trees in parallel and a 9V one to run the 10.5V trees. You can't wire them in series unless the current draw is the same with all of them and the voltage adds up to 120 (or 240)V depending on your location. Ideally you should measure the actual current draw to make sure your power adapters can handle the load, but anything made to run off of AAA batteries will not draw very much, maybe 100mA.
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On 3/11/2009 4:18 PM, James Sweet wrote:

From the OP's description the trees all use 3 cells each hence they are all 4.5 volts but guessing different loads because some use bigger cells than others.
A 4.5 volt supply (AC or DC if there is no funny electronics) would drive any tree. A bigger 4.5 volt supply (More current ) would be needed to run 11 trees. As we do not know the current of any tree we cannot say how much but just measuring the current used by one of the trees with AA batteries and multiplying by 11 would be very close.
Series connection is neither practical because of the (possibly) different currents. Nor is it SAFE because the trees will only be insulated for Very Low (6 volt) voltage and the tree at the hot end of a series string would be at a full 110/240 volts. VERY VERY Dangerous.
John G.
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wrote:

In addition, series requires 50V not 120V so a transformer or dropping resistor would be needed- more complications - still not exactly the safe approach. Wall warts should do the job-and are probably as cheap as any other alternative for the purpose. Assume that each tree requires 4.5 V, If you can find a wall wart of that voltage rating- fine. likely 9V wall warts are more common and that would do for 4 of the trees in series /parallel. The others in series should be OK with a 9V wallwart as well so a single wallwart at 9V and 200-500ma should do the job . This would be two groups of two of the larger trees in series/parallel and a second set with 3 parallel groups of 2, 2 and 3 trees in series. One set of trees will be dimmer than the others but that may not be all that bad. You don't want a wall wart that is too large as the light load voltage will be too high. I do think that James 6 volt and 10.5 volt setup assumes that the existing trees use batteries in parallel.
Don Kelly cross out to reply
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Batteries in parallel would be 1.5V or 1.2V depending on NiCD/MH or Alkaline. The batteries are in series to get 6V and 10.5V out of 4 or 7 cells.
The trees should be wired in parallel with one another though. There is absolutely no reason to wire them in series.
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From the original post, there are 11 trees
7 use 3 AAA cells 4 use 3AA cells
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Rick wrote:

Oh, I mis-read it then. They're all the same voltage, 4.5V nominal, so a relatively common 5V wall wart ought to run them just fine, assuming a regulated style, not the old iron transformer type, as the voltage on those may be considerably higher than rated under low load.
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Agreed!
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Don Kelly
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It was stated 3 cells per tree. The assumption was that these batteries were in series. That may be wrong. If you have a 3- 4.5V source , then I agree that parallel is best. The suggestion that I gave is not perfect but uses a cheap 9V source -hence a series/parallel arrangement.
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Don Kelly
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Don Kelly wrote:

A lot of cell phone chargers put out 5V at an Amp or more. There's millions of those out there, most thrift stores have a bin of them.
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John G is right. The wiring must be rated for at least 120 volts. They probably aren't. Don't try it.
RE
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