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I have a couple Hallmark Star Trek ornaments that plug into Christmas light strings. I'd like to convert the power supply to them from the light string plugged in the wall to a battery pack so I'm not anchored to a string of lights and to better protect them**. My experience with electronics is minimal so I'm having a hard time even Googling for where to begin. The box for one of the ornaments says to use it with light strings of 2.5, 3.5, or 6-volt bulbs. The other says us strings with multiples of 35 or 50 lights - it needs 6 volts, 1.2 watts. The plugs on the ornaments are the push-in T1¾ style if that helps.

Just going with the 6 volts that each can handle... I assume plugging in a 4 pack of C cell batteries would do nothing or damage it with the constant current going in one direction. I assume I need to convert my battery pack from DC to AC. Is this feasible without breaking the bank and without having a brick-sized box of electronics for each ornament?

** regarding the protection, they're both almost 20 years old (wow, I'm old) and, with them currently on AC, I'm worried about a brown-out stressing them or power spike just zapping them. I'd like to have whatever electrical protection I can reasonably add (fuses, resistors, etc.) inline with the battery pack.

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+1 for having fun with christmas lights =) –  Kyle Feb 5 '12 at 5:59
    
Has anyone tried modifying Hallmark Magic Cord? hallmark.com/products/christmas/keepsake-ornaments/… –  user32935 Nov 19 '13 at 20:30
    
@user32935, this one-liners with only a link work best as comments, maybe if you get some experience with that solution you can expand it in an answer. –  clabacchio Nov 20 '13 at 9:08
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7 Answers

up vote 2 down vote accepted

If they use ordinary small "incandescent" filament bulbs you will be able to run them on DC just as well. For practical purposes AC and DC of equal RMS value will work the same.

IF you can access the bulbs you will be able to replace them in due course with LEDs of similar appearance and brightness - but probably not something you want to try unless essential.

The operating specifications are somewhat contradictory.

  • 2.5, 3.5 or 6V is a VAST range, suggesting they may be 6V bulbs that will run on lower voltages if needed, but at lower brightness.

  • 110VAC/35 lights is about 3 V/bulb. 110 VAC/50 ~= 2.2 V/bulb

  • 6V, 1.2 Watts is at the high end of what you'd expect.

It sounds like these are nominally 6V bulbs.
But operation on 6VDC to start is not recommended.

SO

Starting with a single alkaline cell (1.5V nominal) would tell you something.
I'd expect a dim orange glimmer.

Then try to a alkalines in series. That's 3V nominal. Doing this with no series resistor is extremely unlikely to do any damage. Being very old there is a very small chance that it might but it's very unlikely. I'd expect an OK appearance - maybe not as bright as on some strings. From what you get you can decide what to do next.

Above 3V I'd start with a series resistor.
Start with a 22 ohm resistor and if not bright enough try 6V and 22 ohms.
If 4.5V 22 ohms is bright enough then something like 6V with 33 ohms may be similar.

Once you have a 6V pack looking OK you can adjust the resistor up or down to suit brightness. Er on the side of too dim if you want them to last.

I've suggested going to 6V as battery voltage will vary with time and using 6V and a resistor will keep the brightness more constant over the battery life.

For a high tech [tm] solution that helps protect the filaments a constant current driver may be used. Ask if of interest.


Resistors mentioned above can be half Watt or more. 1 Watt safer but probably not needed..


Constant current supply:

Am LM317 IC can be used to provide a simply built constant current feed.
A "problem" is that the circuit "uses up" a minimum of about 3Volt to operate. So, if you run it from 6V you can only get 3V out. Whether this is a problem depends on Vbulb when it is a bright as you want it. Ideally you'll want even more than 4 batteries :-(.

Here R1 is shown adjustable but you can use set resistors which are changed to suit. Maximum likely bulb power was given by 6V, 1.2 W = 200 mA lamp current (0.2 x 6V = 1.2W. )

Current source current = Vref/R or
Resistor = Vref/Icurrent_source.
Here V = 1.2V regulator Cref, I = 0.2A max.
So R = V/I = 1.2V/0.2A = 6 ohms.

So if you make R1 >= 6 ohms at all times, then Ilamp <= 200 mA.
Add extra resistance to R1 to get lower lamp current.

Connect B+ to Vin.
Iout to bulb top
Bulb bottom connects to battery -.

enter image description here

enter image description here

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I couldn't have asked for a more detailed and complete answer. Thank you! I've never heard of a Constant Current supply limiter but from what I've gleaned here and on a quick Google search, it sounds quite helpful. My solder-fu is weak -- I'm confident that I can put batteries & resistor in series but when it comes to this current limiter, is there a way I can test my work? Instead of putting the ornament in the circuit, could I put some load (like a single lamp) and measure across the leads to verify the voltage is what I'm expecting? How could I measure current? –  Curtis Nov 30 '11 at 14:51
    
@Curtis: Use a single LED? –  Ed S. Dec 2 '13 at 4:46
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You might want to try a Lionel transformer - AC type. They have a variable control from 0 - 18 volts AC with varying amounts of watts, depending on the transformer you go with. Make sure it's the old style Lionel as some of the newer ones and the ones designed for HO are DC.

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I tried some experiments with this a year or two ago. My donor ornament is a Star Trek shuttle from DS9 that has lights and a button for voice. The voice is dead but the lights still work when plugged into a light strand. One experiment was to use an AC transformer that dropped to 3V AC. This did NOT light the ornament. I measured the current and it was very low. (No numbers since I lost my notes).

I then tried to measure the actual current and voltage from a bulb on the string. The voltage drop of the magic ornament (working and on the string) was considerably higher than across a bulb on the string.

I have the feeling that the circuit for constant current may be the key. I know from disassembling a dead ornament that they do use a bridge rectifier. I think it is across a resistor. There may have also been caps in there to use reactance to drop voltage. If this is the case DC will not work.

Frankly I'm surprised that nobody has solved this (that I've found). Even Hallmark has not produced an octopus power unit for older ornaments. This leads me to think that it is not a trivial problem to solve.

I don't mind putting a string of non-leds on my tree, but I have so many magic ornaments that I need several.

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My solution was a Leviton 48212 http://www.smarthome.com/865120/Leviton-48212-DCS-DC-Supply-Module/p.aspx

I then found a small plug in transformer that output 8.5 volts AC it MUST be ac not dc.

I then took an old strand of lights and cut off the plugs leaving about 3-4 inches of wire, leaving me a little pigtail with a female plug on the end. From there I simply went out got a spool of 2 strand thin wire in black (could not find green) Cut my wire into varying lengths, attached one end of the wire to the 2 leads from the pigtail i made earlier and the other end goes to the distribution block.

Ideally you would use a lower voltage transformer but I could not find one that output AC power.

I put it all inside a small project box and its been running for a few weeks with no problems.

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Judging from the photo that board as a polarised electrolytic cap across the input, so connecting it to an AC source probably isn't a good idea without removing it. –  PeterJ Nov 19 '13 at 5:09
    
Your talking about the black thing behind were the power plugs in? Is it a fire hazard, or would it just burn out? –  user32935 Nov 19 '13 at 14:18
    
Yes that's it. It would likely just burn out at that fairly low voltage along with the small current the plug in transformer could provide but they can pop open / catch on fire etc. But either way it wouldn't do any good for AC so would be best to remove it. –  PeterJ Nov 19 '13 at 21:21
    
I just tried a 9v DC (as well as a 5v DC) power pack. The 5v barely lit the ornament up. The 9v did pretty well tried plugging in 3 ships all worked fine. Tried a Romulan cruiser, The Borg cube and an Enterprise. The sound worked fine on the cube AND the Enterprise light even blinked. –  user32935 Nov 19 '13 at 21:44
    
I was looking for a 7v but I don't have one with the right plug on it. –  user32935 Nov 19 '13 at 21:46
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Some of the Star Trek ornaments "BLINK", which is caused by the use of AC not DC. Some other STAR TREK ornaments have sound effects. These have AC to DC converters built-in. This may cause a problem when using DC as the input.

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Also many of the ornaments are motorized. some use leds so im assuming they already have ac/dc converters inside.(disassembly is not and option). I'm also look for help on doing something like this. My idea is to make an octopus like power supply that could power many ornaments at once. First time on this site , is it protocol to create a new thread or continue with this thread ?

Thanks Jeff

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I've wondered for awhile about those. The amount of current that's expected to flow in a 50-light string is greater than the amount that's expected in a 20-light string, and the resistance posed by the lights in the string will be much higher when the set is first powered than when the lights have heated up (a few dozen milliseconds later). I have no idea how the ornaments deal with that. –  supercat Dec 13 '12 at 16:30
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My new solution. A 9v AC power transformer connected to a CCTV 1 to 8 adapter. Easily powers 8 ornaments. I am going to test to see if it will power 16.

https://www.youtube.com/watch?v=K84GvaBZsuQ

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