Halloween Forum banner

1 - 7 of 7 Posts

·
Wild Fandango
Joined
·
1,494 Posts
Discussion Starter #1
I've talked about this in a few other threads but I think I'll get better results combining it all into 1.

I want to find an inexpensive way to change all my 3-battery (4.5v) LED props to AC power. Everything from blinking strands to those color changing tap lights. While using an ATX power supply is great to run multiple things for a haunt, it's kind of bulky and obtrusive especially if you want to run just one thing. I also want to make it as non-damaging as possible so the props can be used with batteries again if needed. This will also let you move it from prop to prop so you can use it with your Christmas lights and anything else you decorate for, as well as being able to wire up a tap light in the closet to power so you don't have to keep changing the batteries.

My thoughts were to create a kit that has 2 fake batteries that are wired up to simply complete the circuit and one battery that's split in the middle into a power jack. I bought jacks and plugs off Monoprice to use for this. This way all you would have to do would be to drill/melt a hole in the battery cover to push the jack through. This part should be pretty easy to accomplish.

The second part is a power supply. I bought several 4.5v AC adapters off of Parts Express. They're rated at 500 mA. However, without a load they run at 8v and melted the first item I hooked up to it (I should have used the multimeter first). I had also bought a universal AC adapter, with a voltage selector, and even without load it tests at a perfect 4.5v. At $20 vs $6, this is a bit pricey to turn a 3-LED strobe disc to wall power - $14 is a lot of batteries from the wholesale club. I'm not good with working with resistors and calculating voltage drops, etc (especially since I don't know the amps of the products being converted), and I also want something that's going to work properly for a long time and not have resistors needing to be replaced all the time or multiple resistors needing to be inserted in different parts of the circuit.

I would also like the ability to wire this up in parallel to run 2-6 different devices off of one cord. Almost all of the lights I want to convert use 3x AA or AAA batteries. Some have 3 LEDs and some have up to 6 but since they all run off 4.5v I'm sure there's further regulation inside the device. I have no idea how much amperage the average 3 LED tap light uses. 500 mA may be too small for more than 1 or 2 things, though for certain items it would still be a lot better in the long run. This way I could also turn several items on and off with one switch.
 

·
Registered
Joined
·
25 Posts
battery powered devices use DC current not AC so you would either need DC adapters or some other way of converting ac to dc. You can get a universal ac to dc adapter from walmart that you can select 3v to 12v but they cost 18 bucks or so. Not sure if your on a budget but that would be the best way. Just clip off the end and install alligator clips so you can attach it to the power supplies. Thats what I do and it works just fine not to mention you can over power some of the leds and make them brighter without burning them up.
 

·
Wild Fandango
Joined
·
1,494 Posts
Discussion Starter #3
AC adapter means AC to DC current. The adapters I bought are 4.5v DC. The problem is they put out 8v, not 4.5v (meaning they're not regulated). I'm trying to find out if there's any cheap, safe way to fix this, or if there are other brands out there that put out the correct voltage.

I'm glad that I tried this on a cheap LED light and not, say, a CD player or expensive prop and wind up destroying something important. It seems to me that nearly double the voltage with low load is a bit unsafe.
 

·
Registered
Joined
·
880 Posts
Consider either buying a 5v or 5.3v zener diode (5 watt size) to clamp the unloaded voltage to something your props can live with. Or buy a better 4.5 wall wart, try a surplus place like Allelectronics or Halted specialties, call ask them to verify the unloaded output.
 

·
Wild Fandango
Joined
·
1,494 Posts
Discussion Starter #6
The 7805 looks pretty good. Since I'm just using lights and not audio equipment or anything fancy that would need noise reduction I can probably get away with just using the regulator and not have to breadboard it, right?

I also see these on eBay. Supposedly regulated:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110584330344

(For those checking archives a year later when the eBay auction has died out: Digital Concepts AC Adapter for Canon/Minolta/Pentax, 4.5v, regulated, overload protected, model may be CH-720N but I think that might be wrong)

Now I wonder if cell phone chargers are regulated. There's plenty of websites that sell dirt cheap cell phone chargers and I think I have a few Motorola 5v ones. I'll have to test the voltage with no load. Hmm. I think I'll have to send the AC adapters back. I'll try a voltage regulator on the one I cut the cord off of since I can't return it now.
 

·
Wild Fandango
Joined
·
1,494 Posts
Discussion Starter #7
Okay, I bought a 7805. It has input, output, and ground. Since I'm running the negative/ground wire from the negative terminal in my LED, do I need to solder a wire to the ground? The same wire? Or do I need to use a second ground wire? I did a quick alligator clip wireup without using the ground pin and it was pushing 3.5v once connected to one of those tiny clip-on LEDs. I left it running for a few minutes and it didn't get hot.

I'm still debating whether or not to ship these power supplies back and try to obtain a few of those Digital Concepts one which have a higher amperage. It's going to cost me the same amount to ship them back as it is to buy 5 more voltage regulators but I'm still not sure this is the best way to go.
 
1 - 7 of 7 Posts
Top