6Pac - the 9v lit the lights but they were dim, so I will need a little more power. I may try the 12V idea as Hoozie mentioned.

Hoozie - I looked for another set of lights, it seems only the higher end (20 a string) have the rectifier. I will keep looking. I contacted that company you linked the video from. They won't help as I didn't buy the lights from them and can't give advice on a product they didn't sell. I will try the car battery - I have some lawnmower batteries around and try that. I'll keep the link to the rectifier in mind next. I don't know why I can't find the simple inline rectifier as that is used in all these light sets... it is like a trade secret or something!

Okay, you want 12 volt here you go.

12V Supply

Why can't you find one? It's like the tag on almost anything electronic currently "No User Serviceable Parts Inside". It's not intended to be replaced when it fails so it isn't available from the OEM and there isn't enough demand for a third party to step up an make one.

Someone makes them and you would think they would want to sell as many as they could. So why not list the individual components for sale. If Radio Shack was still a big box store, I am sure I could get one there.

OK, the 12V lawnmower battery is not enough voltage. Looking at the info on the new set, here are the specs. The string is rated at 2.4 watts (0.02Amps). The supply is house power... 120 volts and the fuses are rated for 125V, 3 amp.

What determines the power draw? How many LEDs there are or is the rectifier also a power limiter?

the rectifier only converts from AC to DC.

There will be a resistor in the string somewhere to limit the current.

Each led will drop 2-3v, depending on the color. The average led also draws around 20mA (0.02A)

For example, with mostly real numbers:
35 leds x 3v => 105v.

155vDC (rectified 110vAC)

155v - 105v = 50v that needs dropped by the current limiting resistor.

50v/0.02A = 2.5kOhm resistor somewhere inline.

Since the input voltage has tolerances (110v-120v) the current through the string will change (since the resistor is a fixed value), but because leds have a range of currents that they will work with they'll be just fine. Just don't give them 220vAC, lol.

Sounds like you do indeed need a rectifier to get the high DC voltage. That one from amazon would work, or you could get four discrete diodes and wire it yourself. They would be much lower profile and look more like the original rectifier. The output polarity will make a difference though. They should only work one way.

Thanks for that info, Hoozie. The lights are polar, only work wired one way. I am guessing the resistor is somewhere inbedded in the wiring / leds as I don't see any other kind of component anywhere on the string.

I emailed a company called Mouser, they have a lot of electronic components. Hopefully they have something I can use. If not, I will try your idea of making my own rectifier.