How Do U convert These lights to track power?

You have a couple of problems; one those lights are DC and track power is AC, second the track power can vary from 6 to 21 volts. You would do better with LED's that are made for the exact voltage range you want, to buy parts to convert may cost you two to three times what you paid for those lights. You need at the least bridge rectifiers and resisters.

Lee F.

Actually, what you need is a simple diode and resistor for each light you want to run from track power.

If you run command, let's assume 18 volts on the track.  I'd use the diode, a 1K 1/4W resistor and the LED in series across track power.  Job done.

Ok Let me rephrase the question. I have a dedicated power source for accessories and not comming off of the track. Power will be ac but max power acessory bus would  be 18V.

Since they use 4.5 volts, they must be running in parallel with the resistor you mention dropping the 1.5 volts.  That being the case, you'll need to provide dropping resistance from your 18V supply.

Assuming 18 volts, with a single diode to rectify, you'll get about 9 volts effective power to the LED's.  You have three volt white LED's and a resistor that was designed to drop the 1.5 volts from the 4.5 volt battery pack

You need to drop and additional 4.5 volts in some fashion to run these off the aux supply.

The easiest method is to compute a resistor that will do the job.  For each of these LED's, you need about 220 ohms to drop the power an additional 4.5 volts at 20ma.  If there are 10 LED's in parallel, that ends up being a 22 ohm resistor.  Since you're supplying 200 ma, 20 for each LED, the resistor is dissipating about a watt.  So, I'd want at least a 2 watt 22 ohm resistor and a 1A diode, such as the 1N4001 in series with the power.  The diode direction is important, if it's backwards, they won't light.  The cathode (banded end) should be connected to the LED string where the battery pack positive terminal was connected, the other end of the diode goes to the AC supply.  The 22 ohm resistor goes in series with the diode and LED string.

Another approach - a bit more ambitious - is to use a voltage regulator module that you can get on eBay for about $1.50 with free shipping from Asia (so you'll need to wait a few weeks).  For example, enter the auction number 280942757086 into the eBay search box. Several of us on the forum have purchased modules similar to this one and they do work!

You would need a bridge rectifier (or 4 cheap 1N400x diodes wired up as a bridge) and one of these modules.  Note that you can adjust the output voltage with a small screwdriver so you could get the brightness you want.  Another advantage is this module could drive many more 4.5V LED strings with no additional parts.

I also believe more and more accessory and layout lighting will shift to LEDs and hence more regulated DC voltages will be needed on the average layout.  So if, say, you needed some 12V DC to power up the white LED strips that are a frequent topic on this forum, you only need to add another $1.50 module adjusted to 12V DC output (using the same bridge rectifier).

For $1.47 and free shipping, that is pretty amazing!   I'm gonna' order a few.

NOw would these Bridge Recifiers Suffice for the board suggestion above?

http://www.ebay.com/itm/50pcs-...sd%3D321038983695%26

http://www.ebay.com/itm/GI-W04...;hash=item4abf5142ef

Either would work fine, and that's a very decent price.