Model Railroading > Tain't No Lectrician - But Need Help!!

This has to be basic knowledge, but I need help.  At Christmas season I purchased from Walmart two short strings of white battery powered LED lights.  Each string has a battery box that holds 3 AA batteries equaling 4.5v. for each string.  I want to power two strings simultaneously using a battery eliminator (a 110v. adaptor input with a 4.5v. output).  My question is,-- what would be the recommended minimum rating in milliamps required of this power source to safely operate the two strings, nor create damage to the LED's?



Edited 1 time(s). Last edit at 03/18/19 11:22 by rrman6.

How many individual LEDs on each string?

lnrr1066 Wrote:
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> How many individual LEDs on each string?

There are 18 LED's on each string.

Use an ammeter to measure the current through one string, then pick a wall wart with an output current that exceeds double the value measured. When you remove the battery holder, make sure toleave the limiting resistor with the string, and connect the strings in paralell to the wall wart.

The rated output is what it CAN produce continually, not what it WILL produce. The actual current in determined by the resistance of the load, if in parallel as above, then the load current will be twice what you measured because the effective resistance will be half.

Bob, I appreciate your help here.  Where is the limiting resistor you speak of?  I was planning to leave the battery boxes intact to the string and connect the two boxes by wires soldered to battery terminals and to a female connector for the male end of the wall wart (aka battery eliminator).  Does this sound reasonable if I connect the two strings in parallel as suggested?

rrman6 Wrote:
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> Bob, I appreciate your help here.  Where is the
> limiting resistor you speak of?  I was planning
> to leave the battery boxes intact to the string
> and connect the two boxes by wires soldered to
> battery terminals and to a female connector for
> the male end of the wall wart (aka battery
> eliminator).  Does this sound reasonable if I
> connect the two strings in parallel as suggested?

Excellent idea. The resistor will not be big, and there is a very good chance that it's built into the battery holder somewhere.

Diodes are like electronic check valves, so polarity will be important. If you hook everything up and something doesn't light up, switch the supply wires.

Thanks again Bob.  Hopefully I can be lighting some HO buildings before long.