cjack posted:ogaugenut posted:I have the 3 outlet Menards power supply. I plugged it into my new Menards light and power, it light up. Tested the voltage at a second outlet from the supply and got 7.05 volts. Won't this burn out the LEDs prematurely?
Bill
It depends if the electronics in the building has a current regulated supply for the LEDs. If not, I would think that you might want to use a 4.5 vdc regulated supply. One question, do they get brighter if the voltage goes up and dimmer if the voltage goes down. You can check this by plugging in additional buildings to your power supply which will reduce the voltage because of loading.
Now to get all technically:
Rule of thumb for Leds is whites are about 3.3V voltage drop and draw about 20mA nominal. Others have different voltage drops dependent on color and diode materials.
That said a resistor is used to current limit Led voltage, because LEDs for the most part tend to keep a constant diode voltage drop, thus the resistor has to "take up the slack". The Menards buildings use very small surface mount resistors that don't have alot of surface area thus low milliwatt power dissipation.
So lets say we have 4.5V voltage and one 3.3V @ 20mA LED. The resistor is (4.5V-3.3V)/0.020A = 60 ohms.
Power dissipated is (0.020A * 0.020A) * 60 ohm = 0.024W well within the resistor dissipation
Retaining the resistor value lets up supply to 7,05V
(7.05V - 3.3V)/60 ohm = 0.0625 A.
Resistor power is now ( 0.0625* 0.0625) * 60 ohm = 0.23W !! Almost a 10 fold power dissipation and after short while the resistor will burn open unless designers properly sized resistor wattage worst case.
This would explain, all things being equal, why some Menards building LEDs fail.
Any buildings of mine are powered from a regulated 4.5V supply, because you can't repair the all glued together darn things!
The Menards supplies are the cheapy transformer, diode and maybe capacitor combo. The more transformer iron the better voltage regulation and closer the voltages stay the same with varying current load. The 4.5V is achieved when fully loaded, lighter the load higher the voltage from the Menards adapters. If you use an HO supply you can adjust the voltage to be 4.5V as long as all the loads remain connected. Adding or removing loads will require adjustment. And of course items with lamps and motors that go on and off will yo-yo the supply voltage.
Clear as mud, right?? 
