Help with 5V Wall Wart and LED lights SOLVED

Ron: LEDs require a current limiting resistor to operate properly. Does your string of LED Christmas lights have any resistors in it? They would also be limited as to voltage (depending on the color 3v to 1.4v). Your wall wart is driving them too hard. The 9v battery is somewhat depleted and would not drive the current as high.

Thanks for the reply Leo.  I have used LEDs in the past with resistors but they were strings made for 120V AC outlets.   I looked through this battery string and I do not see resistors, so just assumed if I was using 5VDC, that I would not need them.

Could the number of lights be an issue too?  When I used the cell phone wall wart on the entire string of LED's they all lit and stayed lit.

vr, Ron

They are probably wired in series in groups. The wall wart (make sure it's DC output!) is probably unregulated. It says 5 volts. You have to test it. The true output can be all over the charts.

 I would use one of the DC-DC converter boards to regulate the input to the LEDs. They are pretty cheap and do the job. I test the output of them while un hooked from the LEDs until I get the voltage right.

 My first scratch built building has LEDs in series wired directly to the output of my old HO transformer. They are in numbers where they can handle the output up full. If I did it again, I'd use the boards to protect them from a different voltage.

Trying to follow the original post. You say the LEDs all "fry" when you hooked them up to the 5 volt wall wart, but then you say they all lit and stayed lit. 

Although a wall wart may be unregulated, I would imagine that one for a cell phone is regulated. However, when they are unregulated, the unloaded voltage is high and drops down to the stated voltage at rated current. In either case, I don't see how it should fry the LEDs. If there are four LEDs, in series,  and the voltage of them takes 1.5 to 3 volts, that seems like it should work without a resistor to drop the voltage.

I've never seen a cell phone charger that wasn't regulated.  I'm pretty sure it'll be close to 5V.  Given that fact, there's something else in play here if a 6V string croaks with 5V on it.

Engineer-Joe posted:

 I would use one of the DC-DC converter boards to regulate the input to the LEDs. They are pretty cheap and do the job. I test the output of them while un hooked from the LEDs until I get the voltage right.

Like this? 

DC to DC

Ron

The cell phone charger should be putting out a known voltage.  Of course, it's always wise to do a test.  With a DC-DC converter, you have to supply the rectifier and filter cap to use it with AC voltages.

Sorry for the confusion... Let me start over.

So here is the charger...

I'm trying to power these 4 lights.  I wired them to a terminal block and supplied the wall wart power to the block.

When I connect... Instant poof.  But as you can see, if I connect to the string of Christmas lights that I cut off from the battery supply.  It works.  

Are your four LEDs in parallel?

It's kind of important to examine Chuck's point, the only way that 5V supply takes out the LED's is if they're in parallel.

cjack posted:

Are your four LEDs in parallel?

I believe so.  Each light goes straight to the terminal block.  That's my problem isn't it?  In the Lemax kit they were all wired in succession.  I have to wires these in series, don't I?

Ron

Scratch my post. I never saw those boards before. They are a more advanced version showing the voltages. Pretty cool. I have the cheaper versions.

I thought you were already wire in series. So listen to the other guys here.

Ron045 posted:

Engineer-Joe posted:

 I would use one of the DC-DC converter boards to regulate the input to the LEDs. They are pretty cheap and do the job. I test the output of them while un hooked from the LEDs until I get the voltage right.

Like this? 

DC to DC

Ron

 

That's a nice one. The input voltage has to be one volt higher than the output...so that might give you pause with a 5 volt input. But how are they wired? It looks like parallel. In that case each LED would see 5 volts which is too high without a resistor...actually 4 resistors. One for each LED. Use around 270 ohms? Experiment with the resistor value, until you get around .015 amps into each LED.

Engineer-Joe posted:

Scratch my post. I never saw those boards before. They are a more advanced version showing the voltages. Pretty cool. I have the cheaper versions.

I thought you were already wire in series. So listen to the other guys here.

You can't see it, but I'm beating myself with a rubber hose right now.  A good lesson for me to learn.  Fortunately, not an expensive lesson... just a time consuming lesson because I have to disassemble the lights to unsolder and resolder in new lights.  Then rewire.

Thanks All.  Will post a final result assuming I'm successful.

Ron

My system works well for me so I thought I would describe it here.  Streetlights are a real problem, especially if you need (like me) say 20- of them.  I have seen LED streetlights for about $10-15 each- and so I wanted to avoid $300 for what is a non-major feature.  The lighting is not critical, the "ambiance" is. 

So I also used the Lemax streetlights, which are incandescent bulbs, rated at 3V DC (2 X  1.5v AA) batteries.  They are way inexpensive, available at Menards, and look decent.

For ease of installation (access underneath), I wired them in series, so DC power source + out to light #1- then to light #2 etc, with that last light (#20) output back to the power neg. 

Because I don't want to have to replace them, I run them at reduced voltage. lower than rated.

Setting the buck converter:  I hooked up an AC_DC buck converter to a bench AC transformer, ran up the power a little and set the buck converter to output 1.5v .  It is rated at 27 v AC IN- and regulated DC output that is adjustable.

My system runs off of the B terminals from a ZW AC transformer, easy to adjust voltage and not a likely to get bumped.  The wire off the ZW leads to a Buck Converter. 

I then wired up a section of my streetlights through the buck converter and ramped up the ZW a little at a time.  Tested the output of the converter-  around 1v.  the lights were too dim.  So I added power to the ZW until the lights were at an acceptable brightness- checked and converter output was still 1.5v.   

Each time a s I added more lights, the system would get dimmer, since the load of the lights increases (and they all get dimmer) as you add to the system.   All  I had to do was increase ZW output to an acceptable level of light- 

Since all lights are limited to getting 1/2 their rated voltage- they should last a long time.

So here are some results of my series wiring.

I could not get the lights to light with the 5v wall wart.

I was however able to get them to light using a 9v wall wart that is putting out nearly 14v.  I don't understand.

Each led has a forward voltage of about 3.2 volts. In series you have four leds, requiring 4 X 3.2 volts, or 12.8 volts. 5 volts probably would not light 2 in series, but would blow just 1. This is a handy calculator for wiring leds.

LEDs burn out when the voltage is too high. They won't lite when it's too low or their wired backwards. (unless there non-polarized)

Engineer-Joe posted:

LEDs burn out when the voltage is too high. They won't lite when it's too low or their wired backwards. (unless there non-polarized)

I guess 5v it too low in series?  I double checked polarity and even reversed the wires. They would not lite with 5v.

So, these work with this other 9v wall wart.  BUT... Why is the 9v ww  putting out nearly 14v?  Should I be concerned that something is defective?

Maybe I need one of these.  LEDs for dummies.

LED controller

John H posted:

Each led has a forward voltage of about 3.2 volts. In series you have four leds, requiring 4 X 3.2 volts, or 12.8 volts. 5 volts probably would not light 2 in series, but would blow just 1. This is a handy calculator for wiring leds.

Thanks for the calculator John.  I wired two sets of lights in series and wired those 2 sets in parallel with the 5v ww.  They light now.  A lot dimmer... But they light.

It's been a very educational day.  Thanks all.

Thanks to all of my wonderful OGR friends for helping me today.  I still have a lot of work to do on this scene... But my curb street lights are operational.

You folks are the best.

Thank you, Ron

I think I am right here- LEDs turn "on" at a set voltage- not like incandescent bulbs, which light at any voltage, starting where you cannot see the light to full brightness at maximum rated voltage.  So, LEDs are rated at Xv - Yv, where "X" is the activation voltage (say 1v DC) and "Y" is the voltage beyond which their life is reduced or zero, say 5v DC

I think what is going on in your case- is that the VOLTAGE output of the wall wart is adequate, but as you add LED's for some reason the amperage is not.   I would think that you would be far better using your transformer through an AC/DC converter buck.  There will be more available amperage while the converter buck limits the voltage to the LEDs themselves.  A DC "train transformer" is likely not up to the task. 

I run my "city" full of lit buildings, my streetlights, my MTH trolley, and a smaller suburban scene w/ 7 MTH houses, and other buildings- all off of one ZW.   In my system in my first post I referred only to the incandescent streetlights, (but...)  I also run all of buildings on one half of the layout  (probably a total of 100+ individual LEDs) off one output of a 275 W vintage ZW.  I run the trolley off another, and the trains in that section can run off a third output. 

The Menards York Hotel alone has an "approximate power draw" of 3100 Mahs- that's 3.1 Amps!!  But the ZW puts out 15 Amps.  That Hotel plus all of the others- on one ZW.  I use a second ZW for the other half of the layout and a ZW-L to run trains, signals, and switches.

The larger buildings (all LEDs) each run through separate AC/DC converters, so I can turn the voltage up or down to control the amount of lighting in each.  The York Hotel at full voltage will run you out of the room!   So it runs on 3.5 v DC for a more realistic level of light. Same for the Todd Architectural Stauffer Biscuit building, turned down to 3.5v.

So I think your issue is not enough OOMPH from the wall wart.  ZWs Rule!

More pics below.

Ron, get yourself a computer power supply for lighting. You will have 300 to 400 watts of 12 vdc power for lights and accessories. They also have a 5 vdc tap that I use for relays and, with a diode to get to 4.5 vdc, battery operate conversions. You can salvage one from an old PC or find them for under $20 at computer repair shops. Once you get into this led thing, you don't want the problem of hooking up 10 wall warts under your layout. You can do it all with DC to DC converters and resistors. Keep asking questions!

John H posted:

Ron, get yourself a computer power supply...

<Slaps himself in the head>

I use those for powering my lipo chargers for my RC airplane batteries  when I'm at the flying field.  Never thought about using them for trains.

Aarrrrg!  Thanks!!!