A few weeks ago, I finished installing the overhead lighting on my layout, and today is the first time I had a chance to try it. Originally, it was powered by a voltage regulator circuit stepping down the voltage from an old laptop power supply. However, this circuit failed and overheated, which I suspected was due to too much current (~5A) going through it.
I then replaced it with a 2.5A, 12vDC wall wart. Today, I had the lighting on while working on the layout. After about half an hour, the lighting turned off, and the plug pack was hot. It won’t turn back on, and I suspect my near future will involve a trip to the nearest electronics store for a replacement.
I know there’s something here that I’m missing. In both setups, the output of the voltage regulator is connected directly to the LED lighting strips. Currently, the circuitry is as follows:
Plugpack → 2.5mm line plug → LED strips.
Given that the issue seems to be too much current flowing through and damaging the plugpack, I have a feeling I should be using resistors between the 2.5mm plug and the LED strips. Is this correct? If so, what wattage should I be using?
Well, it all depends on how much current the LED strips draw, and how many you’re using. Driving a 5 amp load with a 2.5 amp supply is asking for trouble. Not just transformer burnouts but potential fire hazzard. Adding resistors won’t help if the LED strips are running at their rated draw. You need a higher current power supply.
You’re missing matching the power supply to the LED strips. You need to calculate the amperage DRAW of all your LED strips and use a power supply that is greater than the total current required by the LEDs.
Depending on the size of each LED and how many LEDs you are using, they could draw anywhere from 3 to 4 and even 6 amps per roll !
Example 1: A 5m roll of SMD5050 (0.24 watts) with 60LED/m would be: (5m x 60 x 0.24) / 12 = 6amps +10% = 6.6Amps.
Example 2: A 5m roll of SMD3528 (0.08w) with 60LED/m would be: (5m x 60 x 0.08) / 12 = 2amps +10% = 2.2Amps.
If you have an old desktop, or know somebody who does, yank the power supply out of that. Nicely regulated 12V and a pretty high capacity; 300 to 400 W.
Do you have a link to the ebay place where you bought those strips? Maybe there was something in the description that states what the power requirements are.
I’ve done the measurements, and the length of the modules is 6.44m, x3 for the three rows of LEDs. This gives us a total current draw of 19.32A. A friend of mine has a couple of spare desktop power supplies he’s happy to let me use, one of which is 500W.
I’ve tried a whole bunch and adding that load resistors have been pretty much unecessary. Maybe mine were better quality power supplies. Back in the 286 days, AST computers came with a load resistors in the case that you had to hook up unless you added a hard drive. Talk about low quality power supply…well, the whole things were low quality but that’s beside the point.
And especially if there is any sort of load on the power supply - the load resistor definitely is not needed.
As for the LEDs - the reel of RGB LEDs I bought, 3M worth, came with a 5A power supply. That’s about standard for the 5050 strips and maybe for the ones that use more but smaller LEDs. So 15 meters worth will ned 3x the power, and so forth. Individual LEDs are low current but string together a few hundred and it adds up. There are also limits on how many strings you cna run end to end, because even if you supply the proper power, the printed circuit strips in each section will only be able to handle so much current - you can;t just keep stringing them end to end around your entire room and just have one power feed at the end. You need to have dedicated feeders for every couple of sections at least (I think I would just feed each section directly and never use the end to end connections). This also allows seperate sections limited with fuses or breakers - 20+ amps at 12V is 240+ watts which is plenty of heat to melt things or even start a fire. Rather than trying to make one 20 amp power bus, which would need somewhere in the neighborhood of #10 wire to not have excessive voltage drop, run seperate lines to each 3M section of LEDs, limited at 5 amps each.
In the table in the eBay listing, it states that the 5050 LEDs (which I used) have a draw of 5A/5m.
This is the first time I’ve worked with a system that involves more than 4 or 5 amps, so I want to make sure I have my approach correct this time.
At the moment, none of the LED strips are connected end-to-end. My layout is divided into 5 sections, the longest of which is 1.74m, and the rest are all around 1.2m. Each section has 3 strips, all of which are connected with their own feeders, in parallel. On each section, these feeders (on the top of the shadow box) go to a single pair of wires, which runs down behind the backdrop and joins the lighting bus.
Now this is where I think I’m going to have to redo the wiring, as the fe
