LED lighting-an odd 'overload' situation!

In recent months, it's been asked a couple of times on the forum approximately how many LED lights can you use on a given supply,- after all, they are very low current draw, aren't they? Well, as a retired "Sparks", I've just gone into this a little deeper, as on my layout, I have around 100 LED lights in the form of street, yard, building and station lighting, which I've split into 2 separate bus circuits, fed from 2 separate supplies via 15 volt transformer secondaries into bridge rectifiers and a 7812 12 volt voltage regulator and smoothing capacitor, giving me a stable 12 volt supply with a 1 amp capacity. All has seemed fine until I updated my main station from 'Superquick' buildings to some of the Bachmann 'Scenecraft' Art Deco station buildings, utilising LED strips for the under canopy lighting. After switching on, all was ok for about a minute, then the station LED strips just slowly faded out, all other LED's remaining lit! I quickly connected my multimeter across the bus supply, and on switch-on, had a little over 10.5 volts showing, but after about a minute, the voltage began steadily dropping, finally reaching around 4 volts before I cut the supply. At this point, I thought maybe I'd overloaded the supply, so again using the multimeter, checked the current draw and found to my surprise that it was only 0.75 amps, so well within the circuits capacity. On looking to the power supply setup, I found that as the voltage was dropping, the 7812 voltage regulator was going from cold to too hot to touch. These regulators are supposedly rated at 1 amp nominal, and around 1.5 amps with a heat sink (which mine don't have). As a result, I decided to look for an alternative power supply, and a search of Ebay (UK) produced item 291087849273 12 volt DC 10 amp regulated metal cased unit intended for LED power supplies. These are available with either 5, 12 or 24 volt outputs at just over a tenner, and although Chinese made (isn't everything these days?!) seems a robust and well made unit, which is doing the job for me, as it has twin outputs, so one for each circuit in my case. Although I'm no wiser as to what was causing my lighting 'fadeout', (perhaps the lighting strips have a capacitance which could affect the current draw?) this unit has solved my problem, and since I'm not likely to need much more capacity for further lights, it's good to have something that is up to the job.
Basically, I guess I'm just recommending that if you have a good number of LED lights on your layout, then it's probably best to get something thats intended for the job rather than make do.
Keith.

 

Hi Paul.
As part of my checking procedure, I disconnected the sets of LED strips, but this made no difference to the voltage dropping. It seems that standard LED's with the usual 1k resistor in series will stay lit even at around 4 volts from supply, but the LED strips (in my case the flexible ones, not the aluminium backed ones I bought after your post about these) fade out as the voltage falls below about 7 volts. I was thinking that on the LED strips, since the copper strips are alongside each other with insulation between, it might be acting rather like a capacitor, which is basically similar, ie, two strips separated by insulation. I can see no actual capacitors on the LED strips, only the resistor for each trio of individual LED's. Ah, the joys of electronics, no wonder it gets referred to as "The Dark Side"!!! Still, every day's a school day!
Keith.