LED 12V Strip lights directly connected to AC track power

@Jeff_the_Coaster_Guy posted:

So what am I risking by doing the same in my passenger cars?

The LED lights will flicker more without a constant voltage board. The life of the LEDs may be shorter.

@Jeff_the_Coaster_Guy posted:

I'm sure @gunrunnerjohn can shed some light on this, and let me know the reasoning behind the constant current modules.

Sure, I can list a few factors.

• Flicker-free lighting.  With no capacitor, LED lighting flickers more than incandescent because the LED extinguishes immediately, the incandescent bulb has a short fade time due to the hysteresis of the filament heating.
• No DC bias on the track.  Since the module uses full-wave power, no DC offset is imparted onto the transformer output.  This may or may not affect operation of other items powered from the same transformer.
• Adjustable intensity.  I and many other folks find that a direct connection of the 12V strips is way to bright for realistic lighting in passenger cars.
• Potentially a longer life from the LED's as the peak reverse voltage across the LED strip may indeed exceed the peak reverse voltage specification of the LED's.

FWIW, I did the exact same thing as you propose with the then more expensive LED strips about 12-13 years ago.  I quickly discovered I didn't like the excessive flicker and the super-bright lighting.  I could correct the brightness with a series resistor, but there was no way to control the flicker without a capacitor.

You're not the first guy to come up with this rational, and my feeling is that if it works for you, go for it.  It didn't work for me, so I came up with something better, at least IMO.

FWIW I recently did something like this recently for an RK Esso gas station, in this topic:

Enhanced Building Lighting Using Leds  that's on page 4 of this forum

It works reasonably well but it's only operating on 14VAC accessory power. I wouldn't use it for passenger car lighting for all the reasons GRJ mentioned, most importantly the the absence of flicker resistance. But that's just me.

@Jeff_the_Coaster_Guy posted:

I see lots of great products for installing 12V strip lights into cars and onto the layout that prevent flicker and convert the voltage to DC for operating these cheap Chinese strip lights.  Seems like y'all are having lots of success with these.

However, I started connecting sections of these lights directly to my AC track power (set to 18V) a couple years ago to light Plasticville buildings.  In some cases, I soldered a diode in line to prevent back voltage, but in some cases I literally just soldered wires from the AC power and Ground directly to the input +/- pads on a section of strip.  Since each LED has an on-board resistor I don't draw too much current.  And the half-wave of the AC doesn't make the lights too bright either.

I see lots of folks saying not to do this, since the AC half-wave at 18V is pulsing greater than the DC rating of the LED, or that the back voltage far exceeds the likely breakdown voltage of these cheap LEDs, but so far after 2 years I really haven't had any problems at all, and none of my 12+ buildings or scene elements have gone dark yet.  Yes, there's a moderately noticeable 60Hz flicker, but in buildings it really doesn't bother us.

I also connected a whole other set of these to a DC power outlet (a Tech II HO transformer) and set at 12VDC.  They are about the same brightness as the ones directly wired to AC, minus the high frequency flicker.  None of those have gone dark either.

Most of my Lionel Switches are still powered from an independent tap on one of my KW transformers using the external power plug, and I feed them all 18VAC.  I use 18V incandescent bulbs in those, and find that I have to replace one or two every month (out of about a dozen switches).  So even if I'm 'damaging' the LEDs and shortening their life by backfeeding them on a non-rectified AC power source, they're still far better than the DC incandescent lamps from a maintenance and reliability standpoint.

So what am I risking by doing the same in my passenger cars?  Directly swapping the AC lamps for 12VDC led strips, powered directly from the AC track power of 18V or so?  (I use DCS, but I've not noticed any kinds of problems with signal or anything while powering my city off of one of the AC channels that also runs the trains).

I'm sure @gunrunnerjohn can shed some light on this, and let me know the reasoning behind the constant current modules.

I use the 24volt units, this cuts most of the brightness as for flicker of the lights, with two pickups and track in great shape I get very little flicker if at all……then again I tend to not sweat the small things, more into the let’s run trains.  Lights also fall under the 4 foot rule it is looks good it’s good.

@ThatGuy posted:

I use the 24volt units, this cuts most of the brightness as for flicker of the lights, with two pickups and track in great shape I get very little flicker if at all……then again I tend to not sweat the small things, more into the let’s run trains.  Lights also fall under the 4 foot rule it is looks good it’s good.

I have never used 24VDC led strips; just curious about the architecture. How many series leds and what value is the load resistor for each section? Might you know that offhand? Thanks.

No problem with building lighting from accessory output from the transformer.  If using the 24V LED strips, the flickering and DC offset problems are solvable, but the amount of wiring to do so is about the same as placing and wiring a constant-current regulator card.  And the latter aren't expensive, especially Rod's kits.

I found some 24V on ebay and it looks like 300 leds per 5 m, 3 leds per 2" section. So I am guessing the resistor is 750 ohm or thereabouts.

@Rod Stewart posted:

I found some 24V on ebay and it looks like 300 leds per 5 m, 3 leds per 2" section. So I am guessing the resistor is 750 ohm or thereabouts.

That seems like a very inefficient use of the power, the resistor is dissipating more power than all three LED's!

@gunrunnerjohn posted:

That seems like a very inefficient use of the power, the resistor is dissipating more power than all three LED's!

Nothing about running trains is energy efficient but your point still stands!!

@Rod Stewart posted:

I have never used 24VDC led strips; just curious about the architecture. How many series leds and what value is the load resistor for each section? Might you know that offhand? Thanks.

I use the ready made for under cabinet lights on a sticky strip. The power supply is AC the strips are build for up to 24v AC at 16 or 18 they are just perfect.