rrinker If AC is the only power source, the simple fix is to put a regular diode across the LED terminals in the opposite direction.
Yes, that works too, but I think it's easier to wire in one bridge rectifier to handle all the LEDs than to put diodes on each LED individually.
If it were me, I would just get a 12-volt DC supply online. I've got a bunch of them, and they only cost me about $8 each from China, shipping included. Wire each power supply with a fuse block and fuse, because they do not have breakers and a prolonged short will leave you with an ugly black paperweight. By using several of these, I can put one on each major section of benchwork and use it for all the scenery lighting and electronics.
It takes an iron man to play with a toy iron horse.
The simplest solution would be to go with 12 vdc. Many do that on layouts. A common voltage in decoders also.
The same voltage that operates the TT motor. Our club does that.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
SpaceMouse richg1998 Generally power packs for are rated at the current being drawn. With no power being drawn, the voltage will always be higher. So, how do I dermine if the power will be right for the LEDs?
richg1998 Generally power packs for are rated at the current being drawn. With no power being drawn, the voltage will always be higher.
So, how do I dermine if the power will be right for the LEDs?
That's why you calculate the resistor for the LED based on a middle valus of current, not the LED's maximum rating. With the nominal 12 volts and a resistor sized to run the LED at the middle of its current capacity, if the voltage goes a couple of volts higher or lower, the LED will still be well within the safe zone and the fact that the voltage isn't precision regulated won't be a problem.
Use 12V DC. AC works, kind of, because the D in LED is Diode, after all. But it also subjects the LED to 12 volts going the wrong way half the time. It's still current limited by the resistor, but unlike a regular silicon diode which is made to stand 50, 100, or more volts trying to go through the wrong way, an LED generally can't handle that. If AC is the only power source, the simple fix is to put a regular diode across the LED terminals in the opposite direction. So when the AC is in one half, the LED lights, in the other half going backwards relative tot he LED, it goes through the regular diode in its forward direction. The LED then only sees the single diode drop backwards, instead of the full 12 volts (.7V or less, vs 12). Usually the resistor value will be a bit lower when using AC as well, since the LED is really only lighting up half the time.
I think you need another switch on that panel - to control the direction of the turntable rotation. Unless you are good with always going around the long way.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
SpaceMouseI was under the impression that 12VAC would work, but it would cause an impreceptible flicker--unless you were doing video, then the camera would pick it up.
It will work, and the flcker will likely be imperceptible, even to a video camera. My concern is that using DC, the LED is either on or off, while with AC it is turning on and off 60 times a second. It probably won't matter, but that will be slightly more stressful on the circuit and you may only get a century or two before the LEDs start to fail.
richg1998Most LED's are 20 ma limit. Many use a 1k resistor at 12 vdc, not 12vac. if that is what you are thinking. Just guessing. That allows 9ma of current and plenty of brightness.
I was under the impression that 12VAC would work, but it would cause an impreceptible flicker--unless you were doing video, then the camera would pick it up.
Chip
Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.
SpaceMouseSo, how do I dermine if the power will be right for the LEDs?
Hook up a couple of them wired in series with a 2K resistor, or 2 1K resistors, themselves in series, if you don't have 2K. The combination of a 12 volt supply and a 1 K resistor works as a starting point for most small LEDs we use. The extra resistor will protect the LED in case the power supply really is putting out too high a voltage. You may find yourself tweaking the resistors anyway to get the brightness you want. Once you've got them connected, measure the voltage.
If you're using the AC terminals of the power supply, consider using a bridge rectifier to convert the AC to DC. You will still probably never damage a LED, but they are less likely to fail with DC than the constant polarity reversal of AC.
SpaceMouseHowever, while the track needs only half of one side of the switch, powering a LED for both on and off would take whole side of the switch. Unless, I'm totally off base.
You're right. If you are using lights for both ON and OFF, then you'll need a double-throw toggle.
MisterBeasleyYou really only need DPST toggles, not DPDT. The other side of each toggle will be unused as you have them. The DPDTs you've got will work fine, though.
I get that I'll only be using half of the MOM. WHen I bought it I thought I was scratchbuilding a TT. However, both the motors I have were just too fast. I was able to get my second hand Atlas working which is omnidirectional instead of bi-directional.
However, while the track needs only half of one side of the switch, powering a LED for both on and off would take whole side of the switch. Unless, I'm totally off base.
The fact that you are probably right about the back of the switch being opposite is throwing me for a loop. I think I have to completely redesign my wiring in regards to the LEDs. Either that or I'll have to live with the switch being up, while the lower light is lit.
Most LED's are 20 ma limit. Many use a 1k resistor at 12 vdc, not 12vac. if that is what you are thinking. Just guessing. That allows 9ma of current and plenty of brightness.
richg1998Generally power packs for are rated at the current being drawn. With no power being drawn, the voltage will always be higher.
You really only need DPST toggles, not DPDT. The other side of each toggle will be unused as you have them. The DPDTs you've got will work fine, though.
It's likely that the internal design of the toggle will be such that when the toggle lever is up, the connection will be made to the lower pair of posts, not the upper pair.
An unloaded power supply might show a higher voltage than it will under some load, so it may be just fine to run your LEDs. Put a meter on it once you've got a few LEDs connected.
I would attach a barrier strip or other wire connection device to the panel and do all off-board wiring through that. Once you're under the layout, you'll appreciate the simplicity and convenience of screw terminals or whatever vs. having to solder underneath.
Generally power packs are rated at the current being drawn. With no power being drawn, the voltage will always be higher.
Put a meter on the pack and as you had a load you will see the voltage drop until it gets to around twelve volts.
Over the years I have seen this issue mentioned, many times in different forums and magazine articles.
I sat staring at my turntable mini-panel for a couple hours trying to determine how to wire the dang thing. From the back it looks like this.
The large switch on the right is a MOM and will be used to power the rotation of a pitbashed Atlas turntable. The 4 DTDP switches will be used to kill power to four tracks coming off the the turntable and light LEDs above and below the switch (note two holes above and below each switch) to remind me which tracks are powered. I figure one side of each switch will be the track power and one side will power the LEDs. I'm going to do something similar with staging tracks.
The MOM wiring is very straight forward.
My current plan is to glue a copper fiberglass tie to the left side of the panel which will be divided into 3 sections by filing a groves through the copper. From the center section I will solder 4 green wires that will run to the left center posts of each the 4 DTDP switches.
From the other two sections I will run a single red wire to one the outer lead wires of each LED.
From the switches I will solder resistors from the outer posts to the other side of the LEDs.
IT also makes sense that I go ahead and hook up the track wires and connect them to a terminal strip since laying the turntable tracks will be a ways down the line.
I'm lookiing for suggestions if anyone can think of an easier way to do it.
On another note, I hooked up power to my homemade circuit board that I'm using to power my structure lights.
The power was the AC side of my Bachmann DC power pack. I tested it and instead of being 12VAC like it said on the power pack, it was 17VAC. So I need a new new 12V power supply.
Now I have one the is currently powering 3 UP5s, so there's plenty of current left over. Still, I feel reluctant to share power between LEDs and my LocoNet.
What's your take?