This circuit will work fine, EXCEPT... those two diodes that are in series with the LEDs really should be resistors. The two bridge rectifiers will get you 2.8 volts across the LED. But as others have already pointed out, LEDs are not to be thought of as "voltage" driven devices like light bulbs. They are current-controlled devices.
With no resistance in series with the LEDs, the only thing that is keeping them from smoking is that the rectifiers are clamping the maximum voltage across them to 2.8v, and while many LEDs can tolerate a forward voltage that high, it's not the way to control current through an LED.
Let's assume you want to limit the current through the LED to no more than 20 mA. If the LEDs themselves have a forward drop of around 2v, then we have .8/.020 = 40 ohms. But LED forward voltage drops are quite different, anywhere from 1.7 up to something like 3.7 for the white ones, so you should experiment. Somewhere between 10 and 56 ohm will get you a brightness you like and will protect the LEDs.
The other thing I don't like about this circuit for LED use is that the motor current is being pulled through the rectifers AND through the LED path. While the rectifiers end up carrying most of the current, there is no real guarantee that this will happen, especially if there is no resistance in series with the LEDs. If you put a resistor in there, then you really do limit the current through the LEDs and all the rest of it HAS to flow through the rectifiers.
To folks who said to just put a resistor in series with an LED and be done with it... that is not as effective as a constant lighting circuit. It "sort of" works because LEDS put out a decent brightness over a wide range of current, but they still do glow dimmer and brighter as you turn up the throttle when you use a simple resistor scheme. The circuit in this thread actually makes sure that a very rigid, fixed current flows through the LEDs at all times, so their behavior is much more constant. Giving up 2.8 volts to the motor is no big deal. Engines run way too fast on a full 12 volts anyway. There is no harm at all in having the engine not start to move until you get up to 5 volts. You'll just be running the engine between 5 and 12 (slow to fast), instead of 0 to 7.
So... yes, this is an "old school" circuit, but if you've got the room for the rectifiers, and you wire it right so they don't get hot (which it sounds like you've figured out), this will work perfectly... I would put some resistance in series with those LEDs, though.
Just in case anyone is interested this is a good link covering the circuit:
http://www.trainelectronics.com/LED_Articles_2007/LED_104/index.htm
Well, I think I've beaten this subject to death....but if you have a better way..sure like to hear about it...
Cheers
On a BB Athearn motor, putting the diodes between the top clip and the frame results in a direct short around the motor limited only by the voltage drop of the diodes. To do what you are showing on the schematic you would put the diodes in series with the motor, say between the truck blades and the motor, so that the power to the motor runs through the diodes.
PennStation i had temporarily wired the PC board to the copper clip on top of the Athearn motor..and to a screw installed on the chassis. Previously hard wired this Athearn...if you're familiar with them you know what I mean. It didnt stop it from running but it definitely reduced the power...so, assume i had something wrong..I'll redo all of it just to be sure...and report. If wired accurately your saying the power drop should be minor? And I also assume no overheated bridge rectifiers?. Paul @ Penn Station
i had temporarily wired the PC board to the copper clip on top of the Athearn motor..and to a screw installed on the chassis. Previously hard wired this Athearn...if you're familiar with them you know what I mean. It didnt stop it from running but it definitely reduced the power...so, assume i had something wrong..I'll redo all of it just to be sure...and report. If wired accurately your saying the power drop should be minor? And I also assume no overheated bridge rectifiers?.
Paul @ Penn Station
For LEDs, I see no reason to use anything besides a resistor with the LED. I do like using a simple constant lighting circuit for 1.5V mini-bulbs though. Instead of bridge rectifiers, I use half a dozen 1-amp diodes, and I wire it all like this:
There's a 2.1V drop, so the motor only gets 9.9 out of 12V, but it's no big deal as long as the whole thing can still run at realistic speeds. The results have been very good for me!
_________________________________________________________________
Thanks but I actually prefer to make my own in this case. I want to use LEDs and the engines I'm going to light are old BB Athearns. I bought these about 20 years ago and they've been sitting in boxes. For me to spend 40.00 bucks apiece or more to put as many lights as I intend in each diesel is not economically sound. I'm no engineer, RR, electronics or otherwise and have screwed up a few times till I get it right but Its part of why I enjoy this hobby.
I don't mind the work...in fact part of the enjoyment is doing the work so I appreciate time saving but I get much more satisfaction out of doing it myself.
And if anyone is interested the total cost of a warm white LED, a resistor and the LED drivers mentioned in the link...http://www.members.optusnet.com.au/nswmn/con_brill_dc.htm ...amounts to about 3.00 bucks per light...probably less... Check Mouser Electronics web site for the semi conductors (drivers) I get my LEDs from LED-Switch...on line retailer and the resistors from Radio Shack. There are many other outlets for these components as well. Yes, you need a soldering iron and steady hands but its not brain surgery. Get a good soldering iron if you are going to solder tiny circuits. Can't do it with the 12.00 iron from Home Depot..well, you might but you will also melt your motors possibly.
Best rgds
I came across that circuit here: http://www.members.optusnet.com.au/nswmn/con_brill_dc.htm
I've trashed that other circuit.
Thanks
Penn Station, save yourself the grief and time. I order them from Miniatronics. They have single bulb and dual bulb directional units.
Miniatronics constant lighting
Marlon
See pictures of the Clinton-Golden Valley RR
I'll throw my two cents in here as well. That circuit the OP is using was designed many years ago as a way to create a constant VOLTAGE to run 1.5 volt BULBS at a steady brightness.
The flaw with this "upgraded" design is the fact LEDs aren't voltage devices, they are CURRENT devices. While the design - as poor as it is for an LED application - does create the proper operating voltage for the LED, it does not regulate the current.
An LED with a single resistor is just as effective as that mess and doesn't rob any voltage from your motor. The downside is the fact white LEDs require at least 3 volts to illuminate. So the first three volts to your motor will result in no lights.
The best method for using LEDs in a DC engine is to create a constant current (not voltage) circuit - which is actully much easier than what has been seen here.
Try this - you will be much happier with the results ....
http://www.pollensoftware.com/railroad/index.html
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
The beast in question..just some leads I'd soldered on..
ok, I've shut down the shop for the night
Chad, man that sounds great..let me know bill of materials and I'll get on it. Hope to light this thing up stem to stern. I have a shiny new Hakko FX888 so can't see why I couldn't manage some SMTs. My soldering skills are getting better daily. I'm heading out of town for a month next week so I'm not going to get to it till January so no rush on my side. I'm semi retired Chad so I got nothing but time.
Take the lead man, I'll be ready. I'll send you a direct message.
Brgds
Paul
OK, Sweet, how confident are you at soldering & using surface mount components?I do not want to run away from you, but I am going to use mostly NGeneering micro components for this build out.
Why, Because I like compact parts, I already have them 'in stock' & my intention is to build one & then repeat it on many other units. Cuz, if it works here, it should be good to go!
Oh, as for a Stay alive Capicator, you would want to tie that in behind the light, you do not want to back feed the other circuits & power the loco motor, but you want the light to stay lit for a bit after track power is cut. They are also polarized, & I may even try to add one in to this project, as another chapter, or improvement.
So stay tuned! But don't expect anthing fast as this last photo, I have to go to work & deal with reality too..Sorry...
Just standard Athearn BB over hear..no RTR chassis...it looks the same
PennStation I realize that I wired this to the motor in parallel..I think..after another look at the circuit it is supposed to be wired in series..between truck pick up and motor...I had it on the motor..could that be my problem?
I realize that I wired this to the motor in parallel..I think..after another look at the circuit it is supposed to be wired in series..between truck pick up and motor...I had it on the motor..could that be my problem?
Paul, is this what you were also starting out with?A standard Ath BB, but now RTR styled chassis?If "I get you" I think we have it here..This is a Dakota & Iowa GP50, that works ore cars over there.. I will use this one as the lighting refresher, it is DC & will stay that way.It has been a while for me too, so I need the 'remedial training' too...
Appreciate the feedback...
Rich..I didn't get a chance to measure the amps but like you said its old school...I'm done messing about with it for the moment...except to give it one more test..wired in series. But just to satisfy my curiosity. I can see what the intent may have been..in the old days as you've said. I just couldn't understand what the purpose of this circuit was...it doesn't do anything beyond what a led and resistor do.
Jim..LEDs + resistors..works for me...
Chad..I hear you. As a guy that returned to the hobby just this last year after 23 years away, making this sort of mistake provides the best training in how to do it right. There have clearly been significant advances in model RR'ing and I've got much to learn. Missed them all. So, I realize the complexity of this circuit, or just how complex it can be but that is exactly why I enjoy the hell out of it...these older Athearns make good test cases and I may even get a few sweet PRR diesels out of it for very little investment. I wish I could get my hands on one of those Athearn light boards just to see what is doable with it. Ill end up getting a RTR Athearn and pulling the board out for my old Athearn if I can't find the boards alone. I'm not opposed to making this as simple as possible.
Well should you find your BB specials...let me know.
Paul,
in Diode terms, (whether a regular or Light Emitting) they are polarized, the schematic shows 2 rectifiers, or Diode boxes. Those circuits create a polatrity balance, the arrows with a bar show the direction of voltage travel: >| means the voltage will go through from the left, to the right, will be stopped from the right to the left. Meaning you now have a directional flow.However, LED's are diodes that can only be activated by voltage in the right direction, so they do that without the bridge, as folks said, this is probably a design for incandecesnt bulbs & adapted for LEDS.Each Diode the voltage goes through has a cost of 0.7 volts to pass through that logic. There are ready made diode bridges that you can get to avoid making a big array shown in the schematic. Also, this setup would work in DCC as it would pass the the opposing voltages, BUT the Reverse & the Headlight would both be on at the same time, due to it being AC voltage, & as we know it: DCC ...
I hope that helps a little, it can get complex..I think your heat issue is either an amperage one (you are putting motor balance current through the Diodes, or a wiring one). I know that in the early days, I accidentally wired a premade unit in parallel to the motor, (not in-between the pickup & motor, in series), & melted a spot on a locomotive shell, as it was trying to process all that motor current.. Make sure it is in series with the motor, not bridged across it.
Good luck! (PS: Looking for that Athearn BB/RTR loki to try a writeup on)..Later,
Your estimate is not too far off.
The author of the website http://www.awrr.com/ConstantLighting.html claims a 4-5 volt drop if using white LEDs or 2.8-3 volts using yellow. Scroll down to "The price you'll pay".
No thanks,
I'll stick with a couple of LEDs and 470 resistors.
Jim
That circuit is old school. Designed many years ago for constant lighting using 1.5 volt light bulbs. Headlight in the loco and tender light for reverse. Someone modified it for LED's. The users back then knew it reduced the voltage to the motor by about 1.4 volts for each bridge, total of 2.8 volts for two bridges, but many power packs could get by that much voltage drop anyway. To my knowledge, that was never and issue. Maybe today it is.
Unless the motor is drawing a lot of current, the rectifies should not get very hot. Many used 1 amp bridge rectifiers and the motors did not draw over 1/2 amp. As I recall, many used can motors, not high amp open frame.
Did you measure the actual current?
At the time, a 1.5 volt bulb was placed across each bridge.
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.
PennStation Chad...sorry, last thought for today..I realize that I wired this to the motor in parallel..I think..after another look at the circuit it is supposed to be wired in series..between truck pick up and motor...I had it on the motor..could that be my problem? Best, Paul
Chad...sorry, last thought for today..I realize that I wired this to the motor in parallel..I think..after another look at the circuit it is supposed to be wired in series..between truck pick up and motor...I had it on the motor..could that be my problem?
Best,
Yes indeed. Without the motor in series with the bridge rectifiers, they will get hot.
David Starr www.newsnorthwoods.blogspot.com
PennStation Has anyone installed this circuit into a DC engine? I am hesitant to use it because I built the circuit and while testing it the bridge rectifiers get very hot and either it is supposed to get very hot (which seems wrong) or I've got something wired wrong....but I don't think so. It really sucks the power up as well. Anyway, just wondering if anyone had any experience with it? I intend to light some old Athearn BB U30C's (PRR)..headlights, number boards, back up lights..the other option will be to just make a simple LED circuit using a few LEDs and fiber optic filament. That is just LEDs + resistors. Very simple and no heat generated. Just curious if anyone ever used this circuit. And wondering why? I found it through one of the forums .. Not sure if it was MRR. Originally I was trying to see if there is anyway to light in DC and get so called lights on while the engine is standing still. Don't want to use batteries. And it's just not worth it to install DCC in these engines. Thanks
Has anyone installed this circuit into a DC engine? I am hesitant to use it because I built the circuit and while testing it the bridge rectifiers get very hot and either it is supposed to get very hot (which seems wrong) or I've got something wired wrong....but I don't think so. It really sucks the power up as well. Anyway, just wondering if anyone had any experience with it? I intend to light some old Athearn BB U30C's (PRR)..headlights, number boards, back up lights..the other option will be to just make a simple LED circuit using a few LEDs and fiber optic filament. That is just LEDs + resistors. Very simple and no heat generated.
Just curious if anyone ever used this circuit. And wondering why? I found it through one of the forums .. Not sure if it was MRR. Originally I was trying to see if there is anyway to light in DC and get so called lights on while the engine is standing still. Don't want to use batteries. And it's just not worth it to install DCC in these engines.
That circuit is mostly right. Assuming you have wired it in accordance with your schematic, you ought to have 1.4 VDC across each bridge rectifier, and 2.8 VDC across the pair of them. If at full throttle you have 12 VDC across both bridge rectifiers, then either the motor isn't turning, or the motor is shorted somewhere and that's why the bridge rectifiers are getting hot.
Rule of thumb. If you cannot lay the back of your hand (or finger) on it for the count of ten, it's too *** hot. This rule is good for just about everything electrical except incandencent lamps.
That LED circuit is touchy. There is no resistance in series with each LED. LED's need about 2.75 volts to switch ON. Once ON, they act like short circuits. So if the bridge rectifiers are showing a little high, say 3.0 volts, and the LED turnon voltage is a little low, say 2.5 volts, a LOT of current will flow thru the LED's making 'em burn VERY bright and maybe even go Poof.
I put constant lighting into three Athearn GP38's with a varient on this circuit. I used 1.4 volt incandescent lamps so I don't need diodes in series with them. And the color is more realistic than LED's, which show awfully blue. I only used a single bridge rectifier, to supply 1.4 volts. Lamps don't need series resistors the way LED's do. I made false cab ceilings from Perfboard to mount the rectifiers and the cab headlamp bulb. The ceiling blocked light from showing thru the cab windows. I mounted a second bulb at the end of the long hood to light up that headlamp and number boards.
I don't use directional lighting. First of all, it isn't all that prototypical. I have clear memories of prototype diesels burning the rear facing headlamp in daylight. When an HO train stops moving, I look to the headlamp, if it's lit then my track and power wiring are OK and the problem is in the locomotive. With directional lighting I have a 50-50 chance that the headlamp I can see is OFF because the engine is trying to run away from me. I'd druther have both headlamps burning whenever I have track power. Simplifies trouble shooting.
Thanks Chad. Well I believe I wired it correctly however I will lay it out again...I'd installed components on a small PC, not soldered. I am pretty sure the LEDs and diodes were in there, + - as per the schematic...but worth rechecking it. I'm a greenhorn with electronics but I do know the positive from negative of an LED.
The purpose of this circuit is what I don't get. I was thinking this would somehow store the juice to keep the LEDs lit although the engine was stopped...I have read somewhere..still looking for that link...using capacitors to store power so the LEDs would stay somewhat lit after running the engine for a while. Probably dreamed it.(:
i had temporarily wired the PC board to the copper clip on top of the Athearn motor..and to a screw installed on the chassis. Previously hard wired this Athearn...if you're familiar with them you know what I mean. It didnt stop it from running but it definitely reduced the power...so, assume i had something wrong..I'll redo all of it just to be sure...and report. If wired accurately your saying the power drop should be minor? And I also assume no overheated bridge rectifiers?
love to see your Athearn project you mentioned in the other post...I have a feeling its going to take me a bit of trial and error to get it right. Your list of lighting for it...using separate leds for all that? Debating if for all those lights would separate LEDs be unmanageable or use the fiber optic filament to cut down LEDs? I've seen a 2 mm fiber used successfully for marker lights ..2mm filament could also suffice for Athearn headlights, tail lights as the stock openings in the U30c are just about 2mm. The distance from led to light opening is short so light is still very bright.
Well, appreciate the feedback.. If you got the time..love to see the GP in action..particularly whats going on the back end. but don't sweat it.
Paul, I really want to caution you, if you did what I did, the only drag would be 'letting the smoke out' of those LED's, they would not stop your motor if wired properly.One thing that would stop your motor is if they interrupted your power pickups, or the motor leads.An LED, (or any diode) can only steal a 0.7 volt, if placed in the correct position, they are polarity specific, if backwards they would retard any voltage from getting to it's destination. An LED & a standard Diode are a once way path for electricity, so they are polarized.It is very easy to put them in the wrong way at times, been there, still doing it...(Test, test, solder, test, re-solder, repeat, test, re-test, etc.)...
If you would like, I can record & show a video of that exact GP35 in action, & have the DC Powerpack there to show the voltages.
Let me know, may take a bit to arrange it. But it can be done...
Hey Chad,
nice lighting on your GP35. I had come across an Athearn Dummy Lite Board..I believe they were coming with Athearn RTR units..seems they were being replaced/upgraded and the boards were plentiful...maybe 10 years ago..would love to find one..cheap..but no luck so far..I found one on eBay but I guess they're scarce now so 15-20 bucks is not worth it for me..at this point..
maybe someone reading this have 5 of these boards laying around..(:..
And Chad..yep, limit the juice to the LEDs/bulbs sounds right..but when I hooked it up the LEDs were very bright..so I don't know, but the result was the LEDs were on fire .... Very intense. They were sucking all the voltage. The loco was struggling to move. I had the throttle ( a standard MRC transformer) at more then 1/2 way.
Rgds
Here is what I meant about 'using' a Kato's existing board.I only needed to use a balancing resistor to make the the lamps on the cab & the ditchlights match in intensity, fairly easy.Hope you find it interesting.
http://cs.trains.com/mrr/f/88/p/198637/2175074.aspx#2175074
that looks interesting..I'll have to study it
thx
I used the exact components per the diagram. Radio Shack..LEDs from another supplier..I assume the components are rated high enough assuming the guy that posted the link knew what's what?!?..
Here's the original link:
http://www.awrr.com/ConstantLighting.html
There are various circuits: using bulbs and LEDs, 1 bridge, 1 Led, directional and so on. I don't know enough about electronics to answer why 2 bridge rectifiers or diodes in the particular circuit, only enough to get into trouble. I chose it because it was so called "constant, bi-directional" ....obvious it ain't gonna be constant in DC. I had come across a circuit that claimed to build up enough juice to keep the leds glowing after running for a minute or two..when loco stopped..in DC...still searching for the circuit...I'll post it if I find it. But I'm just not clear why bridge rectifiers, diodes, etc.
So far can't find a reason to use anything more complicated then leds + resistors (Or a circuit that's gonna give you constant lighting in DC) Front and back. Reverse polarity turns them on and off..if wired accordingly. I'd like to have the whole array, marker lights, ditch lights, but will wire up headlights, number boards, reverse headlights for now...unless someone has a better alternative? These Athearns are sort of experimental for me. If I fry one I won't like it but I've had them for 23 years sitting in the boxes ... So not a huge investment..
and yeah, there is definite power loss to loco with all these LEDs wired in there. It's a trade off.
Thanks & Brgds