I don't know of a light bulb replacement but you will have to be very careful because you may not have much room to work with in the post war engine as the old engine mechanisms are rather large at times. The reason I mention this is because some of the light bulbs I have seen need an electronic piece to go with them for use with the headlight.

You might be better off using a larger watt transformer then what you think you will need to help with light bulb power requirements. I have a pair of 224 steam engines and they have very little extra room inside the cab.

Lee Fritz

There is no "secret to what's in the package, it's a bridge rectifier and a resistor.  Cut one open and look...

Do it the easiest and cheapest way: get bayonet or screw base LED bulbs from Town & Country Hobbies (among other companies). They're direct replacements. I use them in my engines, passenger cars, accessories, etc. They come in warm white and bright white, the warm being most like PW bulbs. Why complicate things?

You should have enough room.  I would remove the bulb socket off the bracket and build the circuit dead bug style using the bracket as a mechanical anchor. Shove the led where the postwar lens is.  The bridge rectifier doesn't have to carry much current so it could be really small.  Add a resistor and a cap and you're done.  If wanted fancy you could put a 3 terminal regulator in there for fairly constant brightness.  

 How much does the Evans version cost?  Do you have a picture?

I think he's referring to their so-called Universal LED

That is indeed small.  As GRJ suggests, it may be just a bridge rectifier (or 4 diodes) and a resistor.  A capacitor that would be large enough to do any good (for flicker reduction) might be too large but I may be wrong.

Anyway, if you have good eyesight and don't mind re-inventing the wheel (or just like a DIY challenge), how about this.  For about, say, 6 cents in components you can make a bridge rectifier and a pair of resistors suitable to dissipate a 1/4W for command track voltage. 

These surface mount parts are so danged small that you need a way to assemble them.  To that end I recommend so-called scissor-cut copper-clad board.  As the name suggests you can cut it with scissors then use a x-acto hobby knife to "score" islands of copper.  Then mount the tiny surface mount components and apply heatshrink.  The following are not the circuit in question but illustrate the method of assembly.

Here's what I think you need in terms of components.  Qty 2 of BAV99 dual-diode and qty 2 of 330 ohm 1206 sized (1206 means .12" x .06") resistor.  The photo below is of a pair of BAV99 dual-diodes though the 1206 resistor is not a 330 but shows the size to illustrate how tiny you can make this.  The LED is a 5mm type.

Everyone has their favorite assembly technique for messing with tiny surface mount parts.  I happen to like the scissor-cut copper clad circuit board.  Adhesive-backed copper tape/foil is another way to make a thin substrate for mounting surface mount components.

Thanks to all of you for your responses. 

Stan is correct. His first photo shows the Evan Designs LED assembly.

I had stripped the shrinktube from the Evan's product before posting my need for assistance. Enclosed are two photos of that product. Photo 1 shows the complete assembly with shrinktube removed. The second is a photo of Evan's component assembly. The only part I could pull a number from was the rectifier. It reads MB10S. A Google search indicates that item is a 0.5 amp 1000 volt bridge rectifier. The amperage rating is half what I have been using and the voltage rating is 20 times greater. That concerned me. As for resistor and capacitor, I identified on Photo 2 what I think might be a capacitor and resistor (have never seen anything like this before), along with the resistance read by my cheapo meter.

Have I properly identified the parts in the Evan's assembly? What are your thoughts about specifications for the MB10S versus requirements? What about the resistor and capacitor?  Should I forget about the need for a capacitor?  

Thank you, swede

You can buy a mini full wave rectifier board on the bay for about $1 each. It contains four 1A diodes, and a filter capacitor. I use them to power structure lights on my layout that use LED bulbs ( .50 to 1.00 ea) that screw into a socket. and have the built in resistor for 12 v operation. This setup works great.

I am also doing an experiment using LED bulbs for my landscape lighting and running them off 12 VAC. Over a year on them and they are still lighting fine. This goes contrary to how LED bulbs are supposed to be used but they work and burn bright but probably not as bright if powered w filtered 12VDC.

Can you read any numbers from the other side of the capacitor and resistor?

Common sense suggests a 1000V bridge rectifier is somewhat overkill for the matter at hand!  Consider that the track voltage is, say, 20V AC the the most.  Sure, you have track spikes/glitches but 1000V ?!

Also the current rating of 0.5A or 500 mA is also overkill for an LED that probably running about 20 mA at the most!

I don't believe a capacitor of the physical size you show materially helps with the function of such a device in this LED circuit - to demote flicker from dirty track or intermittent wheel contact.  The value will tell all if you can tell us whatever is printed on the other side.  Sure, any capacitance is better than none...

I had guess-timated using qty 2 of a 330 ohm resistor so that would be 660 ohms.  You're measuring 800 or so ohms but if you can read the lettering on the other side it will tell you exactly what value it is.  800 ohms is an unusual value.  Probably see lettering with 75.. or 82.. corresponding to 750 ohms or 820 ohms.

Stan, thanks for the response. I did not even think to turn the assembly over. There are no markings on what I believe is a capacitor and the mark on the resistor reads either 8200 or B200. Hope that helps.

Thank you, swede

So, that's an 820 ohm resistor, and doubtless a small ceramic capacitor.  I would bet the reason they're using the 1000V bridge is the same reason I use them.  I got them cheaper than any other rating, so I went with them.  It's certainly not needed in this application.

Are all the SMT capacitors ceramic? I was looking around on Digikey and wasn't sure I was looking at the same type of stuff? Of course they had so many options to select I could have goofed up there somewhere too as I wasn't exactly sure what I was selecting on some options? If you don't select something you get like a gazillion or more in the list (BTW, that's a LOT!!).

Maybe I will do better with the resistors, haven't yet tried looking for those.

Thank you all, again, for the responses.

The following are two links from the internet for bridge rectifier and resistor. I certainly have no need for the quantities offered but would appreciate your confirmation that both would be suitable for this application.

1) Bridge Rectifier: https://www.aliexpress.com/ite...d5-af86-dccf1a4ff8ed

2) Resistor: https://www.aliexpress.com/ite...74-8a19-1aabc2eca32f

As for the capacitor, could you offer advice as to specifications it should meet? Searching the internet for capacitors that look like the one in my photo, I see them described as Ceramic SMD Capacitors. The biggest I have spotted is only 10 microfarads (uf), however. The following is a link to such an item. Will it suffice? 

https://www.aliexpress.com/ite...88-8b05-da6364848e37

Thank you for the assistance. For most of you, deciding what might work is a snap. Unfortunately, electronics, however simple, is not a subject I am versed in.

swede

rtr12 posted:

Are all the SMT capacitors ceramic?

Heavens, no!   The green arrows are pointing to a couple of SMT electrolytic capacitors, and the red arrow is pointing to a tantalum capacitor.  Naturally, I used my Super-Chuffer as an example.

Here's a Digikey Search for SMT Electrolytic Capacitors, it turns up almost 10,000 in stock items.

You can have 500 of the appropriate 1206 1/4W resistors for $1.22 from Digikey.

http://www.digikey.com/product...11-820ERCT-ND/732289

If you only want, say 25 of them, it'll cost you 40 cents.

Here's a 47uf tantalum cap, that's more like what you'd want to have some flicker resistance.

20 PCS 47uf Tantalum Capacitor

 Edited to change the resistor I erroneously specified too small.

Thanks GRJ!

I still have a lot to learn about SMT stuff. I didn't realize that the larger electrolytics (your green arrows) were still SMT. It was the smaller sized like your red arrows that I was looking for. The link you provided for RRSWEDE for the tantalum caps was what I was thinking of when I was searching Digikey. And some of those things are incredibly inexpensive!!

I think I feel another parts order starting to come together... 

gunrunnerjohn posted:

.... You don't need one as large as the 1206 footprint.

You're suggesting an 0603 footprint 1/10 Watt resistor (vs. 1206 footprint 1/4 Watt) ?  According to the Evans site the "universal LED" operates up to 19V AC/DC.  So if dropping from 19V to ~3V (white LED) at, say, 20 mA ...

As for the capacitor, note how they put the resistor on the AC side of the bridge.  So the voltage on the DC side of the bridge is effectively "clamped" by the LED's ~3V forward voltage.  Thus you can use a 6V or 10V capacitor which allows substantially more uF for the same volume/size of capacitor (vs. a 25V capacitor).

The cap can be smaller, but so will the ability to prevent flicker!  You'll store a LOT more energy in a cap at 25 volts than the same cap at 3 volts.  In truth, the cap across the LED will have minimal effect.

A 100uf capacitor at 3V will store 450u Joules, most of it unusable as when the voltage drops a few tenths, the LED won't light anyway. That same 100uf capacitor in front of the resistor will store 31.25m Joules, some sixty times the energy, and most of it will be usable to keep the LED lit.  You can drop the capacitor from 100 to 22 for a much smaller size and still have almost 7 joules of energy to keep the LED lit.

You're right about the resistor, it needs to be larger, I'll edit my previous reply.

Right.  But now that we're playing musical chairs, I wonder if the reason Evans put the resistor "before" the capacitor was for DCS compatibility.  Done the way shown, any capacitance is isolated from the track voltage by 820 ohms.  If the capacitor is "before" the resistor, agreed it can charge up to 25V or whatever but now the DCS signal will likely be affected. 

Also, if the done as proposed I'm not happy with "only" a 25V cap rating.  I realize Evans specs 19V AC max as apparently Lionel says for some products...but there are AC controllers putting out 20-22V AC.  Just my opinion of course.

Stan, I was wondering about the resistor being on the AC input? Is that good or bad? I get your point about allowing a larger cap, but GRJ's suggestion about 25v caps storing more energy is also a good point. Looks like compromises are required??

Why would I want it there as opposed to putting it on the DC output side, other than there is more room on that side?? Answers to any questions I missed here are also very welcome.   And please type slowly so I can keep up! 

Edit: I think you answered some of this above while I was trying to figure out what to ask down here. 

rtr12 posted:

Thanks GRJ!

I still have a lot to learn about SMT stuff. I didn't realize that the larger electrolytics (your green arrows) were still SMT. It was the smaller sized like your red arrows that I was looking for. The link you provided for RRSWEDE for the tantalum caps was what I was thinking of when I was searching Digikey. And some of those things are incredibly inexpensive!!

I think I feel another parts order starting to come together... 

 

SMT caps can even get a lot larger.

Size / Dimension 0.709" Dia (18.00mm)

Height - Seated (Max) 0.846" (21.50mm)

stan2004 posted:

Right.  But now that we're playing musical chairs, I wonder if the reason Evans put the resistor "before" the capacitor was for DCS compatibility.  Done the way shown, any capacitance is isolated from the track voltage by 820 ohms.  If the capacitor is "before" the resistor, agreed it can charge up to 25V or whatever but now the DCS signal will likely be affected. 

Also, if the done as proposed I'm not happy with "only" a 25V cap rating.  I realize Evans specs 19V AC max as apparently Lionel says for some products...but there are AC controllers putting out 20-22V AC.  Just my opinion of course.

Stan, I use 35V caps for all my applications, and I also include the 22uh choke to solve the DCS issue.  As far as the location of the cap, I don't know why they bothered, it's next to useless in that location.  Why waste the time and money putting it there at all, the resistor and bridge will light the diode.

Well, I suppose we should let the OP comment on where he wants to go with this. 

Just my opinion, but if going thru the trouble of a DIY, I'd want to bring something to the party rather than just duplicating what Evans did.  But to that end you could find someone with a capacitance meter to measure that ceramic cap and it appears the MB10S can be had for 10 cents or so. 

I think adding flicker reduction with a 35V capacitor is a fine idea.  And to make it universal I'd install the DCS inductor.  You can in my previous photo that a suitable surface-mount DCS inductor is about the size of that ceramic cap and probably about 10 cents or so.

Frankly, what I don't understand is how the Evans assembly doesn't "snap" when the heatshrink is applied.  Without some kind of substrate or base to mount the components it seems the compressing heatshrink would stress the solder-joint between the resistor and the leg of the bridge rectifier?  Anyway, based on what I've read on OGR they've obviously sold a ton of these so they know what they're doing but still...

Thanks again, GRJ. I think some of this explains the layout on the LEDs in the discussion as well. I was aware of the caps needing a choke on the DCS systems, but didn't think of that when asking questions above. Also interesting on the sizes of the SMT parts, I always thought they were only the ones requiring a magnifying glass to see. I guess it should have been a little more obvious to me that SMT is the way of mounting things (Surface Mount). That's why I asked Stan to type slowly!! 

Stan, I've shrunk a bunch of stuff with heatshrink, and I've never had any issues, even with something on the order of what Evan's does.

I use a small 22uh choke on my lighting module, the FIXED IND 22UH 255MA 490 MOHM, it's 11 cents if you buy 25 of them.

Truthfully, if I were going to make a few of these, I'd just layout a tiny circuit board at OSH Park and make it easy to slap them together.  I did this little assembly for doing ground lights under walkways on steamers.  You just cut the sections and glue them down.  The pads are for soldering the wires that come through very small holes drilled in the boiler.  For small circuit boards, costs are quite low to get a bunch of them.

Tantalum caps are marginally cheaper than ceramic in 35V 22uf caps, but still $1 in quantity one.  Cheapest I found on eBay was similar caps for around 50 cents quantity 10.  Here's the best prices on Digikey.

http://www.digikey.com/product...18-1071-1-ND/1559565

http://www.digikey.com/product...5-14428-1-ND/3956094

This is the reason I typically use aluminum electrolytics if I need voltages higher than around 16 volts, these are simply too expensive.

One wonders why you wouldn't just make the bump in the heatshrink package slightly larger and use an aluminum cap, say a 47uf 35V one.

http://www.digikey.com/product...32-8508-1-ND/5728465

28 cents quantity one.  This brings the price of the little LED module into a reasonable range.

Size / Dimension 0.248" Dia (6.30mm)

Height - Seated (Max) 0.217" (5.50mm)

Exhibit one, the resistor and 22uh choke are on the other side.  Looks like 40 cents apiece for the bare boards, probably another buck or less for the components.

The aluminum electrolytics are a lot smaller than they look in the pictures. Roughly 1/4" x 1/4" is still pretty small. I like the circuit board idea too! Holy mackerl, you whip those up so very quickly!!

There's only four parts, doesn't take too long to do one of those.

I could make it a bit shorter but more "rounded" by putting the cap on the other side, I thought of that.

Getting cheaper, now the boards are only 30 cents each.

This might be slightly more compact, they're only .65" long and just over 1/4" side.  Looks less than 1/2 an inch thick...

That's probably smaller than the ones in the OP's pictures (length & width), but maybe slightly thicker. Pretty impressive and very small. At 30 cents per board that's really cheap too!!

What's curious about the last design is it appear you can also use the board to replicate the Evans design by installing the 820 ohm into L1 (assuming the pads are spaced accordingly), a ceramic cap of TBD value into C1, and a 0 ohm resistor or piece of wire into R1.  Interesting.

I've replaced a ton of incandescent headlights on my PW stuff and I find myself in the "Evans" camp. It's simply "plug and play".  Many of the PW steamers (736,726, 773 etc.) have a hollow tube behind the headlight lens. I push either a 3 or 5 mil warm white bulb into the tube and either Goop the back of it or tape it to hold it in place (photo below). It creates a torch of a headlight. With diesels (F3s, Alcos etc.), I cut a small piece of brass tubing that will just fit around the Lucite "tube" behind the lens. I Dremel the rear part of the "tube" so that it's flat (it comes angled to pick up light from a bulb in the floor of the chassis). The brass tube is just long enough to go around the  plastic lens tube to the inside of the shell and also to allow me to push an LED into the rear of the tube. It's important to keep the bulb straight so the beam is projected straight forward. This will sometimes involve Dremeling the rear "collar" of the bulb so it just fits and fits straight. Photo below

For steamers that don't have a hollow tube behind the lens, I Goop a Mega-chip flat LED directly to the rear inside of the lens. I also do this with engines like the Budd cars that don't have a true lens, but have a plastic flat "lens" inside the shell. Works much better than the bulb that's in the chassis. 

With all of these LED mods, I like to turn out the lights and watch these engines light up the track in front of them with a powerful beam of light. Looks great.

-Roger

OK, here's Stan's "powerful beam of light".   This is the real "value added" module, I've swapped out the resistor for a CL2 package that regulates the 20ma to the bulb all the way down to about 4 VAC on the inputs.  The board got slightly larger, about .1", but now you have regulation, flicker protection, the complete package.

Go big or go home.

Nice!  35 cents per board is simply astonishing.

And, again, by inspection one might observe that replicating the Evans design can be done using this bare board as a mounting substrate by a) inserting an 820 ohm resistor into L1, a ceramic cap in C1, and a bypass jumper wire into U1.

Of course Stan, why would I want to replicate the Evan's design, the point was to do a better design.   Sure, it's a bit larger, but the constant current, a capacitor buffer, etc. all make this a better performing module.  The board and components are around $1.50-$2.00, depending on quantities and where you buy them.  Add an LED and you have a nice light package.  You can even connect a couple LED's in series for dual-headlight applications, unless the voltage falls below around 6 VAC on the track, they'll still run at full brightness.

If you buy quantity one, the costs are as follows.  Since it was so similar and the same footprint I bumped the cap up to 100uf for better flicker resistance.

• CAP ALUM 100UF 20% 35V SMD: (1) .38, (25) .22
• IC LED DRIVER SOURCE SOT89-3: (1) .41, (25) .35
• IC BRIDGE DIODE 1000V 4-MICRODIP: (1) .40, (25) .32
• FIXED IND 22UH 255MA 490 MOHM: (1) .13, (25) .11
• PCB from OSH Park: .35

Parts for quantity one: $1.67

Parts for quantity 25: $1.31

This is for parts all from Digikey and the boards from OSH Park.  Cheap, but not the absolute lowest price you might find.  I use Digikey simply because when I want a part, I can get it, even two-three years later.

I have not been able to view the forum since my last post. Wow, a lot has transpired.

Stan, if you would like me to find someone to measure the capacitance of the Evan Design capacitor, I will. Let me know. 

Although the DCS concerns do not apply to my immediate quest, I agree a commercial product should take that into account. Is it possible the Evan Design has done so by its placement of components?

If I have properly followed GRJ's dimensional information, his finished product would measure 19.38 mm L x 7.16 mm W x ~12.7 mm H. I know the Evan Design of 7 mm L x 4 mm W x 2 mm H , that functions, fits in the space available. I don't believe GRJ's will fit. Overall dimensions of the board, itself, as well as dimensions of the capacitor are the obvious culprits.

GRJ, your diagrams provided dimensions as well as cost. If I wanted to purchase the boards as you designed, How would I go about doing that?

Again, I thank you for you assistance. 

swede

I'm going to make them available on the OSH Park website with a bill of materials.  However, I've also attached the Gerber and drill files to this post and you can order them directly.

Note that the reason my board is bigger is for a number of reasons.  First, it does a lot more.  It has full DCS compatibility, eliminates flicker, and offers constant intensity lighting over the full voltage spectrum.  I could also shrink it quite a bit if I were to go with a Tantalum capacitor and a smaller and more expensive bridge rectifier.  I was trying to balance the size with the price of components.

If I wanted to duplicate what Evan's did, it would be a lot smaller, but that's a pretty primitive board, and all it offers is lighting the LED from AC.  No flicker resistance, variable intensity with voltage, etc.  I supposed due to the location of the resistor that it probably doesn't have too much of an adverse effect on DCS, though I suspect that's just by luck.  I wouldn't even bother with the capacitor in their design, at that size a ceramic capacitor across the LED can't have much of an effect on flicker, it's probably of minimal worth.

GRJ, how much more would this be with the tantalum cap and smaller bridge rectifier? Would the tantalum cap be the same 100uF as the one selected?  Ball park is fine, I was just curious. 

Also thanks for sharing all this stuff with us. 

Wonder if you can drop in an 0805 resistor to allow use of an LM317 SOT-223 to let user set the LED brightness.  I'd think anyone who has the soldering skills and patience to put together this board would not mind the 2 extra solder joints. Looks like the board outline can stay the same.

The CL2 regulator is still (to my knowledge) a sole-sourced IC whereas the LM317 is made by many suppliers.  And while I get your point about DigiKey availability, the LM317 is widely available on eBay with deals to be had - whereas the CL2 is hard to find on eBay.  A 62 ohm resistor (for 20 mA) is about a penny...though you must pony up 96 cents minimum.