By adding a full wave bridge rectifier in front of the (fixed) DC input device you will get a fixed DC input to be reduced by the regulator.  It really isn't very efficient and you will generate some heat.

G

Yup, all you need is one those DC to DC supplies, but you need to put a full-wave bridge rectifier in front of it. Not to worry, you can either buy one at Radio Shack for a few bucks, or make one out of 4 diodes for $0.40.

Thanks all.  So I assume the DC to DC board above won't change the output (once set) even if the DC in out of the full wave bridge rectifier is variable (based on the variability of the Track voltage) - is this correct?

Here's a recycled photo from another thread showing one of those DC-DC modules that goes for $1-2 on eBay with free shipping (search eBay for "LM2596 module").  Also shown is a bridge rectifier to perform the AC-to-DC conversion...or as Arthur says just wire up 4 diodes which might be cheaper.

These DC-DC modules are regulators so they keep the output DC voltage constant even as the input voltage varies.   You need to set the module to 3V once.  If you don't have a meter, you can get one "free" from Harbor Freight with coupon from Sunday paper; the point is you don't need a "fancy" meter.

And, yes, you can also get a eBay module that has the bridge rectifier included but they run $4-5 (search eBay for "LM2596 AC module"):

It takes a couple weeks to get the eBay modules from Asia.  You can find these modules from US suppliers and get them faster but are usually more expensive.

For inexpensive converters, search ebay for LM317 ac-dc converter or LM2596 dc-dc converter. Only problem is they almost all come form China with (free shipping), but can take 2-4 weeks to get. The DC converters will need to have a bridge rectifier added for ac input. The others will take ac directly as an input.

Amazon also offers some of these items at higher prices, but they might have faster shipping times as some may be shipped from here in the US. Or I suppose one could order the 2 day or whatever Amazon has for shipping at even more cost if you really need them faster.

I think there are some forum members here that are using both of these type of converters for their accessories, lights, LED's, etc. There have been a few threads on them over the last couple of years. Don't recall seeing any posts with anyone reporting problems?

Edit: stan2004 just posted one above as an example while I was typing this.

This is how I do my pass.cars, works great.

Greg

Old Pa:

Could you let me know, via private email, your source for the LED strips?

Thanks,

info  (at)  SIBTA  (dot)  com

Here's the ones I've most recently used: 5M 3528 SMD 300 LEDs Strip

Stan and rtr12,

If running MTH's DCS system, it is recommended to add a choke to the circuit so as not to degrade the DCS signal.

I do run DCS. Is one needed in Stan's nice diagrams and if so where is it installed?

Are the chokes relatively inexpensive and where is a good source if they're needed.

Thanks,   Joe

You can always go the easy way, and full DCS compatibility as well.

NEW Passenger Car LED Lighting Kit & LED Regulator

The regulator boards or full kits are available, depending on your preference.

Arthur, the roll of strips John posted is a great deal.

Greg

Correct.  For DCS operation, you need to add the 22uH choke or else your DCS signal will be degraded.  Suitable chokes are about 25 cents each in small qty.  Even if you don't run DCS, you might be taking your car to a club layout or wherever that does run DCS. As I see it, if you're performing surgery on your car anyway to install the regulator why not pony up another 25 cents.

Here's one from eBay for about 25 cents each WYB 10, shipping included:

http://www.ebay.com/itm/10-x-2...;hash=item4aa3163d0d

Or here's one from DigiKey (US) for about 25 cents each but shipping will run you about $3:

http://www.digikey.com/product...K-TR-RCCT-ND/3741659

You insert it before the bridge rectifier on one of the AC wires.  It doesn't matter which AC wire but by convention it's usually placed on the wire from the center-rail roller pickups.

Separately, oldpa illustrates another consideration.  He added a capacitor between his bridge rectifier and the DC-DC module.  For lighting, this improves flicker tolerance by storing energy in reserve for intermittent loss of AC track voltage from dirty wheels/rollers, going over switches, whatever.  The DC-DC modules have some capacitance already but an additional capacitor that doubles the energy reserve would add about 25 cents; we can get into specifics if there's interest.  It would be installed as shown in photo or refer to oldpa's photos.

GRJ, did you make provision on your regulator for constant-voltage operation?  I recall we discussed this in the design phase.  I realize you call them LED regulators and specify constant-current control.  But for the OP's problem of generating 3V DC constant-voltage for his sound module, I'm hoping not to confuse matters as these are different animals

OOPS, they slipped the lights in there and I thought they were talking lights.  My mistake!  I see that we had two topics going, one about lighting and one about a 3V supply, very confusing!

stan2004 and gunrunnerjohn cover it much better than I ever could. They are also a lot more knowledgeable than me, so go with what ever they say about the lighting and chokes. Those folks (and some of the others here) are where I have learned most of what I know about all this stuff. 

I don't have any passenger cars, only lights on layout and in buildings so my DCS signal isn't in the picture with my lighting circuits.

Thanks for the help Stan, rtr12, oldpa and GRJ.

Electronics is far from my forte. Always amazes me what you guys know and do.

Joe

2 AA batteries would be more reliable and you would not loose sound from bad contact to the track.

Joe, Nice of you to say, but for my part all that I know about train electronics I have learned here on the OGR forum from John. Stan. Dale, RTR12 and  unnamed others.

Thank you all.

Greg

Stan,

Two last questions (I hope)!

I bought the recommended LM2596 AC Modules.

If I wanted to add the capacitor you mentioned, where would it go on these units with the bridge rectifier already mounted on the circuit board? Is there a polarity issue to contend with when mounting these capacitors?

Second, can you recommend a capacitor and a source?

Thanks very much for the sources of the boards and chokes also! Ordered yesterday and today.

Wish I had studied electronics/electricity more!!!

Joe

Yes. Once you enter the realm of DC (after the bridge) polarity is important. The 4 leads of the bridge rectifier should be labeled...something like the following.

The capacitor will be marked with a white strip indicating the - side...something like the following.

Needless to say, + of capacitor to + of bridge rectifier, and - to -.  If for whatever reason your bridge rectifier is not marked you should be able to following the printed wires on the board and you would attach the additional capacitor to the same polarity leads as the on-board capacitor.  It will probably be easiest to solder the leads of the capacitor to the leads of the bridge rectifier.

A slight digression.  If you bought the AC module, you may not need to add more capacitance.  Here's why. The DC-DC modules assume a steady DC voltage coming in and include a suitably sized capacitor.  When the DC-DC module is used with an AC input (and bridge rectifier) the steady input assumption goes out the window and you need to add more capacitance to supply reserve energy as the input voltage collapses to zero 60 (well, actually 120) times per second.  But with the AC-DC module, the designers obviously realize the input is AC and would have to have installed a larger capacitor than an equivalent DC-DC module.  OK, enough of the techno-babble.

I'd just hook up the AC module and see if it's OK.  But to answer your question, most guys are finding a total capacitance of about 470uF works LEDs in passenger cars.  Total capacitance adds together so if the on-board capacitor is, say, 220uF and you add another 220uF you now have 440uF.  The other key spec is the voltage rating which should be 35V or greater.  On eBay you simply search on, say, "470uF 35V capacitor" and you'll see them 99 cents for 5 with free shipping from Asia so 20 cents each.  That's a good price. US mail order sources are maybe 2x, and Radio Shack is typically more than 5x.  If you reach the point where you're not sure about the suitability of a specific component, provide a link and lots of guys here will be able to give you a thumbs up/down.

Stan,

Thanks very much for the helpful information and guidance. I only ordered 10 of the LM2596AC to start with and if I'm successful and don't screw them up I'll order a bunch more to complete the 100 or so passenger cars I have.

Again, thanks for taking the time and effort to walk an admittedly electronic ignoramus (me) through the use of these modules. Much appreciated.

Joe

oldpa,

Nice of you to say also, but you could really shorten this list to John, Stan, & Dale. That's where I have learned most of what little I know. I have also picked up a lot from a lot of other folks around here, way too many to list. But, thank you for the compliment!

Two things.

First I forgot to thank Allan for initiating the question. Thanks, Allan.

Second, is the orientation of the choke important? I mean is it marked on the ends and has to be put in line on the wire from the center rail pickup in a particular way? The color coded bands probably mean something that I don't understand.

Thanks again.

Joe

Orientation not important for inductor.  Like on most resistors, the color-coded bands indicate the value:

http://www.instructables.com/i...or-Color-Code-Guide/

So assuming the 22uH inductor you got follows the code, it should have the bands red-red-black (or 2 2 with a multiplier of 1, 22 x 1 = 22uH).

I realize you asked about and we've discussed the importance of capacitor orientation but must re-state the importance.  Another guy on this forum hooked up a capacitor backwards in an LED circuit and it literally exploded in his face (fortunately not injuring him) and started a fire that required an extinguisher.

Thanks Stan,

I'm going to start with 10 units and since they are the LM2596AC Modules, I'll make sure to try them without an added capacitor. They will probably be good enough that way. If I do have to add a capacitor, you can rest assured that, because of my lack of expertise, I will double and triple check the polarity to avoid issues.

Al your assistance has been greatly appreciated.

Thanks,

Joe

All - thanks for the input. This will help me not only with my sound question, but also with converting my passenger cars later!

Hi All - I got the board and installed it today and here/hear is the result.  It works great - the one thing you might notice is the sound board requires a switch to actually be turned on after power is applied, so I have to flip the switch after power is turned on.

Please excuse the shaking of the video.  

Cute, nice touch!

Brilliant!!!

Can you attach more than one lead on these converters so to light a couple of buildins with one converter thanks.  Tstark

Yes, as long as the voltage requirements of the buildings are the same and you don't exceed the current output of the device you should be fine.

Installed the initial ten modules I ordered with no issues. Ordered more and hope to complete the majority of the cars by Christmas. Going to convert all my Blue Goose passenger cars next and can't wait to see about 30 of them on the track at the same time. Not possible as manufactured. Again, thanks to all for all the help. Stan, you were right....they AC/Dc modules do have enough capacitor value to prevent any flickering.   Joe

Thanks to all who contributed.  I've got three "dark" postwar F3 B units that will be receiving "modern" lighting as part of their retrofit--these are PW units which LIONEL did not light.  The B units don't have roller p/u's, though I could add them.  I'll probably go with micro connectors and tap the A unit.

Then, it will be on to the passenger cars.