3VDC supply

Why not just buy the converter modules on Ebay from China. They are only a couple bucks, and take about 10 days to arrive. I bought a 10 pack for $20 shipped and they are adjustable.

Google for a "buck converter."  There is an LM2596 available from Aliexpress, which says it's adjustable down to 1.5 volts.  Price is 5 for $14.35, including shipping.  I have several for powering 12-volt LED strings and a 6-volt motor.  Be sure to get one that's for AC input.

 

I would suggest powering directly from transformer if you use DCS, or feed it through a choke.

here is one try this! the only similar one would be buy a 3 volt transistor regulator and then run the ac from the track rail into a full wave bridge rectifier and the output of the full wave rectifier would feed in to the 3 leg transistor regulator.

let me know which one you like and ill give you a parts breakdown list

Alan

you would not use the transformer shown just feed your track ac power to the circuit input on the full wave bridge

I have two PC power supplies for lighting. I paid $15 for one from a local computer repair, and the other one I "procured" from the electronics recycling bin in town. 300 watts of 3v, 5v, and 12v DC power with a cooling fan, too. Very simple fix. I just saw 2 at RS marked down to $14. Plus you can share the layout common if it saves wire.

I think from some previous postings that these may interfere with the DCS signal as the input is not isolated from the output.

These are cheap and easy to use.

 

http://www.ebay.com/itm/Hot-LM...;hash=item2ed01c0345

 

http://www.ebay.com/itm/YS-03-...;hash=item566ce5112c

Roy, those are DC in, so you have to provide a bridge rectifier and additional filter cap to use them for track power.

 

 

Half the fun is building it yourself.  Luckily I have easy access to a well stocked electronics warehouse within driving distance.   I'll probably ask if they stock anything pre-made but if not....  All the basics I have already at hand.

 

This need not include a variable cap....just transform 18VAC track power into 3 VDC.

 

Bruce

Whether you build or buy, I encourage you to consider a "buck" or switchmode step-down design.  If going from 18V AC to 3V DC, a traditional linear regulator design as shown in the schematic above is terribly wasteful generating all kinds of heat.  For example, if drawing 1 Amp on the output you also draw 1 Amp on the input. 

 

Power (Watts) = Volts x Current.  So 18 Watts goes in (18V x 1 Amp) but only 3 Watts goes out (3V x 1 Amp).  That means 15 Watts goes up in heat and 15 Watts is fairly hard to get rid of even with bulky metal heatsinks!   Efficiency is another metric used and in this case you efficiency is 3W out for 18W in = 3/18 = 17%.

 

OTOH, with a switchmode regulator module as suggested earlier you will probably have an efficiency of 85%.  So for that same 3 Watts going out, you only need about 3.5 Watts going in.  This means the current draw on your track voltage is only 0.2 Amps rather than 1 Amp.  And only 0.5 Watts is "wasted" as heat.

Roy, Those little power supplies you linked to... Is there any documentation online.  Is the output voltage adjustable or is it simply proportional to the input voltage.  I can think of lots of uses for a supply like this... all at slightly different output voltages.

 

Paul

I bought a board from a company called DROK that takes low voltage AC in to variable DC out. They no longer sell. Then I found the exact same picture for a company called RioRand.

 

I have only tried them on the bench, they have not been given a torture test. I was going to install it and a string of LEDs inside a K-Line caboose until I took the caboose apart.

 

Here is the new item. For some reason I can't put a link in.

 

http://www.amazon.com/RioRand-...04Y4W7HNNYS802F6QN79

 

 

Here's the same AC to DC switch mode supply for 1/2 the price, $2.99 + $1.30 shipping.  If you buy more than one, each additional shipping is only 50 cents.

 

 

GRJ, for once, I had a lower price than you.

Sure, but you have to buy five of them to get it.

 

Funny thing, I actually bought those exact ones from AliExpress, but I couldn't find the link to post it.  I just searched there and can't find that one now.

 

Edit: I found my old order and got a link: http://www.aliexpress.com/item...step/1150414198.html

 

 

  Can these be wired directly to 18vac dcs track?

Yes, right to the track.  However, I'd include a 22uh RF choke in the supply lead to prevent issues with the DCS signal.

GRJ, those links change often, as do proices, which is why I said to google the product.  I have 5 more more or less on the way from China.  I'm not in a rush, as I have a few left from my last purchase of 10.

 

GRJ is totally correct on the 22uh choke.  They are dirt cheap.

Here one like the one John showed you! http://www.ebay.com/itm/LM2596...;hash=item566904a94e         

 

Alan

 I believe this is the same one John showed you but you can buy 1 at a time if you wish!

Alan

Alan, those are DC-DC, they don't accept an AC input.  That's why we were tracking down the other one.

 

OK thanks , just trying to help out. Have a nice day ,can't wait for this weekend breakfast.

Alan

I see what you mean, i spotted the full wave bridge  rectifier on the board you showed in the picture!

Alan

  Do you prefer axial or radial chokes?

Those are the same exact ones I bought from EBay, in a 10 pack price. Since then, I spent a little more and got some with digital meters built in because it makes it so much easier to adjust when you're working under the layout. Then I double check with my volt meter just to make sure they are accurate.  

Makes absolutely no difference.

 

 

 

If you check them with the meter anyway, why spend the extra money?  Truthfully, when I use them, I set the voltage on the bench and then just install them.

 

I just checked the 1st couple to make sure they were accurate. Its too hard to hold the meter probes and adjust the pot with a tiny screw driver at the same time. I did it all under the layout and not at the bench.

When I get a batch, I line them up on the workbench and set them for the desired voltage, before installing them, using my meter.  I don't check later for drift.

Me too, I just set them on the bench and then install them.  I do have a couple of the ones with meters, just because I was curious and thought they were cool.  I love this stuff, it's so cheap that I don't feel bad buying a couple of almost any of these little modules.

 

GRJ, I suspect you have a lot of gadgets and supplies hanging around.  My sons are always  after me to get rid of such stuff.

WAY more than I could ever use, I'm a sucker for a new gadget.

 

Laidoffsick,

 

Do you have the links to the AC-DC step down converters you bought in a "10 pack" deal?

 

Also, do you have the link for the ones with the built-in meters that you bought?

 

Best,

Dave

I suffer from the same addiction, worse than trains, but also much cheaper! It's also fun to get little gizmos in the mail ever so often.

 

I have some of the digital read out ones as well. I use them on the bench for fiddling with all the other gadgets that you guys keep 'forcing' me order by posting all these threads and pictures.

I have all the power supplies and other stuff to tinker out full time.

 

 

Dave, I don't see the same exact ones that I bought on the bay at this time. Not even singles.

 

I like THESE with the large adjustment dial though... much easier to adjust than the ones I bought.

 

I bought THESE when they had a sale on them. I like them a lot. A bit more $$ but I don't mind spending $10-$12 to power a bunch of lights when engines are $1K+

Hi John like your work bench and test equipment setup, Where's the O - Scope!!Just kidding

 

Alan

looking forward to the breakfast this Saturday and meet you and the other train Guys

Could you send me you cell  number to Amustng@aol.com in case i have trouble finding the Allentown directions!

GRJ, looking at your bin, you obviously haven't been hoarding for long.  I pity my poor Executor.

The digital 'scope is in the closet, along with the analog 'scope.  That's just the work area.

 

 

 

That's just my workbench with some drawers for commonly used stuff, there's a LOT more under the bench, beside the bench, and even in the closets.

Those are LM317 based, a linear design.  They don't have near the current capacity of the switchers.

 

Hi John

How is the current rating of the LM 2596 vs. LM 317?

Tommy