Bridge Rectifier For LEDs

I guess it’s a matter of taste, but I prefer the car on the left.  Car on the right seems way too bright.  Perhaps it’s the power at ~18vac that is too bright.  Your leds are intended to be powered at 12vdc according to the specs.  Just my opinion. The electronic experts will chime in on the proper components for capacitor and rectifier, and maybe a resistor of some type.

TedW posted:

I guess it’s a matter of taste, but I prefer the car on the left.  Car on the right seems way too bright.  Perhaps it’s the power at ~18vac that is too bright.  Your leds are intended to be powered at 12vdc according to the specs.  Just my opinion. The electronic experts will chime in on the proper components for capacitor and rectifier, and maybe a resistor of some type.

I have a potentiometer I could add and a bunch of 330ohm resistors for that matter. I just want the LEDs to be protected. 

Bridge rectifier is fine electrically speaking (1 Amp, 1000V).  Agree with Ted; car on right looks way too bright - so bright I can't make out the silhouette passengers as you can on left. 

If all you do is insert the bridge rectifier you will be driving the LED strip almost twice as hard as you are now.  That's because the bridge will drive the LED on both halves of the AC cycle.

Then, if you insert a 1000uF capacitor (choose 35V or higher voltage rating on the capacitor), the LED strip will get brighter yet since the capacitor will charge up and apply even more voltage when the AC track voltage would otherwise collapse to 0V when it, umm, alternates.

In any case, you need to limit the current driving the LED strip.  Some combination of 330 ohm resistor would work.  Depending on what kind of potentiometer you have, that too could be used to limit current and even provide some adjust-ability.  If you run DCS or plan to in the future, you need to add a 10 cent inductor/choke so as not the degrade the DCS signal.  You can find all this hashed out in tedious detail in the original OGR thread which resulted in GRJ's off-the-shelf LED module. 

stan2004 posted:

Bridge rectifier is fine electrically speaking (1 Amp, 1000V).  Agree with Ted; car on right looks way too bright - so bright I can't make out the silhouette passengers as you can on left. 

If all you do is insert the bridge rectifier you will be driving the LED strip almost twice as hard as you are now.  The bridge will drive the LED on both halves of the AC cycle.

Then, if you insert a 1000uF capacitor (choose 35V or higher voltage rating on the capacitor), the LED strip will get brighter yet since the capacitor will charge up and apply even more voltage when the AC track voltage would otherwise collapse to 0V when it, umm, alternates.

In any case, you need to limit the current driving the LED strip.  Some combination of 330 ohm resistor would work.  Depending on what kind of potentiometer you have, that too could be used to limit current and even provide some adjust-ability.  If you run DCS or plan to in the future, you need to add a 10 cent inductor/choke so as not the degrade the DCS signal.  You can find all this hashed out in tedious detail in the original OGR thread which resulted in GRJ's off-the-shelf LED module. 

 

I'll take a look for the thread. The pots I have are 1k ohm. I do run DCS, so I'll look for the choke. 

banjoflyer posted:

The rectifier you reference shows a 1A rating, That's pretty low for toy trains. I use these as they are rated at 6A.

The Type of 1000uF capacitors I use are found here.

I would add an LM2596 regulator to your circuit so you can lower the light intensity and make the LEDs last longer and run cooler. I set mine at 10VDC output.

This is how the circuit looks when complete:

 

Here's a post showing it in use. 

Mark

Thank you. 

banjoflyer posted:

The rectifier you reference shows a 1A rating, That's pretty low for toy trains. I use these as they are rated at 6A.

The Type of 1000uF capacitors I use are found here.

I would add an LM2596 regulator to your circuit so you can lower the light intensity and make the LEDs last longer and run cooler. I set mine at 10VDC output.

This is how the circuit looks when complete:

 

Here's a post showing it in use. 

Mark

You'll never see anything close to an amp for this usage, no reason to go with a huge bridge for this application.

gunrunnerjohn posted:

banjoflyer posted:

The rectifier you reference shows a 1A rating, That's pretty low for toy trains. I use these as they are rated at 6A.

The Type of 1000uF capacitors I use are found here.

I would add an LM2596 regulator to your circuit so you can lower the light intensity and make the LEDs last longer and run cooler. I set mine at 10VDC output.

This is how the circuit looks when complete:

 

Here's a post showing it in use. 

Mark

You'll never see anything close to an amp for this usage, no reason to go with a huge bridge for this application.

So the 1A bridge will work fine?

Will these be good chokes?

The 1A bridge will be fine, more than sufficient.  We're lighting LED's, not soldering track!

The chokes you reference are yet another overkill, the lighting will consume at most 100 MA, probably less.  I run 18" passenger cars on around 25-30ma to those 12V strips, any more current and the lighting is too bright.

eBay: 371874799826 is more than sufficient for the 22uh choke, you get 100 for $3.85 from a US seller, free shipping.  If you don't mind waiting a few weeks, they're even cheaper from China.

gunrunnerjohn posted:

The 1A bridge will be fine, more than sufficient.  We're lighting LED's, not soldering track!

The chokes you reference are yet another overkill, the lighting will consume at most 100 MA, probably less.  I run 18" passenger cars on around 25-30ma to those 12V strips, any more current and the lighting is too bright.

eBay: 371874799826 is more than sufficient for the 22uh choke, you get 100 for $3.85 from a US seller, free shipping.  If you don't mind waiting a few weeks, they're even cheaper from China.

Thanks for the help. 

I think this thread has a good answer for passenger car lighting. The LM317 does all the heat dissipation so you don’t have to worry about a hot dropping resistor.

https://ogrforum.com/...45#73509797294001045

An adjustable current regulator, capacitor for eliminating flicker and a bit of storage. A tiny circuit board if you buy them ready made. I can understand rolling your own, that’s half the fun in this hobby...maybe use a square inch of perf board and build it yourself.

Read this thread also, scroll down to the part about not too much light and warm LEDs.

https://ogrforum.com/...ner-henning-s?page=1

cjack posted:

I think this thread has a good answer for passenger car lighting. The LM317 does all the heat dissipation so you don’t have to worry about a hot dropping resistor.

https://ogrforum.com/...45#73509797294001045

An adjustable current regulator, capacitor for eliminating flicker and a bit of storage. A tiny circuit board if you buy them ready made. I can understand rolling your own, that’s half the fun in this hobby...maybe use a square inch of perf board and build it yourself.

Read this thread also, scroll down to the part about not too much light and warm LEDs.

https://ogrforum.com/...ner-henning-s?page=1

Thank you!

How's this for a LM317? I know it's big but I'm going to custom detail the car so I'll find a way to hide it. 

"As long as possible"...? 

Capacitance IS the answer, or at least partially, and 1000uf might not be far off. I use 470uf for four and would have happier with a bit more, maybe double.

It’s circuit is as a voltage regulator. Ok, but I kind of like the current regulator for the LEDs. I did some cars without interiors and found that even the Hennings regulator was in the way for where I wanted the LED strip.

If you search on eBay, they are abt 2.70 from China.

Trainlover9943 posted:

How's this for a LM317? I know it's big but I'm going to custom detail the car so I'll find a way to hide it. 

That sucker is HUGE!  Again, it's massive overkill for the job.

Photos taken from build notes on the O gauge archive: http://www.jcstudiosinc.com/Co...-Using-12V-LED-Strip

DC-DC converter module installed in a silhouette style passenger car so space available for the electronics.  The small separate hand-built board has the DCS-inductor, the bridge rectifier, and the capacitor.

The DC-DC module was a so-called buck-boost type since this car can run on conventional or command so the converter might have to boost the voltage for low track voltages.  If you are only operating command mode, then you can use the slightly cheaper buck-only type as banjoflyer shows. 

You showed a surface-mount bridge rectifier in your earlier post.  So if you're comfortable working with that style of component packaging, I use scissor-cuttable circuit board and use a hobby-knife to score copper "islands" to accommodate the surface-mounting (i.e., no holes thru the board).

Front-end components can be all surface-mount if that's what you're after.  Very inexpensive...about 5 cents for the bridge, 10 cents for a 470uF/35V capacitor, 10 cents for the 22uH DCS inductor, less than $1 for the DC-DC module.   I happen to use eBay a lot and don't mind waiting a couple weeks for parts to come from Asia.  All components are obviously available from Amazon or US sources though the prices run around 5 times higher on average.

Not quite clear on what your extended lighting time requirements are, but you can always double-up a 470uF capacitor to "make" a 940uF capacitor...or of course just buy a 1000uF capacitor to begin with.  Point being you can add capacitors after-the-fact to increase operating time.  But with values that have been discussed you are only talking about flicker suppression in the less-than-a-second category.  If you're thinking of operating for seconds or minutes after power is removed, you'll need a different energy storage method (e.g., supercapacitor, battery).

The article link also provides some ideas of dealing with the observation car's marker lighter and tail-light.

Adriatic posted:

"As long as possible"...? 

Capacitance IS the answer, or at least partially, and 1000uf might not be far off. I use 470uf for four and would have happier with a bit more, maybe double.

Do you mean 470uF for 4 cars and are tethering the regulated DC voltage from one powered car to 3 others?  If so, can you post photos of your tethering method/connectors?

If you're comfortable working with surface mount stuff, I'd use one of the many free PCB layout packages and go to OSH Park and have the boards made.  For instance, if I were to get my lighting boards made at OSH Park, it would cost me $1.05/ea shipped for boards. 

There are some even cheaper places nowadays, Seeed Studio will make 20 of them for $11.72 shipped.

You might even find an existing design on the OSH Park website that you can order.  For example, here's a design that GRJ posted that anyone can order without having to learn anything about circuit board layout.  I think it was something like 3 boards for $1 and that includes shipping.  

You have to do some homework to find it, identify or find where to buy the components that match the board, etc.  But for 35 cents per board, it can be a real time-saver!  This board has the 3 key components (inductor, bridge, capacitor) but also a LM317 regulator and some other supporting parts that would not be needed if using a $1 DC-DC converter module.  The idea would be to populate this board with just the 3 key components and then wire over to a DC-DC converter. 

There are more options than you can shake a stick at!   I think when all's said and done, after going around in circles evaluating all the options, for most guys the path of least resistance is to simply buy GRJ's assembled LED lighting modules from Hennings!  That's my 1 cent.

I forgot about that one Stan.

stan2004 posted:

You might even find an existing design on the OSH Park website that you can order.  For example, here's a design that GRJ posted that anyone can order without having to learn anything about circuit board layout.  I think it was something like 3 boards for $1 and that includes shipping.  

You have to do some homework to find it, identify or find where to buy the components that match the board, etc.  But for 35 cents per board, it can be a real time-saver!  This board has the 3 key components (inductor, bridge, capacitor) but also a LM317 regulator and some other supporting parts that would not be needed if using a $1 DC-DC converter module.  The idea would be to populate this board with just the 3 key components and then wire over to a DC-DC converter. 

There are more options than you can shake a stick at!   I think when all's said and done, after going around in circles evaluating all the options, for most guys the path of least resistance is to simply buy GRJ's assembled LED lighting modules from Hennings!  That's my 1 cent.

You have a link to this?

After doing a lot of homework, here’s a link for one option.  Need the components, capacitor(flicker), resistor(brightness), diode(ac to dc), choke(dcs).  $2.20 for 3 boards shipped.  Not as elegant as GRJ’s adjustable module, but sure does work.

Pass car led lighting pcb

You can start from the beginning of this thread to see the evolution but I believe the end-result is this post:

https://ogrforum.com/...18#71678964473081318

Apparently GRJ did not post this to the OSH Park shared projects page as there are only 2 boards with the username

https://oshpark.com/profiles/gunrunnerjohn

All the design info to order boards is bundled into the zip file.  As I recall it's pretty simple to order boards though I think you need to establish an account.

stan2004 posted:

You can start from the beginning of this thread to see the evolution but I believe the end-result is this post:

https://ogrforum.com/...18#71678964473081318

Apparently GRJ did not post this to the OSH Park shared projects page as there are only 2 boards with the username

https://oshpark.com/profiles/gunrunnerjohn

All the design info to order boards is bundled into the zip file.  As I recall it's pretty simple to order boards though I think you need to establish an account.

Thanks. 

I just put it up on OSH Park, I hadn't done that before.

gunrunnerjohn posted:

I just put it up on OSH Park, I hadn't done that before.

Nice!  And GRJ even provides part numbers! 

https://oshpark.com/shared_projects/58Gp3gHv

The price is still $1.05 for 3 boards.  Wow.  Note that you have an option to order 1/32" or 0.8mm thick boards (for apparently the same price).  Most boards you see in O gauge trains and accessories are 1/16" thick.  Thinner boards can be handy in some tight-quarters scenarios.

TedW posted:

After doing a lot of homework, here’s a link for one option.  Need the components, capacitor(flicker), resistor(brightness), diode(ac to dc), choke(dcs).  $2.20 for 3 boards shipped.

Pass car led lighting pcb

Note how the use of surface-mount components cuts the board area in half.  With OSH Park which charges by the sq. inch, GRJ's surface-mount version is then half the cost per board.

Additionally, note that this version only uses a single-diode (vs. a bridge-rectifier) for the AC-to-DC conversion.  To be sure, there are situations where the single-diode version can be useful since it allows the DC to share a common "ground" with the outer-rail.  But that's a different discussion.  And if you know enough to grasp the significance of this, you also know that you could simply install a 5 cent surface-mount diode instead of a bridge-rectifier to achieve the same result.

Note that my design allows either constant voltage or constant current.  I personally like constant current for LED's, it insures a small change in voltage doesn't impart a wide swing in the LED current.  Since LED's are current mode devices, I've always felt that constant current is the best way to drive them.  Of course, you can configure for constant voltage as well by changing resistors.

Like Stan says, I almost always order the .08" boards, no reason for thicker boards for most of the stuff I do.  The only thick boards I've done have been for the track signal sensors and the TMCC buffer boards, they need structural strength.

I find a regulator isn't especially useful or much of an advantage.

All my passenger cars are now LED.  I run a 4amp 400v full bridge rectifier , LED strip lighting with a 1k 1/2 watt resistor (you can run the resistor on either + - side of the LED light circuit and they are non-directional), 1000uf 35v capacitor  (run before the light circuit, if you run it at the end of the  the LED strip it won't work as well, and pay attention to the + - connection on the capacitor; they must be mounted - to -,  + to +), TVS across the + - input power leads (non directional) , also chokes ( non directional) on both.  Cars run in forward or reverse properly, aren't too bright, and the set-up doesn't take much room.

I've found that a 1K resistor works for most all LED lights, and there isn't much brightness difference between a 500 or 600ohm resistor and a1K ohm resistor.  I also found that simply daisy chaining an additional small resistor didn't dim LED lights that much.   And with the 1K resistor, voltage variations between transformers isn't an issue, and they still light up OK on conventional, but probably not as perfect as with a regulator.  The thing is a regulator can't make electricity, so at low power the lights will still dim or go out unless you have a HUGE capacitor. With this circuit, the LED's just get a little dimmer, or brighter, depending on the individual transformer and locomotive speed.  At really low speed in conventional the lights won't go on even with a regulator, unless, like I said, you have a huge capacitor.

Hope this helps, and if you want a picture or an install, or diagram of the circuit, send me an email, and I'll scan and send one.

Waddy posted:

I find a regulator isn't especially useful or much of an advantage.

All my passenger cars are now LED.  I run a 4amp 400v full bridge rectifier , LED strip lighting with a 1k 1/2 watt resistor (you can run the resistor on either + - side of the LED light circuit and they are non-directional), 1000uf 35v capacitor  (run before the light circuit, if you run it at the end of the  the LED strip it won't work as well, and pay attention to the + - connection on the capacitor; they must be mounted - to -,  + to +), TVS across the + - input power leads (non directional) , also chokes ( non directional) on both.  Cars run in forward or reverse properly, aren't too bright, and the set-up doesn't take much room.

I've found that a 1K resistor works for most all LED lights, and there isn't much brightness difference between a 500 or 600ohm resistor and a1K ohm resistor.  I also found that simply daisy chaining an additional small resistor didn't dim LED lights that much.   And with the 1K resistor, voltage variations between transformers isn't an issue, and they still light up OK on conventional, but probably not as perfect as with a regulator.  The thing is a regulator can't make electricity, so at low power the lights will still dim or go out unless you have a HUGE capacitor. With this circuit, the LED's just get a little dimmer, or brighter, depending on the individual transformer and locomotive speed.  At really low speed in conventional the lights won't go on even with a regulator, unless, like I said, you have a huge capacitor.

Hope this helps, and if you want a picture or an install, or diagram of the circuit, send me an email, and I'll scan and send one.

Yes, a picture would be nice. prr2100@gmail.com 

Waddy posted:

I find a regulator isn't especially useful or much of an advantage.

We'll have to agree to disagree on that point.

The regulator allows you to set the brightness simply and ignores the track voltage variations if there are any. I think the elegance trumps simplicity in this case.

If you wish to lower the brilliance of an LED use a diode and a resistor inline and not a bridge rectifier. A bridge rectifier supplies DC on both the positive and negative excursion of the AC sine wave.  Adding a capacitor keeps the RMS voltage value even higher.  A diode only supplies 50% (or half the sine wave) of power.  A cheap trick that I use (if the LED socket bulbs are too bright) is to paint them with a coat of amber bulb dye. That gives them a glow of the incandescent bulbs used in years past.  Since my layout is representative of the 50's era it looks perfect.

Dennis LaGrua posted:

If you wish to lower the brilliance of an LED use a diode and a resistor inline and not a bridge rectifier. A bridge rectifier supplies DC on both the positive and negative excursion of the AC sine wave.  Adding a capacitor keeps the RMS voltage value even higher.  A diode only supplies 50% (or half the sine wave) of power.  A cheap trick that I use (if the LED socket bulbs are too bright) is to paint them with a coat of amber bulb dye. That gives them a glow of the incandescent bulbs used in years past.  Since my layout is representative of the 50's era it looks perfect.

Could I use throw in a pot instead of the resistor or should I put the resistor in with the pot?

Use a resistor for maximum brightness and a pot to lower it to a minimum, in series.

I use what ever is left in the little drawers that day 

cjack posted:

Use a resistor for maximum brightness and a pot to lower it to a minimum, in series.

Remember if the pot is in series with the load, it has to handle the total current.  With my constant current regulator, the pot value is considerably lower than a plain series pot would be, thus it also dissipates a lot less power.

Just my opinion, but this thread is very difficult to follow because though individual questions are being answered,  the answers must be taken in context.  The initial question was simply whether a particular surface-mount bridge-rectifier was suitable for LED passenger car lighting.  Then the discussion meanders to regulators, adjust-ability, extended operation (presumably flicker suppression), and so on.

To put things in context, here's GRJ's LED module in the center.  The point is this is an engineered-design meaning the components were selected to operate together with specifications commensurate to the application. 

One side discussion was on the use of larger bridge rectifiers.  Well, take a look at the variation in sizes as you go from the surface-mount bridge on GRJ's module, to a 1 Amp bridge (what OP initially inquired about), to a higher Amp bridge as suggested by others.

Then the capacitor.  Take a look at the size difference between the 330uF surface mount cap on the module vs. 470uF and 1000uF caps one might buy if components are acquired one-at-a-time.

Then the DCS inductor.  Take a look at the tiny surface-mount 22uH inductor on the module vs. a 1/2W part you might buy if acquired one-at-a-time.

Then the idea of a resistor plus a potentiometer for brightness adjustment.  Compare the resistor and potentiometer on the module to a 1K 1/2W resistor as suggested and the 10k potentiometer most recently brought up from Amazon.

Then the regulator.  The LED module uses a LM317 IC.  A DC-to-DC module from eBay is many times larger though can handle much more power.  But is this power needed to light a passenger car? (Answer: No.  But the module is inexpensive and simple to hook up).  The low-power AC-to-DC converter board discussed earlier also has all the components (including a regulator IC) but is more suited to powering a few LEDs rather than a full-length passenger car LED strip.

Waddy posted:

 

I find a regulator isn't especially useful or much of an advantage.

The regulator has the advantage of maintaining constant brightness for intermittent track-voltage loss due to dirty-track, going over a switch, and so on.  If you only have a capacitor, as soon as track-voltage is lost, the capacitor voltage immediately starts dropping as it supplies current to keep the LEDs going.  This voltage drop appears as a drop in brightness.

If you have a regulator IC, the LED brightness is maintained even as the capacitor voltage drops.  This gives superior flicker reduction.  To be sure, that's simply my opinion and what's good-enough is a to-each-his-own, your-mileage-may-vary.  But since an LM317 regulator IC is less than 15 cents, it's something to consider.

As GRJ mentions, if you use a voltage/current regulator IC like the LM317, in general you can use lower-power resistors and potentiometers.  Note the difference in sizes between the surface mount resistor+potentiometer as used on the LED module vs. "loose" components as were suggested in other posts.

The picture of GRJ's LED supply and all the suggested other components is inspired. One picture is worth a thousand words...again.