How do I make a simple power buffer for coach lighting.

Greg Elmassian

Greg Elmassian

Registered
8 Mar 2014
2,356
28
San Diego
www.elmassian.com
I've been sort of ignoring this thread, but if I wanted simplicity, I would fall back to the basics. The LED does not care what voltage is applied, it needs current limiting.

Adding a regulator is something you really don't need, although the DC to DC converter is a great idea, it solves 2 problems, low track voltage, and also it allows you to use a higher supply voltage and put LEDs in series.

What I would do is have the DC to DC inverter (fed by a FW bridge of course) running at a voltage that was convenient, ideally what would be needed by all the LEDs in the car in series. Then I would use a CL2 current regulator in series with the diodes to control the current.

example: say I wanted to run 6 white LEDs which had a nominal forward voltage of 3.6 volts each. So, I would want slightly more than 3.6 * 6 volts, so say 24 volts... put all the 6 LEDs and one CL2 current regulator in series. Feed from the DC to DC inverter and a nice big 35 volt cap on the output. I don't see a reason to put a cap on the input.

Now this is a pretty efficient setup, and will store the voltage in the cap, and the inverter will work down to pretty low input voltage. put any extra money in a larger cap.

This should run for quite a while with virtually no power... you might have to make the output voltage on the DC to DC inverter a bit higher but with today's LEDs they run at significantly lower current (and voltage somewhat) than the 20 milliamperes the CL2 provides. You could also make a series parallel setup of the LEDS, paralleling 2 strings of 3 LEDS, and split the 20 milliamps from the CL2 among the 2 strings, giving each LED 10 ma, which is normally just about as bright, and this lets you lower the "voltage" requirements of the DC to DC inverter, allowing "charging" of the capacitor at a lower voltage, or keep the voltage at 24 and have a lot more reserve.

Greg
 
Slawman

Slawman

Deckline
9 Apr 2018
277
0
Sydney
Here's a few pics of my latest DIY install. I am very happy with the warm white strip it gives excellent coverage along this car and is dimmable. I am running a 35v, 2200uf capacitor which gives me about 2 seconds at 10 volts. The pickups are a single axle of the Piko ball bearing conductors.


 
John S

John S

Registered
5 Nov 2017
489
11
Exeter, Devon, UK
Nice one, yes, and it's simple, it works, common everyday components, probably built for less cost than a single CL2! ;)

The dc to dc buck converter board used is an easier option, easier to adjust the screw on the blue pot with an ordinary flat bladed screwdriver, than the mini dc to dc converter, can sometimes be a frustrating exercise to get the voltage adjustment accurate, but at 11p each, the challenge can be quite character building! :D
 
Slawman

Slawman

Deckline
9 Apr 2018
277
0
Sydney
Thanks John. The bits cost about AUD 4 dollars so about 2.2 pounds plus the Piko Axle which was about AUD 25.

I am determined to use the tiny converter as I bought a few of them but you need a magnifying glass to work on it and to set the voltage.....
 
John S

John S

Registered
5 Nov 2017
489
11
Exeter, Devon, UK
Thanks John. The bits cost about AUD 4 dollars so about 2.2 pounds plus the Piko Axle which was about AUD 25.

I am determined to use the tiny converter as I bought a few of them but you need a magnifying glass to work on it and to set the voltage.....
Wasn't far out with the cost! ;)
https://www.ebay.co.uk/itm/MICROCHIP-CL2N3-G-LED-DRIVER-TEMPERATURE-COMPENSATED-CON/172196272362?hash=item2817b298ea:g:MHYAAOSwhRxXLL1S

As far as adjusting the mini types, I found that a watchmakers set of screwdrivers seem to be the best tools for the job, don't actually have a problem seeing it! :)
 
  • Like
Reactions: Simon Potter
Greg Elmassian

Greg Elmassian

Registered
8 Mar 2014
2,356
28
San Diego
www.elmassian.com
a cl2 is about 53 cents..

Nice one, yes, and it's simple, it works, common everyday components, probably built for less cost than a single CL2! ;)

The dc to dc buck converter board used is an easier option, easier to adjust the screw on the blue pot with an ordinary flat bladed screwdriver, than the mini dc to dc converter, can sometimes be a frustrating exercise to get the voltage adjustment accurate, but at 11p each, the challenge can be quite character building! :D
 
M

Michael

Registered
26 Jan 2010
69
2
I cannot see the point of having a constant voltage source followed by a constant current source, you either have one or the other.

According to the specificaton, the minimum voltage across the CL2 is 5 volts, so you are wasting 5 volts at 20mA of power. This solution will therefore be less efficient, reduces the time for the LEDs to dim and costs more than the dc-dc solution recommended above.
 
stockers

stockers

Trains, aircraft, models, walking, beer, travel
Staff member
GSC Moderator
24 Oct 2009
25,390
6
60
Nr. Ashford, Kent. England.
Well it works. 35V 2200uf cap. lasts about 4 or 5 seconds - running off a single ball bearing axle. feeding 3 standard warm LEDs at 3V
Result!

Now to find some bulk buys on Ebay china!

One thing - as the LED goes out it does flicker for about a second - any ideas, do I need a small resistor in circuit. (output 3V driving 3 x 3mm LEDs in parallel.)
 
Last edited:
stockers

stockers

Trains, aircraft, models, walking, beer, travel
Staff member
GSC Moderator
24 Oct 2009
25,390
6
60
Nr. Ashford, Kent. England.
Are all capacitors the same? (other than the obvious rating). What is the temp ? Anything else I need to know before buying the cheap option from China.
 
Slawman

Slawman

Deckline
9 Apr 2018
277
0
Sydney
John S

John S

Registered
5 Nov 2017
489
11
Exeter, Devon, UK
One thing - as the LED goes out it does flicker for about a second - any ideas, do I need a small resistor in circuit. (output 3V driving 3 x 3mm LEDs in parallel.)
That's normal, the cap has discharged and there is insufficient residual voltage left to power the LED, and also it's because your eyes can actually see it, a LED in it is normal state, is flickering on and off continuously at such a rate your eyes and brain can't react that fast, so it looks as if the LED is on all of the time.

I'll edit this later with a link for capacitors.
Edit: Try this.....Start from the second row
https://www.aliexpress.com/w/wholesale-35v-2200uf-capacitor.html?spm=2114.search0104.0.0.3c64342fKgpfG6&initiative_id=AS_20180601114648&site=glo&groupsort=1&SortType=price_asc&g=y&SearchText=35v+2200uf+capacitor
 
Last edited:
stockers

stockers

Trains, aircraft, models, walking, beer, travel
Staff member
GSC Moderator
24 Oct 2009
25,390
6
60
Nr. Ashford, Kent. England.
John S

John S

Registered
5 Nov 2017
489
11
Exeter, Devon, UK
Wot with your new soldering iron, you'll be making DIY Loco Power Buffers next! :)

96925_04ed3d937b1a68e750c910f88bd9940d.png
 
stockers

stockers

Trains, aircraft, models, walking, beer, travel
Staff member
GSC Moderator
24 Oct 2009
25,390
6
60
Nr. Ashford, Kent. England.
Just got supplies (Cap, Volt Reg, Bridge and loads of LEDs) to make 10 units. Under ten quid the lot (except wheels of course!). You should see my old iron John, used on the Titanic!
 
John S

John S

Registered
5 Nov 2017
489
11
Exeter, Devon, UK
Just got supplies (Cap, Volt Reg, Bridge and loads of LEDs) to make 10 units. Under ten quid the lot (except wheels of course!). You should see my old iron John, used on the Titanic!
Alan, you got a good price for the components, now if we could work some magic on the price of the wheelsets, everyone would be onto a winner!

I'm sure your new purchase of a soldering iron will stand you in good stead.
 
  • Like
Reactions: stockers
Greg Elmassian

Greg Elmassian

Registered
8 Mar 2014
2,356
28
San Diego
www.elmassian.com
I cannot see the point of having a constant voltage source followed by a constant current source, you either have one or the other.

According to the specificaton, the minimum voltage across the CL2 is 5 volts, so you are wasting 5 volts at 20mA of power. This solution will therefore be less efficient, reduces the time for the LEDs to dim and costs more than the dc-dc solution recommended above.
I cannot see the point of having a constant voltage source followed by a constant current source, you either have one or the other.

According to the specificaton, the minimum voltage across the CL2 is 5 volts, so you are wasting 5 volts at 20mA of power. This solution will therefore be less efficient, reduces the time for the LEDs to dim and costs more than the dc-dc solution recommended above.
Not sure on how to answer you, because I'm not sure you understood all the parts of my suggestion. There's multiple pieces.

Did you get why higher voltage on the output side? Does not need to be regulated, just why? We can start there if you really want to understand "the point". If you want to argue, let's forget it.

Greg
 
Last edited:
Slawman

Slawman

Deckline
9 Apr 2018
277
0
Sydney
Here's mark 2 - Cheaper AND Smaller.....

 
S

Simon Potter

Srpott40
14 Jun 2016
38
0
Dorset
Here's mark 2 - Cheaper AND Smaller.....

Sorry to raise this topic again, but I am really impressed with this circuit and want to replicate it myself. I have actually spent a few hours this weekend trying to make a circuit just like this (but failed). Would you be willing to list the components used? And if possible provide A circuit diagram. (I assume that this circuit will work for both digital and anaglog layouts?)
 
stockers

stockers

Trains, aircraft, models, walking, beer, travel
Staff member
GSC Moderator
24 Oct 2009
25,390
6
60
Nr. Ashford, Kent. England.
You need 5 things -plus a bit of wire and solder. Also a meter to adjust the voltage regulator (you can get fixed output regulators if that's easier.

1. Pick up wheel set - what ever your chosen variety may be.
2. Some 'warm white' LEDs - I used 3 per coach
3. A bridge rectifier - something like this - KBL406 Rectifier Bridge 4A - 600V, PCB Mount | eBay
4. A capacitor - 25V, 2000 uf will do, 35V, 3000 uf is ample. - 5 pieces 2200uF 25V 105C Radial Electrolytic Capacitor 13*21MM | eBay
5. a voltage control board - MP1584 Adjustable 3A DC-DC Converter Step Down Buck Voltage Regulator UK | eBay
 
  • Like
Reactions: Simon Potter
stockers

stockers

Trains, aircraft, models, walking, beer, travel
Staff member
GSC Moderator
24 Oct 2009
25,390
6
60
Nr. Ashford, Kent. England.
106969_a45ae0bb566bb93ac24a779ccc807d58.png
 
  • Like
Reactions: Simon Potter