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

stockers

stockers

Trains, aircraft, models, walking, beer, travel
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I am thinking of using a single set of pick up wheels (because they are expensive) to run some carriage lights - LEDs. If I add a capacitor it could run the lights whilst the wheels are not picking up for any reason.
It cant be that simple, can it?
I assume I need some form of voltage limiter feeding from the capacitor to the LEDs, and what about over supply to the capacitor.
Can anyone come up with a seriously simple design - a bit crude is OK - its only a few LEDs after all.
 
stockers

stockers

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Thanks - parts ordered on ebay. Multiple quantities will be cheaper - i just spent about £6 to make one.
 
Slawman

Slawman

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9 Apr 2018
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I am doing that now by just putting a capacitor (whatever size you need depending on your lights) across the output terminals of your regulator. You don't even need to solder it if your converter has screw terminals already. ie:

https://www.ebay.com.au/itm/LM7812-DC-AC-Three-terminal-Voltage-Regulator-Module-15V-24V-to-12V-1-2A/183164014089?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Plus 1000uF cap:

https://www.ebay.com.au/itm/5-x-25V-1000UF-105C-Radial-Electrolytic-Capacitor-10x20mm-G5M2/183032835297?epid=1969065735&hash=item2a9d9b6ce1:g:tzwAAOSwn9VaZwUU

Equals flicker free lighting.

This wont hold the lighting up for any period of time, just enough time to stop them dropping as the carriage makes intermittent electrical contact while moving along your track.
 
PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
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Hi John,
Value, and source of 'Super-Caps' please?

TIA,
PhilP.
 
Slawman

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John S

John S

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I would recommend a 25v if you are connecting from the trackside
These are two different and separate approaches, Super Cap is fitted after the Voltage Regulator which is tweaked to limit the voltage to 5V.

SMD Cap as shown in post#2 is rated at 35V, 25V as suggested is far to close for comfort to be safely used, MTSIII Central Stations have been known to peak at 27V, NMRA standards make the observation that for G Scale, that 27V is max allowable.

25V Caps could well result in a big bang!
 
Slawman

Slawman

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I agree it is worth clarifying which side you are planning on attaching. I am using 25v now with no problem. My system peaks at 22v.

Do you recommend attaching the Cap to the output side?
 
stockers

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I like the board with rectifier built in. using 35V cap here.
 
John S

John S

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Standard Cap....
Track input to Bridge Rectifier, then Cap, then voltage regulator.

Super Cap, Track input to Bridge Rectifier, then voltage regulator, then Super Cap, remember to fix voltage output to 5V!

Inherent problem with the board as mentioned in post#4 is heat dissipation due to it being a linear device.

For example, Massoth track voltage input to a bridge rectifier is somewhere around 22.5V, 5V linear voltage device only requires a minimum of 7.5V to work efficiently, the 15V left over has to go somewhere, as in heat!
And that's a hell of a lot of heat to disperse.

Here's a neat trick, give the voltage regulator a few minutes to warm up, then grab it with your fingers!
More or less guaranteed 3rd degree burns, maybe even 2nd degree burns, how do I know? Don't even ask!

Far better to use a dc to dc converter, about 96% of voltage is used, only around 4% is dispersed as heat, means the whole shebang can be accommodated in a much smaller area, and less likelihood of heat damage to the surrounding area.

I'll knock up some examples of what I've installed, and post some pictures to give some ideas on how it all fits together.
 
stockers

stockers

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Thanks for that John.
 
John S

John S

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96294_1018c30872892923d1ddb6872dfcef65.png

Example's, with different Bridge Rectifiers and DC to DC converters.

96295_3533a3bea1d5ded3b9dab316c6409059.png

Simple coach lighting, under the blob of glue is the four pin bridge rectifier, AC/DCC in from the Brown/White wires, positive and negative legs from the bridge rectifier soldered directly to the DC to DC converter, twiddle the silver pot for the output voltage (4.5V), red and black wires, positive and negative to the Warm White Led's, can add the capacitor if required as mentioned in the link in post#2, no excessive heat, no fancy circuitry involved, not even a resistor is needed for the led's, and that's all there is to it, it is really that simple...……...
 
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stockers

stockers

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That is exactly what I was on about - simples.
Thanks.
 
John S

John S

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Based on the "simples" principle, this is the new PCB for the 2-8-0 I'm repairing, the one with the dodgy non existent electrics.

This replacement board is for powering the warm white front headlight, and the flickering led's in the firebox.

96670_4937b4ba7377b7768471e99d160d46ab.png
 
Slawman

Slawman

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9 Apr 2018
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That looks a neat unit John. How are your terminal blocks mounted? I can only find ones you must solder into the board. What size cap is that?
 
John S

John S

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Cap is a 35V 2200 low profile SMD, 2 Screw terminal connectors are soldered to the PCB, they do make for a better electrical connection.

Prior to these, have used "choc blocks" suitably cut up and either screwed or bolted down on to a piece of plastic card etc, for example the whole thing could have be assembled as in the "dead bug" way, i.e., just solder the components together without using a PCB, as in post#13.
 
Bill Barnwell

Bill Barnwell

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Ormond Beach, Fl
I am thinking of using a single set of pick up wheels (because they are expensive) to run some carriage lights - LEDs. If I add a capacitor it could run the lights whilst the wheels are not picking up for any reason.
It cant be that simple, can it?
I assume I need some form of voltage limiter feeding from the capacitor to the LEDs, and what about over supply to the capacitor.
Can anyone come up with a seriously simple design - a bit crude is OK - its only a few LEDs after all.
Well I would like to recommend battery powered LED's. I used 10mm soft white , was able to mount them in the factory location , hid the batteries(2AAA) and RC car switch in the clearstory. Used stained glass copper foil tape to make connections so that there were no wires hanging down. Accidently left on for 3 weeks and were still lit when found.
No flicker and stay lit when in station, Bill
 
stockers

stockers

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Thanks Bill but I dont want the hassle of batteries. I have several coaches already running with bulbs but am sorting out a simple way of using LEDs with minimal pick ups. With over twenty coaches, the recharging would drive me nuts. Have loads of power in the rails already.
Stick coach on rail - lights work, 'Simples' as the meercat would say.
 
stockers

stockers

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Well, it works. My strip of LEDs has an inbuilt resistor to be fed at 12 V. At this output the capacitor lasts about a second - not really long enough. The advice above indicates using bare LEDs at 3V which should result in a much longer supply from the cap. I need to go collect my plain LEDs which are at the Kent &East Sussex Railways model railway.