LION is thinking about constant lighting (again)

[BroadwayLion]

The LION is thinking (always a bad sign) about constant lighting in his subway trains. Subway trains with all of their starts and stops really does need conatant lighting.

PLAN of LION features two (maybe four) 4.7 Farad capacitors at 2.5 volts.

Lion plans to wire pairs in series (5 volts at 2.3 Farad) for the lighting bus of him.

As is well known Layout of LION operates on 10.2 volts, and so him thinks of using a 5 volt regulator to provide current for the lighting bus.

But maybe that is too much of a voltage drop for one regulator, Mayhap it would get too hot or maybe would fail.

Components in order of operation are (or could be)

1) Full Wave Rectifyer to convert track power to known DC power

2) Power Regulator

3) two caps in series across the regulator output

4) Six 3 LED strips across the regulator output (one in each car)

3B) and adittional two caps in series across the output if more lighting time is requyired.

NOW the question in my head (or maybe hanging from my tail)  is maybe I ought to put a resistor ahead of the power regulator to eat up some of that voltage so the regulator does not have to do so musch work.

OR maybe I can eliminat the regulator and just use resistors for the voltage drop to the capacitors. (Me thinks the Regulator would be more reliable.)

10.2 volts is track  power. What does the full wave rectfier do to my voltage? Remember it is a DC input to the rectifier, so only one half of it would be working at a time.

We sort of know how much current we want to light 18 LEDs, they should be able to work at 4 volts just fine. What resistors would my LED system need, would it need any resistors if I am using a pre-built 3 LED strip. Will that strip work at 4 or 5 volts or does it really want 12 volts (10.2 volts) to work.

Math Majors (or DrumMajors) are invited to enlighten the LION since him not knwo much about numbers but can usually follow directions.

 

Thanks and ROAR

 

[gregc]

BroadwayLion

PLAN of LION features two (maybe four) 4.7 Farad capacitors at 2.5 volts.

Lion plans to wire pairs in series (5 volts at 2.3 Farad) for the lighting bus of him.

As is well known Layout of LION operates on 10.2 volts, and so him thinks of using a 5 volt regulator to provide current for the lighting bus.

But maybe that is too much of a voltage drop for one regulator, Mayhap it would get too hot or maybe would fail.

I think you're proposing a 5v charging circuit for the the two supercaps in series rated at 4.6V.

Normally there is a rectifier, a filter cap (1000uF) and the regulator.    A 5V regulator would waste a lot of power (assuming 1ma current, 10.2 - 5 V would be across the regulator, therefore 5.1 mW of heat.   Proportional to current).

But eventually the regulator voltage would exceed the 4.6V rating of the caps, and that wouldn't be good.   An LM317 regulator is adjustable and could be set to 4.6V volts.

there should be a resistor to limit the inrush current into the caps when the caps are drained.   When completely drained, a 1k resistor would limit the current to 4.6ma assuming a 4.6V regulator and less current as the cap voltage rises.

 

BroadwayLion

Components in order of operation are (or could be)

1) Full Wave Rectifyer to convert track power to known DC power

2) Power Regulator

3) two caps in series across the regulator output

4) Six 3 LED strips across the regulator output (one in each car)

3B) and adittional two caps in series across the output if more lighting time is requyired.

NOW the question in my head (or maybe hanging from my tail)  is maybe I ought to put a resistor ahead of the power regulator to eat up some of that voltage so the regulator does not have to do so musch work.

OR maybe I can eliminat the regulator and just use resistors for the voltage drop to the capacitors. (Me thinks the Regulator would be more reliable.)

either the regulator or a resistor would waste heat.

I think you need to be careful not to exceed the capacitor(s) voltage rating.   Otherwise they pop!

 

BroadwayLion

10.2 volts is track  power. What does the full wave rectfier do to my voltage? Remember it is a DC input to the rectifier, so only one half of it would be working at a time.

We sort of know how much current we want to light 18 LEDs, they should be able to work at 4 volts just fine. What resistors would my LED system need, would it need any resistors if I am using a pre-built 3 LED strip. Will that strip work at 4 or 5 volts or does it really want 12 volts (10.2 volts) to work.

the 4.6V capacitor voltage is the limiting factor.  

You could put four 4.7F 2.3V supercaps in series, but while the series voltage would be 9.2V and still require something to limit the input to that, the capacitance would only be 1.1F

 

Since HO passenger cars are spacious, maybe two 4.8V AAA ni-cad batteries (9.6 V series) would be a option.   Rectifier and resistor may be enough for charging.  Maybe not -- eight 1.2V batteries may be too much.

not sure what the LED voltage rating is, but i would wire as many as possible in series, that can operate at up to 4.6V or 9.6V and put a resistor in series to limit the current.

if the caps are used, the brightness would diminish as the cap voltage decreases, or they would go dark when the cap voltage is less than the minimum voltage.

 

others can check my math.

 

[BroadwayLion]

gregc

I think you're proposing a 5v charging circuit for the the two supercaps in series rated at 4.6V.

I *thought* I was proposing a 5v charging circuit for the two supercaps which are rated at 2.5 volts each. In old math that would = 5 volts, which may be cutting it rather fine. Are are there gremlins that I have not met yet.

 

ROAR

[gregc]

sorry, i misread the following sentence and mistook 2.3F as 2.3V.

So a standard 5V regulator with an inrush resistor between the regulator and supercaps.   The value would be 5V over the current of the regulator (7805 1.5A).   say 1A, 5 ohm, but probably a 1 or 2 W resisitor.  Or 100ma, 50 ohm, 1/5 W.

[RR_Mel]

I’m a retired techno weenie so I always go overboard on things like constant lighting.  I’ve used several far out circuits for lighting over the years.  Check out my recent lighting project on my blog.  It maybe far out but it works great for me.

http://melvineperry.blogspot.com/2015/02/february-22-2015-passender-car-lighting.html

The battery will carry my lights for an hour easily and the battery recharges fast enough that it has never been low enough to effect the lighting.

Mel

[gregc]

RR_Mel's approach using a single battery and grain of wheat bulbs is pretty simple.    I assume a rectifier and resistor is enough of a charging circuit.  The drawback is that the LEDs i'm familiar with require ~1.4V and I think more modern LEDs need 3-4V.

What about using a 9V rechargable battery and similar charging circuit?

an advantage of using a battery over caps is that the voltage will remain fairly constant.   a couple of LEDs and a resistor can be in series across the battery.   Several strings can be made, all in parallel.  This would probably be less complicated and more efficient than using a caps and regulator at a lower voltage.

[RR_Mel]

Greg is correct about using LEDs, the reason I went with 1.4 volt incandescent GOW bulbs is because that’s what I used many years ago and they were already installed in my passenger cars.  If I was starting over I would go the LED route and use a 3.7 volt 500ma Lithium battery instead of a capacitor.  Warm white LEDS operate between 3.2 and 3.6 volts and draw very little current.  A 100 Ω ⅛ watt resistor in series with the LED would limit the current to 10ma with the battery at full charge (4 volts).  A 80 to 100 Ω 1 watt resistor should keep the battery charged from the rails (assuming 12 volt rail power).

There is a drawback using batteries, turning them on and off, thus advantage of a large capacity capacitor.  I have two powered sidings for keeping the batteries charged.  I also went to a DCC function out to operate a relay to turn on and off the lights (that impresses visitors too).  If you use a micro DIP relay powered from rail power to drop the LEDs with the power off the battery won’t discharge.

Mel

 

[gregc]

LEDs may provide an automatic shut off once the battery voltage is less than the combined forward voltage of the LEDs.   In other words, the LED current is zero when the battery voltage is <= 7.4V (assuming two 3.7V LEDs in series).   This means the battery may not fully discharge when not in used.   adding a regular diode in series would raise this to 8.1V, preventing the batteries from discharging further.

[RR_Mel]

Unless you mix and match LEDs you might have a problem using them in series.  Different manufacturers LEDs draw different current.  I toss like LEDs in like bins in my parts drawers.  Spending time dinking around balancing current is not my thing, some are close and others are in left field.

 

White LEDs draw some current until the supply voltage drops below 2.5 volts.  If several paralleled LEDs are connected continuously over time the battery will become discharged with out some charge current.  Most 9 volt NiMH rechargeable batteries are static at 8.75 volts or 1.25 volts per cell (7 cells).   During discharge, lower than 1.0–1.1 volts per cell may cause permanent damage of multi-cell packs, due to polarity reversal of discharged cells.  Most manufacturers use a battery cutoff circuit in their equipment to prevent the voltage from dropping below 1.0 volt per cell.

 

If you operate your NiMH battery operated LED illuminated units several times weekly you shouldn’t have any problems. My problem was I would forget that I set a few cars on my display shelf and dinged several batteries.  I installed switches under the cars and that was a pain in the neck.  I also tried latching reed switches under the roof and they just aren’t reliable.  Battery powered lights sound like a good idea but they can also be a real problem.

 

Regulators are neat and work great but some times with space at a premium there isn’t enough room for them.  I use LM317 1.4 volt regulars in all my Cab Forwards for headlights and markers, I use warm white LEDs for number boards.  I gave warm white LED a shot for headlights but there’s nothing that will come close to a incandescent headlight in a Cab Forward.

 

Mel