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Aristo passenger car conversion to DCC

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CliffyJ

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Discussion starter · #1 ·
I have some Aristo passenger cars, each with 6 incandescent bulbs, ~12v type. When I was using DC, I switched the bulbs to 28v, to shine less brightly and make the bulbs last longer.

Specifically, the bulbs are 28v, .04A, made by Eiko: http://1000bulbs.com/product/8322/I...4Aodh24A0w

The lights seem to run fine on DCC, but these 28v bulbs are now seeing ~21v, correct? So they're pretty bright again, and I'd like to knock that down. I should have put out an alert that I'm electronically challenged, but most of you know that already. Anyway, a single diode across either feed to the car gets the brightness down, I'm guessing because it's chopping out half the DCC's power. And is that all I need to do for incandescents? I've got plenty of these 3A diodes, and would rather not use bridge rectifiers, nor do I see a reason to convert to DC. Please correct me if/where I'm wrong!

BTW these Aristo cars are tough to rewire (the circuit board is sandwiched between the floor and the undercarraige), but there seems to be an opportunity to add diodes in each truck, at the pickup. I tried to find a thread on the topic, no joy. Any links to share on this?

Thanks,
===>Cliffy
 
#2 ·
Cliff, I am more electronically challenged, you have added DCC. Couldn't you use a resister rather than a diode in the circuit? They have the advantage of allowing current to go in both directions as apposed to one way. No bridge rectifier needed. Chuck
 
#3 ·
since incandescent bulbs run on voltage, not current like leds, you want to drop the voltage.

Diodes would work, but you would be getting 1/2 wave DC... try this circuit: (the one on the right... a full wave bridge with one or more diodes in the middle... you can construct this whole thing from individual diodes)

see my page: http://elmassian.com/tra...trong>


Image
 
#4 ·
Greg, in his original post Cliff mentioned adding a diode to the wiring on each truck. Couldn't a small resistor be added to one of the wires in each truck, from the same side, and reduce the voltage, without building a diode bridge? I use a 10 ohm resistor a couple of feet in front of the diode I use to,stop my train on a point to point track. Rather than have the train come to a sudden stop it slows down by about half before it stops. It is visually a little less jarring. A resistor in a wire coming from each truck should have the same effect on the bulbs. Chuck
 
#5 ·
Yes, but it would not work as well.... diodes have a constant voltage drop irrespective of current.

Resistors vary and he would have to measure the current of the lights at the desired voltage and then calculate the appropriate resistor, and also double check the wattage.

Again, incandescents are really "controlled" by voltage, so you want a voltage dropper that works irrespective of load.

If these were LEDs, then the recommendation would be resistors.

Also, variations in voltage on the rails would have a greater effect on the lamps using resistors, while diodes will, again provide a constant and consistent voltage drop.

The output of a lamp is nonlinear, light vs. voltage, so you really want to control voltage, current will not be an indicator of brightness...

Regards, Greg
 
#7 ·
The answer to the question is yes... but when I do electronics, I try to make them operate in different environments, different track voltage, etc.

Only DCC systems that supply a regulated output have really constant voltage.

But the question is more of how easy it would be to drop the voltage... In this case it's even easier since Cliff has lots of the building blocks, diodes.

In the circuit I have shown, the lights will work on DC and DCC and just adding or subtracting diodes from the center "chain" makes for easy fine tuning.

With resistors you will have to calculate and find the right resistor...

Greg
 
#8 ·
Even though DCC supplies a constant voltage to the track, my system has a voltage control adjustment and my track voltage can be set from 14 volts (think HO here or even N scale) to over 24 volts (I could use 28 VAC input, but I have 25.2).

The other method would have been a bridge rectifier and a LM338 regulator set to 20 volts for the 28 volt bulbs.

Myself, I would have rewired the 12 volt bulbs in series for 2 at 24 volts and use a regulator to lower the voltage or use leds in series and then just use 1 resistor. Both of these methods need the bridge rectifier, and a capacitor would help the leds on intermittent track power contact.
 
Discussion starter · #9 ·
Thanks Chuck and Greg, you've given me more to think about.

Greg, for the record, this was one of those times I DID go to your site before posting here. So thanks for that link... I missed it!

Not that you guys need it, but here's the area of my interest:

Image


The black deck won't pull off, because it, the trucks, the body (with floor, walls, lights) and circuit board all all hard-wired together, with no service loops.

These pickups are on each truck, and the (hidden) board is already doing the distribution. That's why it would be nice to do something simple, small and cheap to both trucks; and I have 6 cars.

Greg, I've yet to get a really-bulk pack of diodes, but I do have at least 12 rectifier-type @3A, and about 90 non-rectifier-type @1A. Would the latter work for a home made rectifier? (I should just so see...)

Anyway, if this is going to work on DC and DCC, I see why the bridge rectifier. On DC, a single diode would cut the lights, depending on direction of train; and a resistor would not have the desired effect, with variable DC.

So, two ways to go:

If I never run on DC, or sell these cars to anyone, what's the simplest mod here? 1 diode, half-wave DC? Is there a down-side in reliability, heat buildup, or...?

Or, if DC/DCC op is best (and I get it), can I get away with a 4-diode rectifier? Do I have to have the 4 across the middle... oh, wait, that's how you're tuning the voltage drop. Huh...

Well, to get the same effect as chopping the wave in half, I suppose I'd need to drop from 21v to 12v, which (at .7v / diode) means ~13 diodes, plus 2 more for the bridge... x 2 trucks, x 6 cars... 180 diodes... mebbe that's not the best approach either.

To recap the problem: voltage reduction to all those bulbs, to reduce draw, increase life, and get brightness down to something believable. With DC (0-18vdc), swapping out my 14v bulbs for 28v did that. Now, at 21v, should regulated to DC, and somehow whack the volts down. Or chop the wave in half, and go DCC-only.

Huh... sorry, my mind just boggled, need to re-set...

But thanks for helping me think this through guys!

===>Cliffy
 
Discussion starter · #10 ·
There's a lighting switch on the underside, it would be nice if it were for DC vs. DCC op... Well, it's just on/off. A DPDT could be used to go either straight from rails (DC), or with a diode between (DCC). Big hassle to install that though.

Back to Chuck's resistor idea for a moment, I was just messing with the calcs:

Bulbs 6 6 6 Amps (ea) 0.04 0.04 0.04 Amps (total) (I) 0.24 0.24 0.24 Input volts 21 21 12 Bulb max volts 28 28 28 Desired op volts 40% 42% 9% Desired op volts 11.2 11.64 2.64 Voltage drop (V) 9.8 9.36 9.36 Ohms (R = V / I) 41 39 39 Watts (W = V * A) 2.7 2.2 0.6

The power would be coming coming through 2 trucks, i.e., 2 resistors; so maybe a 39 ohm / 2 watt resistor at each truck might work?

So when put on DC track, say, at 12VDC (column 3), the bulbs would be a lot dimmer (9% of bulb max). But, they'd come on. Of course, they'd vary w/ track voltage, but they already do that.

Still, I have those 3A diodes...

===>Cliffy
 
#11 ·
you want a bunch of 1 amp diodes, 1n4001 or above.

radio shack has a 25 pack of assorted ones, $3.50, that's 14 cents each.... clearly less than 2 watt resistors.

so you can afford the circuit that works all the time in all environments.. I would not mess with half wave vs. full wave...

Also you need to test the bulbs and see what voltage gives you the desired brightness... 40% voltage will not give 40% light.

Greg
 
Discussion starter · #12 ·
Posted By Dan Pierce on 01 Sep 2013 05:29 AM
Even though DCC supplies a constant voltage to the track, my system has a voltage control adjustment and my track voltage can be set from 14 volts (think HO here or even N scale) to over 24 volts (I could use 28 VAC input, but I have 25.2).

The other method would have been a bridge rectifier and a LM338 regulator set to 20 volts for the 28 volt bulbs.

Myself, I would have rewired the 12 volt bulbs in series for 2 at 24 volts and use a regulator to lower the voltage or use leds in series and then just use 1 resistor. Both of these methods need the bridge rectifier, and a capacitor would help the leds on intermittent track power contact.
Thanks for your ideas Dan.

My original move from 14v bulbs (I'd said earlier 12v, I think they were 14 now) to 28v didn't require rewire, and the bulbs were cheap. But point taken, I should just do it right at some point.
 
Discussion starter · #13 ·
Posted By Greg Elmassian on 01 Sep 2013 08:55 AM
you want a bunch of 1 amp diodes, 1n4001 or above.

radio shack has a 25 pack of assorted ones, $3.50, that's 14 cents each.... clearly less than 2 watt resistors.

so you can afford the circuit that works all the time in all environments.. I would not mess with half wave vs. full wave...

Also you need to test the bulbs and see what voltage gives you the desired brightness... 40% voltage will not give 40% light.

Greg Those 80 or 90 1A diodes I have are 1N4007 I believe. What's the significance of the last digit?

Right on about the 40% thing, as I discovered a couple hours ago. Here's a very rough comparison, the only quick one I could think of.

Setup 1: 28v bulbs on the 21v DCC rails, no diodes or anything: 75%.
Setup 2: stock 14v bulbs on full DC power (for my MRC throttle, 18v): 125%.

#1 was a LOT dimmer, maybe 1/4 the brightness of #2 if that.

So maybe I'm not too far off, like dropping the 21v to ~18.

Anyway, this is sounding like I need to dig into the buried board, and modify it:
- preserve 2-truck pickup
- rectify downstream of the dual pickup combining
- add dropping diodes a/r
- add capacitance for flicker reduction (more research needed...)
- add JST jacks to get the undercarriage off in the future
- maybe re-introduce smoke stack capability (I've just got them switched off for now), for that once-in-a-while photo op...

At the moment, I think I'm safe in running the cars on the layout without mod's. Which I just did for the first time, a half hour ago, woo hoo! But what what I've seen so far, the above mod's seem reasonable. I'm sure someone's done it already though...


Thanks again Greg,
===>Cliffy
 
#14 ·
The last digit of the 400x and 540z is a voltage rating
1=50v
2=100v
3=200v
7=1000v.

his is the reverse v rating.
If you use a diode to charge a capacitor on A/C, you need to figure out the total voltage taht could be across a diode feed ing the cap.
Lets take a 24 volt transformer as an example.
To start, many transformers are 25.2 volts, not 24 volts A/C.
Peak waveform is 25.2 times the square root of 2 (1.414) which is ......35.6328.
This means in theory a capacitor can be charged to 35.6 volts (of course there is a small voltage drop across the diode.
Now look at the opposite cycle where the input AA/C goes to negative 36.628 volts and you now have 72.2 volts across the diode and if it is a 1N4001, you have greately exceeded its 50 volt rating!!!!!!

So, in large scale 100 volt rated diodes are a must and I prefer a much higher rating as the power line can have spikes and these power spikes could make the transformer output exceed even the 100 volt rated diodes.

Your 1N4007 is a great choice with 1000 piv rating (Peak Inverse Voltage which is what my rant is addressing).
 
Discussion starter · #16 ·
I ran the train some last night, my first night run.

I still think the bulbs might be too bright, but maybe I was too hasty. The problem is that the yellow plastic castings of the car bodies light up like a lampshade. The 28v bulbs definitely help, but it still looks weird.

So I need to paint the interiors. After that, maybe 21v DCC is OK. But for bulb life, maybe bringing it down 2 or 3 volts is still a good idea.

The main issue learned from last night is the flickering; it's far worse than I'd imagined. So if I fix anything, it needs to include that. Here's a stinky video:





There's many continuity and cleanliness issues (wheels and track), so I'll focus on those. But if anyone can think of the simplest constant voltage circuit, without changing to LED, I'm all ears.

BTW, there is an LED replacement bulb for the tiny E5 bulb sockets, but they cost about $11 each -- gulp!

Thanks,
===>Cliffy
 
#17 ·
Flickering is a fact of life with track powered car lights. I think that some have build a capacitor circuit that stops the flicker. The other option which a number of people have done is to go to battery with bulbs or LEDs.


Chuck
 
#18 ·
Please keep in mind when Dan mentions AC, he really means sinusoidal AC like you find in your house.

DCC is AC also, but a square wave, not a sinusoidal one, so the calculations he shows (multiplying by the square root of 2) have NO application to DCC...

24 volts DCC is 24 volts DC when rectified by a full wave bridge.

1000 volts is way overkill for a 24 volt situation, won't hurt but way overkill.

Greg
 
Discussion starter · #19 ·
Greg, I'm reading your write-up under "Add a capacitor for uninterrupted power"
http://elmassian.com/trains/dcc-battery-rc-electronics/misc-electronics

Are there only the rectifier, cap, and resistor involved? If so, it sounds like four 1N4007's would work (got plenty), a couple more for V-drop. Or maybe the resistor is instead, and maybe I have those. That leaves the cap.

Because of size constraints, can I use 2 or more caps of lesser value, and are their mfd's additive?

True, the flickering isn't nearly as bad, now that I've cleaned all the rails this morning. So I might not take on this modification right now. But still, it's nice to become familiarized with the factors for later on.

Thanks,
===>Cliffy
 
#20 ·
That's kind of an old part of my site.

Actually I would use a negative coefficient thermistor, which basically would be low resistance to run the leds, and high resistance when charging from cold, or I would use the time honored method of a diode to feed the leds and a resistor for the inrush.

The thermistor is probably the simplest and most elegant solution...

If you look at the capacitor bank that Aristo sells, there's a thermistor on it.

Greg
 
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