Pickup rollers

[Anonymous]

I have a PRR observation car (6-16003) that the lights blink alot. I clean the track and the pickup roller and it works find for awhile and then the lights will start blinking again in a short amount of time. The other cars in the train do not do it. Could the pickup roller on the observation car need to be replaced or is it the fact that it is on the end that makes a difference?

[Big_Boy_4005]

That roller may have a weak pressure spring, causing it to not make good contact with the rail. Is that one with copper spring strip?

[ChiefEagles]

Elliot is probably right. I have a NS caboose that did the same. Finally added some weight [lead weight] to the inside of the frame. Stays on all the time now. Funny, have two others just like it and they work perfect without weight.

[Anonymous]

Yes I believe so.

[lionelsoni]

Apart from the good advice about keeping the roller on the rail, there is a trick that can virtually eliminate flickering: Put a small bridge rectifier between the roller and frame, on the one hand, and the lamp(s) on the other hand. Add an electrolytic capacitor across the lamp. The capacitor will keep the lights on through the interruptions in the track power. This is especially useful with a single roller, which will always encounter gaps at switches and crossings. In fact, I have some MTH heavyweights from which I removed one of two pickups from each car, to reduce the rather large rolling resistance. The capacitor trick more than compensates for the loss of half the rollers.

[Anonymous]

Bob,
Wouldn't happen to have a sketch handy would you?

John

[lionelsoni]

I'm afraid I never did work out a way to post a sketch. I may investigate it again some time. For now, I will try to describe the circuit for you. It's not very complicated:

Get a small bridge rectifier, like the Radio Shack 276-1152, for $1.49:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F006%5F000&product%5Fid=276%2D1152
and a 5000-microfarad electrolytic capacitor, like the Radio Shack 272-1022, two for $5.29:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F004%5F001&product%5Fid=272%2D1022

Disconnect the wires from the car's lamp(s) and reconnect them to the ~ terminals of the bridge rectifier. Connect the lamp(s) to the + and - terminals of the bridge rectifier. Also connect a capacitor to the + and - terminals, being careful to connect the - terminal of the capacitor to the - terminal of the rectifier.

The bridge rectifier's markings may vary. Not all the terminals may be marked. However, the order of the terminals is + ~ - ~ around the circle, so you can figure out any missing symbols.

Postwar cars with metal frames are more of a problem than modern plastic ones, because the lamp socket is often permanently connected to the frame. In a case like that, I usually get a new socket and mount it so that the bulb of the lamp is in about the same place as the original one, leaving the original socket in place but empty.

[dougdagrump]

Can anybody do a schematic for this? It is so much easier to see and understand it with both the wriiten and schematic to work from. [D)] [%-)]

[lionelsoni]

I could create a schematic in "paint" and e-mail it to anyone who would volunteer to post it.

[ChiefEagles]

Bob, I will see what I can do with it. Send it on, you have my address.

[FJ and G]

yeah, the darned track probably needs some cleaning. Too bad I've not got a subway layout. Those NYC subways I rode in the 1960s sure did a lot of blinking as well as rock and rollin.!

[ChiefEagles]

Here it is. Now I think I can read but not sure. Bob might have to explain symbols.


Thanks Bob [Lionelsoni].

[lionelsoni]

The pickup is the circle labeled "PICKUP". The frame (of the truck or the car, or whatever connects to the wheels and outside rails) is the triangular symbol of parallel lines, or "ground" symbol, labeled "FRAME". The diamond-shaped arrangement between them is the bridge rectifier, which is all in one package with four leads. The leads are labeled with symbols something like those at the corners of the diamond. The parallel lines to the right of the ground symbol are the electrolytic capacitor, labeled with its capacitance value of 4700 microfarads and a + to show the polarity. (This is the conventional way of showing it on the schematic; but the actual part usually has only the - terminal labeled. Go figure.) On the right is the incandescent lamp, labeled "LAMP". If there are more than one, they are likely connected in parallel in a modern car or in series in a postwar car.

The exact value of capacitance is not critical. For more or larger lamps, you may need more capacitance. You can parallel capacitors to increase the value. (If you're doing only one car and bought your capacitor at Radio Shack, it looks like you got two anyway.) The voltage rating of the capacitor should be about 25 volts. More is okay, but won't make it work any better.

[ChiefEagles]

Bob is giving us a good course in electronics. Wish we had that folder to store this in.

[Anonymous]

I wired the car per the above sketch and I also had previously installed red LED lights on the back of my observation car. When I wired the capacitor and rect with the red LED lights the train acted like it needed more power to get going. The main thing though was the red led light on the right side of the car would not light. When I took the capacitor and rect out then both LED lights lit.
I must not have something wired right.
Lionelsoni was nice enough to send the answer:
That LED circuit was meant for AC operation; and you are now giving it DC. However, the fix is very easy: Wire the two LEDs in series rather than parallel.
The AC circuit was designed to turn the LEDs on alternately, each one for 1/120 of a second during the half-cycles of the AC waveform. With DC, only one comes on, since the polarity of the voltage never changes.
It is important to have the polarity of the LEDs correct in the DC circuit--Wrong polarity will destroy them. Note which LED comes on. Then disconnect the ballast resistor from both LEDs, but leave the two connected together at the node where the ballast resistor used to be. Then disconnect the LED that wasn't coming on from ground and reconnect that lead to the ballast resistor. This should leave both LEDs in series with the cathode of the formerly-lit LED grounded, the anode of the formerly-lit LED connected to the cathode of the formerly-unlit LED, and the anode of the formerly-unlit LED connected to the ballast resistor.

[Anonymous]

Lionelsoni,
Is this the correct way to eliminate the lights from blinking on my passenger cars?
Radio Shack capacitor (272-1022) positive lead to the positive leads of the lamps and the
capacitor negative lead to the negative leads of the lamps. The positive and negative leads
of the lamps (and capacitor) to connect to the positive and negative leads of a Radio
Shack bridge rectifier (276-1152). The leads from the trucks (mine were yellow) are to
connect to the ~ of the rectifer.
Thanks John.

Answer From Lionelsoni:
Yes. Remember that you may need to add another capacitor, depending on how much current your lamps draw and how long the track interruptions are. But try it first with one and see how it does.

If you're working with a modern car, you will have no trouble. But postwar and earlier cars often had the lamp socket connected permanently to the car frame. If so, you have to replace the original socket with one that has an insulated connection for the shell of the lamp. I leave the original socket in place and try to locate the new socket at right angles to it, so that the bulb is in about the same place as before. Postwar 2400-series cars have two lower-voltage lamps in series, only one of which is connected to the frame.

[Anonymous]

You can add a second pick up to the other truck as many lighted passenger cars have two for this reason. Also you can run a wire from the car before the observation car light and borrow the pick up from that car. This will help both cars.


Charlie

[lionelsoni]

A second pickup can't hurt. But, as I mentioned above, it becomes far less important when you have the rectifier-capacitor modification. Then, about the only difference with the second pickup is to make it more likely that the lights will stay on when the train is stopped with voltage on the track.