The rheostat is connected in series with one of the track leads, usually the center rail, the #1 post on the lockon.
Here is an end view of a Lionel rheostat with the two connection binding posts:
One goes to the transformer, one to the lockon.
Rob
Hi, Bob... I recently bought a Lionel 81 rheostat and I am not quite clear about how to make sure it is in working order. I don't quite understand how the terminals work. What I am seeing is that the coil of wire that goes around the ceramic core is connected to the back right terminal, and the switch is on the connector that slides along the two bars with its wiper on the coil. I get how it changes the resistance. On what seems to be a terminal on the right front is missing the finger nut, which is no big deal I can use two nuts to hold the wire, It appears to be the second terminal or the third if it can be used as a potentiometer but is not connected by any wire to the coil or the switch. It does touch the metal housing which also touches the two rods...is anything missing?
I would really appreciate any reply at all, thanks. I am intending to use this with batteries.
Thanks, Katie
Actually, they are wound on a ceramic form; but the end of the wire from the winding to the terminal is insulated with a little asbestos. They're nothing compared to the 107 and 170 reducers, which had about a square foot of asbestos covering the entire assembly.
Bob Nelson
I just measured a bunch of Lionel rheostats. The 81 and 88 are 4 ohms; and the 95 is 5 ohms.
I also tried putting one in series with a 2037 pulling 2 postwar and 2 modern cars. The locomotive runs reasonably fast with about 10 volts on the track. Switching in a number 95 rheostat set about halfway (2.5 ohms) drops the voltage to about 5 volts and stops the train but keeps the e-unit from cycling. Five volts across the 2.5 ohms of the rheostat means that the e-unit is drawing 2 amperes. This corresponds to a conventional rheostat rating of 2 amperes squared times 5 ohms, or 20 watts.
So it looks like any of the Lionel rheostats might do the job if your locomotive is anything like a 2037. If you're looking at other rheostats, I would suggest 5 ohms with a power rating of at least 20 watts. I got 27 hits on E-bay with: rheostat "5 ohm" , mostly with power ratings over 20 watts. However, Lionel rheostats are cheaper, about $5 at a train show.
Yes, it's the No. 132 station. I don't yet have a rheostat so I can't try out what you're suggesting. I've been looking around for a No. 95 Lionel rheostat for a while but haven't had much luck without spending more than I want. So I decided to query the forum to see if what I want to do with it is even reasonable. It seems that it is and I now have several good ideas from you when I do get one.
I'm not wedded to the Lionel version which is why I followed up on your earlier comments about the specs for a rheostat. Given that, what rheostat specs should I look for in a local geek shop here in the Bay Area or even at a "real" store? I would appreciate your thoughts on this, especially since you now know what I want it for.
Thank you,
Nino Yannoni
It seems that you are using the 132 station. If so, the rheostat goes between Fahnestock-clip terminals 1 and 3, which is the same as between the unisolated center rail and the isolated center rail, or between any other pair of points connected to those two.
It is possible that, depending on the locomotive and the track voltage that you're using, there will not be enough voltage across the nichrome wire to heat the bimetallic strip enough ever to close the contact. If this should turn out to be the case, there are ways to rewire the 132 to fix the problem, if you're willing to modify it.
Another possibility is that enough track voltage to keep the e-unit from cycling is also enough to keep the locomotive's motor running. The simplest fix for this is a heavier train; but there are also modifications that you can make to the locomotive.
Hello Tom:
Thanks for your help.
The Lionel engineers of that era were clever guys. This is how the passenger station works: the locomotive connects an isolated block in front of the station to track power. Current then flows through a high-R (65 ohms) nichrome wire. The resulting current drop causes the locomotive to stop. The nichrome wire is wound on a bimettalic strip which bends until it makes contact putting a low-R metal strip in the circuit. The train then gets enough current to move but it will move only if the reversing mechanism has not dropped into the neutral position. The reversing unit requires at least 4 - 5 volts or the unit will drop into the neutral position. So maybe the best bet is to put the rheostat in parallel with the resistance structure in the station and tweak the rheostat until the voltage does not drop below 4 - 5 volts but is still less than the voltage required to move the locomotive.
Does this sound like a good idea?
Nino
The Lionel engineers of that era were clever guys. This is how the passenger station works: the locomotive connects an isolated block in front of the station to track power. Current then flows through a high-R (65 ohms) nichrome wire. The resulting current drop causes the locomotive to stop. The nichrome wire is wound on a bimettalic strip which bends until it makes contact putting a low-R metal strip in the circuit. The train then gets enough current to move but it will move only if the reversing mechanism has not dropped into the neutral position.
The reversing mechanism requires at least 4 - 5 volts or the unit will drop into the neutral position. It sounds like you are suggesting that I put the rheostat in parallel with the resistance structure in the station and tweak the rheostat until the voltage does not drop below 4 - 5 volts but is still less than the voltage required to move the locomotive.
Does this sound right?
It may very well be true that the rheostat gives very fine control of resistance. The problem is that, in this low-speed application, that translates into fine control of current and therefore of torque. You will have little control of voltage or speed.
I am guessing that a wire that normally goes from the transformer to the center rail is connected as well to a terminal of the station. Call this point A. Another terminal of the station is connected to an isolated center rail in front of the station. Call this point B. The station connects A to B internally when the train is not supposed to stop and disconnects A from B when it is supposed to stop. If you connect the two terminals of your rheostat to A and B, that will provide a path for a little current to get around whatever is disconnecting A from B, so that the disconnection will not be complete and, with any luck, the e-unit will not cycle.
It is certainly true that a resistance that will do the job for one locomotive and train may well not work for another locomotive and train. This is why you may find it necessary to use a couple of rheostats (or more) in series, to keep a light modern train stopped.
Perhaps I can be of assistance. First, a disclaimer-I am an American Flyer operator but the same principles apply to Lionel. Gilbert made a 755A Talking station that has a fixed resistor to limit the current draw below that required for the motor to run but high enough to keep the. Reversing unit from cycling. The resistor is only in the circuit when the train is stopped at the station. Replacing this resistor with a rheostat will allow finer control of the current. The original resistor is sized based on the current characteristics of the postwar open frame motors.
When a modern production engine is operated the low current passed is high enough that the engine just keeps running. I can tell you based on both theory and personal experience there is no single value of series resistance that will both keep a post war reversing unit from cycling and stop a modern production engine.
If that is your objective then a more elaborate solid state control device is required.
Tom
Bob: Thanks for your note. Your grasp of electromechanics is light-years ahead of me.
I do think I read somewhere that the voltage control using a rheostat following a transformer would be finer than the transformer alone and hopefully sufficiently fine that I might be able to stop the train more precisely, e.g. on a remote control track. Even though I am not able to thoroughly understand your analysis, it sounds to me like you feel it might not work, not that it won't work.
About your idea on the passenger station: are you suggesting that I use a rheostat connected to a source additional to the transformer to provide enough voltage to prevent the reversing mechanism from dropping into neutral? Even though your description of the circuitry is accurate, you say connect a rheostat "around" that switch but I do not see where the rheostat would go.
For switching, I suspect that a rheostat would not work as well as a variable transformer output. The rheostat under those conditions acts as a nearly-constant current source. Thus it keeps the motor torque almost constant, independent of the motor speed. At low speeds, the motor is likely to stall with any slight increase in load. Once stopped, its static friction is greater than the kinetic friction that it was able to overcome while moving; so it stays stopped until you increase the torque by increasing the current. Then, when it starts again, the friction dropps to the kinetic value; and the motor overspeeds.
The constant voltage from a variable transformer, on the other hand, causes the current and the torque to increase substantially when the motor encounters that slight increase in load, tending to keep it moving. You just need finer resolution on the variable transformer. There are ways to do that; but nothing simple and cheap occurs to me.
The station probably has a connection to the transformer output that normally goes to the center rail, and another connection to the isolated center rail in front of the station. Between those two is a switch or some other kind of "pass element" that disconnects the isolated center rail. You should be able to connect a rheostat around that switch or whatever, to supply a little current when the train is stopped. Depending on the locomotive and its load, you might need two rheostats in series, to keep the current low enough to stop the train.
Bob, thank you for the quick reply.
Maybe I should just ask what the specs should be for a rheostat for my setup. I have a ZW transformer, and I measure 20 volts from any of the terminals.
Here are the two reasons I want to use a rheostat:
1. my understanding is that a rheostat might allow sufficiently fine voltage control that I could ease an operating car onto a remote control, and
2. I have an automatic passenger station that stops the locomotive by reducing the track voltage. The problem is that the voltage drop causes the reversing switch to drop into neutral position so that the train will not start up again. I was hoping to be able to tweak the voltage between what is needed to stop the train and what activates the reversing switch.
Are these even realistic hopes for the use of a rheostat?
NIno
Just knowing the voltage doesn't tell us how much power the source (transformer) can put out.
The rheostat power rating is actually for the full-resistance setting. So a 20-watt rheostat can safely dissiplate 20 watts when set to its full 5 ohms. This corresponds to a current rating of 2 amperes, which would be a more sensible way to rate rheostats; but unfortunately they don't do it that way.
Just how much current would actually flow depends on the train and its speed and the rheostat setting. But the rheostat described wouldn't be suitable for use with a train that drew more than 2 amperes. Almost any small Lionel transformer can supply that much current.
So the situation is pretty complicated. But the rheostat that you describe would be suitable for most older starter sets and could probably handle good-sized modern trains, which draw much less current than the older ones (incandescent-lighted passenger cars excluded).
It seems from what Bob Nelson says that a variable resistor that has up to 5 ohms resistance and handle 10 to 20 watts would work for a Lionel train.
Would 10 to 14 volts (ac) generate the 10 to 20 watts at 5 ohms?
Please let me know if I have understood this correctly?
Thank you.
Nino Yannoni (San Jose)
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