Rheostat question

Any one got a part # for that 18v Radio Shack rheostat?  I searched their online catalog and couldn't find it.

TIA,

Dick Adams

The Radio Shack rheostat has most likely been obsoleted by now.

Rob 

Seems like Rheostats are a hot topic this week. I was going to start a thread myself :) Here are my questions:
I understand a Rheostat is made up of resistors. Should I worry about burning out a Lionel rheostat by putting too much load on it? Say running a powerful engine pulling many cars at low speed for, I don't know, lets say 2 hours? Lower speed means the resistors are eating up most of the voltage and therefore most likely to burn out, right? (full power out of a ZW with the rheostat set on the lowest speed)

 Finally, what are the differences between the Lionel Rheostats (#81, #88, #95) and which is most desirable? 

I see #88 listed as a "battery" rheostat. Does that mean it will only work with DC current? #81 has an "on/off" switch, and #95 has something that looks like a red button. Is this red thing a button or on/off switch? If it is a button, how does it work?

Thanks guys.

lionel2986 wrote:

Seems like Rheostats are a hot topic this week. I was going to start a thread myself :) Here are my questions: I understand a Rheostat is made up of resistors.

The Lionel rheostats are wire-wound, & the tap is made to bridge two coils at once so there is no current interruption when adjusted.

lionel2986 wrote:

Should I worry about burning out a Lionel rheostat by putting too much load on it? Say running a powerful engine pulling many cars at low speed for, I don't know, lets say 2 hours?

The rheostat will heat up as much in ~ 2 minutes as much as it will in 2 hours for a given load.  It's resistance wire - like toaster wire - and will heat up.  If it gets red-hot, that's too much. 

lionel2986 wrote:

Lower speed means the resistors are eating up most of the voltage and therefore most likely to burn out, right? (full power out of a ZW with the rheostat set on the lowest speed)

Actually, the load will be distributed over the entire set of rheostat coils at low speed settings.  the coils will get hotter at high speed settings(but fewer of them). 

lionel2986 wrote:

Finally, what are the differences between the Lionel Rheostats (#81, #88, #95) and which is most desirable?  I see #88 listed as a "battery" rheostat. Does that mean it will only work with DC current? #81 has an "on/off" switch, and #95 has something that looks like a red button. Is this red thing a button or on/off switch? If it is a button, how does it work? Thanks guys.

#88 Battery Rheostat is the simplest, with speed control only, & "off" to the far left.

#81 Controlling Rheostat has speed control and an on-off switch on the slider, & does not go to "off" to the far left(you use the switch).

#95 Controlling Rheostat has speed control and a direction(press to interrupt) switch on the slider, & "off" to the far left.

They can all be used with batteries or transformers, AC or DC.  They are all of otherwise similar construction, & I use them for short duty cycles in block control applications, so they are all equal as far as I'm concerned.  The #81 has a wider control range for running trains, so between that and the on-off switch on the slider it's probably the most versatile.

Rob 

Thanks for the valuable information guys!  I too have a TW.  I would have never have thought that I could take advantage of the accessory terminals to run trains!  I was thinking of setting up a small loop for my son to run trains on the floor and utilizing a rheostat may be the best way to power the track.

Thanks again.

JO

Rheostats are generally specified by resistance and power.  The power is the maximum that the rheostat can dissipate at full resistance.  This is a little misleading, since the real limitation is how much current the rheostat can stand, and current is typically at its maximum when the resistance and power dissipation are low.  You can find the rheostat power rating that you need by squaring the maximum current that your train draws and then multiplying by the full resistance.  For example, if your train draws 3 amperes at most and you are using a 5-ohm rheostat, you need a power rating of about 45 watts.  The rheostat will never dissipate nearly this much power; but the maximum current will be the same as if it were dissipating 45 watts over the entire length of the winding.

Hi Rob, I bought a pre war Lionel rheostat, the 81, and  I'm trying to see if it is complete and in working order. My trouble is, I don't quite see how the circuit goes. After a crash course I get the difference between a rheostat and a potentiometer, which has three terminals hooked up, for one thing. I can see where the first terminal is, it hooks to the wire that coils around the core. I can see the switch slides on the two rods while in contact with the coil to regulate the resistance. But I don't see either a clear terminal on the switch or how the front right bolt connects to the circuit. I intend to use this with batteries. In photos I see a lead going from the front right bolt and the front left bolt, but so far none from the switch. I can't find an image of this rheostat in a setup showing the complete circuit. I think there is a nut missing from the front right, but is there a wire missing? I can't find a photo of th bottom to check.

Any reply appreciated, Katie

Hi Rob, I bought a pre war Lionel rheostat, the 81, and  I'm trying to see if it is complete and in working order. My trouble is, I don't quite see how the circuit goes. After a crash course I get the difference between a rheostat and a potentiometer, which has three terminals hooked up, for one thing. I can see where the first terminal is, it hooks to the wire that coils around the core. I can see the switch slides on the two rods while in contact with the coil to regulate the resistance. But I don't see either a clear terminal on the switch or how the front right bolt connects to the circuit. I intend to use this with batteries. In photos I see a lead going from the front right bolt and the front left bolt, but so far none from the switch. I can't find an image of this rheostat in a setup showing the complete circuit. I think there is a nut missing from the front right, but is there a wire missing? I can't find a photo of th bottom to check.

Any reply appreciated, Katie

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.

Okay, that is a big help. The lockon I have has two leads, does the second one go back to the power source, in this case a battery box? I would imagine the red lead goes to the right hand bolt and the black back from the lockon to the black connector?

Katie

Katie first welcome to the forum and please continue coming and in time post pics of your prizes.

I think some of the confusion may come from the fact that one side of the rheostat circuit is its metal frame.  There are various ways to hook it up that will work; but here's one way:  The current flows through a wire from the positive battery terminal to the back-right terminal (the one with the asbestos insulation)  The current flows through some part of the resistance wire wound on the ceramic core, then into the wiper that touches the resistance wire underneath, then through the switch (if it is on), then through one of the rods that the switch slides on, then through the metal base, to the right-front terminal.  From there the current flows through another wire to the lockon terminal that connects to the center rail, then through the pickup into the locomotive, then out through the wheels to the outside rail and back to the other lockon terminal.  From there the current flows through another wire back to the negative battery terminal, through the battery and back out to the positive terminal, where it started.