lionel 88 rheostat

[Laurastom]

I did an online search for "Lionel #88 rheostat", one of the results was a link to a CTT 2013 thread in which Bob Nelson provided a lot of additional information. It is worth reading again.

Bob always provides useful responses, in the post above there is a slight oversimplification of what I know he meant to convey. All materials follow Ohm's Law in that when the voltage and the current are measured simultaneously the resistance is voltage divided by the current. The reality and ugly complication is many things are highly non-linear. One of the most non-linear common devices is an electric motor. The current draw at a given voltage is a function of both the applied voltage and the rotation speed (applied load) of the motor. The added impedance caused by rotation of the motor is called the back EMF.

This is why using rheostats can sometimes work well and sometimes not at all. The old series wound 3 pole open frame universal motors had a DC winding resistance of 2 to 3 ohms. Yet pulling some cars around a flat layout track they only drew 1A to 2A at 15V. The back EMF adds around 10 ohms to the DC winding resistance at moderate speed and light load. As the engine starts up a grade the load increases, the motor slows down, the back EMF drops causing the current draw to go way up. Unfortunately with increasing current the voltage drop across the rheostat also increases,further slowing the engine. The opposite of what we want. On a layout with grades one rheostat for level track, one for up grades and one for down grades could be necessary for satifactory speed control.

These rheostats will not work with modern can motor engines. One of my can motor engines draws about 1.7A up a steep grade pulling 20 cars. Running on the level it draws only about 1/10th A. 1/10th A through a 10 Ohm rheostat is only a 1V drop, the engine will not even change speed perceptibly.

[trainlivebob]

lionelsoni

That depends on how much current the trolley draws.  A rheostat is just a variable resistor, so when you connect it in series with a transformer's output voltage, it lowers the voltage at the load (the trolley) by an amount proportional to the rheostat's resistance setting and to the trolley's current (Ohm's law:  voltage = current * resistance).  If the trolley runs slower than you want at the maximum rheostat resistance, then there is some lower resistance setting that will give you the speed you want to run the trolley.  Otherwise, the trolley's speed will be too fast.  Just try it out.

By the way, I should explain that Ohm's "law" is an odd law in that it applies only to those materials that obey it, and there are many materials that don't obey it.  In the case of the toy-train rheostats, it does apply, because the rheostat winding is a metal wire and metals generally obey the "law".

 

Thanks Bob.

It the lionel trolley and it usually like 10 to 12 V

Should work

[lionelsoni]

That depends on how much current the trolley draws.  A rheostat is just a variable resistor, so when you connect it in series with a transformer's output voltage, it lowers the voltage at the load (the trolley) by an amount proportional to the rheostat's resistance setting and to the trolley's current (Ohm's law:  voltage = current * resistance).  If the trolley runs slower than you want at the maximum rheostat resistance, then there is some lower resistance setting that will give you the speed you want to run the trolley.  Otherwise, the trolley's speed will be too fast.  Just try it out.

By the way, I should explain that Ohm's "law" is an odd law in that it applies only to those materials that obey it, and there are many materials that don't obey it.  In the case of the toy-train rheostats, it does apply, because the rheostat winding is a metal wire and metals generally obey the "law".

[trainlivebob]

As a follow up can I use the 88 to lower the voltage on a accessory circuit (18 or 14v) to run a trolley?

[Flintlock76]

pennytrains

But keep in mind that both the 81 and the 95 have a thin blanket of ASBESTOS under the metal shield.  Using them does have a risk.

Certainly a good thing to be aware of, but the asbestos won't bother you if you don't bother it.  Basically, don't go under that metal shield if you don't have to. 

[pennytrains]

Yeah, you don't want to be using an 88 for modern trains.  Batteries produced a lot less resistance through the coil than standard 110 house current would.  I use a 95 rheostat with my prewar type K transformer to run my Standard Gauge trains on 24 volts.  The 95 has a cover to protect your fingers from the heat of the coil and works well.  Plus the 95 has a button on the slide that you can use to cut power in case of a problem.  (Especially useful if, like me, you're using a transformer with 5 taps and the lever doesn't go to zero.)  You can also use an 81 rheostat for that "vintage look".  The only real difference between the 81 and the 95 is that the 81 has a lever instead of a red button.

But keep in mind that both the 81 and the 95 have a thin blanket of ASBESTOS under the metal shield.  Using them does have a risk.

[trainlivebob]

Yikes! quite dangerous.

Thanks for the quick reply and history lesson Bob.  I'll just put in on a shelf.

Bob

[lionelsoni]

Yes, rheostats and (wet or dry) batteries were how you ran trains in a house without electric service.  And the universal motors in the locomotives ran on either AC or DC.

Other early power supplies included the type C transformer, rated for 25 or 40 hertz, the type K transformer, rated for 220 volts, and the number 107 and 170 "direct current reducers", rated for 110 or 220 volts DC respectively.  Lionel warned that the reducers were "not to be used on alternating current", but they worked just fine on AC--and they were equally lethal to the user who touched the track accidentally.

[trainlivebob]

I just got a Lionel 88 and its says it's for use with batteries on the box.

Is this what was used if a user did not have electricity (and thus no transformer) to their home and had some dry cell batteries and used the 88 to control engine speed for dc motors? could it be used for Lionel AC engines?

In the modern era, is this just a display item or is there some use for it?

Thanks,

Bob