O gauge rheostats

I don't think you want a rheostat for running the trains, a variable transformer is clearly a far superior solution.

A rheostat is just a large variable resistor.  So, when the current increase, the voltage drop across the rheostat will also increase, slowing the engine down even more.  Also, the rheostat will have to be pretty large to run any decent sized consist, it'll cost as much as a nice transformer.

Well here is what I am trying to do.  I just finished the Corgi PCC car conversion and it has two small DC motors in it connected to a circuit board that converts AC to DC...When using a regular transformer, the voltage comes on at about 6 volts, and then it runs too fast.  So I thought I could run the transformer wide open thru the rheostat and control the PCC car with the rheostat, thereby slowing it down.  I remembered that back in the 70's you could buy them and also the HO ones to create a handheld controller. 

Marty

In this day and age with all the other voltage control options available, there is absolutely no reason to EVER use a rheostat for ANYTHING.

Assuming the two motors are wired individually to the circuit board, one of the quickest changes you can make is to wire the motors together in series and that would cut the voltage to each motor in half, reducing your speed.

I have a Corgi PCC car powered by PA Heritage Models conversion. Picked up and HO power pack for less than $5 - works great.

jackson

Just use some diodes shown here. 3 amp ones are good for a trolley. You can tap the diode string for constant voltage directional or non directional lighting using bulbs or LEDs.

http://www.jcstudiosinc.com/Bl...=488&categoryId=

Dale H

Agree with everybody.  A good variac is fairly easy to come by.  For 2- rail DC I use a variac, a step-down transformer, a pair of circuit breakers, a Radio Shack bridge rectifier, a pair of gauges, and a DPDT switch.  So easy and inexpensive I have four of them just so I don't have to carry one to the workbench, garage, layout, or hangar.  I would never consider a rheostat, even though the old Marn-O-Stat liooked like a real throttle.

You can but rheostats at online electronic supply places such as Digikey.

Please learn how to use the LINK tool. Don't just paste URL's here.

I understand that rheostats are still available, however there are a terrible way to control voltage, especially considering all the other options available today.

I had a boatload of them and have successfully used them for fine tuning the voltage on my accessories. These rheostats are only active while the accessory is active, so they are not "wasting" power except on use.

I don't know if I would recommend that someone buy them if they don't already have them on hand. But, in my case, I am very happy with the results.

I do notice that on this forum rheostats have a very bad name Maybe deserved

Denny

Just curious--why is the rheostat such a terrible idea? I'm planning on wiring the downhill graduated trestle section of my small 4' x 8' layout with a prewar Lionel rheostat so that I can leave the transformer at a fixed setting and prevent derailing. Seems like a sound solution to me, and a pair of the #81 rheostats cost me 99 cents. What's a simpler, inexpensive solution here?

Rheostat is a variable resistor. In series with a load it will react according to Ohms law and voltage drop will vary with load. The diodes will always drop voltage by a set amount (pretty much anyway) and drop will be consistent with load.

 As far as the #81 rheostat,it works but the amount of wattage it will handle varies with where it is set. If you tap it in half for example,wattage rating is reduced in half. Also if the tap is set at a low setting and there is a short on the track you could burn up the resistor. For example if it were set at 2 ohms and 20 volts was applied. A short on the track would still be a circuit through the resistor with a 10 amp flow. 10 amps at 20 volts is 200 watts the resistor would have to shed.. A ZW breaker would not trip most likely.

Dale H 

I went out and brought a Radio Schack 25 0hm rheostat rated at 3 watts, I got it to run alot slower, which I wanted, but noticed that the rheostat got pretty hot, so I feel I need one rated differently, but don't know what rating to get??

Marty

Maybe just get a transformer that starts off at close to zero volts, like an mth z-750, 1000? Maybe a CW-80?

Rob

That's the very reason I recommended against the rheostat in the first place.  You end up dissipating a lot of power in the resistance of the rheostat.  If you really insist on using a rheostat, you'll need to go up in rated power, probably a lot.  Look for something in the 20-25 watt rated power range.