Got several accessories running off of the same transformer and want to reduce the action on some.

[ChiefEagles]

Anyone wanting to change the voltage to reduce or slow down the action of an accessory operating with several on fixed voltage from a transformer. Use Bob Nelson's [lionelsoni] bridge rectifier "arrangement" to change the voltage. I was messing around and wanted to slow the action of a Lionel oil well pump. Had it on fixed voltage with some other things. "Built" two bridge rectifiers together and slowed it down a lot. Easy to do and not that expensive.

[FJ and G]

Nice tip.

Could you instead, I wonder, just stick some resistors in the AC circuitry w/out changing to DC?

[lionelsoni]

Yes, a series resistor is entirely practical. The only problem with it is that the load voltage varies as the load current varies. So it works best with a load that draws the same current all the time. The bridge-rectifier idea that Frank mentioned is actually not using the bridge rectifier as a rectifier, to convert AC to DC, at all. Rather, it is simply a convenient way to get an unchanging voltage reduction of the AC. In fact, it has the important advantage of keeping the AC as AC. So AC remains AC; and the voltage reduction does not depend on the load current. The waveform is distorted a little from its original sinusoidal shape, but not very much for modest voltage reductions, and not enough to make any difference to practically anything that you would run off of it.

[ole1]

A simple solution that we use on our club three rail layout is to control accessories (street and structure lighting in our case) with a separate transformer. An old Marx transformer does the trick and a lower voltage prolongs the life of the bulbs besides being cheap.

[3railguy]

lionelsoni is right about straight resistors. I tried this on a small prewar layout and it turned out to be quite a nightmare. The resistors would suck amperage causing voltage drop across all the accessorys. It got worse as I added resistors and I was constantly swapping values. Intermintent operating accesorrys such as a gateman and banjo signal would cause the lighting to dim all over the layout. I ended up tossing the idea and went with a couple cheap set transformers like ole1 suggests. I was using 20 watt wire wounds and they got hot enough to scorch wood.

[ChiefEagles]

Guys, I use a lot of different transformers to get different voltages for accessories. This is just a way to fine tune the operations of an individual accessory running off of a fixed voltage.

[Roger Bielen]

If you can find a variable resistor, a.k.a. tuner, with high enough wattage this will allow fine tuning. I'm planning on trying this when, and if, I power up my old cattle platform and car. Darned thing never worked right, cows always fall over inside the car.

[ChiefEagles]

That might work. I tried a volume control for a big system. It got HOT.

[lionelsoni]

A variable resistor is also called a rheostat, but I don't see how it could be called a "tuner".

Lionel made several models of rheostats, for running trains, which could likely be used to reduce voltage for accessories also. They usually go for less than $5. The limitation still remains that any varying load, like John's gateman and banjo signal, on the circuit will affect the voltage to other loads.

Most volume controls are very low-power potentiometers (rheostats with a connection to both ends). Only those that might be intended to go between an amplifier and a loudspeaker are likely to be big enough for our purposes.