Variable Voltage Switches for Accessories with Vibrating Motors

Truthfully, I'd just look for one of the really small 30 or 40 watt transformers and use that.  They can frequently be had for $5-10.  Trying to find an AC adjustment is going to end up being a lot more expensive I suspect.

Would an ERR mini Commander work?

Or just a string of diodes to drop the voltage.

I agree with John's recommendation in this case.  But controlling voltage independently of a transformer comes up from time to time.  Its often been said here that rheostats are not ideal (heat, lost power & cost) though they would work in this situation.  Professor Chaos brings up using a string of diodes.  I have been wondering if an old school multi-position switch that puts diodes in and out of the circuit could provide a variable voltage control from a fixed source.

Bill

GRJ and OGN -- the difficulty with using transformers is that each accessory requires a different voltage to work optimally so I'd have to have several of them and need a place to plug them in.  I didn't mention this before but my layouts are modular and portable and occasionally do some traveling to local shows, where I encourage kids to find a button or switch and see what it does.  They have even more fun with it than I do.

I have a Lionel rheostat that I will test in line with a  momentary pushbutton controller.  The rheostat can be mounted permanently and out of the way and would not be subject to extended periods of use so I don't think heat and power loss will be much of an issue (that said, I'm keeping my fingers crossed that my layout doesn't go up in flames).

PC -- these old accessories tend to work better or worse depending on the day so I'd like to be able to adjust the voltage as needed or simply speed up/slow down the process depending on the user.

I agree with you that it would be nice to have a switch for each accessory to control the voltage.   

Unfortunately I never found an easy way to do it, so I just group as many accessories that have the approximate same voltage requirements together and run each group off their own dedicated transformer.

You can also use zener diodes in pairs, back to back for individual accessories.

ogaugenut posted:

I agree with John's recommendation in this case.  But controlling voltage independently of a transformer comes up from time to time.  Its often been said here that rheostats are not ideal (heat, lost power & cost) though they would work in this situation.  Professor Chaos brings up using a string of diodes.  I have been wondering if an old school multi-position switch that puts diodes in and out of the circuit could provide a variable voltage control from a fixed source.

Bill

Good reason for a multi position switch or making the voltage or current adjustable. The fact that most vibrator motors depend on little rubber fingers as well as foam rubber.  The characteristics of these rubber components change with temperature fluctuations.  Horse and cattle corrals are the perfect example of this. My 3656 cattle corals  never work best at the same voltage setting where they were left the day before. Two factors at play here, the ambient temperature of the room as well as the fact that the rubber softens as the accessory warms up even if the ambient temp stays the same. The ideal voltage setting at startup is different than after it has run a while.  Add to this that each accessory has a different set of sweet spots  and that as the rubber ages it changes.  To me part of the charm of these toys is a feeling of accomplishment when you get them working perfect. The flip side to that is you never know if they will work right when company or the grand kids want to see them.          j              

Amen!

ogaugenut posted:

... (heat, lost power & cost) though they would work in this situation...

Maybe, maybe not work. A rheostat is a current limiting device, so for the barrel loader as an example(very light load), a Lionel rheostat(81, 88, 95 eg.), the rheostat will have little or no effect on the voltage going to the loader.

I realize that you have space restrictions, but I use  Type V transformer for my AC accessories. Four variable circuits; 8 volts for drum loader, 12 volts for milk car, 14 volts for log loader and switches, and so on. I paid $45 shipped from eBay.

I did what GUNRUNNER JOHN said, had a different transformer for each accessory and, a push button for the guests and a on/off switch for me on the inside.  

Clem

John H posted:

I realize that you have space restrictions, but I use  Type V transformer for my AC accessories. Four variable circuits; 8 volts for drum loader, 12 volts for milk car, 14 volts for log loader and switches, and so on. I paid $45 shipped from eBay.

Yep, Type Z for me. Same deal with four variable channels. Great way to fine tune voltage for those finicky Lionel PW accessories.

OK, it looks like I'm going to have to go with a transformer then.  Thanks for everyone's advice!

12 postion rotory sw. and General Purpose diodes 50v oromore (rectifying diodes), will eat approx .7v (ish) per position.  Choose sw& diode amps higher than output of power supply .

  Off now,turning clockwise increases voltage allowed across it. (removes diode pairs)

This will eat about 6v-8v total depending on diode efficiency.

  Use 4 diodes, 2 pair in series, at each junction for a bigger 1.2-1.6v drop at said postion(s). (or a bridge recrifer=4 diodes)

You can read about the dropping method described above by Adriatic and others in the following OGR thread:

https://ogrforum.ogaugerr.com/...18#78297654343697718

Here's a relevant photo from the thread. 

To be sure, this requires DIY assembly/wiring so more hands-on than applying a multi-output transformer or multiple transformers.  OTOH it can be done for less than $5 out-of-pocket.  Note that multiple accessories can be serviced by a single assembly.  And if adjustment is required for a particular accessory, a rotary switch could be used to select from 3 or 4 "taps".  

One may ask whether resolution of 0.7V is enough versus continuously variable control with a throttle-type transformer.  Fair question.  I see you mention a portable/modular layout.  When you take your setup from location to location, the AC wall outlet voltage can easily vary, say, 5%.  So even a throttle transformer will vary about that much in each accessory voltage from changing location alone!  If you have an accessory that "only" works in a narrow voltage range of 1/4V or 1/2V, you have a another problem.  

Off now, clockwise increases voltage allowed by, by 0.6-0.8v depending on diodes. To include a bigger step(s) at any position, use 2 pairs in series at said position(s). 

This will "eat" about 6-8v total off of any power supply input, ac or dc+ or dc-(reverse dirrection) .  All it will do is eat voltage *. Use general purpose rectifying diodes at 50v or more for our 25vac potential, choose the amp rating over power supply max max output, or use a fuse to protect a lower amp pair of diodes.(eg. 10amp bus feeds a 1.75amp fuse, fuse feeds 2a diodes feeding a 1.5amp accesory)

*If you skipped one of diode (might take two, in series) That postion would become a whistle trigger (or bell on modern trains depending on which way those face).

I didn't think the first post took. I refreshed but didn't see it. (must be some kinda amp page issue?)

I built similar with salvaged diodes.  Some spots only used -.5v diodes. (more efficient) Those got used in low volt range of choices.  My can motor starter set 0-4-0 dc with a BR (for ac) makes good use of those and once over 8v, the less efficient ones are in place for larger steps per click. The effectiveness depends on max voltage. Lower max. resulting in a large speed jump per click as the % changes in suit.

ADCX Rob posted:

ogaugenut posted:

... (heat, lost power & cost) though they would work in this situation...

Maybe, maybe not work. A rheostat is a current limiting device, so for the barrel loader as an example(very light load), a Lionel rheostat(81, 88, 95 eg.), the rheostat will have little or no effect on the voltage going to the loader.

I tend to disagree with this. The rheostat raises or lowers the resistance of the circuit. Place a resistor in series with the barrel loader and the voltage will drop through the resistor but the current will stay the same. Place the Lionel rheostat in series and the voltage will drop but the current flow will stay the same. Current flow stays the same through a series circuit. Say the loader draws .5 amp and the power supply is 14 volts. If you want the voltage to be 10 volts to the loader you will need a 4 volt voltage drop across the rheostat. R=E/I  R-resistance, E-voltage, and I- amperage. The amperage in series stays the same .5 amps so 4 volts divided by .5 amps equals 8 ohms. 8 ohms will give you a 4 volt drop thus 14 - 4 = 10 volts to the loader. A rheostat is a variable resistor not a current limiting device when use in series with the circuit.

The lost voltage will be dissipated as heat through the rheostat. Make sure the rheostat does not become too warm for the application.

This combination powers a Diamond Scale turntable.  Variable resistor (speed control) and a double pole/double throw/cross over switch, momentary/momentary/center off (reverses direction).   Requires a DC power source.  

Forest posted:

...

Place a resistor in series with the barrel loader and the voltage will drop through the resistor but the current will stay the same. 

 

Consider a 1 million Ohm resistor in series with the barrel load.  Are you suggesting the current will remain 0.5 Amps in your example? 

Warning - long post.  Reading is voluntary.  I will understand if you find it TLDR.

Resistor Approach

The missing piece here is both the voltage and current will change.  The accessory itself behaves as a resistor.  If you supply 18V to an accessory it will draw more current than it would at a lower voltage.  (The details of this vary if the accessory is a motor, a lamp, electronics or some combination but ignore that in this case.)   So it is not fair to say accessory X always draws Y amps as it depends on the voltage to that accessory.  Also remember that 18V depends on the voltage from the wall.  A transformer that is designed for 18V on a 120V line will output 16.5V on a 110V line.  Further, the transformer itself has a resistance so a fully transformer will put out less voltage that it would for a light load.

If you put a resistor in series you are changing the total resistance in the circuit so the current will drop.  In a series circuit both accessory and resistor will have the same current but the voltage in each will depend on the relative resistance between the two.  This is commonly referred to as a voltage divider.

Example: If the accessory draws 1 amp at 18V it looks like an 18 ohm resistor.  If you find that 8V works well with an adjustable transformer you would want a resistor to drop 10V with an 18V transformer.  For this example the resistance required would be 22.5 ohms.  So 18V is split 10V to the resistor and 8V to the accessory.   The current is 0.44 amps.

In practice you're going to do this empirically and not get into this detail.   You the main thing to worry about is the power rating and heat from the resistor.  The power dissipation in the resistor is I*R so in the example 0.44 amps * 22.5 ohms is 9.9 watts.  I use 100% derating so a 20 watt resistor is called for.  The heat would be comparable to 10 watt light bulb.

Final word on rheostats or potentiometers - the rating for these is based on the full resistance.  If it is 10 watts the power is distributed across the rheostat.   If you have adjusted it to half way the rating is only 5 watts.  This also applies to autotransformers (Variacs).

Another point on these is taper.  The resistance change may not be linear as you adjust the rheostat.  If you salvage a rheostat from an MRC DC transformer you will see the size and spacing of the windings vary as you move the wiper.

Diode Approach

The voltage drop of a silicon diode is typically 0.7 V.  A diode also has resistance so the drop will increase at higher currents.  Just looking at the 0.7 V the power dissipation in the diode would be 0.7 V times the current.  In the example, 0.7 V and 0.44 amps = 0.3 watts, not much of a concern.  Compare this to an engine drawing 3 amps and you will get 2 watts in the diode.

Note that the diode drop affects the peak voltage of the waveform.  The 18V we talk about is the rms value, the peak is 1.414 time this which is 25.45 V.  If you subtract 0.7 from this you get 24.75.  The rms value is 0.707 times the peak, thus 17.5 V.  The rms value is what you see with a typical voltmeter so the diode will provide a 0.5V drop.  (For dc the peak and rms are the same so you see the full 0.7V drop.)

The above applies if you have the diode pairs.  If you only use one diode you are blocking half of each cycle and the output will drop accordingly.  Of course you have seriously distorted the waveform.

Dimmer Approach

If you use a device that chops the waveform you are also distorting the waveform but the accessories should be happy with this.  This is the most common approach for electronic controls.

Final word, just use your fingers and nose to see if you are exceeding the rating of a component.

stan2004 posted:

Forest posted:

...

Place a resistor in series with the barrel loader and the voltage will drop through the resistor but the current will stay the same. 

 

Consider a 1 million Ohm resistor in series with the barrel load.  Are you suggesting the current will remain 0.5 Amps in your example? 

Why would you even state something so far fetched. With no usable voltage getting through would it really matter. I post an example of ohms law and why a rheostat should work and right away someone wants to take it to extremes to make what point. The post was about regulating the voltage and I explained why a Lionel Rheostat should work. Maybe there's more to it.  I never said your method would not work. Please explain to us why a rheostat wouldn't work. 

Forest posted:

I tend to disagree with this.

Try it then, with a GE53 bulb and a 95 rheostat connected to the 12 volt fixed output of a transformer.

The point is the current changes with the resistance value of the rheostat.  Increase the resistance, the current drops and the vibrator motor slows down.  I must be mis-interpreting your statement "Place a resistor in series with the barrel loader and the voltage will drop through the resistor but the current will stay the same."

I don't think anyone said that a rheostat would not work.  What Rob was pointing out was an O-gauge rheostat may not be effective for light loads.  The range of some Lionel rheostats (he provides some model # examples) is in the few Ohms rather than tens or hundreds of Ohms.  A few Ohms does not provide enough current limiting to make a material impact for light loads.

As Cam's analysis shows, the math can get messy.  But if one slogs through the math, the case can be made that the diode method has its place since the voltage drop is relatively constant  (compared to a resistor) independent of the load.

There's absolutely nothing wrong with the rheostat approach.  It's just getting the right rheostat for the job depends on a number of factors.  If you start with what you have at hand and get acceptable results and it doesn't burn up you are good to go.

Another option is to use spare starter set transformers.

A GE 53 only pulls .12 amp. What does a vibrator motor draw?  I might be able to find a vibrator motor in the used parts box but don't have a rheostat. How many ohms do the Lionel Rheostat's rate at?