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All,

 

I am working on a display layout for which I will not be present every time it is operated.  I will be getting various volunteers with various levels of train knowledge.  So I decided that I would not rely on command control as I usually do.  But instead I want to put a few conventional transformers out and just let the kids control the trains.  (6 trains running simultaneously so I would have 6 throttles)

 

The thing I need to do is be able to limit train speed.

 

THere will be Lionel, K-Line, MTH, Weaver, Williams and Atlas engines some command and some conventional but all running in conventional mode.

 

So the key things I would like to achieve are:

 

Simple - It needs to be simple so that guest attendants can operate (So I really don't want to go beyond handle up down f-n-r-n cycling..)

 

Speed Safe - Guest operators, e.g. Kids can can operate and not fly the trains off the tracks.

 

Simple Setup at a session.  - One master switch turns it all on for the attendant, no other set up needed.

 

Simple end of session, just kill that master power.

 

We can assume 6 transformers and six trains and that a train stays with the same closed track loop and transformer all the time.

 

I could do different things for each train/transfomer pairs as long as it is just set up once when I am assembling the layout.

 

I will probably use some a few CW 80s, a Z4000, a few MTH starter set transformers.

 

 

So some of the thoughts I have had are:

 

Maybe some of the transformers allow max voltage output (CW80s don't)

Maybe PS/2 or tmcc engines can be programmed for a max conventional speed (from command mode???)

Putting in resistors at the outputs to limit voltage (seems shaky to me)

 

 

So what are your thoughts on setting this up?

 

Thanks,
Bil 

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Starting at the end and working up...

 

Resistors are for reducing current (amperage) not voltage. This is a common misconception.

 

If you use conventional trains and older, PW transformers, you can put an autotransformer (brand name, for instance, "Variac") to set the maximum percentage of line voltage going into the train transformer. Set it at 50% and the top speed of the train will be half of the maximum allowed in normal operation.

Last edited by Arthur P. Bloom

My idea would be to use Z1000 controllers connected to a multi tap transformer with a lower than 18v secondary.

So, determine the output voltage required by trial and error, and just buy the appropriate transformer. Maybe something like a 9 or 12volt secondary would be about right. And don't forget to add a circuit breaker.

I think a variac would work with the MTH Set style transformers.  Not sure they would work with the Z4000 or CS 80's though.

 

Could use variacs between the output of the transformer and the the track.

 

The diode / rectifier solution is also somewhat simple and I have a bunch on bridge rectifiers in my parts box.  I like that I can get nice steps of of .6 volt reductions...

 

I thought there was some reason that resistors were the wrong thing!

 

I don't think I want to mod any engines just for this one display, but dropping the transformer output is good.

 

John,

 

Yes a good point I am certain I would need independent control of the max on each of the 6 loops because of the wide variety of engines to be used.  

 

So 1 variac in from on all six transformers would not give me enough fine tuning during setup.

 

I think with variacs my best be would be to use them between the output of the transformer and the track.  I am not sure what the effect of some of the not exactly sine wave output would be there either.

 

Keep the good ideas coming!  I appreciate all the ideas so far!

I think finding variacs to put on the LV side is going to be a bit hard to do, and certainly expensive!  OTOH, a boat-load of 6A diodes will be pretty cheap, and they'll do this job quite nicely and allow fine tuning of each setup.

 

The issue of fine tuning each loop is somewhat of a sticking point here.  Short of buying a bunch of variacs or special transformers with a maximum output limit, I think the diodes offer the most cost effective solution.

Originally Posted by BillP:
THere will be Lionel, K-Line, MTH, Weaver, Williams and Atlas engines some command and some conventional but all running in conventional mode.

...

Maybe PS/2 or tmcc engines can be programmed for a max conventional speed (from command mode???)

PS2 engines in conventional default to the same speed vs. track-voltage profile of ~20 sMPH at 12V, increasing by ~20 sMPH per Volt above that.  So you can set a reasonably accurate speed limit - independent of load - by limiting track-voltage using diodes or whatever. No programming is required from command mode. You can turn off speed control using the Whistle/Bell buttons to make the behavior more similar to basic reversing units presumably in some of your other engines.

 

Stan,  Good info to have!  I did not know that!

 

I think the back to back diodes is the way to go here.  Especially since I have a bin full of appropriate parts already!  Two to three bridge rectifiers off of each transformer gives me the ability to vary from 15 to 18 volts as a max.  Easy to wire up and easy to adjust when I am setting up.

 

Thanks to All!

Don't know if MTH has a max speed function, but Lionel command engines can be programmed individually for a maximum speed.  You can get the process from the Lionel service video website.  I'm pretty sure you:  Address the engine, press set in the cab1, accelerate the engine to the highest speed you want it to run, press the boost button once.  That should lock in the max speed for that engine.

You know the old adage that if you give a carpenter a problem all of the solutions will be wood and nails?

 

I love the fact that Dale H always comes up with back to back diodes and I come from another camp and all of my solutions are rheostats.

 

I recommend the use of a 50 Watt 10 Ohm rheostat. (I think that I have as many airplane and Ohmite rheostats in my spare parts drawer as Dale has diodes.) The rheostat would allow you to fine tune the current flow compared to the back to back diodes. They can be found reasonably priced on eBay and easy to insert in your circuit.

 

BTW - both solutions will heat up the joint, but will keep the trains on the track.

 

Denny

Well, the difference between diodes and rheostats are that with diodes the voltage is pretty constant, however with rheostats the voltage varies with current.  Worse yet, when you are coming on a downgrade with little current draw, the rheostat will give you more voltage, probably not what you want if you're trying to control speed.

 

Both will slow things down, I personally think that diodes are a better solution in this instance.

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