Ideas for Setting and Holding a Maximum Track Voltage for My 2YO

[tinplatacis]

Yeh, RadioShack oughta have them. They have the parts I need to make my 8625 run on AC. Need to track it down...

[JTrains]

lionelsoni

You could use a relay, with a rheostat in series with its coil, across the transformer's output voltage.  A normally closed relay contact would open the circuit to the track (but not the circuit to the relay).

Ah, I (think I) see what you're saying. Assuming I want to cut off the power at 14V: it would seem that I need an AC relay which has a control input rating of, say, around 12V or perhaps a little bit less. I would then use a rheostat to adjust the control input down to a voltage that causes the relay's electromagnet to not activate until it reaches my desired 14V track voltage.  Correct?

 

It might be my lack of experience with electronics, but I've always assumed that relays are built to handle control input that's typically either "on" or "off" - not "on but not quite enough to actuate" which is what this would seem to entail. Am I "crossing the streams" by having non-actuating current flow through the control input on a continuous basis?

 

Also, would you know off-hand what might be a reasonble resistance range for the rheostat to need to support?  I'm learning quite a bit by trying to think this through but will take all pointers!  Such as who sells these sorts of little electronic parts now that Radio Shack is, well, no longer a Radio Shack?

[lionelsoni]

You could use a relay, with a rheostat in series with its coil, across the transformer's output voltage.  A normally closed relay contact would open the circuit to the track (but not the circuit to the relay).

[JTrains]

tinplatacis

I could swap you an RW.

Thank you for the kind offer - I'll be stopping by the Great Midwest Train Show this weekend so I'll probably just snag one while I'm there.

[JTrains]

lionelsoni

You could also put a piece of tape inside the transformer case, covering the part of the secondary winding that you don't want him to use.  This would stop the train if he turned the knob too far, rather than limiting the voltage; but only if he tried to exceed the limit of your front-panel tape.  It wouldn't have to be very durable, since he would have no incentive to go that far after discovering what happens if he does.

 

A clever idea - don't "limit" the voltage, just cut the power completely if the limit is exceeded. I'm a little hesitant to start taping (and possible gunking up) the secondary coil - I'll have to give a think about how I can do something inside that achieves the purpose, is electrically safe, and limits the likelihood of introducing gunk into an otherwise-well-working 70YO transformer.

 

I guess that also gives another electronic possibility - is there some type of simple device that cuts power when a voltage level is exceeded? Sort of like a fuse - except for voltage, not current.

[tinplatacis]

I could swap you an RW.

[lionelsoni]

You could also put a piece of tape inside the transformer case, covering the part of the secondary winding that you don't want him to use.  This would stop the train if he turned the knob too far, rather than limiting the voltage; but only if he tried to exceed the limit of your front-panel tape.  It wouldn't have to be very durable, since he would have no incentive to go that far after discovering what happens if he does.

[JTrains]

tinplatacis

So the V doesn't have a lower voltage post?

Exactly - the four power posts A B C and D all have the same variable range of voltages. As a side note, this confused the heck out of me when I was a kid.  Most of the accessory instruction sheets (which were all I had to go by) talked about connecting specific posts on different transformer models for specific fixed voltages or variable voltage ranges. I couldn't get my head around the fact that the Type V (and Z) are a bit unique in that they have nothing but variable voltages - and a full range of them at that.

tinplatacis

Besides, a bank of smaller transformers might work better for you instead of the V.

You might be right - something like a 1033 might be in order when Noah gets a bit wiser!

[tinplatacis]

So the V doesn't have a lower voltage post? The RW has posts for 7-19 volts, and 5-13 I believe. The 1033 has 0-13, and 5-16 variable voltage posts.  Besides, a bank of smaller transformers might work better for you instead of the V.

[JTrains]

tinplatacis

Have you tried hooking the wires to the track to the lowest possible variable voltage settings?

 

 

An interesting idea - but all four controls on the Type V have effectively the same voltage range.  The knobs being different sizes is a bit of a red herring as to their capabilities. But this does bring up the idea of getting a different transformer that doesn't have the power range of the V and using that one for track control. I'll have to give that some thought.

[tinplatacis]

I have the a-u hooked up the the uphill on my layout on the 1033, the b-u on the downhill because it has a lower voltage.

[tinplatacis]

I use a 1033, a CW-40, a 1053, and a pair of RW transformers on my layout. Have you tried hooking the wires to the track to the lowest possible variable voltage settings?

[JTrains]

My 2YO loves operating our layout - and he's usually pretty good at making small adjustments to the track voltage so things don't get out of hand. Usually. But then, as little boys are want to do, he gets excited and before I know it we've got a high-speed derailment.

Like my father did for me, I've now put a bit of electrical tape on the face of our Type V transformer at around 13V so the knob won't physically turn beyond that. But my boy is a fast-learning Sneaky-Pete and I'm thinking he'll learn how to take it off when I'm not looking before long.

So, now that we're in the 21st century, is there a more elegant way to enforce a maximum track voltage? A voltage regulator won't do the trick - as they're built to maintain a constant output voltage which isn't what is needed. I'm looking for something that allows the voltage to vary up to a certain point - and then "clamps down" so it doesn't go any higher. I've got only a basic understanding of electronics so I'm not sure what such a thing might be called.  Or has someone come up with another approach to this age-old problem?