Automatic Downhill Slowdown??

[trainbrain]

I think I remember an article once about a way to wire something(a relay?) that would slow down a train when it decends a grade. I have a grade goin up to a mtn but I also use a large reverse loop to turn the train around so it comes back down the same grade. Could something be done to slow it down automatically even though the I use the same grade goin up? Could something be done to increase power when the train goes up, also? Thanks in advance! The answers are always here!

[thor]

In the HO world of 2 rail DC they use back EMF controllers to get what you want. For all I know the various proprietary boards sold by various train electronics companies may use a similar technique. I've always assumed those EOB circuits worked like that.  At least that gives you a starting point, I hope its of some use.

Failing that though, perhaps some kind of detection device that automatically reduces track power when it detects a train on the descent?

[lionelsoni]

You don't make it clear whether the "same grade" is also the same track.  If the train is on separate tracks going up and down, your situation is very similar to the one in this recent topic:

http://www.trains.com/trccs/forums/951554/ShowPost.aspx

If there is only one track, you will indeed need something like relays to do the job.  For example, you could have a relay or relay pair that is latched by a control rail in the middle of the mountain loop and released by a control rail somewhere on the loop at the bottom.  There are a couple of ways to make such a latch:

Using two relays, connect one end of the coil of each relay to a supply, AC or DC and of the correct voltage for the relays that you use, returned to the outside rails.  Connect the other end of each coil to one of the control rails.  For the relay connected to the control rail at the top of the mountain, provide a normally-open contact from the control rail to ground, so that the relay will remain operated--latched--once the train operates it.  Then connect a normally-closed contact on the other relay in series with the coil of the first relay, so that the second relay will release the first one.

Now arrange the other contacts of the first relay to adjust the voltage on the grade.  For example, you could use two rheostats as in the other topic.  One rheostat would be in series with the center rail of the loops at the top and bottom and adjusted for a reasonable speed on level track.  The other rheostat would be in series with the center rail on the grade and adjusted to slow down a descending train.  However, it would be shunted by a normally-closed contact on the first relay, to boost the voltage for climbing the grade.

Another way to do it, using a single relay, is to put a lamp in series with the first relay described above, with the lamp between the relay coil and the power supply.  Instead of a second relay to release the first one, simply connect the point between the relay coil and the power supply to the lower control rail.  When the train grounds that rail, it turns the lamp fully on and removes all voltage from the relay coil, which of course then releases.  It may be a little tricky to get a suitable lamp coordinated with the relay coil's operating voltage and current and with the power supply; but it saves a relay.

[thor]

Here's your answer with a diagram, its what Bob suggested

http://www.delaware-valley-hi-railers.com/tips/tips_trolley_hill.html

[jkerklo]

Three-Rail Innovations' "Two Relay Controller" has a feature for operating a relay by train direction.  Using two isolated outside-rail track sections, a relay is closed when the train passes over the track sections from the first to the second, but not when it passes from second to first. 

The isolated outside rail track blocks at the top and bottom of the hill arranged so the train passes from the "top" section to the "bottom" section when going "down." The track center rail is connected to the relay's "common" terminal.  Train power for "up" is connected to the relay "normally closed" terminal.  Train power for "down" is connected to the relay's "normally open" terminal. 

Train power is switched when the train goes down the hill.

See www.Three-Rail.com and "Two Relay Controller" for more information.

[lionelsoni]

What Thor suggested is generally called a "latching relay".  "Snap relay" is Atlas's trade name for a latching relay.  It will do the job just as well as the conventional relays I proposed.

However, for the reasons given in the topic I directed you to, I recommend that you not use the 3-transformer method of altering the voltages.  Connecting the transformers in phase as that description recommends will reduce but not eliminate the hazard (unless all three are set to the same voltage--which of course then makes the circuit useless).

For that scheme and for any other using control rails, it is not necessary that the relay supply voltage be in phase with the track voltage (although it is harmless if it is).  In fact, one may be DC and the other AC if that is convenient.

I couldn't find specific information on how to use the "two-relay controller" for direction sensing, just the claim that it could do it, which is plausible.  It looks like a bit of an overkill; and I wouldn't want to depend on a computer ("A small microprocessor is used...") to do something simple like that.  But, if you don't mind, go for it.

[trainbrain]

I do use the same track up and down. Thank you all for your imput. Very informative, as usual. I'll study and decide what to do and keep you posted. Thanks again! Brian

[fjerome]

try using an engine with cruise control. a lot easier that all these suggestions. :)

[Anonymous]

Assuming you are running conventional and running only one train on the loop,I would use 3 relays with 24 volt coils, 2,SPDT and 1, DPDT. I would activate the relay coils using an insulated rail powered by a common dedicated 18 volt tap from the same transformer such as a ZW or properly phased second transformer.

Relay U DPDT is on the upper level ,its outside insulated rail is at least one train lenth from the grade. The insulated section need only be one track lenth.

Relay L SPDT is on the lower level its outside insulated rail is at least one train lenth from the grade crossing. The insulated rail need only be one track lenth.

Relay G is on the grade. The outside isulated section is about as long as the grade or as long as you want boosting or reduced voltage.The coil should be 24VDC with a 35 volt 220 UF capacitor across a bridge rectifer in the circuit to the coil. This will eliminate chattering. The other relays can have 24VAC coils

Wire relay U so its coil latches through one set of its own contacts and through the NC (normally closed) contacts of relay L.

In operation relay U latches when a train passes on the upper level insulated rail and unlatches when a train crosses the insulated rail on the lower level. When you are done running your trains you should park it on the lower level.

Construct a voltage divider out of 6 Amp, 50 volt or more diodes. Mount these on a jumbo Euro style barrier strip from Radio Shack in pairs,one in each direction. Each pair of diodes will reduce AC voltage by about .7 volts. 10 pairs for example would give a 7 VAC drop. Hook the center rail throttle lead to one end of the voltage divider. Tap the middle and end of the voltage divider out. For example if the throttle were set at 14 volts the middle tap would be 10.5 volts and the end tap 7 VAC.

Hook the track center rail lead to the common contact of relay G.

Hook the middle tap of the voltage divider to the NC (normally closed) contact of relay G.

Hook the NO (normally open) contact of relay G to the common of the unused contact set of relay U.

Hook the low tap (7 volts in the example) to the NO contact of relay U.

Hook the high tap (14 volts in this example) to the NC contact of relay U.

In this example with the throttle set at 14 volts,the train would normally run at 10.5 volts. It would receive 14 volts uphill and 7 volts downhill on the grade.
The diode array can be elongated or shortened and adjusted so that the train runs the best up and down.

Dale Hz

[lionelsoni]

Dale, that's a good idea to switch the voltage for the entire track while the train is on the grade; but it only really helps with multiple-transformer option, by eliminating the need to run between blocks set to different voltages.  Using the diode option that you propose, he should be able to get away with the original two relays, since shunting diode pairs is no more dangerous than shunting rheostats.

(It doesn't really matter, but I'll say it again, that it's not necessary to have the relay-supply voltage in phase with the track voltage.)

[otftch]

I use a variable resistor tied into an insulated section for the downhill slowdown track.I use one made for a trailer brake on a car or truck.I wired in a switch to either use the circuit or not.That way I can run speed control engines or regular types.

Ed