Want to use Rheostats or resistor bridge to reduce voltage to certain blocks on layout

[dlagrua]

Since I run conventional on a three level layout I run two insulated blocks. One is on the lowest level track rising to the middle level . That block sees 16V and helps the long train climb. The other is on a downhill grade from the top level to the middle (table) level. To slow the train I use a two ohm power resistor to the insulated block middle rail power. It works well and it keeps things simple.

[lionelsoni]

Here's one way to do it using two relays:

One end of the coil of each of relays K1 and K2 connects to the relay supply voltage.

K1 is the relay that selects the track voltage.  The other end of K1's coil connects to a control rail in loop 1 and also to the track common through a normally-closed contact on K2.

The other end of K2's coil connects to a control rail in loop 2.

[OGaugeRailroader]

Hi Bob, I'm building a conventional layout where I plan to use this kind of setup. My end goal is to have my trains maintain a steady speed going up and down grades and on the level sections of the layout.

Taking your rectifier idea one step further, is it possible to use a relay to "select" the right power level for a "2-way" grade? I want to have a couple reversing loops where the train will go down a grade and then level out into a reversing loop. That same train is now coming up the grade it just came down. Can I use a relay to select the right voltage for going up/down the grade? If that's a possibility, any ideas on the best setup? Thanks.

[lionelsoni]

Dave, that could work.  The only problem might be that the grounding connection to the control rail through the car wheels might not be continuous, letting the relay chatter.  You would improve your chance of success by making the control rail as long as possible, to get several wheelsets on it at once.  In any case, if you use a DPDT relay, you can always add the second control rail and the lamp later if you need them.

If you use a single contact to slow down the train, it will have to be normally closed, not normally open.  However, you might as well use the entire SPDT, wired simply to shift from one tap to another.  That way, you don't short out a section of the rectifier string, so it can be tapped for more than one slowdown situation if you have others on that transformer output.

[cruikshank]

Thanks, I was able to draw and figure it out that way.  But... in doing so I reduced the parts count.  All I need is one trigger track and one SPDT relay.  The trigger track will be just upgrade of where I need to slow down.  Lets call it trigger "A"  The downhill train completes the circuit to ground at "A" which engergizes a relay coil.  This kicks in the N.O. contact connecting the Lionel Rheostat or Diode Bridge to the center rail of the slow down area.  When the last car of the down hill train clears "A" it doesn't matter, the engine is already on level grade and out of the slowdown area.  Then when the uphill train leaves the stop track and heads upgrade, the relay has already return to N.C. which is full track power at the slowdown area.  By the time this engine and train completes the circuit at "A" effectively lowering the voltage at the slowdown area , it just doesn't matter, because the engine is out of the isolated slowdown area.  Thanks for all your help.  Till the next problem.... Dave

[lionelsoni]

I don't have a way to post a picture, but I'll try some ASCII art:

(ground)---(relay supply)---(lamp)--A--(relay coil)--B--(NO relay contact)---(ground)

A and B are the isolated control rails, which are grounded when the train wheels pass over them.  If you ground B, the relay operates, the normally-open (NO) contact closes, and the relay stays operated even when B is no longer grounded.  If you ground A, the lamp lights and the relay releases, since it has ground on both ends of its coil.  When it releases, it opens the contact; so, even when A is no longer grounded, the relay stays unoperated.

This circuit uses one of the relay's contact sets.  The other contact set is used to move the center-rail connection from one tap to another on the rectifier string.

You can also do this with a resistor instead of a lamp; but the resistor draws a lot more current.  The lamp's resistance goes up greatly when it is lit, limiting the current to a much lower value when the train grounds A.

[cruikshank]

For this, I think you do need a DPDT relay.  Return the coil to whatever voltage is suitable for it, but through a lamp which is also rated for that voltage and is large enough that there is not much voltage across it when the relay is operated.  Connect the side of the relay coil that is connected to the lamp to a control rail A at one end of the hill.  Connect the other side of the relay coil to a control rail B at the other end of the hill.  Connect a normally-open relay contact in parallel with control rail B, to layout common ("ground" or the outside rails generally).

Hi, I'm trying to draw this out, and not quite getting it.  Do you have the ability to draw, scan and post your idea? How I envision it is that the light builb and the Realy coil are connected at one end of the coil, and this is connected to the Relay Voltage, be it DC or AC.  Then depending on the trigger either A or B, either the Coil is energized, or the bulb.  The bulb having low resistance when lit would then open the relay. Not sure what is going on through the contacts.  Perhaps you can word it a little different for me, am I on the right track.  Thanks,  Dave.  Also I'm aware of Atlas relays, they are actually their switch machines with contacts.  Have to look at that also. 

[lionelsoni]

Dave, I get from your post that you don't particularly need anything new to start the trains going back up the hill, you just need the voltage reduction on the hill to depend on the direction of the train going up or down the hill.

For this, I think you do need a DPDT relay.  Return the coil to whatever voltage is suitable for it, but through a lamp which is also rated for that voltage and is large enough that there is not much voltage across it when the relay is operated.  Connect the side of the relay coil that is connected to the lamp to a control rail A at one end of the hill.  Connect the other side of the relay coil to a control rail B at the other end of the hill.  Connect a normally-open relay contact in parallel with control rail B, to layout common ("ground" or the outside rails generally).

Now, when the train passes over control rail B, the relay will operate and will be latched on through its contact.  When the train passes over control rail A, it will light the lamp, removing all voltage from the relay coil, and release the relay.  Use the other relay contact to change the tap on the rectifier string to get the two track voltages you need for uphill and downhill running.

The relay can be run on AC or DC of any voltage, whatever is suitable for its coil.  You don't need to worry about "phasing" for this application.

Other possibilities:  Atlas makes a mechanically latching relay that they call a "snap relay".  It has two coils and DPDT contacts (of which you need only SPDT).  You can operate each of the coils from one of the two control rails.  I assume it is meant for 12 volts DC.

You can also eliminate the lamp in my circuit and use a normally-closed contact of another relay, in series with the coil of the first relay, to release the first relay.

[Wes Whitmore]

But then we have a train coming out of the staging area, that needs to go up the grade.  It needs the full voltage, not reduced. 

I think you only need a relay to do this.  Or you can used a timed relay.  Basically if you have a relay connected to the same ground track that the siding engine is sitting on, you can have the supply power of that relay connect to the same 3 slow down tracks as well, since you can "lay" higher voltages over lower voltages safely on the same track point.  That way the train will come into the siding, slow down and stop by using 3 decreasing voltage points on the rectifiers, wait for the "trigger train" to complete the ground when it's safely out of the way, and then it will trip that relay and send higher voltages to the siding train to get it up the hill and past those 3 reduced voltage tracks.  You will have to find a place on the layout to put your release track for that relay so it's ready for the next approach into the siding.

As for a timed relay, that's what I use and a lot easier. 

http://www.etrainshop.com/tek9.asp?pg=products&specific=jocnoqeph0

 It only allows 15 seconds of run time before it closes, so your siding train would have to be able to get past those three slow down sections in that amount of time.  Mine is infra-red, but is made to fit on MTH realtrax.  I have not shopped around for other IR devices.  I bet there are more generic ones that still have the timer.  I'm thinking that Lionel has one that looks like a power box that you see at RR crossing gates.  Anyhow, it's really about the same as the relay above, but easier.  You set it at the "trigger train" location, and run your "higher go up the hill voltage" from the bridge rectifier stip to it, and then connect the output to all 3 of those slow down track sections, just double tapping the higher and lower votage supply cables on the same track.  Then you set the timer knob for 15 seconds.  The trigger train triggers the IR device, closes the relay, and the siding train goes back up the hill at higher voltage than what it came down on.  After 15 seconds (that's 15 seconds after the last trigger train car passes the trigger track, which would really be providing the siding train with 18+ seconds of higher voltage run time, depending on your train length and speed), the relay opens back up and the 3 lower track voltages are there to slow the train down and run the cycle again.

 

Edit - I looked around a little and MTH scaletrax has the same type of timer circuit on a more generic box. 

http://cgi.ebay.com/LOT-2-MTH-ITAD-INFRARED-TRACK-ACTIVATION-DEVICE-45-1028_W0QQitemZ270136700215QQcmdZViewItem

 Also, here is a modification for the MTH ITAD that allows you to bypass the sensor and use a track trigger like you are used to, but lets you keep the timer function, which is really the most important part. This may be the best solution for you since you want rock solid reliability...For $20 it should solve your problem.  Any by doing this, you could just hide the realtrax ITAD under the table somewhere out of sight. 

http://www.toytrainrevue.com/itad.htm

Wes

[lionelsoni]

Did you measure it under load?  The diodes need a little current through them to develop their voltage drop.  A voltmeter usually has a very high input impedance so that it will draw very little current from the circuit being measured.

Nevertheless, the voltage won't be correct unless you are using a "true RMS" voltmeter.  You should also not expect even with a true-RMS voltmeter that the sum of the load voltage and the rectifier-string voltage will equal the transformer voltage.  You can look at the waveform on an oscilloscope; but you would have to do a lot of computation to come up with an RMS-voltage number.

The simplest way to measure the voltage with a small incandescent lamp.  Hook up the lamp with an SPDT toggle switch so that you can instantly switch it between the voltage to be measured and a sine-wave source, like a train transformer.  Adjust the transformer so that the lamp's brightness doesn't change when you throw the switch back and forth.  Then measure the transformer's voltage.  That will also be the RMS voltage of the bridge-rectifier setup.

[cruikshank]

OK, still working on same club layout.  We have a series of stop sidings, and trigger tracks.  The train stops in the stop siding, until another train going in the oposite direction triggers the stop track, through the common outside rail causing the stopped train to proceed.  This Works.  Where we have a problem is this.  We are operating 2 or more trains in opposite directions.  We need to slow down the ones at 3 points going down grade into the staging area through a 1/2 turn helix.  We can do that with the bridge diodes or a # 81 resistor or whatever.  So far so good.  But then we have a train coming out of the staging area, that needs to go up the grade.  It needs the full voltage, not reduced.  So short of a logic circuit what ideas do you have to have the reduction circuit in place for one direction and not for the other ? Thanks,  Dave

[cruikshank]

  You can't measure the voltage accurately with a normal voltmeter, neither on the track nor across the rectifiers, because the rectifiers do not produce the sinusoidal waveform that most meters expect.

 

Maybe this is my problem.  I hooked up three bridge rectifiers (RS 25A 50 V) as described. I tied the + and - together and then ran the Ac in series through the ~ leads.  When measuring with a DVM on AC scale I was only getting a .7 volt drop instead of the expected 1.2 - 1.7 drop the package said I would get.  Did I do something wrong, or can this only be measured with a scope ?  Dave

BTW I wired and attached them to a board.  On the same board a used a Euro Terminal block.  This gave me a place for AC in, then 3 taps, one after each bridge rectifier. 

 

[lionelsoni]

Yes, Kurt.  You can use multiple taps on a single string of modules for different blocks; and you can tap the same point for multiple blocks.  You can even get a half step by tapping the +- connection of a module.  Each complete module will drop the RMS voltage by a little more than a volt.  The steps are not all the same, but close enough.  You can't measure the voltage accurately with a normal voltmeter, neither on the track nor across the rectifiers, because the rectifiers do not produce the sinusoidal waveform that most meters expect.

[Wes Whitmore]

If you look at my strip, the highest voltage in on the left (where the output of the transformer is clipped on), and the smallest voltage is on the right-most prong.  Each prong offers less voltage as you move from left to right.  I think you will find that each prong drops around 1/4V or so.  That's small enough steps for me.

 You can tap as many times off of one prong as you need to.  If you have trains with a speed control, all you probably have to do is step them down to the final voltage since it will slow down (with brakes if you have sound).  If you are running older post war trains and you have the slow down room, I would probably string a bunch of single track blocks together and drop a half volt or so each.  It might be smoother than just dropping your total 3 volts all at once.  I haven't tried it as all of my trains are newer MTH models.

Wes

[kpolak]

Do I understand this correctly???

Can I connect (1) series of bridge rectifiers and tap off varoius locations to provide voltage reduction to various blocks?  It looks like there is one series of bridge rectifiers, with multiple take offs.

Say I have 3-blocks of track and I want to reduce speed 3-times.  Can I build one series of rectifiers, and tap off three times from that same block?

Thanks,

Kurt

[jefelectric]

If you have trouble finding these at RS, a lot of them are dropping components, All Electronics has 6A with a mounting hole for .80 each in lots of 10.

http://www.allelectronics.com/cgi-bin/item/FWB-66/search/6A_600V_BRIDGE_RECTIFIER_.html

Keep in mind that this is a surplus house and what they have in stock varies from time to time.

[lionelsoni]

I just dug out one of the Radio Shack 6-ampere bridges; and, sure enough, there is a hole, just like Wes says.

[Wes Whitmore]

Since I don't know much about syncing all of that up, I'll stick with my strip of rectifiers!

 

[lionelsoni]

Wes, unless you have the phase and the frequency and the waveform and the voltage the same, there will be a fault current and arcing.  But if all those are the same, there will be no change in the speed either.  That is a good reason for using a voltage-dropping element like a rheostat or a diode string.

Spike, doing it that way guarantees a fault current.  It is true that the voltage drop with a rheostat varies with the current drawn by the train.  But the voltage drop using the bridge rectifiers does not.

I made a comment earlier about doubling the current rating of the bridge rectifiers, which was wrong.  I have edited it out.

[Wes Whitmore]

I think you have to worry about transformer phase with ajoining track pieces being run off of two different transformers.  That's what I remember reading here.

You can do it all with one transformer if you use the rectifier diodes. 

So many different ways to do it.

Wes

[spikejones52002]

Major problem with using resistors is heat and different voltage with every different train or load.

Isolate the track section you want to run at a different speed.

Place a small transformer set for the speed you want for that section.  

[Wes Whitmore]

To add to the above post, I use the same RS 6 position switch and it works great.  Pos 6 is full throttle, pos 1 is just enough voltage to stop the train without shutting down the speed control.  I just grabbed 4 more voltages from the strip to fill the other 4 positions. 

Wes

[dsmith]

I have been using diodes to control speed on both uphill and downhill grades on my Lionel postwar layout that uses a standard set of Lionel trestles. This is quite a steep grade. Here's how I do it. For blocks that are level I use 2 sets of opposite facing 6 amp diodes. This reduces the voltage to the level blocks by about 1.4 volts. The uphill grade gets full power. On the downhill grades I use a series of opposite facing diodes running through a 6 position rotary switch (Radio Shack). I have two separate blocks on the downhill grade, so I can select the following:
Position 1. 1 diodes beginning grade 0 diode ending grade
Position 2. 1 diodes beginning grade 1 diode ending grade
Position 3. 2 diodes beginning grade 0 diode ending grade
Position 4. 2 diodes beginning grade 1 diode ending grade
Position 5. 3 diodes beginning grade 0 diode ending grade
Position 6. 3 diodes beginning grade 1 diode ending grade
The ending grade adds 0 or 1 diode to the beginning grade.
The downhill grade diodes run through the level block diodes.  I know that this sounds complicated, but it gives you lots of control over the downhill grade.
Factors that affect the speed on the downhill grade, engine type(magnatraction, traction tires, weight of engine, type of motor), number and weight of cars.
You can see that I have only one selection for going uphill but many selections for going downhill. For some reason the downhill grade is much more variable that the uphill grade.
I also run all track power on my LW transformer through 2 sets of opposite facing diodes to cut the power even more so that the low end speed is easier to control and the top end power is reduced a little.

[Wes Whitmore]

Mine is the 276.1181.  There is a hole in the center...

http://www.radioshack.com/product/index.jsp?productId=2062583

 

[lionelsoni]

Those big ones with the holes (276-1185) are rated for 25 amperes.  But the hole can be handy for mounting, as Wes says, and might be worth the extra buck.

The 6-ampere ones (276-1181) are plenty big electrically.  Even the 4-ampere ones might be big enough; but I wouldn't go lower.  The 400-volt rating (276-1173) is no better for us than 50 volts (276-1146), and it's 50 cents cheaper.

[Wes Whitmore]

And that's how I did all of my voltage reduction, thanks to Bob.  I went the easy way out and used the rectifier modules from Radio Shack, but it was very easy because they are big and have a mounting screw hole.  I had to go to 5 different RS to get enough.  Each one has a couple in stock.

 

Wes

[ChiefEagles]

Bob gave me the bridge rectifier instructions several years ago to reduce voltage for a smoke unit I put in a dummy.  I have used them since for more smoke units and reduce voltage to accessories "in line" with other that operate on a higher voltage.  Works great. 

[lionelsoni]

I'm not familiar with trailer brakes; but that may be a good source of rheostats.  Old Lionel rheostats, like the 81, 88, and 95, which have a maximum resistance of 5 ohms, are easy to find at trains shows and on Ebay and usually cheap.

Rheostats are certainly a simple way to do the job.  Bridge rectifiers have the advantage that the voltage reduction does not depend on the load current.  This could be useful if trains with different current requirements are run on the same grade.  To modify a rectifier module, short the + and - terminals together and put the ~ terminals in series between the transformer and the center rail.  Use as many modules, rated around 5 amperes, as you need to get the speed you want.  You can use the +- point of one module as a half-module tap for fine adjustment.  The drop will be a little more than 1 volt per module; but you can't measure it accurately with any usual voltmeter.  Trial and error is best anyway.

[otftch]

I used a variable resistor from a trailer brake for a car.I don't know the price because I had one laying around but it should be available from any auto store.I have had it hooked up for about three years and have had great results.I just wired it into the block that controls the down grade.I use the same power system you decscribe so I know it will work.

                                                                         Ed