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Frustrated to the max with 2 wiring challenges

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  • Member since
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  • From: Linwood, New Jersey
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Frustrated to the max with 2 wiring challenges
Posted by gyurick on Wednesday, October 1, 2008 12:39 PM

This will be difficult to explain. I'll try to keep it simple.

I'm using DC, not DCC.

I want to use my MRC Tech-II 2800 dual throttle to power main line with one throttle and yard with the other. I have used insulated track joiners to separate main line from yard track.

Problem #1: There is one section of track (including 2 turnouts) shared by both. I don't know how to wire that.

Problem #2: I run only steam locos. Everytime they approach an insulated track joint, they stall because of the pickup arrangement. I don't know how to deal with that either.

Thanks for your help with this. I've been hung up on this for weeks now.

No matter where you go, that's where you are.
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Posted by maxman on Wednesday, October 1, 2008 1:21 PM

For problem number 1, you will need to insulate the section of track that you wish to share from both non-shared areas.  Then you will need to get youself a double pole/double throw, center off, toggle switch.  This switch will have three pairs of terminals (connection points) on the back.  You will connect one end pair of terminals to the power from one throttle, and the other end pair of terminals to the other throttle.  You then run a pair of wires from the center pair of terminals to the shared section of track.  Make sure that you have all your polarities correct.

Throw the toggle switch one way, and that throttle will be connected.  Throw the toggle the other way, and the other throttle will be connected.  Leave the toggle in the center position, and the track will be unpowered.

For problem number 2, move your era up a few years, scrap the steam engines, and get some diesels :)

Regards

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Posted by retsignalmtr on Wednesday, October 1, 2008 1:38 PM

problem #1 the section that is shared by both throttles must be completly insulated from both the yard and the main line. then use a double pole double throw toggle switch to power the section with which ever throttle you select. center lugs go to the rail section with the outer lugs going to the throttles. be sure to observe correct polarity between the throttles.

problem #2 loco's should not stall at insulated joints unless there is no power to the other side of the joint. if another throttle is connected to the other side of the joint, the throttle must be on and the direction switch must be in the same direction as the other. do you insulate both rails at the same joint location? if you are using both throttles at the same time there should be i.j's on both rails. if you are not insulating both rails make sure the uninsulated joint is conducting power through it.

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Posted by maxman on Wednesday, October 1, 2008 3:04 PM
 retsignalmtr wrote:

problem #1 the section that is shared by both throttles must be completly insulated from both the yard and the main line. then use a double pole double throw toggle switch to power the section with which ever throttle you select. center lugs go to the rail section with the outer lugs going to the throttles. be sure to observe correct polarity between the throttles.

 

Hummm, thought that I answered part 1 already.  Must be the space/time warp continuium problem :^)))))))))))))))))))))))))))

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Posted by Texas Zepher on Wednesday, October 1, 2008 7:24 PM
 gyurick wrote:
Problem #2: I run only steam locos. Everytime they approach an insulated track joint, they stall because of the pickup arrangement. I don't know how to deal with that either.
The answer to problem #2 is to put a section like problem #1 in between each place the train must transistion from one power supply to the other.   In fact it would be good to wire the entire layout so that either power supply could power any section (called a block) of track.  That way by flipping the switches the power supply can follow the train wherever it goes. 
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Posted by retsignalmtr on Wednesday, October 1, 2008 10:39 PM
maxman. your response had not yet been posted when i began to type in my response to prob 1. nanu-nanu.
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Posted by gyurick on Thursday, October 2, 2008 7:20 AM
For Problem #2, a friend recommended common rail wiring. Would that solve the stalling problem? I mean, the steam engine pick-up arrangement is what it is.
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Posted by maxman on Thursday, October 2, 2008 11:56 AM

For problem #2 it might be helpful if you could tell us which particular model steam engines (manufacturer and wheel arrangement) with which you are having a problem.  I'm not a steam engine guy, and don't own any.  But it seems to me that most (all?) of the models out there have current pick up from one side of the engine and the other side of the tender.

If one side or the other does not pick up current, the engine won't run.  This does not seem to be your problem, as you said that the problem only happens when you get to an insulator.  The second thing that can happen is if you have a very small wheel base engine it could stall on a dead section of track, such as an insulated non-powered turnout frog.  That also does not sound like what you are describing.  In any case, even the shortest wheel base engine should be capable of traversing a rail insulator without any problem.

So, if you are saying that the engine stalls right as it crosses the insulator, the only conclusions I could jump to are that either the track on the other side of the insulator has no power going to it (in which case the current path through the motor broken), or the track polarity on the other side of the insulated joint is reversed (in which case you will have a short).

You should really invest in a cheap multimeter.  For what you are doing, a cheap one will suffice.  If you have access to a meter, what you can do is first identify which track insulators are giving you the problem.  Remove the engine from the track, set the meter to read DC volts (12 or 30 volt scale depending on the meter), and then turn up the power.  If you have a pair of insulators, use the meter to check track voltage from rail to rail on the same side of the insulators where you removed the engine.  You should see that the meter will read track voltage (if the meter moves the wrong way, swap the meter leads).  Do the same thing on the other side of the insulators.  If you don't get a reading, one rail or the other is not getting any power.  Then you can track down where you have the loose connection, broken wire, or whatever.

If you do read voltage when you measure across the second set of rails, the next thing you should do is check that you don't have a polarity reversal across the insulated joint.  To do this, again turn the power on and set the meter to DC volts.  This time use the meter leads to check voltage on the same rail from one side of the insulator to the other.  If the polarity of the rails on both sides of the insulator is the same, both rails will be at the same voltage and you will not read anything on the meter.  If the polarity is reversed, you will read a value on the meter.  If you have this condition, a short will occur when an engine tries to cross the gap.

Note that if you don't have a meter but have a 12 volt light bulb with socket and a pair of wires coming out, you can use that to do the same test since, for what you need to check, the actual voltage value is not relevant.  Basically if the light lights, you are seeing a voltage.  If it doesn't, then there is not a current path (or the bulb is fried :)).

Let us all know how you make out.

Regards! 

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Posted by gyurick on Thursday, October 2, 2008 12:36 PM

I'm running 2 Mantua yard goats...one is 0-4-0 and the other is 0-6-0.

The stall occurs when the loco crosses from track powered by the main line throttle to track powered by the yard throttle and vice versa. There is no short. But, there is a point where the loco is picking up power from one throttle and the tender from the other. I think that's the problem but I don't know what to do about it.

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Posted by maxman on Thursday, October 2, 2008 2:53 PM

Okay, now maybe we can get somewhere.

If you have the mainline powered and the yard throttle off, then there is no power to the engine at that point and it will stall.

If you have both throttles "on" and set for the same direction, then the engine will start to receive voltage from both sources and will probably either speed up or slow down depending on which throttle has the higher setting.

If you have both throttles on but the directions (polarity) opposite, then you will get a short.

This sounds like it is getting back to problem #1.  Is the area where the engine is stalling the same area that you were asking about in problem #1?  If it is, then what you need to do is install the double pole/double throw center off toggle switch.  Then you will have created what we call at our club a "joint block".  A joint block is a track section that can be controlled by two separate controllers independently.

The way that this would be operated would be that you would set the toggle switch to be powered from the main line throttle.  You run the engine into the joint section and stop it.  Then you switch the toggle to power the joint block from the yard throttle.  Power up the yard throttle and the engine should then run quite happily into the yard.

[If we're talking about a different area than where problem #1 was, the solution is the same.  Basically any area where you want to control a train with two different throttles requires a joint block setup.  You just can't expect the train to run across an insulator from one power source to another either smoothly or without another problem, namely what would happen if the direction switches for the two sections were reversed.]

Try that and see if it all works for you.

Regards! 

Edit #1  {oh, I just have to ask.  Does your forum name really say "gee, you're ick", or is that just a coincidence?  Guess I've been reading too many vanity license plates :)}

Edit #2  {I just noticed that Texas Zepher has also given you this same answer above}

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Posted by retsignalmtr on Thursday, October 2, 2008 3:41 PM
 as your friend mentioned, common rail wiring may be the answer to the problem. if you are observing correct polarity between the main and yard sections you can turn it into common rail by placing a jumper between the two negitive terminals on your power pack then try to run your train over the area with the problem. remember that electricity has to return to it's own source so the positive energy from one throttle cannot return through the negitive of the other. by putting in that jumper you turn the layout into common rail without having to do any extensive changes. you must observe correct polarity! use clip on jumpers and give it a try.
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Posted by TomDiehl on Thursday, October 2, 2008 8:37 PM
 gyurick wrote:

This will be difficult to explain. I'll try to keep it simple.

I'm using DC, not DCC.

I want to use my MRC Tech-II 2800 dual throttle to power main line with one throttle and yard with the other. I have used insulated track joiners to separate main line from yard track.

Problem #1: There is one section of track (including 2 turnouts) shared by both. I don't know how to wire that.

Problem #2: I run only steam locos. Everytime they approach an insulated track joint, they stall because of the pickup arrangement. I don't know how to deal with that either.

Thanks for your help with this. I've been hung up on this for weeks now.

I'd go one step further than all the advice above, wire all the blocks with the DPDT Cab selector switch, including your yard area. When operating, set the selector switches so that only one throttle controls the same locomotive, don't try to cross from one throttle to the other, even if the two cabs are in the same power pack housing.

And I'd definately avoid common rail. Put insulating rail joints on both rails at the block separation.

(Warning, science content) Most DC power packs use half wave rectification, and even though they're on the same step-down transformer, they may be wired so the half-waves are out of phase.

Smile, it makes people wonder what you're up to. Chief of Sanitation; Clowntown
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Posted by Texas Zepher on Friday, October 3, 2008 2:23 PM
 TomDiehl wrote:
(Warning, science content) Most DC power packs use half wave rectification, and even though they're on the same step-down transformer, they may be wired so the half-waves are out of phase.
The manufacturers do this in order to use only 2 rectifiers instead of 4 that would be needed for a full bridge.  In the old days I understand the economics of that.  Today with the price of copper it makes no sense - just habit I think. 
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Posted by wjstix on Friday, October 3, 2008 4:03 PM
I agree with TomDiehl, I would (and did when I was in DC) insulate both tracks at block divisions, and wire the layout with toggles so that any block can be powered by either power pack. So for example if you're just running one engine, you can throw the switches so that the entire layout is controlled by one controller.
Stix
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Posted by TomDiehl on Saturday, October 4, 2008 11:27 AM

 Texas Zepher wrote:
 TomDiehl wrote:
(Warning, science content) Most DC power packs use half wave rectification, and even though they're on the same step-down transformer, they may be wired so the half-waves are out of phase.
The manufacturers do this in order to use only 2 rectifiers instead of 4 that would be needed for a full bridge.  In the old days I understand the economics of that.  Today with the price of copper it makes no sense - just habit I think. 

A full wave bridge is available as a unit so you just need to connect the AC to the terminals indicated and you have the DC output, with polarity indicated on the other side.

The problem I refer to is the use of a step-down transformer with a center tapped secondary. Usually wired with one cab on each section of the secondary, it's used to increase the available power (amps or watts) but it will also give you an out of phase half wave output depending on how the diode(s) are connected. Since most power packs are designed so you can't open them without destroying them, there's no way to tell how the internal wiring is hooked up without a dual trace oscilloscope. I'm willing to bet few model railroaders have one of these.

Smile, it makes people wonder what you're up to. Chief of Sanitation; Clowntown
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Posted by fwright on Monday, October 6, 2008 1:23 PM
 TomDiehl wrote:

 Texas Zepher wrote:
 TomDiehl wrote:
(Warning, science content) Most DC power packs use half wave rectification, and even though they're on the same step-down transformer, they may be wired so the half-waves are out of phase.
The manufacturers do this in order to use only 2 rectifiers instead of 4 that would be needed for a full bridge.  In the old days I understand the economics of that.  Today with the price of copper it makes no sense - just habit I think. 

A full wave bridge is available as a unit so you just need to connect the AC to the terminals indicated and you have the DC output, with polarity indicated on the other side.

The problem I refer to is the use of a step-down transformer with a center tapped secondary. Usually wired with one cab on each section of the secondary, it's used to increase the available power (amps or watts) but it will also give you an out of phase half wave output depending on how the diode(s) are connected. Since most power packs are designed so you can't open them without destroying them, there's no way to tell how the internal wiring is hooked up without a dual trace oscilloscope. I'm willing to bet few model railroaders have one of these.

All MRC dual throttle power packs since the 1960s were purpose-built with separate transformers for each throttle, thus enabling sufficient isolation for common rail and common return wiring for the two throttles.  The 2800 is specifically cited as being compatible with common rail wiring in the MRC literature.

Many MRC throttles have a "pulse power" switch which changed the rectification to half wave instead of full wave.  The purpose of half wave was to partially overcome motor cogging and provide improved slow speed running of locomotives.  Higher end DC throttles injected more complex pulses on a filtered DC base to better achieve this end without the extra heat of pure pulse operation.

For the OP:  as others have suggested, use block control instead of section control.  Block control allows you to use the same throttle everywhere the loco goes, with inherent stability in control.  Block control requires a toggle or similar to select which throttle controls a given block of track.  To change throttles, stop the locomotive in a block and select the new throttle on the block toggle switch.  Restart the locomotive with the new throttle.

Section control - unfortuantely typical in the 3 rail O world - provides a separate throttle for each section of track.  There are always disturbances and issues as a locomotive transitions from one throttle to another in section control.  Since voltages cannot be matched perfectly - and the load changes as the locomotive is drawing power from one, then both, then one throttle - there is a perceptible momentary change in locomotive speed at the junction between 2 sections.  There is also a "fault" current between the 2 throttles as the locomotive bridges the 2 sections that is proportional to the voltage difference between the 2 throttles.  Normally, the fault current is not damaging, but can be in 3 rail O where currents are much higher to begin with.  Section control requires a separate throttle for each section.

just my experiences

Fred W

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