Nit picking Jim Barrett's Dead Mans switch run251

Yep, that's nit picking.

And of course the following will guarantee thread deletion.

Wire the switch and relay coil so that when bridge is raised, microswitch contacts closes and relay coil OPERATES (on) moving its contacts to open the track circuit power. Bridge lowers, microswitch contacts opens, relay coil "UN-OPERATES" (off), releasing contacts to normal rest position that closes track circuit again.

This way we have more juice going to the rails rather than taken by the relay coil uselessly humming while bridge is normal position.

Contact me off line if interested in rewiring details. Simple.

Just in case you didn't know, many blackberry-type devices add that on their own by default.

Sent on my Driod.

Is #251 out??? I have not seen it.....

quote:

Originally posted by rrman:
Jim,
Great idea. Just detected one little problem. If running DCS and bridge up, then train stops as it should. When bridge put back down, a PS2/3 engine would come up in conventional mode. Don't have TMCC so don't know how those engines react to loss/restoration of power.

Of course small price to pay compared to watching your mega $$ custom painted one of kind engine swan dive to floor.

I do not run DCs but have made a few circuits for those who do. If instead of completely killing power you leave 8 to 9 volts on the track,the engine will stall but remain in command mode and resume when power is restored (18-20 volts). Stalling characteristics vary with model engine but most all can be modified with a few added diodes in the motor circuit to stall. The 8 to 9 volts can be put into the unused relay contact blade. A voltage dropper can be made with 25 amp bridge rectifiers and adjustments made in .6 volt increments.

Diode voltage dropping is described on my blog.

http://www.jcstudiosinc.com/Bl...tegoryMain?catId=426

Dale H

Hi all,

rrman, that's a good catch. Dead sections like this are a problem for PS2 and PS3 engines. The real danger comes if the bridge is opened and closed a second time rather quickly. That will signal an engine that has already dropped into conventional mode to take off in the forward direction at full voltage.

The option Dale H mentioned, dropping the voltage rather than turning it off entirely, has a lot of merit on paper. It keeps the engine in command mode and the engine will return to commanded speed when full voltage is restored. However, there are some difficulties and dangers with this approach. If your roster includes both PS2 and TMCC engines you will have a wide range of minimum voltage required to stop an engine. Some TMCC engines (mostly K-Lines) can continue moving below 6 volts and some MTH engines (early PS2 in particular) will drop out of command mode below 6 volts. In that case you won't be able to set a safe minimum voltage that will work for all engines in your roster. If your roster is PS2 only you have a much better chance of voltage reduction working. However, even if voltage reduction will work for your roster I still can't recommend it. Holding PS2 engines at stall voltage is VERY hard on the motors. The electronics will attempt to compensate for the speed reduction by going to maximum pulse width. The motors will see very high current flow until full voltage is resorted. If you leave the bridge up for more than a few minutes you run the risk of cooking a motor. In short, DON"T DO IT!

You have two much better options for wiring a kill switch to a bridge on DCS layouts. The first option is to use an open TIU channel. If you have your layout running well with three TIU channels or less you have at least one channel to play with. Wire track power on either side of the bridge back to the output of this unused TIU channel. Then connect the TIU input for that channel to the kill switch. Connect the kill switch to transformer power and you're good to go. That will ensure that the DCS watchdog signal is generated on that section of track whenever the bridge is put down.

The second option is to use a DCS Remote Commander. If you don't have an open TIU channel or don't want to run long wires back and forth from the bridge to the TIU you can connect a DCS Remote Commander directly to the kill switch controlled track. The DCS Remote Commander can only operate PS2 engines on a single ID address, but the watchdog signal they generate is observed by all PS2 and PS3 engines. Whenever track power is restored the DCS Remote Commander will transmit the watchdog signal.

Either of these options will ensure that a PS2 or PS3 engine that stops for an open bridge will be placed in command mode when the bridge is lowered. TMCC engines will remain in command mode as long as the TMCC or Legacy command base is powered and connected to the outside rails. Both PS2/3 and TMCC engines will come back up in command with sounds shut off and speed set to zero.

Dave,
Elegant solution using an unused TIU channel or Commander. Probably need to balance this "fix" againt how many time bridge may be raised. If once a year or less, the Jims solution is probably way to go. If bridge runs several times each operating session then Daves solution is best fool proof solution.

Question, if engine comes up in DCS quiet mode, is handheld display speed reset to zero or remains where it was? Would rolling thumbwheel cause engine to shoot back to set speed or start from zero regardless of what display showed?

It's all Greek to me. I'll just have to remember to close my lift-ups after I pass through.
.....
Dennis

quote:

Originally posted by dave hikel:
Hi all,

rrman, that's a good catch. Dead sections like this are a problem for PS2 and PS3 engines. The real danger comes if the bridge is opened and closed a second time rather quickly. That will signal an engine that has already dropped into conventional mode to take off in the forward direction at full voltage.

The option Dale H mentioned, dropping the voltage rather than turning it off entirely, has a lot of merit on paper. It keeps the engine in command mode and the engine will return to commanded speed when full voltage is restored. However, there are some difficulties and dangers with this approach. If your roster includes both PS2 and TMCC engines you will have a wide range of minimum voltage required to stop an engine. Some TMCC engines (mostly K-Lines) can continue moving below 6 volts and some MTH engines (early PS2 in particular) will drop out of command mode below 6 volts. In that case you won't be able to set a safe minimum voltage that will work for all engines in your roster. If your roster is PS2 only you have a much better chance of voltage reduction working. However, even if voltage reduction will work for your roster I still can't recommend it. Holding PS2 engines at stall voltage is VERY hard on the motors. The electronics will attempt to compensate for the speed reduction by going to maximum pulse width. The motors will see very high current flow until full voltage is resorted. If you leave the bridge up for more than a few minutes you run the risk of cooking a motor. In short, DON"T DO IT!

You have two much better options for wiring a kill switch to a bridge on DCS layouts. The first option is to use an open TIU channel. If you have your layout running well with three TIU channels or less you have at least one channel to play with. Wire track power on either side of the bridge back to the output of this unused TIU channel. Then connect the TIU input for that channel to the kill switch. Connect the kill switch to transformer power and you're good to go. That will ensure that the DCS watchdog signal is generated on that section of track whenever the bridge is put down.

The second option is to use a DCS Remote Commander. If you don't have an open TIU channel or don't want to run long wires back and forth from the bridge to the TIU you can connect a DCS Remote Commander directly to the kill switch controlled track. The DCS Remote Commander can only operate PS2 engines on a single ID address, but the watchdog signal they generate is observed by all PS2 and PS3 engines. Whenever track power is restored the DCS Remote Commander will transmit the watchdog signal.

Either of these options will ensure that a PS2 or PS3 engine that stops for an open bridge will be placed in command mode when the bridge is lowered. TMCC engines will remain in command mode as long as the TMCC or Legacy command base is powered and connected to the outside rails. Both PS2/3 and TMCC engines will come back up in command with sounds shut off and speed set to zero.

My approach is more for no hands automatic operation stopping engines for brief periods. With Daves approach I think when power is restored the engine will resume command mode but not remember the last command so it will sit there until a command is given. Do I have this right? If voltage is reduced when it is restored the engine will resume whatever it was doing.

While it is true that the PWM will open up to the motor,if tweeked right little amperage flows through the motor since voltage is held in reserve by the compensation circuit. If the motor received high current flow it would not stall. The various starting voltages have to be handled with paired diodes in series between the board and motor(s). If done right all can be set to stall at the same minimum voltage. In those cases,excess heat will be dissapated by the diodes rather than the motor. The motor stops because of little or no voltage going to it resulting in little or no amperage flow in the motor,not because of mechanical breaking which would result in increased amperage draw.

Again my circuit has been used successfully for automatic stopping on display layouts, such as a train automatically stopping at a crossover then resuming when the opposing train has left,not long term parking of engines. No one using it has experienced motor damage. However if long term parking and motor damage was a concern,a simple timing circuit could be installed killing stall voltage after a reasonable time. In that case it would have to be restarted in command manually by the user.

Dale H

Hi all,

quote:

Question, if engine comes up in DCS quiet mode, is handheld display speed reset to zero or remains where it was? Would rolling thumbwheel cause engine to shoot back to set speed or start from zero regardless of what display showed?

The will come up "quite mode" at zero smph, but the remote will still display the last commanded speed. For the sake of demonstration lets say the last commanded speed was 20 smph. When the thumbwheel is scrolled one notch to either 19 or 21 the engine will move directly to that speed. You can use the direction button, double tap brake feature, or quickset speed to drop the remote to zero.

quote:

With Daves approach I think when power is restored the engine will resume command mode but not remember the last command so it will sit there until a command is given. Do I have this right?

Correct.

quote:

While it is true that the PWM will open up to the motor,if tweeked right little amperage flows through the motor since voltage is held in reserve by the compensation circuit.

Incorrect. At anything below 12 volts the motors are seeing full track voltage. There is no "reserve voltage."

quote:

If the motor received high current flow it would not stall.

If your running with much of a train it sure can. The combination of a heavy train and rubber traction tires can easily put a locomotive into a stall situation with heavy current draw. Don't believe me? Ask MTH's V.P. of Service, Jeff Strank, what happens when a locomotive is "parked" on a dead end siding but inadvertently left at 1 smph. The locomotive will stall and the traction tires will prevent wheel slip. The PWM goes to 100% and the motors fry.

Good morning folks,

Has anybody tried the web site Jim listed in the artical? I could not find the parts Jim listed at this site. I would not mind putting together a circuit like this for my bridge because I already dropped an MTH Challanger on the floor when I had the bridge out.

quote:

Originally posted by dave hikel:
Hi all,



Correct.

quote:

While it is true that the PWM will open up to the motor,if tweeked right little amperage flows through the motor since voltage is held in reserve by the compensation circuit.

Incorrect. At anything below 12 volts the motors are seeing full track voltage. There is no "reserve voltage."

So by this logic if around 8 volts was left on the track in command the motor would receive 8 volts. Yet a PS2 trolley stopping circuit I made for a guy stops in command with this voltage and resumes when 18 volts is restored. Can not be since 8 volts on a trolley motor would still run it at a good speed. On his trolleys no didoes were even needed in the motor circuit.

quote:

If the motor received high current flow it would not stall.

If your running with much of a train it sure can. The combination of a heavy train and rubber traction tires can easily put a locomotive into a stall situation with heavy current draw. Don't believe me? Ask MTH's V.P. of Service, Jeff Strank, what happens when a locomotive is "parked" on a dead end siding but inadvertently left at 1 smph. The locomotive will stall and the traction tires will prevent wheel slip. The PWM goes to 100% and the motors fry.

The motor circuit is adjusted as needed with the diodes under no load conditions. The motor receives no voltage in command when 8 volts is applied to the track and the motor would not spin regardless of speed setting. The example given above is for 18 volts left on a siding with the engine left at 1 scale MPH then stalled physically with mechanical breaking. Opening the PWM circuit with around 8 volts track power is akin to opening a water valve completely on a water line having no pressure. The result would be no flow.

Dale H

I have been doing what Dale H is speaking of since the first TIU hit the streets. It works perfectly. With 5 volt boards I needed the diodes before the motors to increase the gap between where the engine would stop and the board would not fall out. With 3 volt boards no need for diodes.

quote:

Originally posted by dave hikel:
Hi all,

.......................................

quote:

If the motor received high current flow it would not stall.

If your running with much of a train it sure can. The combination of a heavy train and rubber traction tires can easily put a locomotive into a stall situation with heavy current draw. Don't believe me? Ask MTH's V.P. of Service, Jeff Strank, what happens when a locomotive is "parked" on a dead end siding but inadvertently left at 1 smph. The locomotive will stall and the traction tires will prevent wheel slip. The PWM goes to 100% and the motors fry.

I have also had this happen to an Atlas unit with EOB. In a consist with another engine, dirty track or the like, I stopped the consist but one of the engines was still in a forward move mode. A few minutes later that horrible smell indicated a significant problem. Note that the motors eventually had to be replaced but the EOB board was fine. I believe it is an 8 amp drive board well beyond the limits of the two motors. Very good discussion, which shows what can be done when we all work together.
All
Mike

quote:

Originally posted by Mike CT:

quote:

Originally posted by dave hikel:
Hi all,

.......................................

quote:

If the motor received high current flow it would not stall.

If your running with much of a train it sure can. The combination of a heavy train and rubber traction tires can easily put a locomotive into a stall situation with heavy current draw. Don't believe me? Ask MTH's V.P. of Service, Jeff Strank, what happens when a locomotive is "parked" on a dead end siding but inadvertently left at 1 smph. The locomotive will stall and the traction tires will prevent wheel slip. The PWM goes to 100% and the motors fry.

I have also had this happen to an Atlas unit with EOB. In a consist with another engine, dirty track or the like, I stopped the consist but one of the engines was still in a forward move mode. A few minutes later that horrible smell indicated a significant problem. Note that the motors eventually had to be replaced but the EOB board was fine. I believe it is an 8 amp drive board well beyond the limits of the two motors. Very good discussion, which shows what can be done when we all work together.
All
Mike

Mike

This is a different issue than what I am talking about. Dropping track voltage will stall the motor with no load. This can be adjusted with the diodes with the engine on a cradle or on the track with no cars. . The motor stops because of no line voltage to it,no line voltage results in no amperage flow. When around 8 volts or less comes from the track, little or no voltage goes through the electronics to the motor because the circuitry in the boards does not pass it.. In conventional a PS2 loco will not move at around 8 volts or less. If run at 9 volts conventional a setting around 1 scale MPH and if the engine stalled due to mechanical load,does that mean if left that way the motor could burn up? If so than we have a real design flaw here.

With 18 volts on the track and the speed set at one mile per hour the whole issue is different. The motor is stalled due to load of a heavy train and there is plenty of amperage going through it since we have 18 volts potential. . If the motor sits still 8 amps at 18 volts would mean 150 watts on a motor sitting still. I think the MTH PWM circuit is limited to around 3 amps,but still 18 volts is enough to do damage.

For that matter it would be a strain on the motor if pulling a large load even if it moved at the 1 scale MPH if the unit was not geared properly. Be nice if the designers considered this. Could have just had a memory option to resume its state after voltage is restored in command and voltage could be shut off completely. Could have had a simple thermal overload on the motors to protect them.

Those who have access to the people at MTH,the next time you talk to them please ask them why spike suppression is not provided for those users who operate their engines conventionally.

Dale H

Hi Dale ,

I think you're missing some key information about how PS2 electronics (as well as EOB and some other motor control boards) function. First, the can motors NEVER see more than 12 VDC; even when track voltage is 18 VAC. The boards all have rectification and voltage regulation. There is no reserve voltage used to accomplish "cruise control." It's all done with PWM. Therefore, when you see a 1 amp draw on your transformer at 18 VAC the motor may well be seeing more than 1 amp at 12 VDC.

Second, in the case of PS2 and PS3 electronics, in conventional mode the track voltage is treated as a command signal. That's actual track voltage at the wheels, not necessarily the voltage you see on a meter at the transformer. Put any PS2 on a conventional track and it will start to move at 6.5 volts at 1 smph. Since a lot of PS2 engines mechanically can't maintain 1 smph they won't physically start to move until around 7.5 volts, but the electronics are trying to get things moving at 6.5 volts. At 12 volts the locomotives will move at 20 smph. So, if you are running in conventional mode and you reduce the track voltage to 6 volts the PS2 electronics will remain active but the commanded speed will be zero smph and no current at all will be applied to the motor(s). Your suggestion of reducing track voltage posses no danger when running PS2 engines in conventional mode. However, in command mode the behavior of the electronics is VERY different. In command mode the electronics will attempt to maintain whatever speed was commanded from the DCS system. If the engine was commanded to run at 30 smph and you suddenly cut the track voltage to 6 volts the electronics can increase the pulse width to the motor(s) to 100%. That means the motor is effectively a dead short across the 12 volt power supply circuit. The critical feature here is that the OP asked about command mode and not conventional mode.

quote:

If run at 9 volts conventional a setting around 1 scale MPH and if the engine stalled due to mechanical load,does that mean if left that way the motor could burn up? If so than we have a real design flaw here.

In command mode, yes it can burn up, even if track power is only 9 volts. The Mabuchi can motors in PS2 and PS3 diesels are not nearly as robust as the big open frame motors of yesteryear. Dale, I understand that you are arguing that the motors should be able to tolerate dissipating several watts of energy as heat, and they can. The problem is in command mode the electronics can supply more watts of energy, even at low voltage, than the motors can safely dissipate. By adding diodes between the power supply board and the motor(s) as Dale suggests you do add some additional heat sinking capability, which would help to protect the motors at stall. However, this also drops the supplied voltage to the motors the rest of the time. Thus, the pulse width is increased the rest of time. This decreases the motor's efficiency, increases operating temperature, and reduces motor life. You're trading a quick death for a slow one. The better option is to avoid deadly circumstances.

quote:

I think the MTH PWM circuit is limited to around 3 amps

That is NOT correct. The PWM circuit has no current limiting at all at normal operating temperatures. There is a thermal limit on the PS2 power supply board that will cut power if the power supply board is over heating, but there is no thermal protection on the motor. This protects the PS2 power supply board if the locomotive is running with a heavy load for an extended period of time but not the motor. The board can safely and continuously supply more than 8 amps of current at 12 VDC, and is capable of significant short term overload currents. This design allows the system to generate huge starting force and tractive effort with relatively small, cheap, readily available motors. At stall, where the motor must dissipate all the supplied energy as heat and none as kinetic energy, the board is more robust than the motor. That might seem like a design flaw, but it's a carefully considered engineering and manufacturing choice. Replacing a PS2 power supply board will set you back about $100. Replacing a motor costs less than $10. Putting in a larger motor that can tolerate a full current stall condition would make it very difficult to build small prototype and narrow hood models.

MTH is not the only manufacturer to choose smaller motors with high efficiency motor drives to build a better performing drive train. All of Lionel's recent designs have made the same trade off. Rather famously, the Vision Line 0-8-8-0 model was shipped with a firmware flaw that causes it to fry its motors if you try to run it with more than 5 or 6 cars. The owners of the 0-8-8-0's unfortunately have paid the price for Lionel's mistake with that circuit board, but the owners of all the other Odyssey II equipped locomotives have benefited from one of the best speed control systems on the market.

The OP started this conversation asking about PS2 engines in command mode with a "dead man" switch as described in Jim Barret's latest Backshop column. Using Dale's concept of voltage reduction to stall an engine would work fine in these circumstances with little risk for short durations. Passing through the bridge to come and go in a few seconds will do no harm. As I said in my original post, there's a lot to like about the idea. However, imagine a scenario where the bridge gets left up for an extend period of time. Maybe an accessory on the other side of the layout misbehaves. You open the bridge to go tend to the problem. The train comes around to the bridge and stops. Then you hear aloud noise and the wife shouting "@#*$!" You leave the layout immediately to go see what's wrong. Troubles keep you detained and you forget about the layout. You return hours later to find your PS2 engine is still sitting there in command mode with track power on. You put the bridge back down expecting that once full voltage is restored the engine will return to last commanded speed. But it doesn't. It just sits there because the can motors are now bricks. It's not a likely scenario, but it's a bad one, and it's one that need never happen. Dale mentioned earlier adding a timing circuit to a voltage reduction circuit, plus diodes in individual engines, all added to the dead man switch. That combination could give you a safe system, but it's getting awfully complicated. I stand by my original post that the best and safest way to implement a "dead man" switch on a PS2 layout is to live with the fact that when the bridge goes back down you will have to restart the engine, but it will safely be placed in command mode by an open TIU channel or DCS Remote Commander.

Dave

Thanks for taking the time and giving a detailed explanation. I do not use DCS but I have made up a few automation circuits for people who do. These circuits were basically stopping trains or trolleys yielding to opposing trains at crossovers with the method described. . All I can say is that I included an adjustable voltage dropper for the user. There is a voltage somewhere between 6 and 8 where a train stalls even if free wheeled with all load removed and it can remain in command mode. Under this condition little or no current should flow to the motor. When power is restored it resumes what it was doing without operator input. Some PS2 unit motors may need diodes in the circuit while others need no alteration.

I have not had complaints of motor burn outs but the circuit is for short term stops,not long term parking of locos. A protective timing circuit would add $16 to the cost and is not that complicated to do which would provide this added protection. My solution to the stated problem was to provide automation,that is for the loco to resume what it was doing after the bridge is down or whatever where the operator does not have to restart the engine by hand. Space allowing adding a few diodes in the motor circuit is not that difficult either and should not harm anything. It would void the warranty for sure as it is a user alteration and I tell customers that who use the method.

Anyway thanks again and I defer to your knowledge of the system. I run conventional because automation is much easier and that is my field and interest. I do have fun fiddling with this stuff and that is the fun of the hobby to me.

Dale H

quote:

Originally posted by beertrain:
Yep, that's nit picking.

Still think he is nit picking? I've learned alot thanks to his "nit Picking"

Al

Been surprised Jim Barrett hasn't chimed in with a comment.

NICE JOB to Jim Barrett. The article was an "ah-ha moment" for me.

thanks for the tip

I, too, was enlightened by this insight by Jim. I dropped my MTH Big Boy off the bridge several times (finally had to take it in for repair)until I installed manual on/off switches before and after I raised and lowered my bridge. But it wasn't fail-safe, even when I put a sign next to my trasformers saying "CHECK THE BRIDGE!".

After I read the article I ran down to Radio Shack and bought 2 dead man level switches and installed those on my double track bridge -- and it works like a charm. I haven't done the relay circuits that Jim described because I'm not too worried about the trains running into the raised section of the bridge -- I was more concerned about the other direction when my trains they get launched off the table!

Mike

quote:

Originally posted by Dennis:
It's all Greek to me. I'll just have to remember to close my lift-ups after I pass through.
.....
Dennis

Μεγάλη ιδέα. Μόλις εντοπιστεί ένα μικρό πρόβλημα. Εάν η λειτουργία DCS και γέφυρα επάνω, τότε τρένο σταματά, όπως θα έπρεπε. Όταν η γέφυρα που πίσω κάτω, ένα PS2 / 3 του κινητήρα θα καταλήξει σε συμβατική λειτουργία. Δεν έχετε TMCC έτσι δεν ξέρουν πώς κινητήρες αυτούς αντιδρούν στην απώλεια / αποκατάσταση της εξουσίας.

Φυσικά μικρό τίμημα σε σύγκριση με παρακολουθούν μέγα $ $ έθιμο σας ζωγραφισμένα στο είδος του κινητήρα κύκνειο βουτιά στο πάτωμα.


There... that should make the idea clear.

quote:

Originally posted by rrman:
Been surprised Jim Barrett hasn't chimed in with a comment.

He probably has not seen this thread.

Some of you folks seem to think that everyone here at OGR HQ monitors this forum 24/7, reading everything that gets posted here. Jim is a busy guy. If he is like me, he has time to read less than 1% of what gets posted here.

quote:

Originally posted by OGR Webmaster:
Some of you folks seem to think that everyone here at OGR HQ monitors this forum 24/7, reading everything that gets posted here. Jim is a busy guy. If he is like me, he has time to read less than 1% of what gets posted here.

Sure seems like it at times when "interesting" threads suddenly disappear or locked. Someone MUST be monitoring 24/7!

I love this solution and I am getting ready to implement it on my layout.  I am running DCS and I am going to use Dave's suggestion to use an an open port on my TIU.  I have one question though.  I have two tracks across my bridge and only one open TIU port.  Can I use the same TIU port for both tracks, or do I need to use the open TIU port for one track and buy a DCS Remote Commander for the other track?

 

Thanks,

 

Chris

Any thoughts on this?

Chris,

 

I see no reason you can't.  I use my DCS in "zones" were each output of the TIU controls all the tracks in a particular zone of the layout vs having one channel per track.  While I am not an expert, I believe this should be fine for you running DCS in the command mode. 

 

The down side is that if you want to use the conventioal aspects of DCS and control track voltage via the TIU, in that area you would hav ethe same voltageon both tracks, which might not be what you want.

 

Rich

Rich,

 

Thanks for the response.  I need to look more into wiring DCS for zones, to see if this might be a better overall approach. 

 

Thanks,

 

Chris