TIU Variable Voltage "Spitting and Sputtering" - How do I get clean power for conventional operation?

I have no clue from the videos as regards what is the issue, however, it looks and sounds, to me, to be power-related and not due to DCS.

Both power sources are the same: a postwar LW transformer.  The power is clean and smooth until it goes through the TIU at which point it becomes garbled. I have tried several other transformers both older and modern era, to rule out a power issue.  

Because the problem with these "rattling" noises only manifests when a voltage change is input from the iPhone, I ruled out the power supply as the cause.

I attempted to demonstrate this issue in the pair of videos where flickering lights and pulsing sounds can be observed. Perhaps the comparison wasn't as obvious as I hoped. Conventional operation is simply insufferable.

Unfortunately, for now, the only solution is to abandon the use of the MTH system for conventional control until this bug is resolved, or the hardware is fixed. It's too bad as I had hoped this system would be able to run both DCS and conventional. 

The bigger issue is that I simply cannot have runaway locomotives. The lack of affirmative control from Wi-Fi devices, the disconnects, tentative behavior and sluggish response to command input is unacceptable and an ultimate deal breaker. I don't need a system that throws locos off my layout onto the floor.

Gregg,

I don't mean to be difficult however, in 15+ years of using DCS and 18 months using the DCS App to drive PS2 and PS3 engines, I've never encountered, or heard of, what you describe. I suspect that it's something unique to your environment.

How is your WIU connected to your smartphone or tablet, MTH or Home mode? If Home mode I'd suggest that you try MTH mode.

Thanks Barry,  I appreciate your help. The system is terrific with PS2/PS3 engines. I'm only complaining about the variable voltage output. I have tried Home and MTH modes. I will try to determine whether there is some kind of signal interference messing things up. Thanks again. Greg

Greg,

Question: Do you have or can you borrow a DCS remote? If so, try that and see if you can replicate the problem. That might help pinpoint the problem. BTW, I've used a DCS remote to successfully run conventional, DCS, and TMCC engines all on the same track (albeit not all at once) and have not seen the effect you are having.

Chris

LVHR

Is the TIU new or used?  Do you have any loose connections on the Variable channel input or output?  How are you powering the TIU when using Variable channels?  G

I haven't been able to borrow a DCS remote. The TIU and WIU are both new. The connections are solid. The TIU is powered by a postwar LW or ZW (I have tested both). The power is smooth and only gets garbled after going through the MTH system.

My earlier post included videos, but did not quantify the problem. I have now measured the flickering power. The voltage fluctuations are up to 10 percent. The problem only occurs within the lower range of voltages. So, if I set the voltage at 5 volts, it will randomly flutter around from about 4.7 volts to 5.3 volts. Then, after about 5 seconds, the voltage will stabilize at 5 volts. While the voltage is flickering, I can actually hear faint clicking from the TIU. If I set the voltage at, say, 16 volts, it will immediately stabilize at 16 volts without any issues. The power fluttering is much worse at lower voltages.

I realize that most DCS users don't notice this issue. Most are focused on modern era DCS and Legacy equipment. The erratic fluctuations in voltage cause E-unit chatter, and rough, unreliable operation. Maybe I have a bad TIU...

Maybe, but again how is the TIU getting power?  Variable channel does not provide power to the TIU to function.  Must be Fixed 1 or the Aux input.  IF you are jumping VAR1 to Fix 1 to power tiu and than trying to run TIU off 5V AC, that is your problem.  Power Fixed one or Aux power input with 12-15V.  Then see how the VAR channels respond to low voltage input. 

Also is this a new TIU or NOT?  While outside connections are tight, there are internal wire connections via nuts.  If the above is not the problem, make sure internal nuts are tight on the TIU input and output wires.  G

Hi!

I have played with the DCS TIU variable channels for a while — trying to achieve smooth operation of my favorite conventional items like bump-’n-go trolleys, speeders, MOW vehicles, and hand-cars — the stuff the kids love to watch!  Most of my layout uses that excellent fixed-DCS with 18-volt power, plus I run some curvy tracks on 18-volt-sourced variable channels.  I have never had satisfying results on the variable channels, even with setting the minimum voltage. No matter what, the trolleys run too fast, are jerky, or they buzz.  Makes me want my old ZW handles back!

What DOES work for me is the addition of a 2:1 step-down transformer between the TIU and the track.  This yields smooth starts/stops and smooth running.  The transformer I use is a Triad Magnetics F-280U (Digikey part #237-1957-ND).  This is designed to be a power transformer with 120 volt input and 60 volt output.  Never mind the voltage — its the ratio I want.  And the beef — it handles 120 watts. I connect the 120 volt input to the TIU variable channel and the 60 volt output to the track. Thus, 2:1, and I ignore the supposed “voltage” displayed on the controller.  Watch the trolley, not the voltage claim!  I leave the variable minimum voltage setting at its default.

This works for every conventional gadget I run, but it does not support the bell or whistle in locomotives.  Most of my favorites don’t have bells or whistles anyhow!  “Direction” does work fine.  There is no difference using the WiFi app or the MTH remote. I installed power switches to add/remove the 2:1 transformer, but “remove” has never been used, not even to run a short consist behind my Lionel dockside switcher.

Why is this so smooth-running? The voltage steps are smaller, and the transformer probably smooths the wave through magnetic hysteresis. 

Overall, I power the layout with non-toy transformers like the Hammond 165V18 (DigiKey part #165V18-ND)  which provides 18 VAC at 20 amps.  I also use 10 amp fast-blow fuses for each channel.  “Fast” is an understatement!  I’ll never run without them.

I hope this opens up another option for you.

I think GGG is going in the right direction. He asked "How are you powering the TIU?"

To elaborate: There are 2 power supplies required: 1 for the electronics in the TIU, and 1 that goes through the TIU to the track and actually provides power to the engine(s). These sources can be separate, or can be the same, depending on how you connect things. In the simplest form, the TIU is powered  through Fixed 1. You apply a constant 16v or so to Fixed 1, and that voltage provides power to the track AND the TIU.  The other common way to power the TIU is through the AUX power port on the end of the TIU. This provides power ONLY to the TIU electronics, and NO power to the track. You need a power source that provides 12-18v  (ac or dc) to the Aux power port. (Barry, feel free to correct me if I have the exact voltages incorrect.) I suspect (and I think G does as well) that you are powering the TIU through Fixed 1. If that is indeed the case, then that is the cause of your problems. The TIU does not perform well with low voltage supplied to its electronics. With conventional engines, voltages under 12v are quite common. You just don't need that much voltage to get the engine flying down the track.

There are several answers: You can power the TIU with Fixed 1 from 1 post of your ZW/KW set to ~12-14v , then power the layout from another post on the ZW/KW and go through 1 of the other TIU channels to  the tracks on the layout. Or, you can get an auxiliary power supply (wall wart)of sufficient voltage to power the TIU through the AUX power port. If you go that route, then Fixed 1 will be independent of the wall wart power.

Chris

LVHR

The problem with the TIU variable channels is they have pretty large voltage steps, so they may result in noticeable sudden speed changes as you change the track voltage. 

Thank you everyone for your feedback and great ideas. My TIU currently receives power from the AUX input at 12VAC. The VAR1 input is at 18VAC. I have also tried connecting FIX1 to 18VAC, with a jumper to VAR1 (without using the AUX input). I have sent the TIU to MTH for diagnosis and verification of connections. They claim it works to specs.

By experimenting, I did find one method of getting smoother power output on VAR1. If I cut the input voltage at  VAR1 to about 15VAC or less, the output is smooth across the entire voltage range. If I set the input to 18VAC, I receive terrible power signal quality within the lower half of the voltage range, with all kinds of flutter.

Of course, as GRJ pointed out, the voltage steps have a coarse resolution, and that can contribute the overall effect. But I am talking about flutter when the voltage is set at a certain value and left alone.

My best solution so far for conventional variable voltage operation, has been to use my TIU in passive mode, with a Legacy Powermaster set as an engine in the WiFi app. The Powermaster, although it provides a chopped wave, provides considerably more stable and smoother power.

The Legacy PowerMaster will do 200 speed steps, far more than the huge jumps that the TIU does, that should greatly contribute to smooth running.