DC Off Sets and Speed Control on MTH Trains

The Z1000 controller drops the overall power to the track when you hit the whistle or bell button it appears.  That probably accounts for the cruise control not having the headroom to maintain the set speed.

 

The are built to handle not just a "small" DC source.  They can actually run on track DC as used in HO and large-scale...of course you lose conventional bell and whistle capability.

John/Stan, 

 

Thanks for the replies. 

 

Let me clear up the speed up/slow down when hitting the bell or whistle. With a meter, I see the juice drop when pressing bell and increase when hitting whistle. Train response however varies - nearly always speeding up but sometimes slowing down if I'm pressing bell/whistle a lot at one moment. Is this normal? 

 

My other big question - I know the cruise control is meant to keep the speed set at X mph/volts. Is there some sort of issue or malfunction when, pressing the whistle that sometimes the train speeds up or sometimes holds the set speed (no reaction to DC off set)? My LC+ engine, when running via transformer (no remote), I don't see speed fluctuations with bell/whistle presses. I'm thinking with speed control, the train shouldn't speed up/slow down regardless but....input would be appreciated. After a few somewhat large repair bills over the past year or two, I'm rather paranoid about NOT blowing something up again!

Don't forget, the AC to the track as positive and negative components, hence Alternating Current. So it doesn't matter if you use positive or negative DC, the offset bumps the AC one way or the other, creating an effective increase with consequent speed up. It's more apparent on an O-scope display than a meter.

 

I never got around to dissecting a Cruise Control board, so can't speak to that.

 

 

I just performed an experiment using a weak 9 volt battery...I placed the terminals of the battery to the outside and center rail of the track with the engine running and the horn blew. ..with that in mind...am wondering about what the safe offset voltage is...I did not notice a change in speed...am running a lionel conventional with railsounds...no cruise...also...could track blocks and limited 9 volt power supplies be used to automate whistles and bells in this manner?

To your last comment first, I don't think anything you did wrt to pressing B or W were the cause of those large repair bills.  A "modest" speed-up and/or slow-down when pressing B or W does not indicate anything is about to fail or that something is not working right.  I say modest to contrast with, say, the train flying off the rails when you press B or W which probably means your transformer/controller went south.

 

Measuring track voltage with a meter can be tricky.  Since track voltage is AC, it's logical to use the "AC" voltage function on your meter.  Try measuring a 1.5V or 9V battery with the meter set to "AC".  Most meters will read 0 Volts since a battery is DC and there's no AC.  Well, now think about putting that DC offset on the track AC voltage which is what B and W does.  Will (or should) your meter now include that DC offset in the AC reading?  Remember that the meter reads "0" in response to DC only (the battery).  This is a trick question which quickly descends into techno-babble.  Hold that thought.

 

Now think of the generating side.  There are many ways transformer/controllers generate the DC offset for B and W.  Some (in the old days) had a battery that was switched into the circuit, some use diodes block one polarity or the other, chopped-sine (triac) controllers might alter the sinewave chopping to give larger chunks on one polarity or the other, and so on.  The DC offsets that appear on 3-rail vary all over the map.

 

So we have poorly defined "what' and "how" in what is being measured, and how to do it.  It's hard to imagine manufacturers getting excited about expending engineering efforts toward fine-tuning conventional control functions.  OTOH, if LC+ engines have sorted this out, I tip my hat to them.

Thanks Len and Stan. 

 

I stress that the trains don't launch into orbit when hitting b or w - just a "modest" slow down or speed up. 

 

As mentioned, my main concern was, even with speed control, how much speed up/slow down should I be seeing, if any, and is there something screwy....guess not. Back to runnin' trains!

What voltage are you running the MTH unit at when you press the B or W button?  Do you have another transformer to try?  Sometimes a faulty transformer can impress too much DC or effect the AC voltage.  Causing the train to speed up or slow down depending on the effect.    G

Voltage I use varies. Generally between 8-12 volts. I can try another transformer but it will be a few days likely before I can swap and test. 

I should also mention that with a meter, I only see about a 1.5 to 2 volt change in AC with bell and whistle on both of my MTH transformer. That does not seem excessive to me, but then again I may be wrong

Note Stan's comment above, the change in AC readings with most meters trying to read a DC offset on an AC waveform doesn't mean much.

You really shouldn't take it to mean anything - its basically a suprious reading.

 

I've noticed new cruise (both PS3 and late Legacy, seem to be much better cruise controls.  No oscillation of speeds, as you could sometimes get with early Odyssey, and I've seen no change in speed on my NW-2 when bell or whistle are activated - none, nor with the Lionchief Plus or Legacy locos I get recently.  I did see it with some earlier models.

 

  

Thanks Lee and John. 

 

In short, should I expect to see some variation in speed when hitting bell or whistle (DC Off Set) even with speed control equipped locos?

It's possible, and it varies based on the locomotive.

 

Fellow Gibson guy,

 

The problem with 9V at track blocks is that the AC to feed the train power would have to feed both the track and the "whistle block" so the 9V would not be limited to just one spot. 

 

Might be better to use an isolated outside rail to trigger a relay that pushes the whistle button.  I have done that with great success.

 

Ed