Noob question on connecting new WTIU to power (transformer)

@James Brown posted:

Keep in mind, I am a relative noob to 3-rail and got in after the pandemic so MTH is foreign to me.  So since MTH did not include ANY sort of instruction on how to connect the WTIU (either in the setup guide in the box or in the instructions on their website), I was able to go to the DCS User Manual which is old (2014) but at least shows how to connect a TIU.  Anyway, the thing that is confusing me is which input to use to go from transformer to WTIU.  The way I understood it, the Variable Inputs are for if you want to run conventional or DCS using a throttle-type transformer whereas the Fixed Inputs are if you are just running DCS and are using a power brick (fixed voltage).  Is that correct?  But then the DCS User Manual says to connect the transformer to the Fixed Voltage In1 and then turn on transformer and increase throttle to 18V.  So that implies that you have a variable throttle connected to the Fixed Voltage input!  I am confused, can someone help so I don't blow up my equipment?  Is there a better description/website/YouTuber that goes thru this in painstaking detail for newbies?  Oh for the record I want to connect a Throttle-type power source (Lionel CW) because I like running new stuff AND old stuff.  Thank you for any assistance!

In this context, "fixed input" means that you will not vary the voltage from the transformer.  Connect your transformer to those posts, set it to 18v, and leave it there.  Run your trains via the app or a tethered remote.

Although the WTIU seems to have some new quirks (based on other posts on the forum), I think that the DCS Companion book is still a worthwhile reference.  3rd edition is still available from Amazon. $30 well spent, IMO.

Re running conventional, I think I'm an outlier - I have a DPDT switch that swaps from DCS to conventional.  There are other approaches, but I'll leave it to others to cover them.

The Fixed Channels of the WTIU will pass the Horn & Bell functions through to the tracks when operated.  So if you connect a ZW or Z4000 to the FIXED 1 & 2 inputs, you can vary the voltage, use the horn & bell buttons, or crank the voltage up to 18 and run DCS command engines as the outputs will generate DCS signal to the tracks no matter what the voltage level is.

You can also connect bricks to the Variable inputs and use the DCS app to control conventional trains on those outputs. In the app, you can adjust the voltage, trigger the Horn & Bell, or once again crank the voltage up and run DCS command engines as those outputs are always generating the DCS signal no matter what the voltage is set to.

If you have no intention of ever running conventional, you can configure the WTIU to set the Variable channels to "FIXED" mode where the two Variable channels will now operate exactly like the other two FIXED channels.

As the name implies, the "fixed" inputs (and outputs) are for supplying a fixed voltage from your transformer to the track. Typically, the reason for this would be for running command controlled engines on your layout such as Lionel TMCC and Legacy and MTH DCS engines that require a fixed voltage such as 18v to operate.

The difference is that with conventional engines you vary the train's speed by modulating the voltage, whereas with a command engine you supply a constant 18 volts from the transformer to the track (through the TIU or WTIU) and then vary the train's speed by using the handheld remote, app, etc.

It doesn't matter to the TIU or WTIU how the 18 volts gets to the fixed input, so you can use either a brick which supplies a constant 18 volts output or a "handle -type" transformer in which case you have to move the handle up to supply the 18 volts - either way is fine.

I heard some buzzing coming from the fixed input on my new WTIU when I tried powering with an improved cw 80 . Put back the 180 brick with no handle and it’s fine ? I wanted to bring down the voltage a volt because the 180 brick puts out 19 volts . Is there concern with 19 volts ?

Zero concern with 19V. The MTH Z4000 can input 22V roughly- it was designed for that much.

Yes putting a chopped wave input from a transformer like a CW80 might be noisy this is known and expected.

Thanks Vernon . Although the 19 volts won’t hurt the WTIU , do you think 19 volts can be harmful to engines ?

To be clear, this is the difference between the fixed and variable channels on the TIU...

Variable channels can "vary" the voltage from the DCS Remote or the DCS App if using the WIU or WTIU. Fixed channels cannot.

All channels can accept either fixed voltage from a "brick" or variable voltage (up to 22 V) from a traditional pure sine wave transformer.

Your mileage may vary if using a "chopped" sine wave transformer. Also, one thing to note... the remote (and app, though I haven't confirmed this) assume that your transformer are capable of supplying 22 V max. If you use an 18 V brick or a traditional transformer (like the original ZW) the voltage displayed on the remote when using the variable channels may not be accurate. I think you can adjust that in the system settings, but it's been a while since I used it that way.

One other note, the original TIU could be itself powered by the transformer connected to the Fixed 1 input OR the auxiliary power port. From what I understand, this is not the case with the WTIU... You must use the auxiliary power port now.

@Edward M. posted:

Thanks Vernon . Although the 19 volts won’t hurt the WTIU , do you think 19 volts can be harmful to engines ?

It's a Lionel transformer for Lionel engines. Yes, all day long I advise 18V for Lionel and O gauge equipment in general as a voltage limit suggestion.

That said, 19V is open circuit voltage with no load. I think you are worried about a big nothing burger because stepping back with some electrical knowledge, knowing the error possible in measurements, the possible unloaded circuit voltage- you take a measurement as an absolute without understanding the bigger context of the total situation.

It will be OK.

Thank Vernon. Very nervous about that . You know how much this stuff cost lol .

Do not use a chopped waveform transformer, such as the CW80 or Z Controller, with the WTIU. The WTIU will buzz and circuitry associated with generating the DCS signal may be damaged.

As Vernon mentions, voltage level is not a concern.

Thanks Bruce . I will just use the 180 brick.