TIU DC auxiliary power input - does DC barrel polarity matter?

can purchase on the mth website !here is the part number!

50-240

https://www.mthtrains.com/50-240

Thank you for your reply, but I do not think the MTH 50-240 transformers are currently available.  All the dealers I checked show backorder or pre-order.  MTH's website says, "This product may not have shipped yet or is completely sold out. Click on the show button to see who might have it on order."

that's not necessarily true you have to call midge at mth trains and she can tell you if the parts are available!

I don't think it'll make any difference, the power is going through a bridge rectifier internally.  Since both sides are truly floating in that power adapter, it shouldn't make a difference. All the ones I've used have had positive for the center connection, but that's just because it's what I had.

eBay: 12V 2A DC Power Supply Adapter Adaptor WALL WART US-PLUG, 222737255104

Less than $6 shipped, this will do just fine for the TIU.

gunrunnerjohn posted:

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eBay: 12V 2A DC Power Supply Adapter Adaptor WALL WART US-PLUG, 222737255104

Less than $6 shipped, this will do just fine for the TIU.

eBay listing numbers go stale in a few months...so if you're stumbling on this thread in the future try "DC12V 2A adapter US Plug" in the eBay search box.

Separately, answering a question that was not asked , the center-pin on the Aux Power Input connector is tied to the Black terminal of Fixed In1.  This allows the same bridge rectifier in the TIU to be used to generate internal DC power from either the Aux Power Input or from Fixed In1 (if nothing is plugged into Aux Power).  This is why you need to use an isolated external power source like a wall-wart for Aux Power.  As noted the external source can be AC or DC of either polarity.

Yes, Isolated is a key requirement, I try to make that clear whenever I post about these.

There where also some issue about using DC on one and AC on other (Aux and F1), can't fully remember but polarity would matter.  May be in Barry's book.  I use a 12V AC for my bench test TIU with Z-4000 for channel power.  G

Barry talked about using DC on the fixed inputs and then having to watch the polarity of DC on the AUX power.  I don't know why that would be an issue if AC on the AUX power works with DC on the fixed channels.  I never got around to doing any testing of that since I don't routinely use DC on the TIU.  I do use DC on my bench to do sound and chain file loads, my experience is they go smoother and faster with DC than AC.