How much Power???

What are the TPC's for?  If you are running command only, just use 1 180 PowerHouse per track with Direct Connect lockons.

Why the TPC 400s when using command control? With that long a

track run, you should also use extra power feeds by running a direct connection from the brick to the greatest distance from the brick. The connections between track sections are not very good with voltage drops at each section.

Tim:

Mostly I am a little confused so some questions first:

You one 180 watt brick going to two TPC 400's - in parallel I assume?

How are the TPCs wired to the layout - is one TPC used for command track 1 and one for track 2 or are both going to the same track? Are the 'command control tracks' interconnected or wired independent of each other?

If you have one brick going to two TPCs then you are delivering 90 watts to each TPC, each of which is capable of receiving 400 watts. They are grossly under powered and with a 60 foot track run (ie a big layout), just may explain the 15 volts you are getting to the track. One thing I have noticed is that there is a voltage drop on the power source. When turning on power to get 18 volts to my TPC I need to set my transformer to 21 volts. Connecting two TPCs to one 18 volt brick may be too much of a 'drag' on the brick dropping voltage. As you stated TMCC needs 18 volts. At 15 volts the CAB command signals to the track are iffy at best, sometimes it may work and sometimes not depending on loco position on the layout. At less than 15 volts you are pretty much in conventional mode. I am surprised you don't have some locomotives taking off at speed in conventional mode at times.

You need one brick per TPC. If the two command tracks are independent then one brick/TPC per track. If all your track is connected to the same power source then only one TPC is required. I believe you can connect two 180 bricks to the one TPC for a total 360 watts. If your layout is very big then block breaks are probably needed with independent power for each block - though wiring power for big layouts is beyond my expertise since I never had to deal with it. Some one else would be more qualified to answer this.

Don't give up on the TPC  - it can be used for running conventional mode also. Never say never on conventional especially when one day a friend comes over with his/her hot new Williams loco dying to try it out on your tracks!

Joe

Maybe his version of command control is controlling voltage to the tracks via 2 TPCs one for each loop and a Cab 1 set for track 1 and track 2.

Power to the TPCs is not divided equally 90 watts each. If 30 watts are being used by 1 TPC than 150 watts are still available for the 2nd TPC.

Voltage should be checked at the output of the brick it should be around 18 volts. It can also be checked at the output of the TPC. With the TPC set in command mode the voltage should read 18 volts. The track voltage should read around 18 volts. If not measures should be taken to lessen this drop. Buss wiring etc. 

I think you've figured out you need more juice.  A lashup of big engines, a string of aquarium cars, lights every 3' drawing from track power.  These are all big draws.  Drop another brick on it.  It's $90, you have the power if you need it, which I think you do.  If you have 2 TPC's on seperate loops with one 180 brick, you are cheating yourself.  At least one per. And go from there.  

What Lashup? If he needed more power the breaker would pop.