TIU DC variable ch??

Noooooooooooooooooooooooooooooooooooooo NO DC

Yes to DC on Fixed.  I do it to load sound files.  I guess I need to review, but not sure why it wouldn't work on VAR also.  G

Since the voltage goes through the output FET control, I doubt it works for the variable channels.  From the DCS User's Manual...

In addition, DC power will NOT pass through the TIU Variable Channels.

OK G, this what I'm thinking.

Since I'd prefer to go thru the tiu for the estop and stronger signal, I'd run two channels active, and the two variable in passive mode?

 I have an outside loop of track outback that is divided into four blocks. It runs good using two TIU channels. The grade is fairly level and not much to go wrong so I'd move those to channels 3 &4 in passive.

 The inside loop is more curvy and hilly, is also divided into four blocks. So I'd put that on channels 1 & 2 in active mode.

 All running from one Bridgewerks power pack 30 amp. I run ten amp fuses at each connection into the TIU (or output in passive).

 I do have a spare old TIU that can be used. I'd prefer to get all four channels on the new version L if possible.

Why not rectify the variable outputs? Rig up a little box external to the TIU with a switch for either AC or DC? We have rectified the output of MTH Z controllers and they seem to run DC locos well.

FETs can't control DC Voltage?  Got it on the manual, I guess that limits HO operation to the F1 & 2.  G

A relay monitoring one or both of the Fixed outputs could kill power to the passive variable channels if you can't run DC thru the variables.  That way you can get something akin to a global estop.  A single relay monitoring both outputs via a pair of diodes (either fixed output activates the relay) allows you to turn off one fixed track to clear a derailment or whatever without taking down the entire system.

I hadn't thought about just killing power to the one track instead of the whole thing.

DCS outside, it's fun when it works!

https://youtu.be/mTvLCRKaukY

I suppose FET's can control DC in the proper circuit, but the circuit is more complex and also they'd dissipate a lot more heat as a rule.  The key to FET circuit low power consumption is when they're fully on, they drop very little voltage, and thus very little heat is generated.  I haven't looked into controlling DC voltage with FET circuitry.  One way would be to build a variable switching power supply, that allows you to run the FET in it's optimum configuration, fully on or fully off.

 A BR on the outputs of the var channels  would create unfiltered DC but I'm wondering if the DCS signal  would make it through the Full wave Bridge rectifier. ???

It will. But a bridge rectifier does not conduct near the zero-crossings...hence the DCS signal does not make it through to the track during those intervals (120 times per second).  With straight DC operation as Joe apparently has, there are no zero-crossings so the TIU's DCS signal has a clear path to the engine(s) all the time.

Suppose for whatever reason you want DCS remote-controlled variable DC on 3 and 4.  So you use a brick/fixed AC transformer into the 3 and 4 inputs and a bridge rectifier on the 3 and 4 outputs. Var 3 and 4 vary the pure-sine input voltage by chopping it using triacs. This means the zero-crossings (intervals when there is no voltage) get even wider as you lower the variable output.  So the TIU's DCS signal has yet smaller windows to get through the bridge rectifier to the track.

this is interesting to read. I really don't expect to run much with variable DC unless guests bring their own engines. In that case I have a Bridgewerks MAG TDR-25 amp.

I plan on using my other 30A brick for the trains. I just installed volt and amp meters tonight following Ray Manley's helpful site. Maybe I'll use both for more power!!

http://www.rayman4449.com/Volt_Amp_Meters.htm

I hope they can since all the latest Motor control uses FETs.   G

All the latest motor control also uses PWM and not straight DC.