Running Lionel Legacy Engines on Variable channels instead of Fixed?

Well, the TIU only puts out what you put in.  So, if you have an 18V power source to the fixed channels, you'll never get more than 18 volts out of the TIU.  The 22 volts is what you'd get on the variable channels if you had a 22 volt power supply, for lower values, that voltage indication is high.

I run Legacy stuff on the fixed channels with the Lionel PowerHouse 180 bricks as a power source.  You are fine, he's making assumptions based on the variable channel reading.

MTH equipment is rated up to 22 or 24 volts, Lionel prefers 18V.  So he was correct on that.  As John stated the TIU can't boost the input voltage.  The Fixed are pass thru, the Variables will drop it some as the input passes through the FETs.  G

Ken,

You might find the following excerpt from page 128 of The DCS O Gauge Companion 2nd Edition to be helpful:

3. How Variable Tracks and Z4K Tracks Manage Voltage

There is a common misconception regarding the method by which Variable Tracks manage voltage. Based on the actual voltage being input to a Variable Channel, the Track Control Screen may display the voltage of TIU Tracks incorrectly.

The voltage displayed can be misleading due to the way that Variable Channels manage voltage. The TIU assumes that the voltage input to a Variable Channel is always 22 volts. This assumption is a natural one since many MTH transformers have a maximum output of 22 volts.

Variable Tracks

Track voltage increases when the thumbwheel of the DCS Remote is scrolled up and decreases when it is scrolled down. The voltage displayed on the Track Control Screen increases by 1/2 volt for each click above 5 volts. However, the actual voltage that reaches the tracks controlled by the TIU Track may be different because of the way that the TIU manages voltage. For each 1 volt displayed on the Track Control Screen, DCS increases the voltage at the TIU channel output terminals by 1/22 of the input voltage to the TIU channel. If the input voltage is 22 volts, the display on the DCS Remote will always correspond to the actual voltage being output by the TIU channel. If the display reads 18 volts, the actual voltage at the output terminals of the TIU channel will be:

22 volts input X 18/22 = 18 volts

However, if the input voltage is lower, the actual output voltage will be less than the display indicates. For example, if the input voltage to the TIU channel is 18 volts and the display reads 18 volts, the actual voltage at the output terminals of the TIU channel will be:

18 volts input X 18/22 = 14.73 volts

This and a whole lot more is all in "The DCS O Gauge Companion 2nd Edition", now available for purchase as an eBook or a printed book from MTH's web store site!

CLICK HERE go to MTH's web page for the book!

Thanks! 

Note page 74 of the DCS manual.  Both Variable channels can be set to fixed.

DCS Setup/TIU(1)/Variable1/FXD.  and DCS setup/TIU(1)/Variable2/FXD.  Allows for (4) Fixed voltage Channels.  Worked well with the TCA Fort Pitt Highrailers modular track, with (4) main tracks.  Less confusion, I think???

John, G, Barry...Thanks for the information.   When I heard him explain he uses the variable channel instead of the fixed channel, it did not sound right to me, but I was not sure.   Good to know running my Legacy engines on Fixed Channels is ok. 

Ken