Powering Conventional Trestle Grades

Could you proive more info on the block controller that determines direction?

How do you avoid feeding power back into the auxiliary transformers through their secondaries?  I love your idea with relays, but the conventional wisdom is to use resistors (if necessary, variable ones to fine-tune the resistance according to train load) to reduce voltage on the level and downgrade portions of the layout, leaving full track power for the ascending grade.

I'm not an EE so I'm not sure whether the resistors could also be controlled with relays.  Would love to hear more about this, as well as some photos or videos of it in action!  Thanks for sharing!!

I built a 14-channel block controller that monitors current draw on each block with current transformers.  I monitor how trains are moving through the layout by keeping a log of the previous block and the present block pulling more than .5 amp.  (LEDs in passenger cars pull very little current.)  So when an engine transitions from the block before an incline and the block incline, the controller switches either boost or buck for the incline.

The boost/buck transformer just adds or subtracts to/from the mainline track voltage provided by the ZW transformer.  The center tap of the boost/buck goes to the ZW transformer mainline track voltage, and the +/- secondary windings feed the incline sections.

Just a follow up on additional testing:  Running at a moderate speed the 1.25 boost/buck worked well, but at low speed the 1.25 buck was too much.  So I added the option to switch off the buck when running a train at low speed.  The 1.25V boost prevents that engine from bogging down and stopping on the up incline.

Jeff

Thanks Jeff!  So if I understand you correctly, the boost/buck transformer increases or decreases voltage to the whole layout, not just the graded portion?  I guess I was concerned about a loco or passenger car with multiple pickup rollers "bridging" two blocks with differing voltages.  (Many of us have built layouts where that happens, but the cognoscenti remind us that it's not a good practice!)  I would LOVE to see a video of this in action!

No, the boost/buck is applied through two relays just to the incline blocks.  And yes, there is a momentary bridge as the rollers traverse from the normally powered block to the incline block.  Of course, that also happens with multiple trains running on the same loop as they traverse from a normally powered block to a "holding" block, which receives enough voltage to maintain the E-unit direction, but not enough to power the motor.  A resistor in series with the voltage applied to the "holding" block limits the max current there because there could be a significant voltage difference at that transition.

Here is a link to a video of a train going up the grade with 1.25V boost.

jvde.us/rr/trestle_demo.avi

At that mainline voltage it bogs down to barely a crawl without the boost.

Does the reduced voltage as you go down the grade, brake the engine and consist??  I have more trouble down grades than up.  

The buck slows the train on the down grade, but at low speed the 1.25V buck is too much.  At higher speed the boost/buck works pretty well to keep the speed almost constant on both grades.  It depends on the weight of the cars and the friction of the wheels.

You can estimate what will happen by moving the transformer lever higher 1.25V when the engine is on the up grade, and lower 1.25V when the engine is on the down grade.  I haven't tried a long train with 2.5V boost/buck yet, but I suspect 2.5V buck will be too much on the down grade.