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Or drop the AC voltage in ~0.7V increments using a pair of has been discussed in many OGR threads.  Less than $1 in parts on eBay (free shipping from Asia).

A potential issue with using a resistor is the voltage drop is proportional to current.  Starting a stopped motor is when it draws the most current so a resistor might starve the motor of the necessary voltage to get going.  Once the motor starts spinning, the current drops.

The diode method introduces a relatively constant AC voltage drop.

Both methods have the issue that a given voltage that effects a desirable slow speed may not be enough to get it up to speed when reversing.  A classic example of your mileage may vary.


Tommy posted:

Diodes are nice. But an old-fashioned rheostat enables you to "fine-tune" the voltage to the least amount to provide the slowest speed at which the bump-and-go will successfully restart.

Agreed.  But note the OP says he has variable voltage control using his DCS system...the problem is the minimum voltage setting of 5V.  By putting in a fixed voltage drop of 0.7V, or 1.4V (2 pairs of diodes) or 2.1V (3 pairs of diodes), etc. he still has variable control to "fine-tune" the voltage.  But now his minimum voltage starts at 4.3V, or 3.6V, or 2.9V respectively.

Separately.  Confirmation needed from one of the MTH TIU experts but here's another idea.  As it appears you're using a variable channel out of the TIU, note that the displayed voltage assumes a TIU input of 22V AC.  If you supply a lower input voltage, then the output voltage is scaled down accordingly.  So, for example, if you supply only 16V AC (or about 73% of 22V), then even though the DCS remote says 5V output, the actual output voltage will be about 3.6V (about 73% of 5V).  So you can still "fine-tune" the voltage but starting from a lower minimum.

A Big Thanks to everyone.   I chose the latter option and found an old train transformer.  Varied the voltage to the TIU and it worked well.  I can get the trolley to crawl if I want.  Nice and slow.  I called MTH but the techs only talk to folks Tues, Wed and Thurs.  However I do believe the VAR out on the TIU is just controlled from whatever is input.   

Thanks again.  Glad I had an old transformer around.

AZLEEPS posted:

...Really would like it at a much slower speed.  Just enough to trip bumpers.   I have switches that do not need this speed to reverse.


Did you have to modify your trolley to get the slow-speed reversing functionality? 

Seems there have been reports of broken switches from high-speed bumper collisions needed to reliably operate the switch.


No Mods,  Just made sure they were smooth to switch by feel.  One was catching the bumper a bit as it was pushed in.  Just made sure they were clear of anything that could catch.  Doesn't take much speed to transfer reliably.  Ran for ~1 hr and no issues.  The old txfr really allowed me to fine tune speed and no I just use DCS Control to set.      I have some other mag reed switches that I could use if necessary but I thought I would see how these run in our Christmas village this holiday.

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