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Thread: PWM recomendation.

  1. #1
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    Default PWM recomendation.

    All posts seem to be archived from way back when. Dead links, photos missing etc. Any recommendations on newer models? I want to run 2 mainlines, very little switching.

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    Any of the MRC Tech II DC-controllers work great and all incorporate a PWM circuit. The MRC Tech II 2500 has a momentum circuit which works very nicely and can usually be had for about $20 on eBay: MRC Tech II

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    I do use PWM control on my traction layouts. But they don't have any features like braking or momentum. Just basic speed control. They are so simple I buy them as kits from Bakatronics http://www.bakatronics.com/shop/

    The ones I buy are for low power because the layouts are small and I run only one or two streetcars at a time. I use a one amp wall transformer from Radio Shack to provide the 12 volts. But they sell PWM units for various loads.

    What I really like about the kit I use is it's versitility...

    It can be built into a layout...

    One switch controls direction, the other overhead or track power.

    In a control panel built into a structure...


    Besides speed and direction other switches control lights, sounds and turnouts.

    Or even used to upgrade a battery powered controller...


    The green unit was upgraded after twelve volts burned out the factory variable resistor in an experiment on external power. The beige unit is untouched using four AA batteries to power Japanese streetcars and interurbans.

    The kits are simple to build and even include solder. For model railroad control I add a knob, a DPDT wired for reversing, LED(s) to indicate direction and speed, plus a mounting place. Slight modifications like the variable resistor on extended leads allows greater flexibility. Adding screw terminals to the board allows easy connections

    The old Model Railroader electronics books had ways to add momentum and braking.

    A word of caution about PWM control.
    It is wonderful for controlling older equipment. The poor design of the motors and the grunge that collects on the commutator often fouls them. The pulsed power is great for getting them rotating. It works so well that DCC decoders use pulses for speed control.

    But if you own any locomotives that have decoders installed, even though they can run on DC, they can have problems with PWM. Because DCC uses pulses to send the control messages to the decoders, the PWM pulses can confuse the decoders.

    If your equipment has the latest motors, you won't need PWM. The high efficiency motors don't need as much power. A good example of this is comparing my older Bachmann Streetcars to my TomyTec LRVs. The LRVs hit top speed within the first third of the rotation of the speed knob. The Bachmanns don't start moving for that first third. Though the newest PCCs should mimic the TomyTecs, as they were upgraded with a very efficient pager motor.

    One good thing that PWM does, is add that hum to equipment when standing still, that Streetcars and Rapid Transit trains have.
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    Dozens of different PWM motor controllers are available on ebay for less than $10 delivered to your door. Just install them in a box or a panel, add a power supply, and you're good to go.
    https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR0.T RC0.H0.Xlow+voltage+PWM+motor+controller.TRS0&_nkw =low+voltage+PWM+motor+controller&_sacat=0

    If you'd prefer a walk-around style already assembled in a case then I've used these units from Ken Stapleton:
    http://www3.sympatico.ca/kstapleton3/Index.html

    Note that with Ken's throttles you will still need to add a power supply such as a 12V wall wart.

    Regards,
    Ron

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