I bought one of these on consignment some time back for $15 and so far when it's been hooked up to test track it works my N scale locos beautifully. It can drive my new Kato SD70ACe smooth as silk at very low speeds (few scale mph). My model does NOT have a pulse-width modulation switch that I have seen on some 1400's so I'm wondering does it even have PWM? If it doesn't would be hard to add it? What would I need to do it?
MILW-RODRI bought one of these on consignment some time back for $15 and so far when it's been hooked up to test track it works my N scale locos beautifully. It can drive my new Kato SD70ACe smooth as silk at very low speeds (few scale mph). My model does NOT have a pulse-width modulation switch that I have seen on some 1400's so I'm wondering does it even have PWM? If it doesn't would be hard to add it? What would I need to do it?
I did some look-ups on the web. I did not see any pictures of a 1400 that had any switches other than power and direction. The manual - available at http://www.modelrec.com/resources/trainSound/AF100.pdf - confirms what the photos show.
The Railpower 1400 ( and some of its cousins in the series) is from the MRC Tech II era. According to the manual, the pulse rate is 60Hz. MRC's "Automatic Pulse Injection" is used to remove the pulses as the voltage is increased. "Proportional Tracking Control" is a fancy name for saying that transistor control of voltage is used instead of a rheostat.
Given that the 1400 operates your locomotives at slow speed very nicely with its existing circuitry, what do you see as the advantage to adding PWM?
PWM is one of many pulse technologies to operate DC motors smoothly at low speeds. PWM is commonly used in DCC because it is electrically and component efficient to generate (produces less heat in the controller and takes fewer components than other pulse generation schemes), not because of any inherent superiority in operation of motors. This gives PWM a big advantage in keeping DCC decoders small, while providing good-to-very-good slow speed control.
The disadvantage of any pulse scheme that produces excellent low speed motor operation is noise in the motor (typically a growl) and extra heat as the duty cycle or voltage expands for greater than the lowest speed operation. MRC resolves the heat issue by diminishing the pulses as speed increases; PWM doesn't. PWM (in decoders with "silent drive") resolves the noise issue by increasing the pulse frequency into the KHz range. The increased pulse frequency has the side benefit of reducing the heat at medium speeds as well, at some cost to ultimate slow speed crawling. Which is why silent drive decoders are sometimes deemed "safe" for coreless motors, which suffer damage from heat faster than other motor types.
Because MRC uses a different pulse technology, and their plastic cases are not easy to get into or modify, the easiest way to add PWM to a MRC power pack is to build a separate PWM throttle that attaches to the AC terminals. There are articles for PWM throttles on the web - one example is http://www3.sympatico.ca/kstapleton3/851.HTM. http://users.rcn.com/weyand/tractronics/articles/ccartcl/ccartcl.htm is an excellent article that discusses and has the circuits for a throttle that will run at switching speeds for long periods without overheating N scale motors. One advantage of DC over DCC is that you are not limited to PWM for obtaining slow speed operation because you don't have the physical constraints of a decoder to deal with.
hope this helps
Fred W
The info I saw must have been about one of the 1400's cousins then. It was either mislabeled or I just had a dislexic moment. I understand you're basically saying it's good now, don't mess with it, but what about a walk-around throttle? The plans I may have mentioned here use a headphone style jack and get power from the AC terminals. Besides using something to knock down output voltage to 12V would the throttle still need PWM?
MILW-RODR The info I saw must have been about one of the 1400's cousins then. It was either mislabeled or I just had a dislexic moment. I understand you're basically saying it's good now, don't mess with it, but what about a walk-around throttle? The plans I may have mentioned here use a headphone style jack and get power from the AC terminals. Besides using something to knock down output voltage to 12V would the throttle still need PWM?
It's possible one of the similar Railpower models (cousin) has a pulse power switch - which is not quite the same as a PWM switch. Typically (but not always) on the lower end power packs, the pulse power switch turned on half-wave rectification instead of full-wave. This allowed for a very simple arrangement to produce very low speed running by knocking out every other pulse from the rectified AC wave form.
As I said, PWM is simply one method to produce a pulse train suitable to run our motors at very low speed. In the last 2 links I provided, there are 2 different throttles - one which used PWM, and one which does not. A search on DC throttles or PWM throttles will reveal a variety of circuits to choose from.
One of the features to consider in a walk-around throttle is memory. Memory allows the train to keep running at the chosen speed and direction while you unplug from one jack and plug into the other. Consider carefully whether this is a feature you want or not. On my small layouts, I do NOT want a train running while I have no control over it (while unplugged). And if the plug doesn't make positive contact on the initial plug-in (Murphy does live in my house), you still don't have control of a runaway train. On large layouts, memory may be more desirable.
Whether you need some form of pulsed power to make your trains perform as you wish is up to you. In HO, I don't necessarily need any form of pulses if the mechanism is a solid slow speed runner to begin with. This may not be true in N scale, or you may wish to have truly seconds-per-tie speeds.
Another drawback of the PWM method of providing pulses for slow speed operation is PWM's incompatibility with many dual mode DCC decoders. If you are running a decoder-equipped locomotive in DC mode, PWM often confuses the decoder into thinking it should be running in DCC mode instead of DC mode, but the PWM signal doesn't generate the proper DCC command sequence. Sheldon ends up removing all DCC decoders from his locomotives because of the confusion generated by his PWM DC throttles. Other pulse generation systems may or may not produce the same confusion for dual-mode DCC decoders.
Last note - using a phono jack (3 conductor) for the walk-around throttle requires a specific throttle design, usually 2 push buttons to accelerate or decelerate. And it needs circuitry or logic to avoid problems when the conductors are crossed as the plug is plugged in or removed. More conventional hand-held throttles need 4 or more wires to handle a throttle and reverse toggle. Mine are set up for 4 wires, which means I can't use a phono jack. In the future, I will probably use DIN or the 4 pole power microphone jacks as a better solution.
my thoughts, your choices
The Railmaster 2400, a higher model cousin of the 1400 has a pulse switch. I have had one of each since the late 80's and still use them to control my new N scale layout until I get my locos converted over to DCC. Both are in the MRC Tech II line with the 1400 being the entry level, followed by the 2400, 2500 and I believe the 2800 which is a dual throttle pack.
Modeling the fictional B&M Dowe, NH branch in the early 50's.
Left out a few, such as the Tech II 1500 which is the one I had. No pulse switch but it did automatic pulse injection, and it did have a momentum on/off and brake switch. The numbers weren't in specific order, at least not as far as features, the 1500 had the momentum and brake which the 2400 did not, but the 2400 had higher current capacity. The 2500 was the upgrade from the 1500, it added more power and a master power light so you know it was still turned on.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thanks, forgot about the 1500
printer65,
Please start a separate thread on your query? You'll get more on-topic responses that way.
Thanks,
Tom
P.S. I'm only temporarily locking this thread until printer65 posts his topic.
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