Hello,
It’s been a while since I’ve submitted a question. I have a few MTH power bricks with accompanying speed controllers. They probably came in starter sets bought around 2008. One by one the controllers have become quite erratic to where just a slight touch of the handle sends a few second surge of voltage to the track and the train goes racing. Is there any fix for this or are there any reliable controllers on the market that can be used with these bricks? I should add that I have or have had several other transformers so that these few have not had to do an abundant amount of work.
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Why is my topic in gray print?
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Not on my screen. It shows as bold black.
That’s odd Coaldust, I’ve got three MTH Z-1000’s, have had them for years and have never had a problem with the speed controllers. Short of replacing them I don’t know what else to suggest.
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You could build your own…
Can you please post a picture of the label on the power brick?
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Thanks for the offer, Engine_1988, but I think I’ll pass on trying to build my own.
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You’re welcome!
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Engine_1988. Would it be possible to put a rheostat between the faulty controller and the track, turn the controller to full voltage and use the rheostat to control the speed of the train?
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Well, that’s entirely possible to do. Now, I, for one, happen to really hate rheostats, but that’s neither here nor there. What you need to do is measure the maximum amperage draw of your most power-hungry trains at full power and full load, plug it into an ohm’s law calculator (try this one: Ohm's Law Calculator) and then you can buy a rheostat (actually, a potentiometer). Maybe one like this: Electronics-Salon 25W 10 OHM High Power Wirewound Potentiometer, Rheostat, Variable Resistor.: Amazon.com: Industrial & Scientific. Now, keep in mind, my recollection of Ohm’s Law is and always will be rather fuzzy, so take this with a grain of salt. Actually, is Woke_Hoagland here? I’m gonna quick send a Personal Message.
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Thanks very much.
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You’re welcome!
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A rheostat is often the same construction as a potentiometer, the difference being how it is connected. A rheostat is like a coil of wire with one end connected to a voltage source and a movable wiper connected to the voltage drain (substitute appropriate language for AC). The potentiometer has both ends connected, and the wiper ‘shorts’ some of the resistance (in other words, there are three rather than two terminals available).
Many toy-train power packs that had a speed control were what’s being discussed here: a transformer (and rectifier) supplying a maximum voltage, with a rheostat reducing that to a range of output voltage suitable to control a voltage-controlled motor. The rheostat could be in its own box, either as a control head or the equivalent of a walk-around throttle, and it would make little difference to the function.
If you want to control voltage a different way, as a specific example by using triggering of SCRs as in Astrac, you’d connect the potentiometer a different way too. There might be considerably less dissipated power that way than by using a variable resistance that must ‘sink’ the traction current. Note that if the ‘electricity’ is AC you could use the equivalent of a variable-tap transformer to control the ‘number of turns’ in a secondary (or primary) and get fine control over AC output voltage that way – but the variable part would have to be within the magnetic coupling of the transformer, so less easily handheld.
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Thanks for coming by with a proper explanation of these whatnots.
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You asked politely.
Hopefully we’ll get more people discussing the options in greater detail, and with firsthand experience with handheld control of AC transformer outputs.
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I nearly built a handheld control box for my railroad. It didn’t work out in the end and I never bought the materials, but I had the rheostat bookmarked online somewhere. As far as I’m concerned, a good variable transformer is superior to a rheostat, but it’s probably not applicable here. My solution probably won’t work here either–I plugged the transformer into a remote-control dimmer. I think that it really screwed with the waveform, and in this case, it probably won’t work as I suspect that the power brick regulates input voltage.
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You may want to read up on the difference between some ‘dimmers’ (e.g. diacs) and full motor speed controllers (triacs).
I don’t see any overt reason why a triac would not run on reduced AC voltage range (or output a grossly defective waveform).
There is a long and often amusing history of ‘grossly defective waveforms’ in relationship to DC powerpacks, particularly those originating with MRC. From a ‘pulse’ setting that actually switched you to half-wave rectification to various distorted output pulse shapes that were supposed to make motors perform better at slow speed (but were suspiciously cheap and expedient to manufacture) – and incidentally producing an output that some ‘hybrid’ DCC/DC decoders would improperly detect and burn up trying to accommodate – well, it makes some interesting reading. And part of the take-home message is that non-sinusoidal AC output can be valuable in quite a number of ways…
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Oh, no, I’ve got it in the other way around: the dimmer (which is sold as such) is plugged into the 120VAC power strip and outputs power to the transformer. The transformer then converts the 0-120VAC variable to 0-16VAC variable (actually 8-16.5VAC, but that’s well beyond this discussion). Still, some of my locos absolutely despise the presumably imperfect waveform, and I don’t think that it’s playing quite right with my Type V either.
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I hate to say this but you might need to procure a cheap oscilloscope (or 'scope app for a phone) and actually look at the waveform, first out of the dimmer and then through the inductive load of the transformer.
At least some dimmers are doing PWM at a much higher frequency than 60 or 120Hz… nominally to reduce perceived flicker at high turndown where the actual on time for each pulse is very short and low-peak-amplitude. This might be NO FUN AT ALL if you’re expecting to run a wound-field AC motor on the resulting ‘frequency’…
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That was my plan–buy a cheap-cheap oscilloscope and inspect the waveform. Some of my locos (mostly the can-motored no-frillls ones) don’t care, but some of the temperamental Pullmor ones make a fuss and I can’t recall if I tested the horn-equipped can-motor locos.
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