As soon as the motor actually begins to turn, the current draw and friction decrease. Friction and current draw of an electric motor peak just BEFORE the motor starts to turn. Which leads into a discussion of smoothly starting a stopped locomotive. I say mild becasue the manual goes to great lengths to stress the unit's compatibility with even the most finicky can motors. The nudge switch probably introduces (manual isn't real clear and I don't have my own to put on an oscilliscope) some mild form of pulse power. The momentum and brake settings further modify the voltage settings and the rate of change of the voltage settings. A voltage regulation scheme is used to directly control voltage to the track. Looking at the manual on the MRC web site, the Controlmaster 20 is specifically designed to delivered filtered DC in normal operating mode - the normal 120 Hertz pulses are smoothed as much as possible, generally with capacitors. Actually, what I'm getting around to, is the 'nudge' switch on a modern power pack the same idea as the 'pulse' on an older one? I do know that the 'nudge' on my power pack will help my BLI's with sound kick in at a somewhat lower voltage rating, and the person I contacted at MRC said that leaving the 'nudge' on won't do any damage to the BLI's, in fact it's reccommended for we DC operators. You wrote: I now have an MRC control 20 with what is called 'Nudge' for slow speed control with can motors, and find that it operates well with the open-frame motors I haven't yet replaced on my older brass. The better controllers (less dangerous to motors) of this type injected a base pure DC that increased as speed increased so that at moderate speeds the pulses were fairly small, with the pure DC doing most of the work. Here, the high instantaneous currents and voltages produced lots of heat, particularly in the medium speed range with healthy pulse durations, where most modelers do most of their continuous running. The power supplies that were/are the most dangerous to can motors were the pulse width modulation type, where the output voltage was fixed, and speed was controlled by varying the width (time duration) of the pulse. However, running can motors on pulse power is normally quite safe unless you are running long trains or have drive train binding where the can motor is being pushed to near its current limit (usually about. To be really safe, I recommend using the Throttle Pack on older motors, and the newer power packs to run the can motors. Newer power packs (like Tech II and later) perform direct voltage control and regulation instead of using a rheostat to dump voltage. Also, the can motors, coupled with a decent gear system, can generally run at very slow speeds without the assistance of pulse power. The newer can motors are much less tolerant of this extra heat than the older open frame motors. Our motors are generally unable to cool much between the power spikes so the result is somewhat higher temps running on pulse power. The extra heat from pulse power comes from running higher instaneous voltages and currents because the power is compressed into a shorter time span. 1 amp times 40 ohms) so that you do have reasonable control of the can motor with pulse power on. The effective voltage is reduced (not in half because of windings in the motor, but reasonably close) so that the rheostat only has to drop approximately 4 volts to run the can motor at 3 volts. Hence, the lack of slow speed control.Īs an earlier poster pointed out, the pulse power switch takes out every other pulse - the old power packs put out a rectified 60 Hertz AC, not pure DC. Since it doesn't have 90 ohms, the minute you move the control off "stop" you are giving 7 volts to the track, dropping 5 in the rheostat (5=.1 times 50). 1 amp at slow speed, then to get 3 volts at the track (typical starting voltage), the rheostat needs to drop 9 volts which at. Typically rheostats had a maximum of 50 ohms (at the slowest speed position). 4 amps gives 20 ohms to be added in series with the motor. The rheostat needs to drop 8 volts (12-8=4) with a current of. 4 amps as an example, and say you wanted 4 volts at the track to run your train slowly. The old open frame motors typically used. The fomula is voltage = resistance times current. The problem with the Throttlepack and other rheostat (resistance) based control systems is that the newer can motors don't draw enough current for the rheostat to work properly.
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