PRODUCT REVIEW: 4 AMP POWER PACK
Manufacturer: Aristo-Craft Trains, 346 Bergen Avenue, Jersey City, NJ 07304. Price: ART-5450 4 amp power supply with ART-5401 5 amp capacity speed controller $149.95 suggested list. (ART-5401 speed controller available separately at $39.95 suggested list.)
THE LATEST INNOVATION in powering model trains is pulse width modulation (PWM). The simplest way to describe PWM is as a series of gentle shoves of electric current. When you apply PWM to a motor, it lets the armature rotate very slowly. The result is an ability to make almost any locomotive creep at a fraction of a scale mile per hour.
Aristo-Craft Trains strongly promote the use of PWM in their new 5450/5401 power supply/speed controller combination. They claim five benefits:
1.) PWM purportedly separates the control of the train from the voltage running through the rails. According to AristoCraft's literature, a high direct current voltage constantly remains in the tracks but a "signal message" from the pack actually controls a locomotive's motor.
2.) Higher d.c. voltage means such features as constant lighting (as opposed to constant intensity lighting), smoke units, and sound systems supposedly work better even when the train is at a full stop.
3.) The train allegedly will run better even on less than perfectly clean track.
4.) PWM reportedly allows the use of a realistic momentum effects in the speed controller without the use of dangerous a.c."pulse" power.
5.) The consistently high d.c. voltage in the rails ostensibly lets trains run longer distances between feeder wires. AristoCraft claims distances up to 300 feet are common.
We were unable to verify the assertions in points 1.), 3.), or 5.) relating to PWM performance through the rails. We did confirm a constant minimum of one volt and .4 amp though the track at all times. We will verify the smoke units and low voltage lighting effects in our test locomotives remained operational even when the engines were at rest. And we were very pleased with the feel of AristoCraft's momentum feature. It was just enough to smooth out our locomotives' lurching starts but quick enough to respond to emergency stops. It imparts a sense of realistic inertia. The slow speed control also was very good, characteristic of PWM-type packs. We think that feature alone allows the AristoCraft units to stand out.
On the other hand the jury is still out on PWM. Some manufacturers and hobbyists consider it potentially damaging to motors and sound systems. The reason? The effect of PWM is analogous to turning a light switch on and off very quickly. Just as the bulb may burn out faster, PWM's detractors say so could your motor. And in the case of sound systems, PWM makes it difficult for some, such as P.H. Hobbies', to lock onto the correct voltage and maintain a constant pitch even while running at a constant speed.
AristoCraft itself warns against using the 5450/5401 pack with sound-equipped Lionel Large Scale trains but, ironically, because Lionel's sound system circuitry may damage the AristoCraft units!
The makers of some model locomotives and sound systems, including LGB and P.H. Hobbies, say using PWM will void their warranties. Actually, it is still unclear whether PWM has any significant negative effect.
But it does cause motor noise. The characteristic buzz of PWM and other forms of pulse power is a result of the motor vibrating. Our AristoCraft sample produced a disquieting, very high-pitched "whistle", as though your ears were ringing, in all our test locomotives. We found the sound extremely disturbing.
As for statistics, the pack reached its limit exactly where the manufacturer said it would: 4 amps. At that point it began to shut down. It reset almost instantly, as soon as the load decreased a convenient charisteristic. The maximum we managed to coax from the pack was 17.3 volts and it might have gone even higher; we ran out of load. That was enough power to run four LGB Moguls on our flat, indoor test track. Outdoors, where you might have grades and/or if you pull a string of cars you should expect that number to drop to two Moguls. The average current draw of a Mogul under less than ideal conditions is 1.5 amps.
Our oscilloscope showed a wave form typical of PWM. With the train at rest the wave began as a rounded, narrow pulse. As we advanced the throttle the image widened out into the square wave indicative of a "duty cycle". At 3.6 amps and 14 volts the wave became a flat line and the annoying "whistling" stopped, meaning the PWM had phased out.
Cosmetically the units are nice looking. The power supply has no cooling fan but adequate venting and, instead of meters, it has a handsome LED-type stepped display to show the power output. It has internal circuit breakers. And on the front, where you can reach them easily, it has a pair of convenient red and black thumb screw power connectors (corresponding to colors of the speed controller's input wires). The case is black, textured plastic 6 1/2 inches wide by 5 5/8 inches deep by 3 3/8 inches high.
The speed controller measures 3 1/2 inches wide by 6 1/4 inches deep by 2 1/2 inches high. It is small and light enough to fit comfortably in your hand. The case is made of shiny black plastic. The output wires plug into the rear through push connectors, another convenience. The throttle knob has a nice feel. And the direction switch has a center-off position for safety. The only way to turn off the entire unit is to unplug it. A green indicator remains illuminated as long as the unit is plugged in.
The units are separate so you may leave the power supply safely indoors while you take the speed controller outside. All power pack manufacturers warn against taking power supplies outdoors because of the risk of an electrical shock.
AristoCraft promotes its power pack's "E.T.L." listing. E.T.L., they tell us, is an equivalent of U.L. and is recognized in all 50 states and Canada.
Pulse width modulation is a new enough development in the large scale model train hobby that we are unable either to recommend for or against it. On the one hand, PWM will void some manufacturers' warranties. On the other, insufficient data exists to condemn PWM. So, with respect to AristoCraft's units, we felt they were excellent in every respect except for the very serious problem of the high-pitched whistle. If AristoCraft could correct that problem we would consider the 5450/5401 units an excellent PWM power pack. GR, RR
Lewis Polk of Polk's Model Craft Hobbies, Inc./Aristo-Craft Trains responds:
We apologize for the whining sound on some packs. That is caused by a change in values of some small resistors used in the pack. This happened only on some of one run of the packs and will not be repeated. If the sound is particularly offensive our repair department can adjust this for the end user. This has only come to our attention recently since it occured only on this last production run.
The PWC [pulse width control] potentially harming motors is a red herring. We've sold this pack for four years now without complaint about motor damage or short life. Many people confuse our pulse width control with earlier "pulse" packs that shot a.c. into the motor. Our system uses pure d.c. only, which is safe. However, theoretically, the PWC does turn the motor on and off repeatedly, but this does not harm the motor or reduce life in our tests. This has now withstood the test of time, and I'm sure none of your readers have ever complained about this potential problem.
