I am just getting back into the hobby after 35 years. I dusted off an old transformer that has a ‘Pulse power’ setting. It used to be great for slow speeds and we never had any trouble with it. But I have been told that pulse power is hard on the engines. Does anyone have any info on pulse power?
Is it still availabel? If not ,is there a similar feature available?
thanks Rich
you must have one of those old MRC gold power packs…i’ve never heard they were bad on the locos and i used it extensively when yard switching years ago…I now use them for accessory power only and the AC side of one for a DALLEE walk around throttle…You’re gonna hear all kinds of stuff about switching to DCC but i’m still a DC guy… and the packs i use now are the new MRC 260 model with braking and momentum which replaces the old “pulse power” …i really like the momentum feature because it makes a train run at very close to prototype speeds…it even features a train pumping up the air because when you turn it on in the "momentum " mode the train doesn’t take off right away …just like the real thing does…I’d like to go to DCC someday but i have a lot of locomotives and putting decoders in all of them will get quite pricey…and yes i’ve heard everyone else say do it one engine at a time but i’d rather do it all at once…chuck
My knowledge of electricity is pretty limited, but from what I understand, the pulse power pack would inject timed spikes of higher voltage when you use low throttle settings. The voltage spikes would prevent a motor from stalling out at low speeds, but it does generate extra heat (and presumably wear and tear) on the loco motor.
…Not sure with DCC and motors of today if this technique is still employed for making an engine move slowly though.
I have an MRC Tech II 1400 that has automatic pulse injection, and some DCC equipped locos don’t run with pulse power. Well, they’ll run, but they run in a very jerky motion. I was told that pulse power is no good for running DCC equipped locos.
Pulse power does make a motor run warmer, but Ive never had a motor fail on me because of using pulse power over the last 20+ years.
There is less need for it today as most motors are now skew wound ( the armatures are at an angle to the poles instead of parallel and therefore don’t “cog” between the poles as older motors did, which is what pulse power was designed to overcome (resulting in better low-speed running).
Even with today’s motors, pulse power still smoothes out low speeds, which is great for switching. Once you get past half-throttle the pulse is phased out and you’re running on full wave power.
Pulse Power was used to give a little extra kick to a motor so it would start at a lower voltage. As you turn up the throttle, the pulse power automatically turns off.
I don’t remember what the frequency of the pulses was on those old power packs, but it was probably taken from the regular 60 Hz household current, possibly rectified to a 120 Hz pulse. Some DCC decoders put out the equivalent of pulse power, though at a much higher frequency.
Overuse of pulse power can overheat a motor, so check them periodically if you run a lot at very slow speeds.
OK, here is the lowdown. Pulse power power packs of the 60’s had a ‘pulse’ switch. What happened when this was on was that ‘half wave’ DC was sent to the tracks. Normal power packs rectify the AC voltage and produce 120 ‘pulses’ per second. With ‘pulse’ or half wave rectification, only 60 pulses/second are generated. Some manufacturers even got smart by having 2 pots attached to the throttle. As you started to turn up the throttle, pulse power was applied by the lower pot, and as the throttle was increased, the upper pot started applying full wave power. Later power packs used ‘electronic’ control and even pulse insertion. Many ‘high end’ DC power packs use either PCW or PCM electronic control to modulate the actual signal delivered to the tracks, and are quite safe running most precision can motors. The Cannon ‘coreless’ motor was one that would burn up with the typlcal pulse power of the 60’s and 70’s. Your modern DCC decoders use a modulated signal generated by the decoder to give you a smooth speed range.
Jim Bernier
I remember Pulse Power–still have an old MRC throttle that has the feature. It gave open-frame motors the ability to run at slower speeds, a feature that wasn’t really necessary after locos started coming out in the ‘Can’ style. It did make the open-frame motors run a little warm after a bit, but I don’t ever remember burning a motor out by using the feature. Of course, today’s advanced DC electronics work just as well on older open-frame motors as they do the ‘cans’–I’ve got some older brass with open-frame that I haven’t converted yet–haven’t needed to–and they work just fine on my new MRC throttle.
Like a lot of guys, I use a few of my older packs for powering accessories. There’s still life in them, yet, LOL!
Tom [:D]
The origin of pulse power lies in a sneaky feature of rectified DC without capacitor smoothing. Think of AC as a sine wave. Ordinary full-wave rectifiers flip the curve so that both legs of the sine wave appear above zero, with nothing below. While the voltmeter might read 12 volts, that is only .707 of the actual maximum voltage, and is known as RMS voltage. The actual peak voltage is just under 17v.
The earliest form of pulse power simply changed the rectified DC from full wave to half-wave. The RMS voltage dropped from 12v to 6v, but that was only .354 of the actual maximum voltage reaching the rails. The peak voltage is still just under 17V, so the motor was getting 60 big kicks per second instead of 120. (Those selenium rectifier packs didn’t do anything fancy to 60hz house current, except to rectify it.) Net result was a motor turning at half the speed but with the same torque.
The pulse power switch simply disconnected one side of the pack’s full-wave rectifier. Throwing it to pulse OFF while the loco was moving would result in a sudden speed surge as the RMS voltage reaching the motor abruptly doubled.
ELOQUENT!
Simply ,60 cycle 'Pulses were injected into the DC to move balky engines, or ‘goose’ them if they would stop running under low power conditions.
MOST Athearn BB ENGINES needed 5 volts + to overcome internal friction, therefor pulse power would aid low speed running. Newer MRC paks use full wave rectification ‘bumps’ in much the same way to ‘creep’.
I have 3 Tech II 2400’s that have a pulse switch. Great for slow speed work. As far as I know I have never killed a motor with it in however many years they have been around.
I also have the Tech II 2400. As has been mentioned above, the pack starts out at 60Hz then smoothes out to 120 Hz between the 30-40 indicators on the pack. When the pulse switch is off, I get 120Hz all the way through the entire range. I measured this with a true RMS Fluke 87-5 but I would sure like to see a waveform of some of these packs. If anyone has any links to such info please post.
Jim
Thank you all for the great answers. I feel a lot more comfortable using that old transformer now. (yes it is a MRC)
Rich