For many years now there has been talk of needing to remove the capacitor or capacitors that are across the motor leads of Bachmann locomotives when installing DCC decoders.Some recent testing with my Aristo Craft Train Enginner throttles, several conventional power packs, and a number of Bachmann spectrum steam locomotives has yielded some interesting results.Two Spectrum locos in particular have always suffered from a reputation for less than smooth starts and a slightly high slowest speed. The locos in question are the DC versions of the 2-8-0 and 4-6-0.While they do perform better on the Train Engineer than on conventional power packs, they still did not equal the performance of many other models, by Bachmann and others.So I got to thinking about why, since the TE output is a pluse widith modulated signal and makes everything run good, why did these two loocs still seem a little balky? So I cut out the capacitors, and presto! They now run as slow or slower than any other loco I have and start much smoother. And, the improvement was seen on both the Train Engineer throttle and several different MRC power packs I have.So all these years these Bachmann locos have been hiding their true potential for DC operation. Well, I'm off to the work shop, I have about 20 more tenders to disassemble and caps to clip.Sheldon
I was unable to tell if you are running your engines DC or DCC. If it DC, I like to discuss it with you as I have a problem some what like yours.
Interesting!
Just because the label says DC doesn't recognize that the DC may include some interesting waveforms.
Somebody must have been thinking about large constant-speed industrial motors, which have capacitors across the leads to hold down brush arcing. Our little motors don't have the potential for kilowatt arcs, and the capacitor blunts the effectiveness of the pulse spikes an advanced power supply uses to nudge a motor into high torque, low RPM motion.
If you want to see really poor performance, try running a DC locomotive on pure (battery or filtered) DC, with a potentiometer speed control. The initial starting surge is enough to toss the entire cab crew into the coal bunker.
Chuck (Modeling Central Japan in September, 1964).
The inductors (coils) and capacitor are required for European use to prevent RF interference caused by the motor. There is a little sparking by the motor commutator which produces RF noise. Some inductors look like resistors. My Spectrum 44 ton diesel has inductors that are clearly wire wound coils. Sometimes two capacitors in series which are equivalent to one capacitor. Clip the capacitors and leave the inductors. The capacitor and inductors form a tuned circuit to filter certain frequencies. With the capacitor out of the circuit, the inductors are a moot point.
Any pulse power can be affected by the inductor/capacitor circuit. Even decoders being run by DC produce PWM to the motor.
Some DC power packs produce pulse power and a non decoder equipped loco motors will see the pulses.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
richg1998 The inductors (coils) and capacitor are required for European use to prevent RF interference caused by the motor. There is a little sparking by the motor commutator which produces RF noise. Some inductors look like resistors. My Spectrum 44 ton diesel has inductors that are clearly wire wound coils. Sometimes two capacitors in series which are equivalent to one capacitor. Clip the capacitors and leave the inductors. The capacitor and inductors form a tuned circuit to filter certain frequencies. With the capacitor out of the circuit, the inductors are a moot point. Any pulse power can be affected by the inductor/capacitor circuit. Even decoders being run by DC produce PWM to the motor. Some DC power packs produce pulse power and a non decoder equipped loco motors will see the pulses. Rich
As a Hi Fi speaker designer in another life, I am very familiar with this type of filter circuit, and I was aware Bachmann used it for RF interference supression. But not knowing the values of the componants, or the target frequency, I did not think about it interfering with the TE pluses, until today!
And, while the TE uses a 12 volt square wave pulse throughout the speed range, many "conventional" DC throttles use some form of pulse in at least some part of their signal. The newer Bachmann locos have a different circuit board because of the change to LED head lights. These locos, like the 4-8-2H, 2-6-6-2 showed some improvement as well, but since they ran much better to begin with, the change was very small.
In any case I am now removing the motor circuit caps in all my Bachmann locos and thought others would like to know.
Sheldon
Did I not mention that in the long thread we had discussion DCC vs DC, in particular the Aristo system you use? I rememebr mentioning that since DCC decoder output is PWM, and the capacitors can interfere with that, then there should probably be the exact same problem with the PWM output of the Aristo system (since the motor sees the same thing, either out of a DCC decoder or from the Train Engineer).
I think the standards for supression are higher in Europe than the US, however I can also say that I've never had an issue with interference with any TVs or radios elsehwere in the house while runnign my trains, none of which have such supression caps and chokes. About the only thing that doesn;t work is AM radio in the train area. When I was a kid, i had no problem watchign TV on my TV with rabbit ears in the bedroom with my train layout, nor did my Mom complain about interference on the big TV which used the outdoor antenna located essentially outside my bedroom window.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinkerDid I not mention that in the long thread we had discussion DCC vs DC, in particular the Aristo system you use? I rememebr mentioning that since DCC decoder output is PWM, and the capacitors can interfere with that, then there should probably be the exact same problem with the PWM output of the Aristo system (since the motor sees the same thing, either out of a DCC decoder or from the Train Engineer).
You may have, but I don't personally recall any conversation about it. Point is they need to go in any case.
I found one more loco of a different brand with this "problem". My brand new Intermoutain FP7's, which I have not even built yet (they are undec kits), came with a cap soldered on the DCC jumper plug. They ran fine on everything but the TE. Removing the cap from plug made them run good on the TE. Out of the box they had no slow speed, just bolted to about 20 smph, now they go less than 1 smph on the TE.
I will be checking a few other suspects today.
watashiwa46 I was unable to tell if you are running your engines DC or DCC. If it DC, I like to discuss it with you as I have a problem some what like yours.
Yes I run DC, using the Aristo Craft Train Engineer wireless radio throttle. How can we help?
ATLANTIC CENTRALSo I got to thinking about why, since the TE output is a pluse widith modulated signal and makes everything run good, why did these two loocs still seem a little balky? So I cut out the capacitors, and presto! They now run as slow or slower than any other loco I have and start much smoother. And, the improvement was seen on both the Train Engineer throttle and several different MRC power packs I have.So all these years these Bachmann locos have been hiding their true potential for DC operation. Well, I'm off to the work shop, I have about 20 more tenders to disassemble and caps to clip.Sheldon
My dad always clipped his caps off the lokies he had. And, of course, we always had people saying he was nuts for doing so. I always wondered about the caps myself because capacitors store and release energy into the system---and in so doing, I thought, it would influence the way a locomotive would perform, one way being those dang balky starts--- I never did like the idea of seeing a loke going to, say, 40smph from a standing start!
Do you have a mass OR for all those locomotives you must perform surgery on?
Any argument carried far enough will end up in Semantics--Hartz's law of rhetoric Emerald. Leemer and Southern The route of the Sceptre Express Barry
I just started my blog site...more stuff to come...
http://modeltrainswithmusic.blogspot.ca/
Its more like and outpatient clinic, roll them in, roll them out. Only a few more to go!
Most of these tenders do open up very easily.
Found one more this morning, a lowly IHC Pacific, the new one that's DCC ready with the RP25 wheels.
Popped that baby right out of there, another big performance improvement!
Hi Sheldon
Not really important but the inductors are 5.6uH in series with each motor lead and a 0.5 ufd or 0.05 ufd capacitor across the inductors. Depends on the loco motor I guess. I am sure the inductance of the motor enters into the formula. Not sure what the frequencies of concern are in Europe.
Some locos have one capacitor, some have two capacitors in series with each other to make a smaller value capacitor. My Spectrum 4-6-0also had a Zener diode and capacitor across the headlight LED connection point on the PC board.
Here is a link to a site by Jim Banner concerning this issue.
http://www.members.shaw.ca/sask.rail/dcc/2-8-0/index.html
Rich,
Thanks for the info on the values. Yes the motor inductance is part of the formula, just like speaker impedance is part of a crossover formula. I know Jim from the Bachmann board, him and I have been talking for years. I did also post this info on there and he has already commented. He ws very supprised by my findings. As mentioned in my orginal post, I was well aware of the problems these filters caused for decoders. Just never thought about their implications to DC - until now!
Just to be doublely clear, I am using the track power Aristo Train Engineer, NOT the one with onboard recievers. And the improved performance was just as dramatic on three different MRC packs I have.
The improvement in perfromance to the 2-8-0 and 4-6-0 is dramatic. Other locos which had better slow speed/start up perfromance to begin with, showed only a small improvement.
Yes I saw the additional caps and diodes on the 4-6-0 board, I left them alone to no bad effect from what I can tell. I may still trace out that whole board to document that circuit and analyze its function.
Actually, my 4-6-0's have medium vandy tenders and I corrected the pin assignments and changed out the loco headlight to make them work with that circuit board a few years ago. But I still have the orginal tender/circuit board and may want to use them with someting else and did test them after removing the motor cap.
ATLANTIC CENTRAL Just to be doublely clear, I am using the track power Aristo Train Engineer, NOT the one with onboard recievers. And the improved performance was just as dramatic on three different MRC packs I have. The improvement in perfromance to the 2-8-0 and 4-6-0 is dramatic. Other locos which had better slow speed/start up perfromance to begin with, showed only a small improvement. Sheldon
I imagine you probably already know this, but -
Removing the capacitor that smoothed the pulses (by removing high freq components of the pulse) will likely result in the motor running warmer at slow and medium speeds, especially on pure PWM full voltage pulses.
This shouldn't be a problem for Bachmann motors unless there is excessive friction pre-existing on the drive (I doubt would be true on any of your locomotives). But a coreless motor or some very small can motors may not be able to dissipate the extra heat as well as a Bachmann motor.
The trade-offs between ideal pulse shape for slow speed running and heat generation have been experimented with for quite a while. The "optimum" power has been a sharp pulse of short duration at very slow speeds. But once a continuous RPM has been reached, the motor will run cooler and more efficiently on pure DC. Which is why many of the better transistor-based DC throttles ramped up a pure DC base under the pulses as track voltage went up. Pulse voltage could be allowed to decay to nothing by the time 6 volts to the track was reached.
The very compact digital circuitry requires the variable motor power to be sourced very efficiently so that minimum heat is generated in the decoder. PWM answers this need admirably by providing narrow, full voltage pulses at low speeds, and wider pulses at higher speeds. The output from the throttle circuit (or decoder) is either full on or full off, meaning minimum heat is generated in the throttle supporting in between voltages.
Early DCC decoders and DC PWM throttles used the typical 60 or 120 Hz pulses for their PWM motor control, and did cause over-heating and noise problems with more sensitive motors. Newer "silent drive" decoders (and better DC PWM throttles) use a much higher pulse frequency to get rid of both issues, at the cost of the absoulute ultimate in tie-creeping performance. But except for contests, very few of us are interested in operating our locomotives at less than 3 scale MPH - at 3 SMPH it takes one 40ft box car 10 seconds to pass a switch stand (regardless of scale).
Thanks for the heads up and reminders on removing the installed capacitors. Just check occasionally for motor heat.
yours in loco performance
Fred W
Fred,
Yes I am aware of the issues with the use of pulse width modulated throttles, and thank you, your input is always intelligent, balanced and welcome.
While I cannot and will not speculate about smaller scales like N scale, my testing and use of the Aristo Craft Train Engineer with both modern can motors and older open frame motors in HO has shown no noticable heating problems and no failures of any kind.
I have not scoped th TE output, others have and that info is available. It is a full voltage square wave pulse that in theory could cause such problems, but in actual application seems to be somewhat different.
More interesting than the effect of these filter circuits on the TE, is their similar effect on more conventional transistor throttles like the MRC power packs I listed. So even whatever pulse component those throttles have is affected and performance of the 2-8-0 ans 4-6-0 in particular is dramaticly improved by the removal of the cap.