I have two identical MRC power packs, MRC-9500s. Using one power pack the locomotive crawls along, using the other one the loco runs like a scalded rabbit. The multi-meter reads the same voltage on the same section of track using the same loco. Can anyone explain why the difference. These are MRC packs with the meters and the needle on both read the same voltage output.
So you have a locomotive that runs at different speeds when receiving the same voltage (verified at the track with a meter) from two different power packs?
I am at a complete loss on this one.
If voltage is the same, they should run the same.
Maybe someone with a deeper knowledge of electrical application can help. I am very curious about this one.
-Kevin
Living the dream.
Did you measure the track voltage with the locomotive running? You need a load on the power pack to see the actual track voltage.Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
These almost certainly use some sort of pulse power, where the speed control regulates the pulse. With a meter, they will appear to have equal output voltages at all times. The one that runs the loco at full speed no matter what is defective, the speed control is not actually controlling the pulse output, and it is outputting full power all the time. The working one is performing as it should, the speed control is regulating the pulse and so the loco gradually speeds up as it should.
These are pretty much a refresh of the Tech II line, so the most likely have a nearly identical control circuit to the Tech II 2500.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
What did an indepedent multimeter read? That is the proper way to troubleshoot.
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.
rrinker These almost certainly use some sort of pulse power, where the speed control regulates the pulse. With a meter, they will appear to have equal output voltages at all times. The one that runs the loco at full speed no matter what is defective, the speed control is not actually controlling the pulse output, and it is outputting full power all the time. The working one is performing as it should, the speed control is regulating the pulse and so the loco gradually speeds up as it should. These are pretty much a refresh of the Tech II line, so the most likely have a nearly identical control circuit to the Tech II 2500. --Randy
RandyThe MRC specs say variable DC so with the Momentum turned off he should see varying DC voltage on the track with a load of the locomotive. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
RR_MelThe MRC specs say variable DC
I am still looking forward to seeing o-scope traces for the two power packs, to see whether what they are actually modulating as variable DC to a voltage-controlled load is PWM voltage variation at some clock frequency vs. half-wave pulse augmentation of DC voltage (which I suspect is 60Hz because that's nominal half-wave rectified house-voltage AC clamped down to low incremental voltage, but I won' digress...)
And then comparing this with traces from known-good packs doing 'what the factory intended' and from some more state-of-the-art high-frequency and possibly "more DCC compatible" PWM packs.
An easy check would be with an 1156 automotive bulb. If your power pack is working correctly you should see a smooth transition from off to full bright with the throttle. The specs on the 1156 bulb are 12.8 volts at 2.1 amps.Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
RR_MelAn easy check would be with an 1156 automotive bulb. If your power pack is working correctly you should see a smooth transition from off to full bright with the throttle. The specs on the 1156 bulb are 12.8 volts at 2.1 amps.
Yes.
I use an 1157 bulb and a True RMS Fluke digital multimeter to verify track power. The Fluke meter shows a usable DC reading even with PWM throttles. The bulb is mounted with a toggle switch to turn the brake lamp circuit on and off to change the dynamic load. It is 0.5 amps with the tail light, and 2.0 amps with the tail lamp and the brake lamp.
The housing has inputs that accept my Fluke test leads, and I can easily attach a Fluke meter in series to check amperage if I need to.
This has proven to be an excellent way to verify trackwork and wiring.
That’s great Kevin!!! You out thunk the Gadget Guy! I just soldered wires to a bulb with clips on the end.Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
Except that the bulb will not show you a whit of any difference between subtractive voltage modulation via PWM @ 60Hz (let alone higher frequency) vs. additive via half-wave pulse @ 60 Hz. The characteristics that make an incandescent bulb so good as an optoisolator for radio mixdown boards do not suit it as a high-speed visible resolver of alternating voltage changes.
On the other hand one of the cheap LED replacements sold for something like 1157s might indeed show flicker proportional to short-term voltage -- indeed might actually go fully dark at some point in an 'off' stage if using no or sufficiently short phosphors -- and most humans can easily perceive (and be annoyed by) 60Hz flicker in displays and such. You could relatively easily 'calibrate' this by assessing brightness at common battery voltage...
I just used a socket cut from a scrapped automobile at Pull-A-Part with as much of the connecting wire still on it as possible. Then just strip the loose ends, or attach probe tips from old VOM lead sets or whatever by the usual expedient methods. Not nearly as elegant but no soldering required and I can change bulb types even quicker than manipulating a box...
Otherwise Kevin's thoroughly excellent setup is da bomb for most of the required testing and loadboxing.
No, there is no way they would see a 'smooth transition from zero to full DC' connected to the nonvariable DC terminals
Not familiar with the 9500, but in the operators manual for my 350, there is a section on setting "Ultra slow speed" by pushing the direction button, while in program mode. Makes he loco go much slower. (Nice when overactive grandchildren want to operate.) You may have one in each speed setting. I have never checked anything with a meter, so not sure what readiings would be.
Good luck,
Richard.
Nobody really answered my question but the replies I got made me realize why I never became an electrician. A few replies seemed to think the "throtle" knob was not working, but, on both backs, I can adjust to voltage up and down and they both show the changes on the milti-meter. The 9500s have meters on them which matched the multi-meter reading. The section of track is the same, the multi-meter confirms the voltage is the same, I know it was the same locomotive going in the same direction. The only thing different is the pack, and they both showed the same output.
The multimeter, like a needle gauge on the powerpack or the incandescent auto bulb, is internally 'damped' to show a definite reading without flicker. So you will not 'see' the action of either 60Hz PWM or pulse DC.
It is remotely possible that if you look very closely at an analog output meter you may see the needle vibrating slightly. But I doubt it.
Since both these modulations are repetitive pulsetrains, a logic probe setting or device is unlikely to tell you much. The definitive tool here is going to be an oscilloscope -- I believe there are inexpensive devices that connect to smartphones, and the simplest of these would serve to display both asymmetrical DC pulse and PWM voltage control on a common trace just reading sequential voltage at high sampling rate.
I know this is more 'electronics' than you want to hear. But your 'voltage' as soon as powerpack magic gets applied to it is no longer a smooth DC 'thing' any more... regardless of whether averaging meters reading 'what a motor would see as effective speed-controlling voltage' agree in reporting a static number at a given commanded knob position.
leewalThe 9500s have meters on them which matched the multi-meter reading.
when driving the loco? or without any load?
problems at work were often described as "bizarre". they eventually had simple explanations
greg - Philadelphia & Reading / Reading
gregcproblems at work were often described as "bizarre". they eventually had simple explanations
Maybe THE answer wasn't given, but pretty much all of the suggestions are potential causes. If th throttle knob is at say half and the one loco runs at a nice speed but using the other power pack on the same track with the same loco and the loco takes off like it has a rocket stuck on the back, then the meter reading is misleading at best. If you measure say 5 volts on the track both time, then the cuase of the loco running significantly faster one one pack's version of 5 volts compared to the other one is a pretty clear sign that one of the readiongs of the example 5 volts is much lower than the true DC voltage seen by the loco's motor.
If we're talking different locos, all bets are off. That just adds more variables. But if the only thing being switched around is which of the two power packs is being used, and there is a vastly different behavior, then something isn't right with the pack itself.
There are no settings for peak voltage or anything on the 9500, according to the instruction sheet on the MRC web site. Is the description of the issue accurate? Because as originally posted, it sounds liek with oen of the packs connected, the loco is uncontrollable, it just takes off no matter how far you turn the throttle knob. If instead you mean it takes off instantly when you increase the throttle instead of gradually speeding up, check the momentum switch. If it's on on both of them and the one still acclerates the loco instanmtly, either the switch or the momentum circuitry has failed. If the slower one had momentuim on and the fast one didn't, well, there's your problem, simple fix.
WOW! I think I'll just live with the problem and adjust the speeds accordingly. It seems obvious that one, or both, packs have a problem. But, which one? I'm going to enjoy what I have and move on, as they say. Thanks to all who replied.
leewalWOW! I think I'll just live with the problem and adjust the speeds accordingly. It seems obvious that one, or both, packs have a problem. But, which one?
I do think there are people in the forums, some following this thread, who are technically qualified to open a 9500 and test the components and systems inside it. They are NOT likely to be able to advise someone how to do that safely or effectively by 'remote control' and perhaps even less likely to attempt to do so over a forum that might be deemed to share liability in some way if something 'goes wrong' or if trade secrets are revealed.
I first came across dog-in-the-manger "technical support" for older products in a particularly irritating way in the mid-Nineties. A company I bought had sold some very expensive 'professional' treadmills to clients, some of which had been built like tanks mechanically but given early-Eighties electronic controls. One of these suffered a failure -- amusingly enough in this context of the gated DC motor-control SCR integrated on the control board. I called to order the part -- as with the Walthers turntable controller, was told it was obsolete and 'no longer stocked'. Anywhere, used, remanufactured, or from firms recycling older components. The shocking part was that they would not provide the board layout or even the schematic of that control board -- it was their proprietary design, by God, and no one could have it. The client left with a $5900 brick bought on our company's word it would last a long time ... and which, indeed, was still about 99% fully serviceable ... well, he was SOL as far as they were concerned, but they would happily "support" us in selling him the latest and greatest for full price.
I remoted the replacement SCR block (with higher voltage rating) to be heatsinked on one frame rail, ran new control leads to it from the original install traces on the board, and reflowed the board just to be sure; that ran happily as long as he lived (and I believe his daughter is still using it).
Then there is the issue of crude tech given cachet it probably doesn't fully merit with clever marketing. The devices used to power Chrysler Panelescent electroluminescent lighting -- still an amazing thing visually 6 decades later! -- are good cases in point. Another was the Collins 'optoisolator module' I described a few years ago. A depressing amount of the time, "no user serviceable parts inside" is an excuse far more than a warning.
gregc leewal The 9500s have meters on them which matched the multi-meter reading. when driving the loco? or without any load?
leewal The 9500s have meters on them which matched the multi-meter reading.
did you answer this question?
gregcdid you answer this question?
it doesn't make sense that the loco behaves differently if the voltage is the same. "bizarre" is the loco seeing the same voltage from both power packs? does the track voltage match the power pack reading with the loco on the track?
is there a problem with the output of one of the power packs that makes the output substantially different with a load? loose trerminal?
regardless of modulation, the meter should indicate the average voltage which is what the loco will respond to.
What he could do without complex electrical knowledge or risk is get hold of an undamped analog voltmeter and turn it into the equivalent of a ballistic galvanometer: put a small mirror on the needle and use something like a laser pointer to greatly magnify small motion of the armature, projected across the room onto a paper scale (which he could reasonably calibrate for average or 'true' DC voltages by consulting his built-in meter).
This will display a bright and fairly tight spot when indicating a pure unmodulated DC potential -- if there is any ripple in a straight DC output it would show a little spot lengthening which needs to be checked but ought to be minor compared to the two effects of more interest.
If the output is half-wave pulsed, the spot will show preferential lengthening to one side of the 'indicated voltage' partly as an artifact of the persistence of vision. Likewise PWM, which creates highly nonlinear instantaneous voltage levels, will cause the mirror to dance to all those intermediate positions, perhaps in fact close to proportional to the times the physical voltage is 'commanded' if the inertia of the meter movement is low enough.* This will give him a spread spot, I expect symmetrical about the 'nominal' voltage his damped meter reads, and if laser brightness is properly adjusted the relative brightness across the longitudinal length of that spot will indicate the relative PWM waveform producing the average voltage commanded.
*There is also a torque and 'inertia' due to the hairspring that returns the pointer to zero, but I think that this would only affect falling-potential resolution. This might be easily confirmed by sending different AC frequencies of clean symmetry through the movement and observing its physical response...
Did you se my response about "Ultra Low Speed?" We were writing at about the same time so you may have missed it. It makes a world of difference with mine.
Just checking,
Richard
The 9500 doesn't have that sort of programmability. New clothes for the old emperor - I am at least 95% sure that the circuit in a 9500 is near as to identical to that of the Tech 2 2500. Just add meters. The features are described the same, including the Accu-Trak thing. Tech 4 was the next generation after that, and the 350 added the ability to program the momentum, maximum voltage, and activate the slow speed mode.