For any give DCC system, with a track voltage of X, pretty much all decoders should give a function output voltage of X - (the same amount), since the first thing in, the DCC track power hits a full wave bridge rectifier and other than that there is the diode drop of the controlling transistor for each output (input, since it's a switch to ground). There are exceptions, like decoders that come with constant current sources or resistors already in circuit to limit current for LEDs, but there's veyr little variation in the actual circuitry from vendor to vendor - the biggest differences are in the firmware of the microcontroller. Voltage to the motor at full throttle, assuming no modifications (CV5 at the default, for example) should be just a few diode drops below the track voltage to account for the rectifier and the H bridge drivers.
Your 179 should be giving accurate track voltage readings, but not all RMS meters will, not even all Flukes with True RMS - they don't all go up to 100KHz, though my old 8060 and my 45 benchtop meter both do. My even older 8012A only goe to 50KHz, but from 20KHz to 50KHz the accuracy is only +/- 5% + 3 digits. To 10KHz it's +/- 0.5% + 2 digits, quite respectable for something from the late 70's/early 80's.
Glad you got it all sorted out. A reset on some of those other decoders should get them performing more like they shoud. I will usually do a reset as the first step in installing a new decoder - just in case. It's not unheard of for some settings to be really scrambled from factory testing or because a decoder may have actually been a return. Some systems also have a decoder reset in the throttle programmiung menu. Digitrax doesn't, NCE does, dunno about MRC. The problem is, this is usually specific to the manufacturer's decoders - the NCE reset, for example, doesn;t use a CV to execurte a reset (there's no standard for that - though all decoders from a given manufactuer usually have the same method), it simply programs specific CVs to what would typically be the out of the box default values - except it sets some CVs that are specific to NCE decoders, so if you would try that on a different brand decoder, you'd end up with Address 3, and no momentum and so forth, but it might also set some CVs that do different things than the same CV in an NCE decoder. Best to use the decoder specific reset when available. The most common are CV8=8 or CV30=2. Some hedge their bets and support both options.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Wait, on some of these locos you have a wirewound pot or a resistor in circuit with the motor? None of them have capacitors for noise supression, do they? You need ot bypass that stuff with DCC (or a DC throttle that uses PWM - the MRC 2500 does not) because you are distorting the drive signal from the decoder, and in the case of the ones with BEMF, distorting the feedback as well. This sort of thing will cause erractic operation.
Locos should be close, but they don;t have to be perfectly in lock step to MU. Better decoders support CVs 2, 6, and 5 for simple speed matching. This is pretty easy to do. CV2 is the start speed - so set both locos to the same address but not coupled, and just crack the throttle. The one that runs slower - increase CV2 until it runs the same or close to the faster one. If they are both already the same, no adjustment needed. Next crank the thing to full throttle. CV5 controls top speed. The default is "as fast as it will go" so on the FASTER one, you need to adjust CV5 to slow it down to match the other one. 0 and 255 in CV5 generally mean the same thing - as fast as it can go. So you want to start at 255 and work down. Finally, put the throttle to the mid point, and see if they are still running close to the same speed. If not, CV6 adjusts this. If the range of CV2 and 5 are 0-255, so is CV6, and setting it to 127 is exactly halfway between 0 and 255, so adjust up or down from there to increase or decrease the speed at half throttle. That should be more than good enough, that's the most I've evr done to any of my locos, but all of mine support all 3 of those CVs (Tsunami does not, I don't have any Tsunamis).
This is really easier to do from the throttle using ops mode. Just remember that if you only want to change one loco, you have to take the other one off the rails. You can use JMRI throttles on screen and access ops mode programming there as well - in which case you don;t have to have them on the same address, just use two throttle panes and run each loco at the same speed step. This is where Digitrax is handy with two throttle knobs on the big throttle, I can run two locos at the same time and quickly use Ops Mode to adjust either one as needed to match speeds. Generally, adjustments to CVs 2, 6, and 5 take place immediately, which is why doing it in ops mode while the locos are moving makes sense.
If you are seeing such massive differences - either there is something miswired, which installing a new decoder fixed, or it has something programmed which is reducing the full throttle output - a limit in CV5 which is the max voltage, or a setting for a speed curve. Factory reset on the Digitrax decoders is to set CV8=8 (don;t worry, it will not read back, CV8 is a read only CV for manufacturer ID and will always read back the manufacturer ID, not what you program in it). The TCS decoder it's CV30=2. I don't think MRC decoders have a reset. AFter a reset the loco should run as address 3. It will most definitely not have any speed tables or other speed control options configured.
Something is really really odd here. Like Byron, I've never heard of anyone having this type of issue, and we have all types in the club, including a whole bunch whose only exposure to DCC is when they come out for one of the dozen or so shows we set up for each year, at home they just run DC. Never have I see someone's loco not have enough power to move a train, at least not stall out. Spin the wheels with too many cars, sure. But just die slike it had a 100HP motor and really needed 200HP, never seen anything like that. If you're stalling a DCC loco and seeing 300ma wheras the same loco on DC stalled is more like 1A, there is something REALLY messed up with the DCC system or the decoder.
RR_MelIf I get sluggish or sound a bit out of it please bear with me, my younger brother passed on last evening.
You have my sincere condolences, Mel.
Regards, Ed
RR_MelI have checked the DCC voltage at the decoder input using a Tektronix 454 scope at slightly under 16 volts and the square wave isn’t pretty but not bad either.
can you check the voltage across the motor at full speed?
greg - Philadelphia & Reading / Reading
This continues to be the most baffling thing I've seen. I've had no problems with locos acting like thay have less power when using DCC - not when they can move over 100 (over)weighted hoppers. Your voltage to the track is fine, the scope is probably the best way to tell - the 'new' old Fluke 8060 I recently aquired should give a good acount on DCC since the True RMS converter on that one goes up to 20KHz. What about track current under load? Because iof an unladen loco can run at sufficient speed but a loaded down one can't, and the voltage is at a good value, that leaves only current.
Do you have any locos that haven't been modified with your extra weight and remotoring? How do they run? My locos are all pretty much stock except for the installation of a decoder and changing light bulbs for LEDs.
The only other thing that could cause lack of power with a decoder would be the motor drive not being suitable for the type of m,otor being used. High frequency PWM does reduce the torque of the motor, especially at lower speeds, but most decent decoders include torque compensation or a similarly named feature that provides an extra boost at low throttle speeds. Some decoders offer adjustment of the motor drive to suit various types of motors - the defaults are usually fine with the typical flat sided can motor found in locos like Proto 2000 or newer Athearns. The Digitrax decoders I know default to having the torque compensation enabled. Those two you have do not have BEMF though. The TCS WOW should have their BEMF which I've always found works quite well. Dunno about MRC, their decoder instruction manuals barely tell you the basics, let alone any extra features. The Digitrax decoders also have CV9 which adjust the motor drive frequency. The default is 0, which is the highest frequency, and goes up to 225 which is the lowest (and may make an audible 'buzz'). You may want to adjust this to see if it works better with the motors you use. The other thing on the Digitrax decoders is CV61 for transponding, which should be either 0 or 1 so Transponding is off. Only on the newer DH126 does it really matter if it's 0 or 1, 0 is for LEDs being used for function effects like flashers or mars lights, 1 is for lamps. Transponding can affect the loco power since it has to effectively shut off the motor for the time it takes it to generate the Transponding pulse in the rails - Railcomm is similar. Of the decoders you listed, I think only the Wowsound has support for Railcomm, which should be turned off. Transponding is only in Digitrax decoders.
cuyama But yes, once it's determined that there's enough DCC voltage on the rails, the next step would be to look at the otuputs of the individual problem decoders and/or adjust CVs as necessary to create a higher top voltage.
But yes, once it's determined that there's enough DCC voltage on the rails, the next step would be to look at the otuputs of the individual problem decoders and/or adjust CVs as necessary to create a higher top voltage.
gmpullman I agree with MisterBeasley's diagnosis. Can you get an ammeter between the decoder and the motor, having the engine on a test stand or even let the drivers slip on a test track, then see the current draw. Perhaps measure the voltage output of the decoder at the same time? I don't think it is anything related to programming. Remember, that tiny decoder and its micro-sized output transistor is taking the place of the bulk of that MRC powerpack. Good Luck, Ed
I agree with MisterBeasley's diagnosis.
Can you get an ammeter between the decoder and the motor, having the engine on a test stand or even let the drivers slip on a test track, then see the current draw.
Perhaps measure the voltage output of the decoder at the same time?
I don't think it is anything related to programming. Remember, that tiny decoder and its micro-sized output transistor is taking the place of the bulk of that MRC powerpack.
Good Luck, Ed
Arto So, maybe, what you need to do is use JMRI Decoder Pro to make it easier to "see" what the settings are on your decoders, and make the changes. And you might need a booster for the booster to get enough power to the proramming track to actually program the decoders.
So, maybe, what you need to do is use JMRI Decoder Pro to make it easier to "see" what the settings are on your decoders, and make the changes. And you might need a booster for the booster to get enough power to the proramming track to actually program the decoders.
MisterBeasley What are the current ratings for the decoder and the motors? It may be that the decoder is limiting the current, and the motor wants more. Try measuring the current in DC. How does a single engine run in DCC? If it seems fine, then you may not have enough power (volts x amps) for two of them.
What are the current ratings for the decoder and the motors? It may be that the decoder is limiting the current, and the motor wants more. Try measuring the current in DC.
How does a single engine run in DCC? If it seems fine, then you may not have enough power (volts x amps) for two of them.
gregc cuyama Have you ever checked to see how much voltage the MRC puts on the rails? If you want to compare the DC throttle output voltage to DCC, don't you want to measure the voltage across the motor leads from the decoder, not the track voltage?
cuyama Have you ever checked to see how much voltage the MRC puts on the rails?
If you want to compare the DC throttle output voltage to DCC, don't you want to measure the voltage across the motor leads from the decoder, not the track voltage?
Some DCC systems have put less voltage on the rails than one would expect. If the voltage isn't there on the rails in the first place, the decoder can't turn it into DC to drive the motor. An Internet search suggested that this has been an issue with some MRC systems in the past.
Since I haven't seen evidence of Mel's problem on any of the NCE, Digitrax, or Lenz DCC layouts with which I'm familiar, I was first looking for something that might be specific to his gear.
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MisterBeasleyWhat are the current ratings for the decoder and the motors? It may be that the decoder is limiting the current, and the motor wants more. Try measuring the current in DC.
you don't need to go thru the trouble of disconnecting a motor lead to measure current. A measurement of voltage across the motor at max speed compared to the track voltage should indicate if the decoder is limiting voltage or current. The only way the decoder has to limit current is to limit voltage (Ohms law).
I've had similar DCC issues, still a newbie, but maybe my newbie two cents might be worth something.
"To Me", it sounds like the decoders are set to a lower level limiting voltage and/or current. One of more Configuration Variables are probably controlling that.
I just started using JMRI Decoder Pro. Decoder Pro seems to be a good place to start if you want to make changing CV easy and understandable.
Here's an issue I recently ran into and how I had to solve it:
The first few locos I programmed were all Broadway Limited, some Paragon2, some Blueline. All were programmed with new addresses on the mainline.
Next up were a pair of Athearn Genesis DCC ready in which I installed Tsunami factory OEM decoders and had to custom install a speaker/baffle/enclosure. The Soundtraxx Tsunami decoders wouldn't program on the mainline. Soundtraxx has that capability locked out to protect me from myself. So, how to unlock the decoder? I tried programming it on the programming track. No Luck. The outputs from the Digitrax DSC100 Command Station/Booster don't put out enough power to program (at least) some SOUND decoders such as Tsunami. So I had to buy a booster (Soundtraxx PTB-100) for the DCS100 booster. Then I was able to program the Tsunami decoder, on the programming track.
But like I said, I'm a DCC newbie, so take this with a grain of salt. There are so many nuances to this DCC thing, it's driving me nuts, actually. And I'm anything but technophobic. But this has been like "One Giant Leap For Modeler Railroaders", and the rest has been like stepping back 25 years in the computer world.
It takes an iron man to play with a toy iron horse.
cuyamaHave you ever checked to see how much voltage the MRC puts on the rails?
Have you ever measured what the output is from the 2500?
Is it a Tech ii LocoMotion 2500? And are these the instructions: http://www.modelrectifier.com/resources/dc-ac/Tech%202%202500%20AF130.pdf ?
If so, those instructions say that the output is 20 volts DC, no load. I don't know what the loaded output would be, but if that voltage is greater than whatever voltage the motors get from the decoder then naturally the motors will run faster on DC.
Another question...have you ever taken your locos to someone else's place to see how they operate there?
Seems like that should be enough, if the voltage holds up under load.
I've never seen a problem like yours on the NCE and Digitrax layouts around here, hopefully one of the more knowledgeable folks on the forum can help you find some programming adjustments that make a difference.
cuyama Have you ever checked to see how much voltage the MRC puts on the rails? This can be tricky to measure completely accurately without a specific DCC meter, but a multimeter set to AC volts should give you a rough idea.
Have you ever checked to see how much voltage the MRC puts on the rails? This can be tricky to measure completely accurately without a specific DCC meter, but a multimeter set to AC volts should give you a rough idea.
maxman Please define "no power".
Please define "no power".