Most decoders have separate CVs (Configuration Variables) for DC-operation max voltage and DCC-operation max voltage. Check their values to see if your decoder is limiting how much voltage goes to the motor under DCC.
Also, get a scale speedometer (or the old method, a yardstick, stopwatch, and calculator) to find out how fast your engine goes under DCC. It might be that the decoder limits the engine to prototypical speeds, which is not the case when there's no decoder installed.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
Yes, try changing CVs 2, 5 and 6 to zero (and maybe 3 and 4, which control momentum). That should make the engine run the same as it does under DC - unless you have (intentionally or not) set it up to use a speed curve. If CV 5 is set at say 125, you've basically cut the maximum power going to the engine by about 1/2.
Your DC power pack, if it's a fairly fancy one, may be doing voltage compensation going up the grades to keep things moving. What happens if you increase the throttle on the DCC when going up hill (being like the prototype, unless motor power is increased, a loaded loco will slow down doing up hills)? The DH123 decoders do not have BEMF so they cannot compensate for speed variations on their own, however there are tuneable motor parameters that may need to be adjusted based on the type of motor in the loco. The DH165 series do have BEMF, but the default settings may not be approriate for the specific motors.
Try a TCS decoder - they have auto adjusting BEMF. It will run a bit erratically when first installed, but as the loco runs for a while, it smooths out as it finds the best settings for the motor. After that, super smooth. And no CVs to set to get it to work well, just set the address.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinker Your DC power pack, if it's a fairly fancy one, may be doing voltage compensation going up the grades to keep things moving. What happens if you increase the throttle on the DCC when going up hill (being like the prototype, unless motor power is increased, a loaded loco will slow down doing up hills)? The DH123 decoders do not have BEMF so they cannot compensate for speed variations on their own, however there are tuneable motor parameters that may need to be adjusted based on the type of motor in the loco. The DH165 series do have BEMF, but the default settings may not be approriate for the specific motors. Try a TCS decoder - they have auto adjusting BEMF. It will run a bit erratically when first installed, but as the loco runs for a while, it smooths out as it finds the best settings for the motor. After that, super smooth. And no CVs to set to get it to work well, just set the address. --Randy
RR_MelThe one that stands out is the T4X, can I use a T4X and a T1 in a tandem A B configuration and will both decoders BEMF auto sync?
That may be a question for the TCS themselves. Also those decoders are not sound decoders. Incidentally, TCS has this: "All decoders are covered by a one year, goof proof, no questions asked warranty. Decoders outside of the warranty which cannot be repaired can be upgraded for a nominal replacement fee."
How old are the SD40-2s?
BMMECNYC RR_Mel The one that stands out is the T4X, can I use a T4X and a T1 in a tandem A B configuration and will both decoders BEMF auto sync? That may be a question for the TCS themselves. Also those decoders are not sound decoders. Incidentally, TCS has this: "All decoders are covered by a one year, goof proof, no questions asked warranty. Decoders outside of the warranty which cannot be repaired can be upgraded for a nominal replacement fee." How old are the SD40-2s?
RR_Mel The one that stands out is the T4X, can I use a T4X and a T1 in a tandem A B configuration and will both decoders BEMF auto sync?
Mel,You haven't told us your DCC system. Seeing that you've said it's 3.5 amps, it sounds like the Digitrax DCS51 Zephyr Xtra. You also haven't told us what your DC analog power pack is. I assume it's something like the MRC Tech 7 Ampac 760.
To me, it sounds like a voltage issue.
Here's the deal - In DCC, the voltage to the motor, after it goes through the decoder, is 12v. On an MRC Tech 7 Ampac 760, the voltage to the motor can be as much as 23 volts (!). It's no surprise that your locos run slower on DCC vs. DC. In fact, we have the same problem at my club.
On our old layout, we had 18v power to the rails. We had many engines that ran passenger trains just fine on our old layout, namely re-powered Athearn FP45's with big can motors and weighted PFM F40PH's. When we moved and converted to DCC, these very same engines were suddenly dead slow, suitable only for freight trains. And that makes sense when you consider that they only had 2/3rds of the voltage available. The F40PH's were sold, and the FP45's had to be repowered with 12v motors in order to get some top end speed.
Paul A. Cutler III
RR_Mel A pair draws 1.8 amps under full load on my 3½% grade from my 5 amp DC power pack.
Total amp draw for the pair is 1.8 amps, right? So, .9 amps each. That is close to the 1.0 amp limit of the decoders. They will get warm, but still work. (But! Never allow them to stall! That will, most likely, be above the maximum limit of the decoder. Then there will be other issues........)
Zero out momentum and the max voltage setting, so it responds like the DC power, and then, go from there.
But, amps is not the issue.... At least from these measurements anyways.
Ricky W.
HO scale Proto-freelancer.
My Railroad rules:
1: It's my railroad, my rules.
2: It's for having fun and enjoyment.
3: Any objections, consult above rules.
RR_MelI was thinking about buying a couple new decoders. I looked at the TCS site and it leaves a bit to be desired. I feel I need the 1.3 amp decoders
Most decoder manufatcurers websites have a decoder selection guide, just find your loco and one or more decoders will be recomended
Digitraxhttp://www.digitrax.com/products/engine-matrix/decoder/
NCEhttp://www.ncedcc.com/#!decoder-selector-tool/c1c03
TCS (list for HO; other scales on other pages. also inludes installation how-tos)http://www.tcsdcc.com/Customer_Content/Installation_Pictures/HO_Scale/HO_Search/search.html
I did not include sound decoders, they have similar pages
George In Midcoast Maine, 'bout halfway up the Rockland branch
If you have only the newer BB motors in the Athearns, they should not exceed the 1.3 amp consinuous rating of the T series decoders. Check the stall current on DC and make sure it doesn;t go over the 2 amp peak.
You need the T4X if you plan to put in ditch lights, if not the T1 is fine (T1 has 2 function outputs, not 1 - legacy name from when TCS first started. All newer ones, the number indicates the total functions). I run multiple locos together and the TCS decoders do not fight one another, they also consist just fine with Loksound and QSI - my most often used combo is a pair of Proto 2000 GP7's with TCS T1's sandwiching an Atlas Trainmaster with QSI and I never did any adjustments to speed match them, this trio runs for hours at club shows without problem. I have a Stewart FT A-B set, both powered, the A has a TCS T1, the B had a Tsunami, they ran fine togethr with no adjustment. The B is now a Loksound, it still runs fine with the A, no adjustments.
Mel,Try measuring your track's DC analog voltage at the spot you're noticing the problem.
Then try measuring the DC voltage going to the motor of one of your DCC-equipped locos (that's the orange and gray wires) at full throttle. This isn't a problem because every decoder is also a bridge rectifier converting the square wave DCC signal to DC for the motor.
My bet is that you're going to find less voltage going to the motor of your DCC-equipped locos vs. the track voltage when you're in DC analog mode. And this will explain the difference in performance.
It shouldn't be that big a difference - the nominal track voltage in DCC is higher to make up for the loss in the rectifier and in the H bridge driver. If it is way off, then either a speed curve is set or CV2-6-5 are set to allow less than maximum top speed. Easy enough to check, compare the speed of a light engine on the level, DC full throttle vs DCC full throttle. I'm thinking if anything needs to be adjusted, it's the BEMF and/or 'dither' to get the PWM drive optimized for the Athearn motors. I don;t have any BB level locos with DCC to compare, even the clone ones I have like P2K Geeps have a better quality motor.
Without some kind of load (engine, light bulb, whatever), you will never measure any voltage loss. You can feed 12 volts through a hair thin wire or 14 guage cable and will measure 12 volts.
Once you place a load on that wire, the resistance of the wire comes into play and you will see a voltage drop - if in fact the wire cannot handle the current load adequately.
That being said, I assume you have adequately heavy gauge wire for your bus line and sufficient drop feeders to your track ?
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
RR_MelI’m a retired long time electronic techie but I haven’t gone into depth in DCC programming
Mel
You may want to consider getting Decoder Pro to help with your decoder programming problems. It is a freeware from JMRI, and lots of folks use it. Take a look at the Quick Tour on the site.http://jmri.sourceforge.net/help/en/html/apps/DecoderPro/
You will need to get a computer to DCC interface. Digitrax makes one; but check with Tony's Train Exchange - they may have a better one.
RR_Mel...In DC mode the highest rail voltage I measure is just under 13 volts under load. For accuracy I measure my DCC voltage with a Fluke 79 at just over 14 VAC under load. All of my power packs are from MRC. I have three DC power packs, used one at a time. 1) Sound and Power 7000 3.5 amps at 14 volts in the HO position. The 7000 is my main DC power supply mainly because of physical fit into my control panel. 2) Tech 4 14 Volts at 4 amps. 3) I use a Tech II 2500 for testing and trouble shooting at my workbench and on my layout...
If you have 14 volts at the rail head in DCC, then you'll have no more than 12.5 volts at the motor because of the ~1.5 volt drop of the bridge rectifier in the decoder. Allowing for the voltage drop of the H-bridge circuit, I would not be surprised to see a maximum voltage of less than 12 volts. This could be remedied by a higher voltage power supply for your DCC system. Also, Digitrax decoders don't seem to output full voltage when BEMF compensation is turned on, so it may help to turn it off (set CV57 to 0).
Check the setting on CV-5. It should be 255 to get full speed. CV-6 should be 128 for half speed. The speed ramp is linear.
Buy a different brand decoder and plug it into one of the diesels. Check CV-5 and CV-6. I'd almost bet it is the Digitrax decoders giving you migrains.
South Penn
RR_Mel I guess I’ll give the Decoder Pro a shot. I haven’t wanted to dig into DCC programming, I retired to get away from that kind of stuff
Decoder Pro makes it easy. No trying to figure CV values and what number goes where. The program recognizes the decoder and a set of screens comes up. Changes are on drop down menus in English, not computerish, no hexidecimal (which some decoders require).
Also, if you have a number of identical locos, the program will let you copy all your changes from the first one to the others, once you set up the program record for the subsequent ones.
Well you certainly know that current is not "pushed" by the decoder, so if all you measure is 700ma between the decoder and the motor, that's all the motor is drawing. Seems a little low for a BB motor stalled, but if you've done some of the basic tune up procedures on them, it may be in line with expected results. Only a few decoders have an actual overload protection, most of them, if you connect a motor that draws 2 amps and the decoder is rated for 1 amp, it will just fry the motor driver. It definitely won't limit the current it supplies.
On the Digitrax decoders, make sure CV54 is 0 or 1 so that torque compensation is enabled. High frequency PWM drive and low end torque are mutually exclusive, the torque compensation helps with this. At high throttle positions it shouldn;t make a difference though.
G PaineDecoder Pro makes it easy. No trying to figure CV values and what number goes where. The program recognizes the decoder and a set of screens comes up. Changes are on drop down menus in English, not computerish, no hexidecimal (which some decoders require).
DecoderPro is a good thing, but in this case I don't see the value of learning something brand new if the goal is just to change one or two CV values. That can be done easily enough with the command station.
My take on this problem is that if a particular motor is getting the same voltage with DC or DCC, the performance should be the same. If all the locos are acting the same way, something else is going on.
Exactly how many of the locos are on a live section of track at the same time?
Do you have any friends with DCC or are near a local DCC club? It shouldn't be too hard to find someone who has an identical loco to yours with a different decoder in it that you can compare your units to.
Before swapping out (or giving up on) the decoders, have you tried running the engines somewhere else, like on a friend's DCC layout? Seems like if the engines run great on DC, but all run poorly on your DCC system, it's more likely that something is wrong with your DCC system than that all the decoders are bad.
BTW it could be your DCC controller is OK, but that you're using smaller wires so the power isn't getting to the track well enough, or that the distances are too far from the power source. Might end up that adding heavier wires or adding a DCC power booster might take care of the issue.
wjstix Before swapping out (or giving up on) the decoders, have you tried running the engines somewhere else, like on a friend's DCC layout? Seems like if the engines run great on DC, but all run poorly on your DCC system, it's more likely that something is wrong with your DCC system than that all the decoders are bad. BTW it could be your DCC controller is OK, but that you're using smaller wires so the power isn't getting to the track well enough, or that the distances are too far from the power source. Might end up that adding heavier wires or adding a DCC power booster might take care of the issue.
As I stated before, you are going to loose at least 1.5 volts, and probably more than 2, through the decoder because of the diode bridge and h-bridge. That's not going to change with a change in decoder, but a change in power supply will overcome it. Also, did you try turning off BEMF compensation?
Lower voltage won;t make them pull less, just run slower.
But wait - the main problem child has TWO AThearn BB motors and TWO decoders? Are they both the same decoder? They may be somewhat fighting each other. With MU locos, I have no problems with one of both having BEMF and the locos fighting one another, but two in one loco may be a different story. Multiple motors is never easy with DCC, parallel is tough to get to work together, the right way is to runt hem in series with a single decoder but then you only get half speed - fine for a small switcher like the Bachmann 44 tonners with dual motors, but not for a road loco. Parallel will need a O/G scale decoder, there are some 4 amp rated ones that should fit in an HO E unit without problem, but you almost certainly have to turn off BEMF. Single decoder with parallel motors will be the closest to the same loco running on DC, since on DC that's exactly what you have, both motors in parallel.