Every time I make a post saying that my locomotives have much more power running on DC than they do when I have a DCC decoder in them I get flack saying I’m doing something wrong. I’m asking for help to find what I’m doing wrong. I admit that I’m a weirdo and rarely do anything “normal”. I went to DCC purely for sound for my steam Cab Forwards, the DCC sound is awesome.
I have over 75 HO locomotives, I have wired all but about 6 for DCC operation (standard NMRA 8 pin female connector). I only have a dozen decoders and I swap them around to run in DCC mode. Every locomotive is fitted with a DC shorting plug that I remove when I plug in a decoder.
I won’t go into my steam locomotives because the wheels slip pulling a dozen box cars full of birds in flight up my 3½% grade.
My diesel fleet is another case, I have a large fleet of E7s. I have 6 stock Athearn Blue Box SD40-2 frames with Cary cast white metal bodies, t
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.
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.
I 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 to feel warm and fuzzy with the Athearn SD40-2 stock motors. I also want 4 Functions on at least one decoder. 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.”
Most of my SD40-2 are last run of the Blue Box series. I bought two new SD40-2s at my LHS in 1994, the rest are eBay clunkers that I have upraded. I replaced older motors, all the motors are be between 1994 and early 2000s. All run exceptionally well. I replaced the bronze bearings if they had any slop and all of the motor mounts. All the motors have low current draw and run very close in speed on DC, that’s an Athearn plus.
As far as sound goes I only have sound decoders in my steam, the sound coming from my Athearns works for me diesel wise.
uahhmmm erm…guyz… I have a Bowser Big Boy which may weigh in the same as his weighted down diesels. This Big Boy could pull the paint off the wall. Most decoders are rated around 1 amps. I could not use a 1 amp decoder on the Bowser Big Boy. Digitrax makes a 4 amp decoder. http://www.digitrax.com/products/mobile-decoders/dh465/ I was working on my N&W Jawn Henry Turbine, changed the motor to a single large NWSL, I used a QSI turbine decoder to dabble the sounds… I fried the decoder. It now has the the digitrax 4 amp decoder. Working on the sound for it, BUT it has the direct connection for their sound bug. You need -current- …-amperage-…not voltage. Heavy duty weighting his diesels this will overpower those decoders and fry them. They will not have the current output to deal with the heavier load. BEMF and more voltage will NOT do it. BEMF is about motor control…NOT current. No power, no movee. No matter what the voltage. Your engines on DC…you are right, they are getting the needed current, throw a 1 amp decoder in it, you restrict the needed power.
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.
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.
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.
OK gents, here goes. I built in a volt meter to my control panel and monitor all the voltages on my layout via a six position switch. The panel meter is a dual volt amp LED with the amp meter section only in the track feeders. (The meter doesn’t work on DCC so it’s in inline with the DC power supplies only)
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.
My DCC power supply is a Prodigy Advance Squared², 14.4 VAC at 3½ amps.
My sound decoders are a mix of MRC and Soundtraxx, all in steam locomotiv
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.
Over the years I’ve checked for voltage losses and quite simply there are none up to the DCC connectors. As I mentioned I’m a 50+ year electronic techie with a EE degree. The problems I have are inside the decoders. With 15 volts of DCC power on the decoders (plural) the maximum DC voltage to the motor is less than 12 volts at full load. The decoder output to the motor is puny. The most current I’ve been able to measure to the motor from a DCC decoder is less than 700 ma.
After spending an hour with Customer Service checking voltages and changing CV values I gave up and reset all of my diesel decoders to default. At least they work, wimpy but they work. I will add that a decoder will work in a stock light weight Athearn SD9, a light weight SD9 draws around 500 ma at wheel slip. My heavy E7s do not know what wheel slip means. So this takes me back to what always brings the flack, “MY diesels have more power running on DC than DCC.”
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 ?
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.
My track feeders consist of #12 solid THHN with #18 solid jumpers to the rails, longest being 10”.
I run my testing at my workbench on a Micro-Mark Locomotive Test Stand. Applying pressure on the frame creates load on the motor to measure motor current.
George
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. After 50 years of electronics I don’t want to go there but if that’s the only way . . . . I have exhausted everything else, the problem has to be internal programming. The decoders won’t putout maximum voltage or current, whichever, to the Athearn motor. It would be a lot easier to just can the decoders in my E7 diesels and use straight DC.
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).