I have a pair of N scale Kato P42 with Digitrax decoders in them. When run separately, both locomotives run fine, but when I consist them, one of the locomotives runs a lot slower than the other. I have tried resetting the decoder by using CV8. I assume there must be some CV with a rogue value in it that would impact starting voltage when the loco is in a consist. i could not figure it out based on the documentation I have (NCE system, and Digitrax Decoder manual-large pdf download, not documentation provided with the new decoders) Can anyone help me with this? Thanks nodima
The key may be to change CV 57 from 6 to 102. This is the CV that enables BEMF (which Digitrax calls Scalable Speed Stabilization). Digitrax ships decoders set so that BEMF is not enabled for the consisted locomotive, just for the locomotive operating on its own. The default value is 6. To enable BEMF while consisting, you need to put in something like hex 66, which is 102 in real numbers. This is buried in Section 6.15 of the Digitrax mobile decoder manual. How do I know this? I encountered the same problem you did, and asked the same question on Trainboard. I have no idea why Digitrax ships decoders with BEMF disabled for consisting
Dave B wins the gold star for the day!!! That was the exact issue, thank you very much!!! Interesting, I made several searches, but could not find any related issues. Cheers!
This goes against what I have always read where BEMF in a consist was not recommended. Is this info incorrect? Do the Digitrax decoders have a different way of dealing with this issue? I am not shooting down your suggestion rather I am very interested if it works. Then speed matching may not have to be such an exact science.
The big problem seems to be when one locomotive has BEMF enabled, while the other does not. For some reason, Digitrax decoders are shipped with factory settings that produce this condition if you put two together a consist without changing CV 57. It seems to work fine if you enable the consisted locomotive to use BEMF. It would probably also work if you disabled BEMF in both locomotives. Maybe early BEMF created consisting problems, but the current decoders seem to work ok.
It was my understanding that before speed matching that BEMF was always to be turned off. So I'm not sure that Digitrax has on on some and off on others. I believe it's on and needs to be turned off. Could be wrong though.
For some reason Digitrax ships decoders with BEMF enabled for normal operation, but disabled when consisted to another locomotive. That's how you can get an on off mismatch with the factory settings. It may be a good idea to turn the BEMF off for speed matching, but that is a little different from getting the locomotives to run together in a consist. Locomotives seem to run ok in a consist if both decoders enable BEMF.
Doesn't really compute with me. The problem should only exist if both locos have BEMF turned on. Is this only a problem when using an NCE system? Because it's not an issue using a Digitrax command station, Digitrax CV defaults work fine (as you might expect).
The mismatch would happen when using Universal consisting which is default on all Digitrax systems. The "top" loco would retain its normal BEMF enabled settings but the "consist" locos would have BEMF turned off. I'm guessing this would not be an issue with sytems that default to Advance Consisting. e.g. NCE Some one should try it.
To clarify - I have ~15 loco's with Decoders (all Digitrax 163 series IIRC) generally they have all played nicely with one another, this is the only one where it did not. I purchased and installed these decoders back in 2006 or so but due to a move had not used them since then. In this case, I was setting up the problematic loco as the lead loco in the consist - I did not try it as the rear loco.
The problem seems to show up when you use CV 19 to set up the consist, which is advanced consisting, I think. I haven't really done a lot of tinkering to see what happens if I get the Zephyr to set up the consist. Mostly, I am setting up consists that I want to use at the club, so CV 19 is what works for me. Also, it is a way to keep things simple inside the Zephyr
Here is the thread Dave referred to concerning this issue. Digitrax decoders are shipped with Bemf tunred off when consisted because Bemf can cause problems in a consist, though it won't always. If you have Bemf turned on when your engines are consisted, it is actually more important that engines that do not run at the same speed be closely speed matched; however, with Bemf enabled, engines from the same manufacturer are more likely to run at the same speed without having to be speed matched(because the Bemf will compensate for some of the drive train inconsistencies). If you are running two engines together with Bemf and one is faster than the other, the slower one will slow the faster one down, so the faster one will apply more power to try to compensate for it. Likewise, the faster one will speed up the slower one and the slower one will apply less power to try to compensate for it. To try to resolve potential problems with consisting engines with Bemf, Digitrax decoders have two separate settings, one for when the decoder is consisted, and one for when it isn't. One nice thing about how they have it set up is the bemf does not just have to be on or off, you can have bemf still enabled when in a consist, but have it's intensity reduced to reduce the likelihood of it causing problems. Unfortunately, both settings are stored in one CV(CV57), so to enable bemf in a consist, you have to look at the CV as a hexadecimal number where the left digit is the consisted setting and the right digit is the unconsisted setting. This is one of the CV's that causes people to say that you have to know hex to use Digitrax, but that simply is not true. All you have to know is each digit can have a value of 0-9, or A, B, C, D, or F, where A=10, B=11...F=15. Select the value you want for each digit and then look up the decimal equivalent in the hexadecimal to decimal chart in the back of the Digitrax decoder manual. The bemf settings are one area where Digitrax has included a lot of flexibility in their decoders, but unfortunately this increased flexibility does entail some increased complexity. When using a Zephyr, consisted engines usually do not turn off Bemf because the Zephyr defaults to not using advanced consisting. The consists are stored only in the command station and CV19 on the decoder is not changed, so the decoder does not know that it is in a consist.
