DCC Decoders question

[Anonymous]

Ok, after about 2 years of indecision I've finally decided to go DCC. Currently planning to buy one of the Lenz starter sets (these have a Lenz Compact throttle, mains transformer, two loco decoders and a switch decoder) at some point during the next few weeks. However, I have noticed one thing about decoders - Back-EMF. As I understand it B-EMF decoders (which effectively "read back" the motor current for smoother running) are best in locos without flywheels and can sometimes have problems with flywheel-equipped locos - is this correct? The loco decoders in the set are B-EMF, though this isn't a problem either way as I have a few non-flywheel locos they can go into, just wondering if I can fit them to the rest of the fleet or if I should buy non B-EMF decoders for them?

Thanks in advance for any help!

[rrinker]

I don't think it's really a problem with flywheel locos. It's just less likely to be needed for smooth running. I would expect that the Lenz decoders, like other brands, have a CV or two that can be adjusted to alter the BEMF responsonse - some locos need more than others to run smoothly, but give it too much and you can sometimes get 'jumping' between speed steps.
It's a bigger problem with double-heading. If both locos have BEMF decoders, they can 'fight' each other. Some, like Digitrax, have two settings for BEMF, one for runnign individually and one that is used whent he loco is consisted to another. Zimo decoders offer a 'fall off' setting so that BEMF is stronger at low speeds and drops off at high speed - thus it works more to ensure smooth starts and stops and slow performance, and doesn't have the 'cruise control' action at high speeds. Real trains need more throttle to climb hills, and less to keep from running away when going down, bt models often need a bit of help getting started and running slowly, so this approach of cutting off the BEMF at high speed seems to be a good one.

--Randy

[Anonymous]

Thanks for the help, looks like I should stick to non B-EMF for most of my locos - a good thing as it's much cheaper! I'll be looking to add decoders to a mix of Athearn Blue Box, Walthers, and Bachmann locos - anyone have any ideas what amp rating I should be looking at? One of the online stores over here has very cheap (but also good) 1amp single-function decoders which would be ideal for Athearn as they have wires rather than a plug, and I'm only looking to fit directional lighting to most locos - would a single-function decoder be enough to support this?

[cacole]

If the Lenz system you are going to purchase doesn't support BEMF decoders, you would just be wasting your money installing them. From what I have read about BEMF decoders, they require two-way communication between the decoder and command station, and only the more expensive DCC systems support this.

[NZRMac]

I've just flicked thru the instructions for my Lenz Compact and didn't see anything about B-Emf decoders I think cacole is correct, just the more expensive controllers.

Ken.

[Anonymous]

That's a bit odd then - the decoders in the set are apparently a LE1025A and an LE1025E - both listed as B-EMF ones (one has an NEM plug, the other has wires, they look identical apart from that). I'm wondering if Lenz are looking at future expansion - they'll work with the Compact without B-EMF enabled but could be reprogrammed for use on more expensive systems? Thanks for all the help recieved so far!

[cacole]

A lot of Lenz decoders have "features" such as BEMF, mars lights, ditch lights, etc. that simply won't function if you don't have a system that supports it. The decoder should still operate with no problems other than the fact that your DCC system won't have any BEMF control.

[rrinker]

BEMF does NOT require any sort of 'support' from the command station. It is strictly between the loco motor and the decoder electronics. What cacole is talking about is bi-directional communications, which Lenz has decoders and command stations to support, but I do not think the Compact offers this.

As far as amp capacity for the decoders, that depends on the loco. Your best bet is to get an ammeter and volt meter and hook them up with a DC power pack and test them, at 12v hold the motor to stop it from rotating briefly and read the current. Make sure the voltage stays at 12v, a lower-end DC power pack will likely sag under the increased current load. Decoders usually have 2 ratings, continous and peak. So long as the stall current of the motor is less than the max of the decoder, you will be OK. It's fairly safe (but not 100%) to say that a modern Kato or Atlas loco will be FINE with a 1 amp decoder. For newer Athearn Genesis locos, the same thing. For the older Athearn locos, you need to have a decoder that runs about 1.5 amps continuous/2 amps peak. For the REALLY old Athearn (about 20 years old or more, with the bigger motor), you should consider replacing the motor, although I have an old Trainmaster and stalled on my meter it read 1.8 amps, and while runnign with a short train it was around .6 amps - and some of the 1 amp continuous have a 2 amp peak rating, so those would work in this case.
As far as function count - some brands refer to the front and rear lights as two seperate functions, others count the F0F/F0R as one. If you can get them over there at a good price, the TCS T-1 decoder is a low-cost decoder quite capable of handling Athearn blue box locos, and it has front and rear headlight support. They even sell a harness, or you can get one from Digitrax as well, to fit to the Athearns with no soldering, except for adding the lights. TCS T-1's over here I have purchased for as little as $14USD and they work great in the locos I put them in so far.

--Randy

[Anonymous]

Thanks for the advice - I was planning to wire the lights as a single on-off function and ideally make them directional using diodes in the same way as normal DC directional lights operate - assuming that's possible under DCC? The decoder I was looking at is the "Mac-coder" LE1000A, which is the cheapest ready to use decoder available over here (TCS are out there, but I can order these online and my LHS aren't really up to speed with DCC yet). Most of my Athearn locos have already had one side of the motor hard-wired to the trucks, so I'll probably go through the fleet doing a full strip, clean, rewire and rebuild as I fit decoders. Thanks again for the help!

[rrinker]

Not sure what that decoder is, but I'm guessing it similar to what sells here as the Lenze LE1000W. That is indeed a single function decoder, one light bulb only. Perfect for cab units like FT, F3, F7, FA, etc. if your prototype only had a single headlight. No mention is made on the peak current, continuous rating is 1 amp, which SHOULD be fine for a blue box Athearn.
You can't just connect diodes and have the lights automatically reverse like on DC, the DCC function outputs are either on or off, with the - lead being the colored function lead and the + terminal being the blue wire. If you want lights at both ends that can change with the direction of the loco, you will need 2 function outputs.

--Randy

[Anonymous]

That's pretty much what I suspected - just a bit unsure as my only contact with DCC-type systems was an LGB G-scale setup I operated for a friend at a train show - this had function control of lighting and smoke units, with automated directional lighting - hence the confusion! I can get hold of 4-function decoders so I guess I'll have to fit these instead - there are a few locos in my fleet that will benefit from extra lighting. Thanks again for the help!