I have been reading for awhile and I have a few questions which I cannot find the answer to without getting more confused. I have a tabletop N-Scale layout under construction 2 1/2’ x 6 1/2’ with Unitrack. I am waiting for a Powercab from Tony’s.
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Would 1 feeder be enough or should I add another feeder to the backside? The Kato feeder wires look to be about 22 or 24 ga. The most engines I will be able to run at a time will probably be 3, 1 PA-1 & a GP-38 + SD-35 consist.
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Has onyone had any experience with the #6 turnout? I have 4 on my layout. The way one of them is oriented I am having to dedicate a terminal section to a siding (Program Track).
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Which is better BEMF or adjustable torque compensation? From what I have read the NCE decoders don’t have BEMF.My PA-1 takes a little voltage to move then it takes off like a rocket. I am not planning on much grades even when I build a larger layout and my curve radius min is 12 3/8".
I live on the NS Mainline between Charlotte,NC and Atlanta, for anyone modeling modern NS plenty of GE power is what I see mostly. See more GE UP&BNSF than EMD and alot of intermodal.
BEMF and torq compensation really are for two different things. To keep motors from overheating, and make them run quieter, decoders use high frequency or ‘supersonic’ drive. ALL power from a decoder is pulse power, but if you make the frequency high enough, it’s safe even for coreless can motors, and any ‘buzzing’ in the motor occurrs at a frequency beyond human hearing. The downside of this is that at low voltage levels, low speed operation, the pulse duration is SO short that there is little torque generated by the motor. This is what torque compensation is designed to overcome.
BEMF relies on the back-emf from the motor (turn the shaft of the motor and it generates voltage, ditto with the motor costing due to momentum). During the pulse off period of the drive power, a decoder with BEMF reads this voltage and uses it to modify the power supplied to the motor to keep it running as close to the set point as it can. With a quality motor and drive, it isn’t as needed, but as soon as you have the slightest bind, at a crawl speed your loco will probably stop without BEMF. With BEMF, the decoder will apply additional power to keep it moving, and then back off as soon as it becomes free. BEMF quality varies from decoder to decoder, it mostly depends on the software algorithm used to control it. The European decoders such as Lenz, ESU, Keughn, and others have incredible BEMF ability, US ones liek Digitrax are not quite as good. A good example of BEMF - my PCM T-1 with an ESU sound decoder can run on speed step 1 around my entire layotu, with not the slightest pause. If it put my finger in front of the loco, it will continue to turn the drivers at the same slow speed, but slipping since the loco can’t move. I have soe decent Stewart and P2K locos with NCE decoders, no BEMF, and they run great at slow crawl speeds, but if I put my finger in front of them, or take one that is crawlign along and hook 20 cars to the back of it, it will stop without applying additional power
Randy gives an excellent explanation of BEMF and how it works with decoders as well as contrasting it with torq compensation very nicely.
I have used both BEMF decoders and NCE decoders that don’t have BEMF. I currently have elected to go with the less expensive NCE decoders because I can get very nice slow speed performance from my locos just using the torq compensation feature. You won’t find any BEMF decoders selling for about $12 each in quantity, and the slow speed performance of the NCE decoders is excellent.
BEMF is a mixed blessing. While it can make your locos run silky smooth through turnouts, through curves, up hill, down hill … that’s also part of the problem. Real locos just don’t run that way … you have to work the throttle to compensate for the effects of such trackwork, and turning up the BEMF all the way removes the need for you to do that. Booring.
Plus if you aren’t careful with BEMF, you can get locos that fight each other in a consist, each one trying to speed up or slow down the other one if it begins to drag. For instance if consisted loco 1 thinks things are slowing loco 2 (also with BEMF) and loco 1 tries to make loco 2 run faster, then loco 2 senses it’s speeding up and will slow down even more to compensate. Then end result can be a violent lurching between BEMF locos in a consist. This is why most BEMF decoders have a setting to have them NOT use BEMF in a consist.
Because of the expense and sometime fickle behavior of BEMF locos in a consist (and I model 1980s diesel lashups, so almost everything is consisted), I find I prefer the slow speed performance from the cheaper NCE decoders just as much or better than more expensive BEMF decoders. And since I run almost everything in a consist, I am generally not running with BEMF turned on anyhow.
Thanx for everyones answers. It made my decision easier, I was going with either the Digitrax or NCE decoders.
Gary
My opion is pretty much that with decent quality equipment, BEMF is only somewhat required for steam locos, simply because of the compelxities of the mechanism, witht he rods and all that. Even completely tuned, there’s still goign to be more friction in the mechanism than in your typical diesel drive. Case in point, BLI PRR M1a vs PCM T-1. Both are 4-8-4’s, both have pretty much identical mechanisms. The BLI still has the original QSI chip, not the new upgraded one that adds BEMF. The PCM loco uses an ESU decoder that has excellent BEMF. HUGE difference in the two as far as minimum crawl speed. ANd it’s not break-in time - the T-1 outperformed the M-1 right out of the box, and the M-1 has been in use for nearly a year prior to buying the T-1.
However, my P2K and Stewart diesels with low cost but very good NCE D13SRJ decoders ($11.99 in 10 packs from Empire Northern) work just fine at crawl speeds depsite the lack of BEMF. If you just need a front and rer light plus maybe a Mars light,t he D13SRJ is hard to beat. The only other decoders that low in price are the horrible Lenz 1000 something or other, basically the one used in the cheap Bachmann DCC equipped locos, and those don;t even have a high frequency drive for quiet operation. Far as I can tell, about the only advanced feature missing from the D13SRJ is the BEMF. If you need more than 3 function outputs, for things like ditch lights and other things, you will have to pick a different decoder. Ditch lights plus front and rear lights = minimum of 4 function outputs. Add a rotary beacon - now you need 5 functions. NCE has others that are identical to the D13SRJ, just with more outputs. They just aren’t $12.
–Randy
That explains a little better. I went with the NCE decoders, Im in N preditch lights so 2 function is fine. I would like to seperate my numberboards from headlights. I’ve noticed at night in consist usually the 2nd loco has numberboards only on. Would be difficult in N with replacement boards.
Gary