Choosing DCC decoders - A "Black Art" or Where is the science in it???

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NedFlanders
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Choosing DCC decoders - A "Black Art" or Where is the science in it???

Postby NedFlanders » Mon Oct 15, 2018 11:37 pm

Hi all,

(Longish story)

Having started back into the hobby courtesy of a trackmat layout I discovered that DCC had come of age(ish) and, knowing the tech geek in me, it was something I wanted to get into. I picked up a Hornby e-link go a couple of hattons decoders and made a start.

Initial results with the Hattons decoders were promising, then the Flying Scotsman started to only work if some other loco was running at the same time??? "I beg your Pardon?"

A couple of Lenz Standard chips then came along ( cant remember the model) and Flying Scotsman worked away - ah, Ok, Lenz is now my Standard.

Fast forward to this year, when after a 6 month break, I found Scotsman was misbehaving - "oh bother". but only on "Straights" - what is going on here?

Strarted thinking about StayAlives and did a bit of hunting around and got more confused between the options with super capacitors and non super capacitors etc.

Found a LaisDCC chip for sale along with a stay alive for less than 20 quid - did I mention that budget is important and realism is at the Hornby Railroad level?.... so I have no pride :wink: I will try anything once to keep the costs of the hobby down.


The chip arrived and I soldered on an 8 ping socket onto a hornby class 58 (picked up on ebay)- connected up the chip and away she went. after a good half hour of running in I turned everything off and headed off on a Dad taxi run. When I came back the 58 was dead, stone dead! "Ah for Fruits sake!" I said - no really, like my alter ego - I cant swear.... Anyway, I was less than impressed.

Out came the e-link ( did I forget to mention I am now the proud owner of a z21 and Mutlimaus for control?), and I used it to probe the chip - all ok on the chip - set the loco ID to a different value ( don't ask) and tried it with the e-link on the programming track and it ran fine(ish), tried it back on the mainline with the z21 and while she ran, she wouldn't win any awards for smoothness and there seemed to be a distinct absence of "Stayalive". More suitable benign swearwords followed...…

Ok, Lets look at it a different way - I still have some Hattons chips with the 8pin plug attached - lets try one of them. Straight out of the box - worked away grand with the 58. Right, what to do next?

Before fitting the LaisDCC chip to the 58 I had checked the Stall current of the 58 and a Eurostar that was to have been the original destination for the chip. I found that the Eurostar ran at about .5 to .6 of an amp normally and the stall current was over the amp and the 58 was .25 and .5 respectively. so as I thought I had the .5 chip I went and fitted the chip to the 58 and put the Eurostar to one side. (apologies if I have the amp unit of measurement wrong - it sounds right in my head)

Fast forward again and I reread the LaisDCC info, after the testing and dying of the 58, and realised that I did have the 1amp chip and not the .5amp chip I thought I had picked up. So, I opened the Eurostar, found it was DCC Ready, so just pulled out the blanking plug, fitted the LaisDCC and stayalive and lo and behold it ran sweeter than a nut!

Right -in Conclusion - Seeing as the budget is tight, picking the right chip for the right ebay purchase seems to be more of a Black art than a science, or am I missing a trick? I can kind of understand why a chip designed to operate with higher current might not work as well in a low current Loco, but why would the Stay Alive not work at all - surely a capacitor is a capacitor and supplies electrickery irespective of how much current the loco pulls - surely it would last longer?

Seeing as I enjoy fixing up/servicing secondhand locos ( its the "fixer" in me), am I better to test the current comsumption on DC first and then tailor/test the chip to that or is it - "ah sure, lets try this one first and then that one and then...." how has anyone else got on specing chips to older locos?

Yours in bewilderment.

Ned.
Getting back into railways, one step at a time.
Ned's Workbench - https://tinyurl.com/y4jby73c
The UppydownyRoundyRoundyRailway - https://tinyurl.com/y6stelsr

Suzie
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Re: Choosing DCC decoders - A "Black Art" or Where is the science in it???

Postby Suzie » Tue Oct 16, 2018 12:35 am

Hi Ned

Poor pickups and dirty wheels are usually the biggest cause of poor running especially with basic decoders. Get yourself some Zimo which cost £19 for the entry level ones (MX600R has the NEM652 8-pin plug) and you will know that you have excellent decoders and not have to worry about that - poor running will be something in the loco.

The biggest cause of decoder failure is short circuits either across the motor or from motor to pickup so use your meter with the decoder unplugged and turn the motor to make sure that there are no intermittant shorts occurring. Second biggest cause of decoder failure is rubbish decoders. If you are spending less than £19 on your decoders you are asking for trouble!

Suzie x

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Mountain
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Re: Choosing DCC decoders - A "Black Art" or Where is the science in it???

Postby Mountain » Tue Oct 16, 2018 2:57 am

DCC can be quite frustrating at times. OK, to be fair, DC has its moments but the DC moments are normally easier to solve.
I must say though that I've only had one single DCC decoder play up and I dont know if it was the loco pickups or the decoder as it could have been either.
Other then that it has all been OK, though all my decoders are well over ten years old. A few are around 18 years old now, though they've rarely been used, so its not a fair comparison to go by.

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Bigglesof266
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Re: Choosing DCC decoders - A "Black Art" or Where is the science in it???

Postby Bigglesof266 » Tue Oct 16, 2018 4:13 am

Spot on useful advice from Suzie as usual. Thanks Suzie.

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Chops
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Re: Choosing DCC decoders - A "Black Art" or Where is the science in it???

Postby Chops » Tue Oct 16, 2018 9:55 pm

"Black Art" about sums it up for me. Some years ago I tried to wire one into a dual motor Bachmann 44 Tonner, and American affair. I was dismayed when it burst into flames, as I had managed to cross wire it. Later, once I figured out how to isolate the motor and attach the various wires, I had better success using MRC decoders, but soon discovered that in the absence of spotlessly scrubbed track communication failures would occur, like having the throttle stuck wide open and nearly plowing into another train. What I have seen with my friends is a variety of hits and misses with different brands hitting and missing as they will.

Like the toad that tried to eat the wasp, I have retreated to my DC burrow.
I don't care what they say. I believe in Nessie.

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NedFlanders
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Re: Choosing DCC decoders - A "Black Art" or Where is the science in it???

Postby NedFlanders » Wed Oct 17, 2018 11:35 pm

Suzie wrote:
Poor pickups and dirty wheels are usually the biggest cause of poor running especially with basic decoders.

The biggest cause of decoder failure is short circuits either across the motor or from motor to pickup so use your meter with the decoder unplugged and turn the motor to make sure that there are no intermittant shorts occurring.
Suzie x


Thanks Suzie - I suspected dodgy pickups/dirty wheels was probably Flying Scotsmans issue as she was fine on the bends where, I reasoned, that the nature of the tight curves forced more contact whereas when she was on the straight she could "sink" slightly between the rails. also she would begin to run without any issues after 5-10 minutes when, I guessed, contacts were cleaner or dirt was burned off or the motor had free'd up. I have some more maintenance tools on order so I will be giving her a strip down and clean and then putting her back together before fitting a TTS chip /speaker to her to replace the Lenz chip that I currently have in her. I also have a number of extra wheel contacts on order. The best runner is the Eurostar and she had pickups on both sides of both of the bogies on the driving car whereas locos like the 58 only seem to have them on one side of each bogie.

I hadn't come across that checking for shorts - that sounds interesting - thanks.

The Class 58 is, as yet, running fine with the Hattons chip, I enjoy the tinkering with the locos when i get a chance so I think I will persevere with the selection box of chips I have for the moment, if nothing else I hope to learn a bit more about them by tweaking them. I remember a line from a book about a golf caddy:
"so you learned a lot from the good golfers you Caddied for?"
"No. I learned much more about what not to do from the bad ones!" :wink:

So long as I have enough locos running well to either have the Small Controller happy or to allow me to have a couple of trains circling therapeutically that will give me the scope to indulge my " I'm going to fix this if it kills me!" gene by working on the misbehaving ones. :D

Cheerio,

Ned.
Getting back into railways, one step at a time.
Ned's Workbench - https://tinyurl.com/y4jby73c
The UppydownyRoundyRoundyRailway - https://tinyurl.com/y6stelsr

Bigmet
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Re: Choosing DCC decoders - A "Black Art" or Where is the science in it???

Postby Bigmet » Thu Jan 31, 2019 4:04 pm

NedFlanders wrote:...Seeing as I enjoy fixing up/servicing secondhand locos ( its the "fixer" in me), am I better to test the current comsumption on DC first and then tailor/test the chip to that or is it - "ah sure, lets try this one first and then that one and then...." how has anyone else got on specing chips to older locos?...

How are you getting on now?

I started out in DCC when there was far less choice in decoder brands. trialled what was readily available in the UK, and was immediately persuaded that Lenz (the Gold and Silver decoders then newly on sale) was the brand to go for, more on that choice later.

Immediate learnings all those years ago.

DCC wants good near zero impedance power distribution, and track and wheels and pick ups all clean and working efficiently. This wasn't a huge problem as at the time I had a regular switched section multi cab DC layout built and wired to a good standard. RTR Locos with inadequate pick up all modified as required. But DCC did 'discover' track dirt that I hadn't! A more regular track cleaning regime was instituted on the layout, and reliability attained a very high standard indeed.

Traction tyres and plastic wheelsets are out. I didn't have any based on past outdoor operation experience, but I noticed the rail dirt significantly increased when visitors brought such things to operate on the layout.

New locos and stock are prolific sources of rail dirt. On my present layout there is a dedicated test circuit for new items to 'clean up' on, simply to keep the filth off the main system.

The modern low current draw can motor powered mechanisms with multistage gear trains that I had first tried were a very easy load for the Lenz decoders. Bachmann, Hornby, Heljan, Rapido, Dapol and kit builds, all worked beautifully, really refined performance available with a slow smooth creep in and out of motion and good smooth progression through the speed range, with stable performance in speed regulation and accleration and deceleration rates.

One PITA though. Repeatedly borked installations of decoder sockets on RTR locos, especially on steam. Often in the least suitable position and seemingly arranged to thieve as much internal volume as possible! The move to sockets in steam loco tenders was a leap forward, until some nana decided that this was where the speaker should go, and then there were compromises there too. I do a lot of internal hacking and soldering in of decoders ('hardwiring') as a result. But latterly some improvement to report, follows.

The centre motor/flywheel(s)/shaft drive to twin bogie chassis were clearly superior in mechanical smoothness. Always on the lookout for a saving, on reading a couple of approving comments on line I tried out the Bachmann decoders 36-553/554 (now discontinued) which had been introduced since I got started, as they were £10 instead of the circa £25 of the Lenz Silver at that time. (These were a badged ESU lokpilot v1.) These would match the Lenz for smooth operation of these mechanisms, if given attention to careful tuning of the feedback regime, which was quick and easy to do. Sadly they didn't have the extended range in CV's 3 & 4 that the Lenz decoders offer, so not suitable for my operational requirements on steam locos.

Then the matter of the savage older brutes of mechanisms, open frame motors, some with direct drive, mostly powering old whitemetal kit bodies of classes not available RTR. Some the Lenz had no trouble with, others there wasn't enough adjustment to cudgel them into submission. By this stage Zimo were actively marketing in the UK, and getting good reports, and I bought half a dozen of Zimo MX64. Cost a bit more than the Lenz, but you got extra value in the way of more motor taming adjustments. Yet to find an OO or HO mechanism they won't force to move like something better engineered. However, they cannot do anything about intrinsic mechanism noise, so these decoders have been peripatetic, 'moving on' as the old coffee grinders are replaced with suitable modern mechanisms.

Lenz some years ago introduced their Standard decoder at a much lower cost than the previous Silver, with the same drive quality and adjustments, abundance of joy. 8 pin only, but I mostly hardwire anyway.

Zimo - is it 18 months ago now? - introduced a budget decoder range, the MX600 series at a similar price, more abundance of joy, especially as one of the connectors available is the Next18 type which at last some manufacturers are using to good effect for very neat, compact and well positioned DCC socket installations. At last some real thought.

As things stand, I'll only buy the Lenz or Zimo to suit what I am about. (I have been fitting decoders for a few friends and have seen a wide range of their choices of decoders, often bought because 'they are so cheap'. Cheap is as cheap does, the performance refinement is lacking. Often a jerk in and out of motion, a sort of granularity and often motor noise over the first two or three speed steps, discontinuity in the speed curves, unstable speed and acceleration/deceleration; none of which can be tuned out. Also seen the Hornby standard decoder in several of my RTR purchases when that was the cheapest model version on offer. Unimpressive. Testing the mechanisms on plain DC from a simple H&M resistance controller, they would actually perform better with these decoders removed. Decoders actually degrading intrinsic mechanism capability! These decoders have gone for use as light switches on sets of Pullman cars and the like. )

The Lenz is usually a quid or two cheaper than the Zimo. If there are better motor drive quality decoders for similarly modest money I would be glad to know it. (I have used a couple of CTE decoders on friend's models that have 'no space inside' and performance is likewise superb, but you pay for it.)

Finally 'stay alive'. The Lenz 'uninterruptible power supply' is very impressive, bought one to try out in my initial purchase. Never used it, because I haven't needed it. Eventually installed it on a friend's 0-4-0 which needed the help.


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