The Advantages of DCC Keep Alives

 
  linton78 Train Controller

Location: South Coast NSW
Hi,

I thought I would raise this subject as a discussion starter.

One of the biggest DCC draw cards for me is the use of on board power packs (keep alive, stay alives). While I have only been a recent DCC convert, It occurred to me that I have not once cleaned the wheels on any of my DCC, keep alive equipped locomotives. This surprisingly is not down to my laziness but down to the wheels remaining squeaky clean ever since the DCC conversion. I was thinking about this on the way to my club one night and thought that perhaps it was the keep alive keeping my wheels clean. I discussed it with one of the club members and we both thought the theory was plausible.

I guess there are a few factors which affect dirt accumulation on model wheels. One would have to be dirt simply picked up of the rail, another would be what the wheels are made of and another would be the amount of electrical pick up a locomotive possesses. In my DC days I have always thought the more pickups fitted to a locomotive the better your wheels stayed clean. My theory here was that if large current spikes were distributed through more parallel paths the affect of a pitting/dirt transfer spark would be decreased through a single wheel. This theory is were I think the keep alive fits also.

The TCS KA2 I have fitted to my Z13 has five 1 farad capacitors on board. This equals a total of 0.2 farads. The charging resister used on the KA2 is 150 ohms. This means that initial current draw on a completely discharged capacitor equals 0.08 amps, presuming 12 volts is present at the rails. This current draw will quickly reduce according to the capacitor resistor time constant.

During a small power interruption the keep alive supplies the motor with power and then once the interruption has passed current flows back into the keep alive at around 80 milliamperes (less usually due to the capacitor rarely being fully discharged). With non equipped keep alive locomotives, during a small power interruption the motor may stop rotating and once the interruption passes a large current will flow through the high resistance wheel contact powering the motor once again. I think this high current, high resistance path can lead to dirt building up on locomotive wheels. With the keep alive fitted the current is reduced through the wheel/rail path (buffered) thus helping to keep wheels cleaner during transient current requirements.

As I said I have not had to clean my wheels at all. They look brand new. Maybe this is just luck?

Would love to here from other capacitor users as to their experiences.

Linton

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  Kevin Martin Chief Train Controller

Location: Melbourne
Hi,

I thought I would raise this subject as a discussion starter.


As I said I have not had to clean my wheels at all. They look brand new. Maybe this is just luck?

Would love to here from other capacitor users as to their experiences.

Linton
linton78

Not sure about the Stay Alive theories, but dirt on wheels is caused when wheels lose contact with the track, causing an arc. Now if at least one pair of wheels is making contact you won't get any arcing. This is why the more wheels have proper working pickups, the better. The Stay alive component, is going to improve things further, so its not just luck, but good practice. So keep going & don't worry about the reasons too much, just accept it.
  linton78 Train Controller

Location: South Coast NSW
Not sure about the Stay Alive theories, but dirt on wheels is caused when wheels lose contact with the track, causing an arc. Now if at least one pair of wheels is making contact you won't get any arcing. This is why the more wheels have proper working pickups, the better. The Stay alive component, is going to improve things further, so its not just luck, but good practice. So keep going & don't worry about the reasons too much, just accept it.
"Kevin Martin"


Thanks for the concern Kev. I am not at all worried about the reasons, just interested in them. How have your keep alive equipped locos faired?

I will keep going, thanks for the encouragement ha ha.

Linton
  andrewstrains Assistant Commissioner

Location: Townsville, Where else but QLD
I have used 2 in my gear 1 was in a Far North Hobbies Pay Bus. It woks brilliantly. I did have a standard decoder fitted but due to the small wheel base and only having 4 wheels touching the rails.
2nd is a old Freidmont 70 class, it works just as good as the paybus and cant be happier.

Andrew
  miktrain Deputy Commissioner

Location: Adelaide SA
The TCS KA2 I have fitted to my Z13 has five 1 farad capacitors on board. This equals a total of 0.2 farads.
linton78

Just a little correction on your maths, if the caps are in parallel (which I believe they would be) it is 5 X 1 = 5 at their rated 16 volts (Stay well below 16 volts as that is the maximum and they will let go very quickly) If they are in series then it is 1 at 5 times their rated voltage

Caps in parallel add together
Caps in series add the voltages

Tony
  Aaron The Ghost of George Stephenson

Location: University of Adelaide SA
Just a little correction on your maths, if the caps are in parallel (which I believe they would be) it is 5 X 1 = 5 at their rated 16 volts (Stay well below 16 volts as that is the maximum and they will let go very quickly) If they are in series then it is 1 at 5 times their rated voltage

Caps in parallel add together
Caps in series add the voltages

Tony
"miktrain"
They'd be in series, the low voltage rating is the only way you'd get sufficiently small package and footprint size. 'Super caps' are not generally constructed for voltage ratings above a few to five volts.
  linton78 Train Controller

Location: South Coast NSW
Just a little correction on your maths, if the caps are in parallel (which I believe they would be) it is 5 X 1 = 5 at their rated 16 volts (Stay well below 16 volts as that is the maximum and they will let go very quickly) If they are in series then it is 1 at 5 times their rated voltage

Caps in parallel add together
Caps in series add the voltages

Tony
"miktrain"


Not quite right Tony,

They are in series, not in parallel.  I have chopped TCS Keep Alives up so as to fit them in some locomotives. The voltage rating is not 16 volts in this case. A single capacitor used in the KA1 is rated at 2.5 V, 0.22f. A KA2 single capacitor is rated at 2.7V, 1f. They are in series due to there low potential rating and hence why there are 6 on board the KA1, and 5 on board the KA2. Capacitance in series = the sum of the reciprocal and potential rating = sum of capacitor voltage rating. Capacitance in parallel = the sum of capacitors and capacitors potential rating = minimum rated voltage.

This thread was supposed to be about the affect a Keep Alive may have on keeping wheels clean. As track and wheel cleaning is such a horrible task I thought the theory may be interesting.
Linton
  NSWGR1855 Deputy Commissioner

'Sniped '

As I said I have not had to clean my wheels at all. They look brand new. Maybe this is just luck?

Would love to here from other capacitor users as to their experiences.

Linton
linton78

Hi Linton,

I also do not need to clean my locomotive wheels these days, as you know I also use the keep alive storage capicators on my H0 steam locomotives. By using TCS keep alive's, I have found I do not need to improve the electrical pick up on my brass steam locomotives. The improvement over DC is I can run my models at one tenth the minimum speed compared to regulated DC. This makes shunting much more realistic, with less 0-5-0 action needed. The negatives as I see them are extra cost, finding the space to fit the keep alive capacitors and locomotives do not stop on layouts using 0 voltage stopping blocks less than about 500mm long as a fail safe feature. The smallest model I have fitted is a Hornby 00 0-4-0 Pug. As delivered it ran like a slot car, and was useless for shunting. Now with a TCS KA1 keep alive, it operates at realistic speeds, and shunts reliably. Unfortunately because of the small space I could only fit the smaller TCS KA1 keep alive, with only 5 seconds of storage, I still need reasonably clean track for the Pug compared to my other engines using TCS KA2's.

The theory about the storage capacitor with current limiting charging resistors stopping arcing between the wheels and track sounds reasonable. The subjective evidence supports it.

Cheers,

Terry Flynn.
  duttonbay Minister for Railways

The smallest model I have fitted is a Hornby 00 0-4-0 Pug. As delivered it ran like a slot car, and was useless for shunting. Now with a TCS KA1 keep alive, it operates at realistic speeds, and shunts reliably.
"NSWGR1855"

I am contemplating trying to fit keep alive capacitators in my HOn30 locos, so knowing you can do so in a pug is good. I'm interested though in how a keep alive improves slow speed performance? I understand that it will take you over momentary dead spots, but why allow it to be done slower?
  miktrain Deputy Commissioner

Location: Adelaide SA
I'm interested though in how a keep alive improves slow speed performance? I understand that it will take you over momentary dead spots, but why allow it to be done slower?
duttonbay

Because there are less drop-outs of power there will naturally be better slow running as erratic power is one of the main reasons for jerky or poor slow speed running. The others being motor quality and motion binding.

If there is erratic pick up of power as the loco is moving then it will get spikes of power with gaps in between. Normally the loco will go with the pules and stall at the gaps, the caps help to smooth out the power by absorbing the highs and adding to the lows so the loco sees a smooth power supply.

Tony
  linton78 Train Controller

Location: South Coast NSW
I am contemplating trying to fit keep alive capacitators in my HOn30 locos, so knowing you can do so in a pug is good. I'm interested though in how a keep alive improves slow speed performance? I understand that it will take you over momentary dead spots, but why allow it to be done slower?
"duttonbay"


I don't think the Keep Alive is technically responsible for the low speed motor control however it negates the problems associated with electrical continuity at low speeds. I suppose when a locomotive is running on either DCC or DC at low speed it does not have the momentum to successfully overcome a short electrical interruption. This is where the capacitor plays its part and provides back up power if you like. As the Keep Alive simply powers the decoder, the decoder will continue to control the motor precisely.

From reading what Terry said, I think he means that generally DCC has improved the running qualities of his locomotives compared to when using DC and the Keep Alive further helps with pick up problems. My Z13 takes 37 seconds for one revolution of its driving wheels at speed step 1. The decoder is responsible for that and I don't think I would have ever achieved this type of running using DC. The Keep Alive allows the 13 class to run at speed step 1 all day long by never allowing the power to drop off the decoder.

I have been using Loksound decoders and was stunned at the slow speed performance when I installed my first decoder. The decoder pulses the motor up to 40,000 Hz and has a back EMF loop resulting in very good motor control. The running qualities and Keep Alive connectivity really pushed me into DCC. I was a die hard DC fan before.

The the best thing ever invented for model trains ha ha.

By the way, the Loksound V4 decoder will only allow a maximum of 4.18 seconds of capacitor backup, you can choose less time also.  After this time the decoder cuts the power. As far as I know this is a Loksound trait, not sure about the other brands.

Linton
  duttonbay Minister for Railways

Thanks for the explanation. I must admit I was assuming that the mechanics of a cheap Hornby mech would inhibit slow performance no matter how well the loco is picking up.

Now for another question. Terry says he rarely cleans his rails now. That's fine while a loco is running, but when it comes to a stop how can you guarantee it will start again if the track is not clean. Isn't it likely that the loco will stop somewhere with poor wheel/rail connectivity, so it will not be able to restart?
  TheBlacksmith Chief Commissioner

Location: Ankh Morpork
Thanks for the explanation. I must admit I was assuming that the mechanics of a cheap Hornby mech would inhibit slow performance no matter how well the loco is picking up.

Now for another question. Terry says he rarely cleans his rails now. That's fine while a loco is running, but when it comes to a stop how can you guarantee it will start again if the track is not clean. Isn't it likely that the loco will stop somewhere with poor wheel/rail connectivity, so it will not be able to restart?
duttonbay

True, but I think Terry's point is that the constant arcing between the wheels and track which deposits carbon on the rails is virtually eliminated, thus his claim to rarely have to clean the rails.

And you are also correct in your assumption that if the loco lands on a dead section it is not going to restart no matter what.
  linton78 Train Controller

Location: South Coast NSW
Thanks for the explanation. I must admit I was assuming that the mechanics of a cheap Hornby mech would inhibit slow performance no matter how well the loco is picking up.

Now for another question. Terry says he rarely cleans his rails now. That's fine while a loco is running, but when it comes to a stop how can you guarantee it will start again if the track is not clean. Isn't it likely that the loco will stop somewhere with poor wheel/rail connectivity, so it will not be able to restart?
"duttonbay"


I don't think there is any substitute for a good mechanism. I have only fitted decoders to locomotives that ran well in the first place.

At the start of the thread I explained the reasons why I think wheels stay cleaner with A Keep Alive fitted. Your right, if the loco stopped on a spot where the rail and wheel was so dirty that no current could flow to the loco, once the Keep Alive had discharged the sound would stop and the loco would not move. I have never had this happen to me, so far. I think even with high resistance wheel/rail contact (not open circuit) there may be enough current flow to keep the capacitor charged and the sound playing.

As dirt builds up on dead wagon wheels nothing will ever stop the dirty track and wheel problem. So far the locos I have converted to DCC with capacitors seem to have an advantage.

Linton
  NSWGR1855 Deputy Commissioner

Thanks for the explanation. I must admit I was assuming that the mechanics of a cheap Hornby mech would inhibit slow performance no matter how well the loco is picking up.

Now for another question. Terry says he rarely cleans his rails now. That's fine while a loco is running, but when it comes to a stop how can you guarantee it will start again if the track is not clean. Isn't it likely that the loco will stop somewhere with poor wheel/rail connectivity, so it will not be able to restart?
duttonbay


Pulse width modulation and back EMF control is what allows the Hornby motor to run at low speeds, and this output type is typical from up market quality DCC decoders.

I have noticed my Hornby Pug if stopped on a dead spot will not restart. This is because it uses a small TCS decoder with no internal software that moves the model a small amount until it gets to powered track. What does sometimes happen with my pug is if it runs over a long dead spot the model goes faster untill it either stops or regaings track power. The particular TCS decoder was not designed for a stay alive. Now days I believe all TCS decoders have been upgraded for keep alives. The move of a dead spot is a feature that Zimo decoders have built in, and now most of my models have Zimo sound decoders. I assume it works. I am very happy with my KA2 Keep alive and Zimo sound decoder installed locomotives. I installed the TCS decoder in the Pug before I decided to try a Zimo sound decoder and did not realize this feature existed until I noticed it later on in the Zimo decoder manual. The pug is to small to fit sound and a keep alive, so I run a Zimo sound decoder attached to a spare motor, under the layout using the same loco number for sound.

I have for years used a small amount of INOX oil on the track. This contributes to making dirt conductive, thus contributing to less frequent track cleaning.

Terry Flynn
  comtrain Chief Commissioner

Location: Near Albury Wodonga
Not quite right Tony,

They are in series, not in parallel. I have chopped TCS Keep Alives up so as to fit them in some locomotives. The voltage rating is not 16 volts in this case. A single capacitor used in the KA1 is rated at 2.5 V, 0.22f. A KA2 single capacitor is rated at 2.7V, 1f. They are in series due to there low potential rating and hence why there are 6 on board the KA1, and 5 on board the KA2. Capacitance in series = the sum of the reciprocal and potential rating = sum of capacitor voltage rating. Capacitance in parallel = the sum of capacitors and capacitors potential rating = minimum rated voltage.

This thread was supposed to be about the affect a Keep Alive may have on keeping wheels clean. As track and wheel cleaning is such a horrible task I thought the theory may be interesting.
Linton
linton78

Gee keep the discussion going Linton This is most "informative" !! He He  I am interested in making my own stay alives to fit to Loksound vers 3.5 which nobody seems to have done yet Smile
Cheers
Rod
  linton78 Train Controller

Location: South Coast NSW
Hi Rod,

If you send me a PM with your email address I will send you a wiring diagram for a Keep Alive if you like. There is not too much to it.

Not sure about fitting one to a 3.5. The Loksound yahoo group would be a useful source of info.

Linton
  jbs101 Beginner

I have been off the Forum for some time and only just found this post.  I have stay alive decoders in my K&M chassis equipped NSW diesel locos (40, 43 and 421 class).  I just pulled the 421 off the layout for a service and the wheels were really dirty.  However, the loco was still running well.  I only serviced it in preparation for the Canberra exhibition this weekend.
  sunnysa Junior Train Controller

Slow running with decoders was happening long before the advent of BEMF and stay alive caps.

I have been op DCC since Aug 1995 and still have early Lenz & TCS decoders fitted in Athearn locos that op as slow as any modern decoders.  EG over 5 mins to travel 1" (25mm)smoothly.

Don,t get me wrong, I love BEMF & stay alive.

BTW, I don,t really think stay alive keeps wheels any cleaner. Good theory though.

Cheers

 Ian
  linton78 Train Controller

Location: South Coast NSW
Slow running with decoders was happening long before the advent of BEMF and stay alive caps.

I have been op DCC since Aug 1995 and still have early Lenz & TCS decoders fitted in Athearn locos that op as slow as any modern decoders.  EG over 5 mins to travel 1" (25mm)smoothly.

Don,t get me wrong, I love BEMF & stay alive.

BTW, I don,t really think stay alive keeps wheels any cleaner. Good theory though.

Cheers

 Ian
"sunnysa"



Hi Ian,

Five minutes for 25mm of travel. That is slow running!

There are many things that contribute to dirty wheels. Without having some sort of consistent test environment I guess the theory would be hard to prove.

For me I have not cleaned a set of wheels since the installation of decoders and capacitor circuits. I probably don't run my locomotives much compared to others though.

Hopefully this trend continues hey.

Linton
  miktrain Deputy Commissioner

Location: Adelaide SA
BTW, I don,t really think stay alive keeps wheels any cleaner. Good theory though.
sunnysa

Quoting  jbs101
I have stay alive decoders in my K&M chassis equipped NSW diesel locos (40, 43 and 421 class).  I just pulled the 421 off the layout for a service and the wheels were really dirty.


It would seem you are right Ian


Tony
  linton78 Train Controller

Location: South Coast NSW
Quoting  jbs101
I have stay alive decoders in my K&M chassis equipped NSW diesel locos (40, 43 and 421 class).  I just pulled the 421 off the layout for a service and the wheels were really dirty.


It would seem you are right Ian


Tony
"miktrain"



Ha ha, case closed Tony.
  sunnysa Junior Train Controller

Hi Ian,

Five minutes for 25mm of travel. That is slow running!

There are many things that contribute to dirty wheels. Without having some sort of consistent test environment I guess the theory would be hard to prove.

For me I have not cleaned a set of wheels since the installation of decoders and capacitor circuits. I probably don't run my locomotives much compared to others though.

Hopefully this trend continues hey.

Linton
linton78

Yes that is slow,some people don't believe it until shown.

Few yrs ago I had a modeler say he would not go DCC because he wanted to shunt slowly.

When he saw my loco's take 5 mins to travel 1" he said "shees, I don't want to go that slow"

You just can't please some people:roll:Laughing

Re not cleaning/not cleaning track.

I clean my track with Track magic in a CMX clean machine every 4-5 mths whether it needs it or not.

Cheers

 Ian
  linton78 Train Controller

Location: South Coast NSW
Yes that is slow,some people don't believe it until shown.

Few yrs ago I had a modeler say he would not go DCC because he wanted to shunt slowly.

When he saw my loco's take 5 mins to travel 1" he said "shees, I don't want to go that slow"

You just can't please some people:roll:Laughing

Re not cleaning/not cleaning track.

I clean my track with Track magic in a CMX clean machine every 4-5 mths whether it needs it or not.

Cheers

 Ian
"sunnysa"


Yes, I was a completed DC advocate until I saw how DCC ran. Now I am a complete DCC advocate. Ha ha yes some people are hard to please. It's hard knowing something is better but not being able to justify the money or effort. Sometimes it's easier to convince yourself there is no need for improvement. Anyway that's the beauty of the hobby, you can do what ever you please.

DCC has opened a whole annex hobby to model railways. I have been consumed by sound projects and trying to create accurate sound files. So much so that the layout has made no progress in months.

The whole stay alive / clean wheels theory was bought up at a club running session between me and another club member. Both agreed that since the install of DCC and capacitors the old dirty wheels problem had decreased. The theory behind it was just that, a theory. Of Course if you have a dusty layout or any other varying factors, wheels will always get dirty. Wheels on wagons still pick up dirt and generally are not used as a current path.

I may do an experiment when I have time here at home. Maybe people with diesels fitted with older mechs or lights do not see the same results. My steam locos have no lighting and draw very little current. In my case the capacitors may perform more buffering of large input currents due to the small constant current draw.

Interesting,

Linton
  Roachie Chief Commissioner

Location: Kadina SA (formerly NSW)
I experimented by adding a TCS KA1 to each of my 2 Powerline 48 class (current series of the model, not the old original). I have also replaced the crapppy original decoders with Tsunami sound decoders, removed the radiator cooling fan, headlights and the entire cab (latter is where the KA1 lives, in full view through the windows!!! YUK).

Anyway, I don't really think those 2 locos perform any better or more reliably than my other 20 diesels (Auscision, Trainorama, Austrains), so I won't be going to the expense of buying any more KAs. Having said that, I have spent a LOT of time ensuring I have good track power everywhere, so I don't suffer from "dead spots" anyway.

I have 2 of the CMX tank-wagon cleaning wagons and about 18 months ago I bought 4x 1 litre bottles of Iso Alcohol off ebay to use in them and still have 3.5 litres left. Once that is all gone I might try this Track Magic stuff. I also use CRC 2-26 applied by a homemade cork pad device about every few months. I find I still have to clean my locos' wheels every now and then due to my layout being in a large/dusty unsealed Colorbond shed.

I currently have another "problem"......everytime I go down to the shed to run trains, I have to do a visual walk-around first to clear any dead mice off the perway!!! We have a plague here at the moment; I have traps set as well as Ratsack spread everywhere. Each day I am getting around 6 mice, usually on the floor, but occasionally they make it up onto the layout to take their last gasp! I got the fright of my life about a week ago.....I was slowly bringing a 44 class out of loco; bending down so my eyes were at rail height (and only about 6 inches away from the loco), and as the loco moved towards the water tank I noticed these whiskers protruding from behind it!!! DAMN!!! hahaha

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