Tcs keep alives

[Pizzapizza]

 Does anybody else on here have the trouble of your keep alives when they go over a dead spot  that you know is dead for a test they continue to work like they’re supposed to but they slow down considerably is this normal ? I use tcs k3,k4

[KPack]

When the keep alive is getting close to drained the locomotive will definitely run slower.  However, for a quick dead spot or dirty track you shouldn't notice a difference in speed.  I'm using KA-4's and my locomotives can keep running with sound and lights for at least 10-15 seconds.  With sound and lights only (no motor movement) the module will have power for almost 30 seconds.  My locomotives do not begin to slow down until the module voltage is below somewhere around 9 volts.


On a somewhat related note, I see that TCS has released the KA1 and KA2.  Any idea Bill when you will be stocking these?  I'm definitely going to be picking up the KA2 for most of my locomotives.  It has about 1/3 the capacity of the KA4, but that's more than enough to get me over dead spots and mild power issues.  I don't need a KA in every locomotive that runs it for 20-30 seconds.

-Kevin

[William Brillinger]

Kevin, the KA1 and KA2 are listed on my website now. I have ordered them, but they should arrive soon!

[Pizzapizza]

No they are fully charged when I test these they just slow down and as you said they will run for 15-20 seconds after power lost very frustrating I’m thinking of not installing one and see how it acts

[Alan]

Are you using KAs connected to the blue and yellow wires of a LM3? Or are you using KAs connected to the red and black wires of a LM1/LM2/LM3 bridge rectifier combination ?

[Pizzapizza]

Blue and yellow no rectifier ,  and like I stated they do work they just slow down and I’ve never seen it before when I used to run DCC

[Alan]

With shell off can you put a voltmeter across the motor wires while the effect occurs? If there are diodes as part of the KA they would cause a 0.7V drop in voltage for each diode used. If that is the case you will see the voltage at the motor drop exactly 0.7V for each diode in the KA during the slowdown. Curious to see if the voltage drop is a multiple of 0.7 i.e. 0.7, 1.4, 2.1, 2.8, etc. If the voltage drop is not a multiple of 0.7 then the diode drop theory is garbage.

[Pizzapizza]

 OK according to Tim ring there is no current keeper on the market that will keep your locomotive going the same speed if it loses power temporarily they are currently working on one now

[Alan]

OK according to Tim ring there is no current keeper on the market that will keep your locomotive going the same speed if it loses power temporarily they are currently working on one now

Oh yes there is. Bill's original bridge rectifier solution: https://rpug.pdc.ca/index.php/topic,327.0.html

[Pizzapizza]

I use LM3s  modules only they have that rectifier built into them I don’t understand why anybody would want to drop their voltage by 1 or 1 1/2 volts maybe I’m missing something here I don’t know.  So you’re telling me if you’re running a railpro engine with your current keepers if you turn the power off you do not see a drop in your locomotives speed? and doesn’t not slow down? in the DCC world that does not happen.

[Alan]

All LMs have a built in rectifier. The LM3 differs from the LM1 and LM2 by having a ground connection available after the internal power conditioning i.e. "behind" the LM.

When the rectifier/capacitor combo is ahead of the LM (red and black) the capacitors charge to full track voltage minus rectifier drop. When the capacitors are behind the LM (yellow and blue) they charge only to the LM internal voltage which is minus internal rectifier drop. Bill's "ahead" keep-alive configuration doesn't exhibit the loco slow down because the capacitors are charged to a higher voltage.

DCC can't use the "ahead" configuration because the AC control signal must pass through.

The performance loss from a track voltage of 1.4V less is negligible as verified by Kpack. At worst you may have to turn the throttle an additional couple degrees. Not a big deal. Considering most models are geared to run too fast to begin with, the difference can actually be a benefit.

If you can't live without the full 14.8V then simply use a 16V power supply. My layout uses series triple diode occupancy detectors. The voltage drop across the detectors is 2.1V. My power supply is adjusted to 17V. The resulting track voltage is 14.9V the same as if there were no diodes in the circuit. 

[KPack]

Alright, I have an update for you guys at John's request.

I tested on my layout last night with a full power drop (turned off the layout completely) while the locomotive was running with full sound and lights.  Locomotives were at a constant speed, running solo, at about 50% power.  Tested both LM-3S and LM-2S, both with external bridge rectifiers installed.  Railpro power supply to the rails, and locomotive modules seeing 12.2 V at rest, 11.2 V at speed.  Locomotives were ScaleTrains SD40-2 and modified Athearn C44-9W (with Kato motor).

When I turned off the layout I saw an immediate decrease in speed.  The voltage to the module dropped immediately to 4.3 V.  The sound and lights stayed on, though the lights visibly dimmed.  The sound was unchanged.  Motion stopped rather quickly and lights and sound stayed on for another 5-8 seconds.  So John is right, there is definitely a drop in speed when power is completely lost.

While running on my friend's layout I hadn't noticed it that much because I normally would just stop the train I was controlling if the power to the layout cut out (happens a lot).

During normal running across switches and dirty track I do not notice any perceptible difference in speed and/or lighting brightness when hitting multiple small power drops in a row.  I can watch the voltage on the module in real time and see it quickly drop and regain power over and over, and there is no effect on the locomotive or consist.  However with a full and permanent power drop it seems that the locomotives drain the capacitors very quickly. 

-Kevin

[Alan]

However with a full and permanent power drop it seems that the locomotives drain the capacitors very quickly. 
-Kevin

The capacitor values are too small. Your observed immediate voltage drop to 4.3V is proof positive of this. Below is a RC time constant graph of capacitor discharge through a load. Your observation should mirror the curve if the capacitors are of sufficient value.

[KPack]

For reference, the KA's I'm running are the TCS KA-4.  It is on the smaller side, but I use them because they are so much easier to fit than the larger KA-3. 

My purpose in using KA's is to get me over switches, dirty track, questionable track, and intermittent power drops.  I don't expect them to move my train much when there is a permanent power loss.  For that, I just use my locomotive with the batter installed.  I can run all day on powerless track with that beast.

That being said, it'd be nice if Tim Ring comes up with a better solution than the current KA's on the market now.  It seems like the Railpro modules draw more power than a DCC decoder.....which makes sense because Railpro modules are powering a RF transponder.

-Kevin

[G8B4Life]

Trying to elaborate on Alan's RC diagram a bit (and I hope Alan will forgive me when I don't use the correct terms), but all capacitor based Keep Alives (at least on the market today) will follow the same law. The length of the curve and it's voltage drop is just a matter of how much power is stored and how fast it is consumed. The law applies whether it's a RailPro module or a DCC decoder the Keep Alive is powering; the locomotive will slow down as the voltage drops as the Keep Alive tries to provide the same level of current to power the module/decoder until there is no power left to consume. This is why some may see what appears to be Keep Alives working in some cases but not appear to be working in others. A Keep Alive providing 1000mA of power will drain (read slow down and stop) quicker than the same Keep Alive only providing 500mA of power.

I'm struggling to come up with a way to explain the initial massive voltage drop Kevin reports when the Keep Alive kicks in after power is lost for those that don't know why with giving an analogy that'll either be wrong or just more confusing. Alan help!

Anyway I've got no idea what the law is called, if it even has a name as a "law" but I'm not sure even Tim Ring can get around it to provide a constant speed until all the available power is consumed, and provide a decent run time.

- Tim