Buffer circuit boards for digital and DC analog

I can see why You wanna embed filtering capacitors, in order to avoid "flicker" with digital circuits, which could lead to malfunction (at least it's what I understood). But, why for ANALOG (traditional) locomotives ? Do You hope such capacitors hold enough power to allow the engine to run over bad contact places ? Or, what is the purpose of such a circuit for "simple" locomotives ?
And, sorry, the forum You are mentioning denies any access to non-members ...

Actually probably the best English term is stay-alive circuit.

Mark

And I like the idea of trying one of these in a DC loco.

Hello David,

It's a pity that these threads from German forum are not visible to unregistered users, unfortunately I can do nothing with this. And I read German very little too and chat on mentioned forum using on-the-fly translation to English in Google Chrome. However, I post there a lot of info in English. First two links lead to my own threads about using these buffer PCB's in combination with DCC decoders. In a couple of words, the effect is excellent and very pronounced, and many decoders work totally differently when buffered this way.

I don't think it makes a big sense to copy all these long-reads here, so I post just a few pictures:

Using type B buffer in Rail Zeppelin (Marklin 88761) in combination with DCC decoder CT Elektronik DCX77z:





Using type C buffer in German Class 52 steam locomotive (Marklin 88830) in combination with multiprotocol sound decoder Doehler & Haass SD10A:



Using type C buffer in German 3-axle baggage car in combination with multiprotocol sound decoder Doehler & Haass SD18A:



About pricing: I would like to offer these boards already assembled and carefully tested. Price is $15 per board (any type).

About compatibility: I did not designed these boards keeping in mind a particular model of locomotive; the main goal was to make them as small as possible, and provide a highest possible capacity in a given volume. For this purpose I found very small 100 μF 16V SMD 1206 X7R ceramic capacitors. These capacitors have a number of important advantages: they are not polarity sensitive, that allows using them for buffering DC analog locos, and they have a much higher capacitance density that cannot be offered by any kind of classic can-type electrolytic capacitors.

My US locomotive fleet consists of various AZL diesels, AZL Mikado, a number of MTL F7's and MTL SD40-2. There is also a number of Marklin version of E8/E9 diesels and Marklin F7's.

All my AZL diesels (and Marklin E8/E9) equipped with Digitrax DZ123Z0 decoders (MTL SD40-2 with DZ123M0), I like very much how they work even on slightly dirty tracks, and I didn't make any tests with such buffers. Furthermore, in most cases there is no room for additional enhancements inside most AZL locos, so I can hardly imagine if someone will manage to add such buffer PCB there. Additionally, there is no info on how buffer capacitors can be attached to Digitrax drop-in decoders (maybe it is possible, however I didn't explored this question yet).
Digitrax offers "Power-Xtenders": www.digitrax.com/products/power-xtenders/, but they intended to use with their other kinds of decoders.

My Mikado is equipped with Doehler & Haass DH05C decoder. This decoder is buffer-capable. However again, there is no room inside Mikado's tender to add anything except decoder itself.

Marklin F7's are digitized with drop-in decoders LDS26306-U from German manufacturer Velmo. These decoders are also based on Doehler & Haass DH05C chips. It is hard to attach a buffer PCB to them due to a fact that they are dedicated to a particular model of locomotive.

About functioning principles and connecting buffer capacitors to decoders: I would like to give a link to a very detailed article on German site (I'm sorry, it's again in German , please use Google Chrome translate):
www.1001-digital.de/pages/basteln-bauen/elektronisches/anleitungen/pufferschaltung-fuer-16-v-smd-kondensatoren.php
My boards are built exactly using the circuit diagram described there (with one exception: I excluded Zener diodes from variants B and C).

In DC analog mode these buffer boards are simply attached in parallel with motor. That's all. However, in order to use with DC analog type B and C boards should be slightly modified - I have to remove a diode and reduce resistor value to about 1-10 Ohms (again, it is a reason why I would like to sell them already assembled). Type A board is not suitable for DC analog since it is based on polarity sensitive Tantalum capacitors.

Regards,
Alex

Hi David,

Thanks! No need to hurry, because after a number of orders from Germany I ran out of empty circuit boards, so I have to order them again from my local manufacturer (I will do this in any case).

Regards,
Alex

Hi Jeff,

Yes, I know these prototype boards. They are also usually too thick for this purpose (1-1.5mm). My boards are only 0.5mm thick, so it allows to save even a bit more space. For using in digital mode each type of board always includes a diode and resistor, however only type A has a Zener diode, since Taltalum electrolytic capacitors are sensitive to overvoltage.

I decided to exclude Zener diode from B and C types in order to save even more space, that is critical in many applications. Ceramic capacitors are very resistant to overvoltage - numerous tests show that many ceramics with 16 V nominal voltage easily withstand up to 30 V without any damage. Even in the worst scenario they will never explode and burn out (unlike Tantalum ones).

Considering that a recommended voltage for Z scale is around 8-10 V (12 max.), it is 100% safe to use these ceramic capacitors without a voltage stabilizing Zener diode, especially in such limited space applications.

As I already wrote, in order to use B and C boards in DC analog mode (type A is only suitable for digital), I have to remove a diode to let the buffer work in both driving directions. Resistor value should be also lowered down to 1-10 Ohms in order to protect a power controller and/or to prevent false triggering of the short circuit protection if controller has any. (In general, resistor can be removed completely if the total buffer capacity is low - say, about 500 μF).

About payments: Surely, I accept PayPal.
About shipping: Usually it takes about 2-4 weeks from Ukraine to USA. I still have to check shipping rates, however don't worry, they are very fair.

Regards,
Alex