Hello,
I like to show how to install a decoder buffer circuit for Hobby models, upgraded with the Märklin mSD ugrade kit 60949.

!CAUTION! This modification is for pure digital usage only. Analog usage is not allowed with this modification or You should add a switch to switch off the capacitor for analog usage and/or use 63V capacitors! !CAUTION!

There is a very good and complete description for the mSD upgrade here from Tom (H0): https://www.marklin-user...er-sets-60948-60949.aspx

Therefore, I reduce my description to the buffer capacitor installation.

The buffer capacitor circuit must be connected to Pin 16 and Pin 20 of the mtc21 connector.

Pin 16 is the orange cable and it is an electrical plus-pole. Pin 20 is the electronic ground (GND, minus-pole). There is no official description about the mtc21 adapter board from Märklin. But I found an description of the connectors here: http://simpledigitalloco....de/hobbylok-m60949.html

Manfred G. Fischer stated, that he isn't sure about the purple GND connector. But it is quite sure, that this is GND (Pin 20).

So, I gave it a try yesterday evening and connected the 2.200µF Elko with load resistor and schottky diode to these connectors (orange and grey cable):



As I do it always, I created a tiny 2-pole plug to be abkle to diconnect the buffer capacitor easily. Here, You see the buffer capacitor (which is too big. I have to replace with a smaller one, the case can't be closed) with plug in the upper case and the chassis:


The buffer circuit works well, the lights remain for a second on and the motor doesn't stop abruptly. So, when there is a short power interruption, the sound will continue, as well as the light and driving.

I think, it is worth to spend 2€ for this enhancement and fits well to the mSD decoder, easy to install. Here You can see the buffer circuit:


R1 = 100 Ohm (minimum 33 Ohm!)
C1 = 2.200µF (470µF - 4.700µF)
D1 = SB130 (30V) or SB140 (40V)

Moritz

Edited by user 02 June 2014 13:36:07(UTC)  | Reason: Detailed part information

Now, here is the modification with two 1.200µF capacitors in parallel:

I asked the Märklin service about the solder points as I assumed to be GND and U+. I asked, if my assumption is right or wrong and that I like to connect a buffer capacitor.

Today, I got an answer from Märklin: We don't provide such a buffer curcuit and therefore, we can't answer about the connectors."

Excellent work, well documented and great implementation.
Hats off to you!
Cheers

Hello,
1st, look at this picture:


the orange and grey wire go to my own made connector, where I connect the buffer capacitor.

In the circuit picture, I just describe how the buffer capacitor circuit looks like!

2nd, don't confuse the meaning on GND and U+ and the connectors to the rail!

Look at this picture: http://file1.npage.de/00...der/m60949-009-small.jpg

brown and red are the connectors to the rail and the point connectors of the rail.

Orange is the common +-pole (U+), where all AUX and light functions will be connected.

All AUX and light ouputs are electrical Minus-poles!

And GND (violet, mtc21-Pin 20) is usually used only internally. But for the buffer circuit, we need the GND connector.

I hope, it is more clear now.

Moritz

Hi Moritz,

More good work.

Have you thought of using SMD electrolytic capacitors ?

I have some left over 1000uF SMD caps that would be around the 12mm x 12mm size. The 470's I've got are 10x10mm.

There not that much dearer than normal caps although you may have a bit of trouble finding the 1000uF ones.

Excellent work once again though Moritz, giving all of us ideas to emulate.

Hello Shamu,
SMD capacitors are not really smaller then "standard" ones. They have only another shape and connectors.

Hello Shane,
I checked in two elektronik stores. SMD capacitors are a bit smaller in volume, but most of them have a bigger diameter.

470µF in SMD is D10xL10,2 and a standard is D10xL16 or D8xL20

1.000µF in SMD is D12,5xL13,5 while a standard is D10xL25

As You can see, the diameter of the standards is at minimum 2 milimeter less then with SMD capacitors. In most cases, this is more important for me.

25 V are enough for locos that run digitally only (but without any reserves). Getting the 35 V can't harm IMHO.
If you want to run in analogue AC mode, get capacitors for 50 V for obvious reasons.

The capacitors used by Märklin are the 50 V type - see this post for pictures of an unpacked power pack:
http://stummiforum.de/vi...pic.php?p=952066#p952066

If the capacitor buffers the 5 V line only (Anti Alzheimer), a capacitor for 6.3 V will be enough. Such a capacitor won't provide power to the motor, it just prevents the decoder from forgetting the current speed setting.

I'm preety sure, that my loco will never be driven on AC analog, therefore, 25V is enough for me. Sure, 35V would have more safety, but in worst case, I will have to replace a capacitor in 10 or 20 years.

If space is no matter, sure I could use 35V or 50V versions.

You are right! There should be a warning that this modification is for pure digital usage. Analog usage is not allowed with this modification!

I will add this in the initial posting.

Thanks,
Moritz