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Offline Athistle  
#1 Posted : 10 April 2021 06:54:00(UTC)

Joined: 25/08/2017(UTC)
Posts: 3
Location: Gippsland, Australia
I have a number of Marklin 24997 electric uncouplers which I installed several years ago as part of a large C-track layout. I use a capacitor discharge system to operate them via Uhlenbrock drivers and they all work well. Recently I installed two new 24997 uncouplers and they operate sluggishly and don't uncouple reliably. On measuring the coil resistance of the new uncouplers I find they are both about 50 ohms whereas all the old uncouplers are typically 11 ohms. This probably explains the difference in performance although I am at a loss to understand why the coil specification would be changed without a different part number being assigned.

Does anyone know if there been a change to the 24997 specification recently or am I missing something?
Offline JohnjeanB  
#2 Posted : 10 April 2021 15:49:14(UTC)

Joined: 04/02/2011(UTC)
Posts: 1,514
Location: Paris, France
I am certainly no specialist in Märklin C Track uncouplers. The little I know is:
* 24997 uncouplers have in series with a coil a thermal protection component: when the coil gets hot, then the component "opens" itself (has a very resistance) to protect the coil)
* 24997 uncouplers work very well provided there is no mechanical tension on the short coupling (the loco must be pushing the consist and not pulling it.
In reality since the new 60831 and 60832, the coil can only be activated for 500 ms. For longer activations, the decoder will trigger bust (like a submachine gun and this works better.

Märklin permanently improves its product (doing the same better for less money and less current)
Compared with the early M track uncouplers, the current need has been sharply reduced.
My first analog layout ran 15 locos and had 100 W transfo. In my digital layout with recent MFX Sound locos, the same 100W of digital power is enough to feed 34 locos permanently under power (I run Rocrail so no power cuts) and only 60% of that power is used now.
Kind regards
My layout videos
latest vid
hump yard
Offline Athistle  
#3 Posted : 10 April 2021 23:40:58(UTC)

Joined: 25/08/2017(UTC)
Posts: 3
Location: Gippsland, Australia
Hi JohnJeanB,
Thanks for the information and what you say makes sense. I think I am seeing the result of change which probably makes Marklin equipment less compatible with Uhlenbrock and other control systems. Fortunately I have located a manually operated older version of the 24997 in the layout and am swapping that with the new one in the electrically operated position. Your layout looks great, will watch the full video later.

thanks 1 user liked this useful post by Athistle
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