Friday 23 February 2007

Uncoupling Electro-Magnets Under DCC Control

Hi All. Mick has invited me to join the Blog so here I am!

As most of you will know I have been building a large 2mil exhibition Layout 'Pool in Wharfedale' for quite some years now. During 2004/5 it became obvious to me that the DCC revolution was reaching critical mass within the hobby and more importantly that the decoders were becoming small and advanced enough to have useful 2mmFS applications. I reaserched the DCC market during the summer of 2005 and in September that year purchased a Lenz 100 system. I then spent 4 months converting my 2mm loco fleet of 7 engines to DCC using Lenz Gold Mini decoders. Thoughts then turned to the wiring on the layout. A start had already been made based on traditional DC control but it soon became obvious that to get the maximum benefit from DCC it would need wiring differently.

I pondered the problem for a few weeks and during the East Midlands Show last March, where I was assisting Tony Simms on 'Masham' I determined that I would take a break from ''Pool' and construct a small DCC test-bed layout, so I could have a good play with DCC, hopefully learn a few lessons and avoid making errors on the big layout. The lightness of Tony's layout, having a single section Foam-Core baseboard, had always impressed me, plus it's speed and ease of set-up/break-down, so I copied him. The result has been 'Niddbeck Bridge' which most of you will have seen at the Group meeting on DCC last year and at the Shildon AGM. It's a small NER through station inspired by stations the Pateley Bridge branch, with fiddle yard to the rear, accessed by kick-back sector plates at each end.

The past month or so has seen the completion of the track, the installation of track feeds and connection to the DCC 'bus', installation of Tortoise and Hare point actuators and the installation of electro-magnetic uncouplers. The E-M's were to bring the first real problem of the project so far! 'Niddbeck Bridge' has no control panel as I want to try total DCC control of points, sector plates and uncouplers from the DCC throttle keypad.

I have a collection of PK/DG uncoupler E-M's left over from a previous layout and 6 of these were installed around the layout. I then ordered a Lenz LS150 6-way accessory decoder, a device designed to fire-off upto 6 double coil E-M devices such as point solenoids on around 16vAC. It provides a peak current of 3A for one second and 1A thereafter. The first PK/DG E-M connected up promptly tripped the overload protection circuit of the LS150 - not encouraging! I then tried all 9 of my PK/DG's and only one of them would work without tripping out. I should add that the LS150 allows current to flow whilst the button on the throttle is depressed and then has an turn-off delay of between 0.1 and 10 seconds, set by CV programming. It is therefore suitable for uncoupling purposes where power might need to be applied for 5 or 10 seconds or so.

Inspection showed that the one that worked had coil windings with wire around 0.3mm dia and the others had windings of about 0.4mm dia. A chat with Andrew Hartshorne at MSE (new owners of the DG range) confirmed that Nick Dearnaley has altered the spec to thicker wire when he took over from Phil Kerr, and that he was continuing with the same spec. I was either going to have to rewind my PK/DG's or find an alternative product! I had a PECO uncoupler E-M in my collection, so this was tried. Whilst it worked without tripping-out the LS150, I found that it's magnetic field was weak, and would only attract the coupler dropper wire if just proud of the sleeper tops, not a compromise I was prepared to accept, as PK/DG can be buried beneath the ballast, at sleeper bottom height and still work well.

At the BRM Harrogate Show last weekend I sniffed out a Gaugemaster/SEEP uncoupler E-M and purchased one. At the same time a conversation with Mick brought about a suggestion that I try some E-M coils stripped out of old H&M point solenoids, and he has since sent me some to try. The SEEP uncoupler works okay on DCC and seems to have plenty of 'oomph'. I now need to cut some nails as cores to suit Mick's coils and try these out. Hopefully I will then have the solution - watch this space ! The SEEP uncoupler has benefit of having the same footprint at the PK/DG and will suit the already installed mounting pads, saving time.

If anyone wants to buy some 2nd hand PK/DG's then give me a shout!

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