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LGB 17100 Track Contacts:

First published 11/01/2022, updated and revised.

The 17100 has replaced the original 1700/17000 Track Contact. The contacts are functionally identical and can be exchanged in all circuits. The 17100 is smaller, easier to install and more reliable.

Whilst the 17100's are part of an Analogue System, they can still play a part in a DCC environment.

From Old Skool, where if possible, repurpose and reuse existing equipment, when upgrading from analogue to DCC, the existing equipment can be utilised and work alongside new equipment.

The housing from the 17100 can be reused to create a replacement Reed Switch for use with DCC Automation.

Extracted from the edited version of the LGB World Manual, re edited to create a brief summary on how the LGB 17100 Track Contacts operate with AC voltage.

LGB 12010 drives, in both switches and signals, can operate with AC voltage, and they take advantage of the fact that AC voltage is a wave, that is, it oscillates in both voltage and polarity.

That AC wave can be chopped in half using a diode. LGB 12010 drives are designed to use this "half-wave" voltage, moving in one direction if they receive the top half of the wave and moving in the other direction if they receive the bottom half of the wave.

These diodes are built into the 17100 Track Contact. When the train passes over the contact, voltage passes through one of the diodes and sends a half-wave to the LGB 12010 drive.

Although LGB 12010 drives only require a short pulse of half-wave voltage to operate, they are designed to withstand continuous voltage. That can happen when a locomotive is stopped above a 17100 Track Contact.

However, LGB 12010 drives will not function properly if they receive both halves of the AC wave at the same time.

Instead, they will oscillate, bouncing back and forth at the current frequency, 50-60 cycles per second. Oscillation problems are often caused by connecting control wires to both outer "control" terminals (∆ and ∇) of a 17100 Track Contact.

Do not try to control more than one LGB 12010 drive (switch or signal) with one 17100 Track Contact.

Do not connect AC voltage directly to a 17100 Track Contact. This can destroy the contact. The circuit must include another device, like a 12010 Switch Drive.

Do not connect wires to both outer "control" terminals (∆ and ∇) of a 17100 Track Contact.

When used to control an LGB 12010 drive, the outer "control" terminal (∆ and ∇) connection on a 17100 determines the position of the LGB 12010 drive.

Further reading..... 

Circuit Protection from Transient Voltage

Reed   Switch Protection

Original circuit for LGB 17100 Track Contacts.

Repairing or replacing the components of the LGB 17100, hopefully the pictures will be sufficient for those who wish to construct an alternative from the original LGB 17100 to use external Reed Switches.

The original Varistor is extremely difficult to source, after much research and consulting numerous datasheets this one, Varistor Metal Oxide B72205S0250K101 by the  Manufacturer EPCOS shown has proven to work.