Installing sound in analogue DC track powered locomotives

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The diagrams below suggest how the steam and diesel soundcards can be installed in locomotives which are
powered off the track using analogue DC. The maximum voltage is 24 volts. Higher voltages will damage the soundcard.
The chuff trigger is not needed for Diesel, Light Diesel, Electric, Tram/Streetcar and Goose/Railbus soundcards.

When the motor voltage is below seven volts it is insufficient to power the soundcard. Therefore a 9v volt PP3 or
a 7.2v cordless phone battery is used to drive the soundcard and produce sound when the loco is static or moving
slowly. This battery will be automatically recharged whenever the motor voltage is at about 1.8 volts higher than
the battery voltage so there is often never a need to remove the battery for recharging. However, the battery
must be a Nickel Metal Hydride type; Lithium and Nickel Cadmium batteries must not be used.

Another option is to fit a recharging socket so that the support battery can be recharged, using an external battery charger, without removing the battery from the loco. We recommend using a three pin, panel mounted DC power socket which, when wired as shown, isolates the soundcard when the charger is plugged in.
On railroads which operate at low speeds, the track voltage is often not high enough for charging to take place. Some owners of slow running locos put an isolation switch on the loco motor circuit so that they can turn up the power to recharge the battery, without having the loco move.