4. Operation principle
The SKD224 replacement board contains a smart power pack (SPP)
and is integrating a DCC decoder with BEMF PID motor control and
4 physical (function) outputs. The decoder controls the charging of
the on board 1 Farad capacitor, and ensures switching to the internal
power supply in case of track contact interruption. This guaranties a
trouble free running of the SKD224 even if the contact with the rails
is lost. The SPP is capable to power the locomotive up to 4 seconds
and can run it up to 30-50 centimeters without DCC power
(depending on the speed). This is especially useful for small 2 axle
locomotives like the SKD224, which has only a few current pickup
points, and suffer very often of DCC power interruption.
At start-up, the board will have a current consumption of 250-300
mA for up to 2 minutes, even if the locomotive is stationary. This is
normal, during this time the SPP is charging the internal capacitor.
In case of external power interruption, after the maximum allowed
timeout has been elapsed (this can be changed altering the specific
CV), the locomotive will stop. The operation can be resumed when
the locomotive is powered again over the rails.
Due to the operational principle, the SPP can be used only in DCC. If
the locomotive is used in DC, the SPP will be not activated.
The lights of the SKD224 are wired to the internal SPP circuit, so
even in the case of contact problems while running, during the
switching between external DCC power and internal SPP, the lights
are stable, and no annoying dimming is visible.
Connections for optional front/rear lights and electrical couplers are
available at both ends of the boards.
