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INSTRUCTION MANUAL

INSTRUCTION MANUAL

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Page 54<br />

Decoder MX620 - MX622, MX630 - MX632 Sound Decoder MX640 - MX648<br />

Connecting an external energy source (capacitor) for<br />

uninterrupted driving on dead track sections:<br />

Energy storage devices connected to the decoder have many benefits; even very small capacitors as of<br />

100uF have positive effects, larger ones even more so:<br />

- Prevents stalling and flickering lights on dirty track sections or frogs, especially in conjunction<br />

with the ZIMO “smart stopping” feature (requires at least 1000uF to be effective)<br />

- Lowers decoder operating temperature especially with low-impedance motors (at least 100uF)<br />

- when RailCom is used:<br />

Eliminates the energy loss created by the “RailCom gap”, reduces motor noise caused by Rail-<br />

Com and improves the quality (= legibility) of the RailCom signal (at least 100uF)<br />

The required voltage strength of the capacitor is given by the track voltage; 25V is suitable for all cases.<br />

Smaller 16V capacitors should only be used if track voltage will never be higher than that.<br />

A simple connection between the decoder and ground is not advisable because of undesired side effects:<br />

Software updates, sound installation, programming in Service Mode and the ZIMO loco number identification<br />

feature can be negatively influenced or may not work at all.<br />

Decoders prepared for direct capacitor hook-up:<br />

Among the decoders described in this manual, only the MX631, MX632 and the sound decoder MX642,<br />

MX643, MX644 and MX645 have the necessary components on board for a direct connection, without<br />

the need of additional external components<br />

.<br />

If larger capacitors are used, which is actually a good idea, the circuitry should be expanded. The<br />

condenser in these cases is recharged through a 100 ohm resistor. This is necessary so that the<br />

command station doesn’t interpret the high in-rush current during boot-up, caused by charging up<br />

those capacitors, as a short circuit when a large number of loco’s so equipped are on the layout. The<br />

diode (e.g. 1N4007) is required to bypass the resistor when power is needed by the decoder.<br />

NOTE: If signal stops by “asymmetrical DCC signal” (= Lenz ABC, implemented in ZIMO decoders<br />

early 2005) is employed, the resistor-diode combination is necessary in any case (even when using<br />

small capacitors) to ensure that the decoder can detect the asymmetry of the signal!<br />

Please use the schematic below as a guide when building your own energy storage circuit. The resistor<br />

shown (100 Ohm, ¼ W) and the diode (1N4007) are required for the reasons mentioned<br />

above.<br />

This decoder comes with a small capacitor (220uF) to get you acquainted with the energy storage<br />

technique. Larger capacitors of up to 10’000uF are recommended and are readily available (also<br />

from ZIMO if necessary) and can simply be connected in parallel. A series of gold caps can also be<br />

used (i.e. 8 gold caps at 2.5V each connected in series).<br />

Decoders not prepared for direct capacitor hook-up:<br />

Here, a simple connection of a capacitor between the decoder’s ground and common positive is not<br />

advisable, since it could lead to undesired side effects: Software updates, sound installations, programming<br />

in service mode (on the programming track) and the ZIMO loco number identification will<br />

be more difficult or even impossible. This applies to the decoders MX620, MX621 and MX630 as<br />

well as the sound decoders MX640, MX646 and MX647, which require additional external components<br />

to be added by the user in order to prevent above mentioned side effects.<br />

Capacitor sizes of up to 220uF (possibly even up to 470uF) only need a choke coil (100mH / 100mA,<br />

also available form ZIMO) to enable decoder firmware updates with the MXDECUP update module<br />

and ZIMO’s loco number identification pulses.<br />

The 3300 Ohm resistor shown in the drawing above (not absolutely necessary) serves the following<br />

purpose:<br />

Even though a large capacitor supplies the motor and lights for just a few tenths of a second<br />

(1000uF) or a few seconds (e.g. 4700uF), the remaining energy keeps the decoder memory alive for<br />

several minutes, although the voltage dropped below the level required to drive the motor and/or<br />

lights. This is sometimes a rather undesired effect. For example: If a running loco is taken from the<br />

track and the speed afterwards set to zero, the loco would briefly run at the previous speed when it

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