Uninterruptible Power Supply for (almost) all

• Buffer circuit for vehicle decoders for scales N to H0
• Supporting all decoders with connections for external supporting capacitors or buffer circuits
• Simiting the charging current to 100 mA
• Automatic interruption of the charging process if the track voltage is below 12 V
• Automatic undervoltage cutoff

What model railroader does not know it?

The vehicle decoders get "out of hand" when running over turnouts or where dirt and rust have gotten lost on the rails. Or the current collector of the locomotive is not (anymore) the best...

The result: The vehicle lights flicker, sound and engine stutter. At least cleaning helps against dirt and rust. The solution of the problem at turnouts (streets) is already more difficult. An additional power supply is often the only solution to help the vehicle decoders over difficult sections.

From buffer capacitor to super-cap

In order for reserve current to be stored in buffer capacitors at all and made available to the vehicle decoders if necessary, the decoders must have appropriate connections. We have been equipping our vehicle decoders with this since 2000 (or in other words, since we developed the first locomotive decoder). For the "small appetite for electricity in between", 470 µF are available, with some decoder types even up to 1,000 µF.

The more decoder outputs are used e.g. for lighting or sound, the more power is logically needed in an emergency. The capacity of a capacitor directly connected to the decoder is quickly exhausted. Super Caps, which have been available for a good 10 years, have much more to offer despite their comparatively small dimensions: Capacities of 0.47 F (= 470,000 µF) and more are common. Their disadvantage: Their dielectric strength is only 5 to 6 V and is therefore not suitable for model railways. To be able to use their large capacity nevertheless, charging circuits are therefore absolutely necessary.

Connection variants for the UPS-mini

Due to the capacity of the Super-Caps used, the use of the UPS-mini for scales up to H0 makes sense. In principle, the UPS can be used with all vehicle decoders that have a connection for an external buffer capacitor or a special connection for buffer circuits:

1. There is nothing to be said against connecting the UPS-mini only to the connections for the "normal" buffer capacitors, the UPS will take care of the rest.

2. It becomes more comfortable if the switching input of the UPS-mini is additionally connected to a free switching output of the decoder. Advantage of this connection variant: With the assigned function key the UPS-mini can be switched on and off during operation. As the decoder automatically switches off all outputs during programming on the programming track, the  UPS-mini is then also switched off.

3. It becomes even "nicer" if the switching input of the UPS-mini is connected to the special output for buffer circuits of the decoder (if available). According to RCN-530 ("Inrush Current Limitation for Decoders & Boosters") the decoder then controls the charging current and the current output.

......		.......
......	Connection variant "Control line to ground" With this variant the UPS-mini is always switched on, therefore problems can occur when programming on the programming track. Therefore this variant should only be executed if there is no output free at the decoder.	.......	Connection variant "Control line to output" The control line is connected to a free decoder output or the special control output for buffer circuits (according to RCN-530). When programming on the programming track, the output is automatically switched off.

The UPS-mini when the system is switched on

When the system is switched on, the high charging currents of several Super-Caps would force the boosters to their knees or - to put it another way - lead to permanent overcurrent shutdown. To prevent this from happening, the UPS-mini limits the charging current for the Super-Cap to 100 mA. Furthermore, the UPS "observes" the track voltage and interrupts the charging of the Super-Cap as soon as the existing track voltage falls below 12 V.

By the way, this always works - regardless of whether the control line of the UPS-mini is connected to a decoder output or not.

The USV-mini when programming the decoder

An active buffer circuit can make it impossible to program a decoder on the programming track. Therefore it is useful to connect the control input of the UPS-mini to a decoder output. When programming on the programming track, all outputs are automatically switched off - and so is the UPS.

If no output is free at the decoder anymore, the control line of the UPS-mini is connected to the negative pole of the buffer capacitor. The USV-mini is then always switched on. Programming on the programming track can also work with the UPS-mini switched on, as the UPS-mini automatically reduces the charging current - without guarantee.

With the main track programming (POM) the situation is different: Here the decoder "enjoys" a reliable power supply.

The UPS mini and the power

Unfortunately, the larger the capacity of the Super-Cap, the larger it is. Therefore we offer the UPS-mini with 3 different Super-Caps (0.47 F, 1 F and 1.5 F) and each ready for connection (protected against short circuits by shrink tubing) as well as a kit. If space is very limited, the kit version can accommodate the PCB and Super-Cap separately.

How long the stored current lasts logically depends on the current demand. In order to prevent the locomotive from stuttering at the end of the power supply, the UPS has an automatic low voltage cut-off. It ensures that the decoder is switched off when the voltage falls below the voltage required for proper operation.

The USV-mini when stopping before signals

In connection with buffer circuits, the question quickly arises as to how an exact stop of the locomotives e.g. in front of signals can be realized. The answer to this question is: basically not different than without a buffer circuit. If the control unit for the locomotive sends speed level 0, the track voltage is still present - there is no reason for the UPS to "intervene".

The situation is somewhat different in holding sections where the track voltage is completely switched off. The holding section can be defined at the vehicle decoder by setting the value for the Packet Time Out. This value defines the time that passes between the reception of a digital signal and the (forced) switching off of the engine. Hint: To prevent the decoder from automatically switching to analogue mode after the packet time out, the automatic analogue function should be switched off.

Even turnout roads which are longer than the holding distance are no problem, because in their course a 100% failure of the track voltage is never to be expected and consequently the Packet Time Out is set to "start" in between.

Tip: If things get tight...

In the kit version the circuit and the super cap can be stored separately. In this case we recommend not to solder the legs of the Super-Cap directly to the PCB, but to connect the Super-Cap via highly flexible wires (e.g. LifY 0.05). This prevents the connection pads from being torn off the board by the stiff connecting wires of the Super-Caps during installation.

Programming the UPS mini

What for? The UPS mini regulates everything independently...

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