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Decoder installation
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Installing a DCC decoder for the first time can be a daunting task. After you've done a couple, it will be like second nature. This guide will help you through the process. However, if this documentation is in conflict with the documentation provided by the decoder, please follow the decoder installation directions.
Contents |
[edit] Outline
The following outlines the process for installing a DCC decoder.
- Determine the locomotive's stall current
- Determine where the decoder will fit in the locomotive/rolling stock
- Select a decoder
- Select a decoder that fits inside the body shell
- Has the required current rating
- Isolate the motor from the track pickups
- Install the decoder along with wiring for any extra effects
- Test the completed installation.
[edit] Measuring the stall current
- You will need a meter that can measure DC amps.
- Connect the DC ammeter in series with your analog power supply and the tracks (see picture on right). The ammeter is wired to measure all the current flowing in the circuit.
- Set the meter on the DC Amps scale, and set the range if needed. It may also require connecting a lead to a specific terminal. Be aware that some ammeters may not have a fuse in the circuit for certain ranges.
- Grasp the locomotive so it doesn't take off and turn the power pack to full.
- Push down until the engine stalls (stops) and note the current. This is the "stall" current. Do not cause the motor to stall for more than 5 to 10 seconds. Doing so can cause damage to the motor, or other electrical components of your locomotive.
[edit] Determine where the decoder will fit
Decoder siting is often the the most difficult problem to solve during the decoder installation. The decoder needs to be located in a place meeting several criteria:
- There must be room for a decoder
- It should ideally have free air around it for cooling
- Without proper cooling, the decoder could overheat and be damaged. Some decoders have thermal protection to prevent this - it will simply shutdown.
- It should ideally be invisible from outside
Finding room for a decoder is unsurprisingly easier on larger models, and becomes more and more difficult as the scale size decreases.
Ideally, the decoder should be located in the same area of the loco as the motor and pickups. It is possible to place the decoders in the tender of steam locomotives if needed. Some people have been successfull at installing decoders in rolling stock and permanently coupling it to the loco. However, this should be a last resort as you will want to change rolling stock in the future.
If a sufficiently large area cannot be located inside the locomotive, it may be possible to create space by removing some of the material from the body or chassis. If the installation appears marginal, try assembling the model with plasticine or blu-tack in the space being considered to find out how big it is with all the parts in place.
"N" and "Z" gauge models are considerably more difficult than say "G", but there are some small decoders around now. However, it is likely that material will need to be removed, though. See below for specific scale information.
[edit] Select a decoder
Once the stall current has been measured and the available space has been found, you can now move onto selecting a decoder. There is alot of information available on various decoder sizes and specifications. You can see a local comparison list of decoders, however since it's brand new, it's not anywhere near complete. You can also find information on various manufacturers websites, as well as other DCC related websites.
Many decoders are made to go into a specific locomotives for a particular scale. Please see the scale specific article below.
However, it is possible (and in fact many model railroaders follow this practice) to use an N scale or even a Z scale decoder in an HO gauge locomotive. As long as the current rating of the decoder meets the minimum requirements of the locomotive (most newer HO locomotives have a rating of 1 amp, as do most decoders currently in production) then there shouldn't be any difficulties using a smaller scale decoder. Because larger scales (O, S & G) have a higher current rating only decoders made for these scales should be used.
The decoder mandatory requirements are that it must have an adequate current rating (ie can supply the stall current continuously) and that it will be small enough. There are however other considerations to take into account:
- Are any "accessory" outputs required? Most decoders can control one or more accessories - eg lights, windscreen wipers, uncouplers, sounds.
- How many speed steps are needed?
- The original DCC standard specified 14 steps: however the steps between these are too obvious. 28 steps are commonly available, but at low speeds can be discerned. Some systems offer 128 steps, which appear "stepless" to most people.
[edit] Isolating the motor
The motor must be completely isolated from all track pickup points. If the locomotive has a built-in command control socket, (usually advertised as "DCC Ready") the motor is already isolated and should be DCC ready at this point.
But an older model or one without a NMRA socket requires that you need to find and eliminate all connections between the motor brushes and track pickups. Typically, this is the biggest problem people have when they first get into DCC. Diesel locomotives are fairly straightforward, but with brass steam engines the mechanical pickups can be quite ingenious and well hidden - and may take some time and work get these units DCC ready. Some models will have a circuit board that routes power to the motor and the lights. You may need to cut a couple of traces to disconnect the motor from the power source. Check the instructions that came with the locomotive.
Verifying the wiring, and the motor isolation checks require an ohmmeter. A simple analog or digital MultiMeter will suffice. Set your meter on the ohms (resistance) scale and touch both probes together. The meter will indicate a short (0 ohms), and will test your meter (and it's battery) for proper operation.
The first test should be to determine that the wiring is correct and functional. Touch one probe to a motor terminal, follow the wire, and the other probe to the truck or wheels it connects to. Check both trucks if the locomotive has "all wheel" pickup. Do the same for the other motor terminal. Correct any wiring problems, such as bad connections or cold solder joints, then proceed to disconnect the motor leads from the power source, as per the decoder and locomotive maker's instructions.
To verify electrical isolation, you will need an ohmmeter. Set your meter on the ohms (resistance) scale and touch both probes together. The meter will indicate a short (0-ohm), and will test your meter. You don't want to see this when you're checking for motor isolation. If you do, it means the motor is not isolated.
Place one of the probes on a brush or power terminal on the motor, then touch the other probe to the chassis or right rail pickup wire, then move to the left rail pickup wire. If the motor is isolated you will read an open circuit on the ohm meter. Move the probe to the other brush and repeat. If both tests indicate an open circuit, the motor is isolated and you can safely proceed with decoder installation.
[edit] Installing the decoder
[edit] Testing the decoder
[edit] Scale specific
Although the above information can be used for all scales, here's some information specifically for vararious scales. Articles include DCC decoder selection tips for various locomotives.
[edit] See Also
- Decoders
- NMRA DCC Plug - Wire colour codes and functions.
