Checking for Shorts when DCC Fitting A Wrenn Locomotive

The Wrenn Locomotives, despite being much older than most things you can get today, are still great locos and normally great performers.  They are not easy to convert to DCC but it can be done and I’ve previously written about the 3D printed sleeves I produce to allow you to do this.  But I sometimes get questions from customers who’ve done the conversions themselves, with my sleeves, and the loco runs very poorly even though it ran well on DC.  In this week’s post, I’ll show you what the most common reason for this is.

Coincidently this week I’ve had two Wrenn locomotives in for DCC fitting so I can use them to point out the issue.  The two locos, as you can see below, are a former LMS Duchess 4-6-2 and GWR Castle 4-6-0.

As well as being very different models visually they are different mechanically as well; the Duchess chassis at the back has a vertical motor and I covered the DCC installation procedure for this here.  The Castle has the horizontal motor and that was covered here.

Before I go any further I should point out one other issue which can cause problems with DCC fitting these locomotives and that is the current draw.  Sometimes older motors, and worn-out motors, can draw lots more current than intended and the DCC decoder can’t handle it.  To find out what the amperage draw is for a locomotive a stall test should be done.  You can read how to do this here.  Both of these locomotives had a stall current of less than 1 amp, so they are ideal for DCC fitting.

So what is the main cause of problems with these?  Starting with the Duchess below you can see I’ve cut off the wires as per the DCC install instructions.  Both motor brushers are still fitted and you can see them touching the collector on the armature.  The left brush holder, which is at the front of the locomotive, is isolated from the chassis, and the right, or rear one, is not.  The problem is often that the left/front brush isn’t totally isolated.  The brush still fits inside a brass sleeve which is wrapped in a rubbery paper-type material to create the isolation.  Over time, remember I said these were old, this material breaks down.  It’s possible heat from excessive running has affected it as well.  The material hasn’t totally disappeared and it’s not a dead short, otherwise the loco wouldn’t run at all, but a very tiny intermittent electrical short happens between the brass sleeve and the chassis.  Running the locomotive on DC doesn’t really affect it too much.  Although it’s not good for the controller, the tiny short will affect the running, but the controller is able to push more amps through the motor to compensate. But under DCC, the decoders are much more sensitive to shorts and are not capable of delivering as many amps.  The result is the locomotive runs very slowly or has no pulling power.

To check to see if this is going to be a problem remove the brush cap, spring, and brush from the left/front sleeve and inspect the insulation.

If it appears to be okay, basically not falling out, an electrical test with a multimeter can be done.  A continuity test, setting the multimeter to the symbol shown below, will check to see if there’s an electrical connection between the meter probes.

With the brush removed and the brush cap replaced, check to see if there’s anything between the two brushes.  This doesn’t work with both of the brushes fitted, as there’s a connection through the motor.  If, when performing the test, the multimeter gives the slightest suggestion that there’s a tiny connection there, it will cause a problem.

The solution for this is to remove the brass sleeve and isolating material and fit a 3D printed sleeve to the left/front as well as to the right/rear.  As the new sleeves are plastic you are guaranteed to have no short.  The customer’s Duchess above is actually in very good condition and is perfect with no sign of a short, so I won’t change the front sleeve, but once the decoder is fitted, if there’s an issue it will be changed.

The Castle with the horizontal motor can suffer from the same thing although it’s not so common. Both motor brush holders are at the back on either side of the motor.  Again I’ve cut the existing wires off but left the heavy gauge wire on the right, which runs from the connecting point to the brass sleeve on the right.  This is because it’s a better connection than relying on the spring to deliver the power.  The right-hand sleeve has the isolating material.

To remove the brush simply pull back the spring and it will slide off and the brush should fall out.

You can then do the same test as shown below.

I originally supplied my Wrenn DCC conversion sleeves in pairs to provide a spare incase something went wrong and one broke, but in hindsight I see it was a good idea as you may need to change both.  The sets I sell are:

Two Wrenn horizontal motor isolating sleeves.

Four Wrenn horizontal motor isolating sleeves.

Two Wrenn Vertical motor isolating sleeves.

Four Wrenn Vertical motor isolating sleeves.

Two Wrenn Vertical & two horizontal motor isolating sleeves.

This vertical motor design was also used in the Hornby Dublo locomotives, 2 and 3 rail, so should you wish to convert any of the locomotives to DCC or repair a DC locomotive which is shorting, the 3D printed sleeves will work.

Using Second Hand Capacitors

This week’s post will be a how-to for a question I get asked a lot.  Can I use second-hand Capacitors?

The reason I often get asked this is modelers often want to use second-hand capacitors to make StayAlive units for their DCC locomotives, and these can be very effective.  But where are they getting second-hand capacitors from?  Most electrical appliances have capacitors in them of one form or another.  A good example of this is an old stereo system I took apart for the motor.  Below you can see the main printed circuit board (PCB) and it has lots of black cylinders which are mostly all capacitors, and ideally sized to fit into small locomotives.

Even the smaller secondary PCBs have capacitors on them.

The main power input board below is a bridge rectifier, the smaller black cylinders are diodes, and it turns AC voltage into DC for the stereo to use, the nice big capacitor is there to smooth out the DC.

These capacitors are all soldered onto the PCB.  With a good soldering iron the capacitor can be removed without damage by heating the two soldered joints, once you have figured out which ones they are, and pulling the capacitor out. 

This capacitor has a working voltage of 24v and a capacity of 1000 microfarads.  The voltage is important because it needs to be higher than the voltage in the DCC locomotive decoder.  This normally does not exceed 16v, so a capacitor like this is ideal. 

But I find the more important question is not whether second had capacitors can be used, its do the work?  Luckily there is a simple test to check this without any expensive equipment.  Some high-end multimeters have the ability to test capacitance but most do not.  Mine does not, but what it can do is test voltage and resistance.

One thing to do before the test is to remove the charge from the capacitor, a full capacitor could damage the multimeter.  This can be done with a metal screwdriver by shorting across the two terminals.  Please note, this is okay for small capacitors in the Microfarad range used in modeling, I would not recommend doing this with large capacity capacitors with capacitance measured in farads!

The two settings I use are both on the left of my multimeter.  Below it is set to 200k ohms and is used for testing resistance.  I will also be rotating the dial clockwise by three positions to 2 which is a DC voltage measurement.

The way this works is first you discharge the capacitor.  Then, with the multimeter set to resistance, connect the probes to the capacitor.  Black negative to the capacitor negative and red positive to capacitor positive.  The capacitor negative is normally clearly marked.  As the multimeter has a battery inside when the probes are connected to the capacitor it will start to draw and store power.  As the stored power increases the resistance will increase so on the display you will see a steady increase in resistance from 0 to infinity.  If there are any big surges or erratic readings, then the capacitor is not working.

The second part of the test is to set the multimeter to volts DC and reconnect the probes.  This will measure the stored voltage and you will see it decease as the capacitor discharges through the multimeter.  Again this should be smooth.

As it happens the capacitor I took out of the stereo was faulty, probably one of the several reasons it didn’t work!

But to show you the principle, I created a short video of me testing a new capacitor.

So the answer to the question “Can I use second-hand Capacitors” is yes, but I would recommend testing them before spending any time wiring them into your locomotives.

If you have a similar question you would like to be answered or explained in more detail, please contact me and maybe I can help.

A New Drive Gear For an OO Airfix Class 14xx

This week I have another replacement part to share with you.  As with most of my replacement parts, this was a request from a customer who has one of these locomotives with a damaged part.

The Airfix class 14xx 0-4-2 model has been around since the 1970s, and was a mainstay on many UK model railways as they were the only maker of the model.  It’s had several upgrades over the years as the model moved to Dapol and then to Hornby but the original can still be seen running today.

However, constant use over time will always cause parts to wear out and with the 14xx it’s the main drive gear that starts to go.   The original chassis had a thicker gear which can be seen at the top in the image below.  The thinner gear is for one of the newer chassis introduced under the Dapol line.  Interestingly Daopol also moved the traction tire to the other wheelset.

The metal worm gear on the end of the drive shaft drives sits directly over the main axel drive gear and the metal eventually wears down the plastic gear, especially if the wheels get jammed up or start to bind, due to lack of lubrication.

The gear in the image below is still in good condition, but you can see the teeth are intentionally not square to the axle.  This makes the mesh between the two gears smoother and improves the running of the loco.

Using the original I was able to 3D model a replacement.  Because the gear is thick, 3.18mm, it should be strong and hard when printed in Shapeways Smooth Fine Detail material.

The test prints came out very well and were immediately ready to use.  The hole in the center has been printed slightly smaller than the axel size to ensure a good tight fit.  If it’s too loose the gear will spin on the axel. If it’s too tight the new gear may crack. To allow for any 3D print shrinkage or oversize on the axel, I’ve 3D printed two gears; one has an even smaller hole to allow for any differences mentioned above.  It’s always easier to remove material if it’s too tight than it is to add some!

To identify the two different gears I’ve marked the side of the gear with the smaller axel hole with a hole in the sidewall as you can see on the gear on the right.

The replacement pair of gears for the Airfix OO 14xx are available using the link here.

As long as I can find an original gear, even if it’s cracked or damaged, I can replicate it using 3D printing, so contact me if you’re in need of a new gear that you can’t get hold of.

Next week I hope to have some more to share with you on the HO DT6-6-2000 project, the brass etches are in production, and the different variants of body shells are being drawn.

A Personal Post

This week’s post is a little different, it’s not even about trains!  It’s about something my partner and I do each year to help a very good cause which is relevant to a lot of people in this hobby.

This coming Sunday we’ll be riding our motorcycles in one of the most important events in our yearly calendar – The Distinguished Gentleman’s Ride.

Those of you who’ve known me for a while know we like to try and combine overseas travel with our yearly fundraising ride, but this year we’ll be riding in the UK again given the travel issues.

Despite the situations created by the pandemic the world over, as motorcyclists around the globe we’ll still come together as a community to raise money and awareness for men’s health.  Instead of the usual organized group rides we’ll be riding solo to support the cause.

The Distinguished Gentleman’s Ride raises funds for research and awareness of prostate cancer, as well as providing programs for men suffering from mental health issues, creating resources to break down the barriers for men to talk and deal with their mental health issues, in the hope of reducing the number of suicides. We support the cause by dressing dapper for the ride and, usually in groups, we put on a fantastic show for the public in whatever city we chose to ride in. It really is a day of celebration and joy designed to bring to the forefront men’s health. This year folks will be riding and fundraising, just solo.

If this is a cause you feel is important to you I’m asking you to make a small donation to do something to help stop men dying from prostate cancer, or by losing their lives to mental health issues.

Understandably a lot of people are experiencing challenging times because of the pandemic, but if you are in a position to make a small donation, please do. The link is here – https://www.gentlemansride.com/rider/thedrawnstudio

If you are not in a position to make a donation you can still help – drop a message to a male friend you haven’t spoken to for a while, and just ask them how they’re doing.  Our hobby is largely a social one, and with so many modelers having to shield through these difficult times it’s easy to get cut off and isolated, so let’s just keep checking on each other. There’s some handy guides on the DGR link here – https://www.gentlemansride.com/about/mens-health, so have a read, and reach out to someone who may need a lifeline right now.

Thank you.

Next week I’ll have a train-related post for you, once I get back from the ride.

A Cover for an In-Track RFID Reader

Model railways have seen many great technological improvements through the years and Digital Command Control (DCC) is one of the biggest, but sometimes I get asked to work on something that’s totally new.  This week I have a small project to share with you for a customer who’s experimenting with RFID.

RFID stands for Radio Frequency Identification and is used in all sorts of things; there’s a good chance you have an RFID chip in your wallet.  Bank cards that have the contactless payment option have an RFID chip inside the card which reacts to the RFID reader when you hold your card up to pay.  This technology has been in use for a long time in all sorts of industries, from such environments as warehouse management to automatic bridge toll devices.  Now it’s making its way into model railways, at least on one model railway anyway.

To add another level of realism to the customer’s railway, all of his freight wagons have been fitted with an RFID chip.  There are readers either under the track or within it at multiple places around the railway.  This means, when a train enters a freight yard, the computer will know exactly which wagons make up that train.  It’ll then work out where each needs to go, such as a local industry or added to another train, and the operator then has the fun of shunting the train as instructed.

With a newly-constructed part of the layout, adding a readily available RFID reader under the track was fairly easy, but on the already existing section it’s a little bit more of a challenge without ripping up the track.  The answer came in the form of these custom made RFID readers by Eccel.

This are designed to fit between the rails allowing space for the wheel flange to pass.  A hole at one end needs to be driled between the sleepers to allow the cable to pass through. However, they don’t look very realistic for a model railway, so the customer has asked me to design a 3D printed cover to make them look like a timber uncoupling ramp.  The uncoupling ramp below, made by Peco, is designed to clip into the track, but also sits above the railhead so it will engage the UK-style couplings.

The customer uses American-style Kadee couplings so the uncoupling ramp will be purely cosmetic and needs to sit just below the railhead.

As always, I have 3D modeled the original part, and some track, to ensure everything is correct.

The ramp is designed to clip over the RFID board, with space inside to allow for the circuit components.  The RFID reader itself will be fixed using the two holes in the board.

To get the wood grain effect I’ve recessed the patten so it will, hopefully, print and be visible when painted.  I’ll spray these to ensure a thin coat of paint as brushing would probably fill the recessed wood pattern.

Although this a simple project it’s been very interesting to do and I’m eager to see them in use on the layout.  Once they’re all printed and installed I’ll take some video of the trains running, and the computer screen capturing the RFID data.  This may be several weeks away, but I’ll share it with you when I can.

If you have something different like this on your layout that needs a special part, get in touch, I may be able to help.

Replacement Bachmann N Scale Chassis Fasteners & Washers

In February of this year, I shared with you my design for a replacement set of Bachmann OO Chassis Fasteners & Washers; you can find the post here.  Since then I’ve had some requests to do the same thing for the N Scale Bachman US locos. So in this week’s post, I’ll share with you my design for a replacement set.

Unlike the OO set, Bachmann still has the N Scale version listed on their website as spare parts, but they’ve been out of stock for some time. The fasteners in question are used in the older locomotive designs from the 1980s.  A typical example of this is Bachmann’s GP50 as shown below.

The chassis is a split frame design also used in several other locomotives, such as their GP40 and U36B models.  It’s held together by the two chassis fasteners at the bottom corners of the chassis.

Viewed from the other side you can see the screw heads which pull the fasteners tight.

With the screws removed, the chassis separates and the trucks and motor will drop out.  You can see the fasteners and a washer still in the upper chassis section.

The fasteners will push out and the washer will drop off.

Both the fastener and washer are made of plastic to electrically isolate the two chassis halves.  The washer also acts as a spacer to correctly position the chassis halves.

As with the original OO versions, with time the type of plastic used hardens and becomes brittle, so when the screw is removed the cylinder part of the fastening breaks off of the rectangular sections as shown below.

Interestingly the OO and N Scale versions at first glance appear to be the same, but after doing some measuring I discovered the N Scale fastener is shorter and fatter.  This means the N Sale washer also has a larger hole.  Below you can see my OO fasteners and washers in white compared to an N Scale original one in black.

Using one from the GP50, it was easy to modify the existing OO version to create a new fastener for repairing N Scale Bachmann locomotives which have suffered from this part failure.

As with the OO set, the hole in the middle of the tube section will need to be cleaned out to remove the 3D print residue before the screw can be inserted.  For the N Scale fasteners, I use a 0.8mm drill bit in a pin vice.

The inside of the tube has not been threaded for the metal screw so it’ll work as a self-tapping screw, cutting its own thread the first time it’s inserted.  But if the tube is blocked, the excess material will create too much pressure and the tube may crack.

These replacement fasteners and washers can be used on a large variety of Bachmann N Scale locomotives and I’ve made them available in a set of 6 here and a set of 12 here.  I thought it best to make the smaller set start at 6 so you have a few spares just in case something goes wrong.

These little fixes are ideal for 3D printing components, so if you have an idea for a part you’d like to see 3D printed please drop me a message, I’m always interested to hear what fellow modelers are working on. You can get in touch through the contact page.