Installing Protocab in a Lima Class 20

Text and Photographs (c) 2016 Michael Miller

I saw the Acc+Ess Protocab advertisement in ‘Model Rail’ back in February, showed it to my wife, Pam, we thought about it … and the hours spent cleaning the rails on our garden layout … and decided we would give it a try. Two units were duly purchased. We have a ‘preserved railway’ approach, so operate both steam and diesel and the intention was to convert one of each. This is my task – Pam does the scenery.

My main interest is the Caledonian and its partnership with the LNWR. However, the garden railway is definitely not prototypical. It is intended to be just fun and provides great relaxation – when the weather is suitable and the tracks are cleaned. Protocab is already proving a great boon and is extending significantly the time when it is possible to run trains outside. Grabbing the odd 10 minutes or half-an-hour without worrying about electrical connections is improving the old lifestyle no end.

When the units arrived the ‘thinking time’ started. You know, you lay things out on the desk / workbench and start wondering how it will all go together in practice. Thinking time over this project proved invaluable. I had not yet decided which locos to convert. I have some rather tight curves on parts of the garden railway and not all our locos cope with every bit of the track. I selected possible candidates – mainly tank engines, shunters and the Class 20s.

Hmm … discarding those which were simply too small for the Protocab units, I came down to a couple of Class 20s, a Bachmann and a Lima. Opening these up to check inside, the Lima Class 20 selected itself (too much modern electrics filling the inside the Bachmann models). There was plenty of free space inside the Lima model. It had always proved reliable, running smoothly with stock on a ‘main’ line and responsive for slow running in a yard and sidings.

Now came more thinking time. I heartily recommend this approach – and measuring everything with the old digital callipers to check where everything may fit. This was time well spent. I also recommend reading (and re-reading) the manual and leaflet which come with the various units. Studying various instructional videos on the the Acc+Ess Protocab channel on YouTube also helped [see: https://www.youtube.com/results?search_query=Protocab ]. Familiarity breeds content.

I did the ‘workbench test’ and assembled the bits and pieces - as advised on page 20 of the manual for the controller. The two units purchased had already been ‘adopted’ to buttons A & B by Acc+Ess (for this, much thanks), so the test was straightforward. What was fantastic was that everything worked first time – and how often can we say that about our railway models? What is more, they went on working first time throughout the modification and assembly process and throughout the testing. At the time of writing, and after a good week of serious running, the system is proving most reliable.

Before dealing with the details, the following picture shows the final assembly:-

You will note that I like gaffer tape … and of different colours! It is all a bit ‘crowded’ – but it does fit comfortably. Photograph (c) April 2016 Michael Miller

Before starting the conversion in earnest I gave the loco a good clean and maintenance; this never does any harm. This included treating the wheels with Bullfrog Snot [see: http://www.bullfrogsnot.com/ and videos at http://www.bullfrogsnot.com/vid_gallery.asp ]. I find it is well worth doing this, even to wheels with traction tyres; this adds that extra bit of grip. The ‘Snot’ is a bit expensive, but a very little goes a long way. I get mine from Wickness Models: [at https://www.wicknessmodels.co.uk/shop/special-products/special-products/product/171-bullfrog-snot-one-part-green-liquid-plastic-tire-traction ].

As this was my first attempt at a Protocab conversion, I admit to working out a way of doing things so that I could easily convert the loco back to conventional DC control if necessary. Clearly I need not have worried! There are a couple of major advantages about the Lima model, apart from a decent amount of available space under the body for the Protocab units. There is plenty of wire from the motor to the bogie with the pickups, and it is simple to unsolder them from the pickups. The way I have adapted it means that you do not have to remove the pickups. I left the wire attached to the motors; this meant it was easy to attach the LCU wire to the motor, for testing, using standard 3A small terminal joiners.

The second advantage is that the body is held on by the buffers; simply pull these out and the body slips off the chassis. This meant that I could organise things so that I did not have to drill a hole for the charging unit as removing the body is a matter of seconds. This also enables the units to be easily accessible for checking. My contemplations of the units and the space available eventually led me to install a couple of ‘shelves’ on either side of the motor. For this I used good, solid 1.4mm plasticard.


Photograph (c) April 2016 Michael Miller
Photograph (c) April 2016 Michael Miller
• The shelf support (A) needs to be curved before attempting to superglue to the chassis block. I used the usual boiling water and bend around an old 35mm canister method.
H&S warning when using boiling water use tweezers … and washing up gloves!!!
• (A) was the only bit that had to be permanently glued to the chassis. Gaffer tape (and similar) sufficed for everything else. It is a personal choice as to whether to fix permanently or not.
• Just make sure that when measuring and cutting (A) you leave a sufficient gap above the drive. Luckily the chassis block at the motor end is exactly the right height.

Photograph (c) April 2016 Michael Miller
• The main thing with the cab end shelf is to keep it clear of the motor and slope slightly backwards to avoid intrusion above the lower level of the cab windows. The other end rests conveniently on the moulded seats in the cab.
• The battery is not too obvious through the cab windows, and the plasticard shelf can be painted to make it even less obvious. This is the only bit where ‘compromise’ had to be made, but losing a view of the seats etc. was, I felt, a small price to pay.

The internal width of the chassis block on the model was around 2cm. Fitting the Protocab components on the ‘shelves’ was no problem as they all came within the necessary parameters. However, I had to use the smaller of the battery options as the large one was too big. It was fortunate that I had ordered one of each to go with the units – just in case.

I had played around with the various components to see where they best fitted on the ‘shelves’. To some extent, this was decided by the length of the connecting wires, so the battery had to go at the cab end and the 0502 LCU and 9601 charging unit at the other. The position of the LCU was decided by Acc+Ess' advice not to install this near the motor – so I didn’t.


Photograph (c) April 2016 Michael Miller
• Once again, most components fixed easily, and securely, with the gaffer tape.

Photograph (c) April 2016 Michael Miller
• *** Ensure that the end of the plug unit does not protrude beyond the edge of the ‘shelf’ as otherwise the body will not fit back on.
• I just had to cut off one row of the unit’s board to ensure a comfortable fit. I used this spare bit to raise the unit slightly to make room for the excess length of the wires to the Locoswitch.
• The unit was fixed with the two nuts and bolts provided. Simply put in position on the ‘shelf’, mark the holes in the circuit board, drill the holes and ‘voila’ it is done.

Photograph (c) April 2016 Michael Miller
• I found that the LCU itself did not need fixing in any way once the Locoswitch had been put in place. The LCU fitted snugly between the copper pad and the charging unit, and was also held in place by the positioning of the various wires attached to it.
• The copper Locoswitch was slightly too big for the body to fit over it comfortably. Rather than cut it down I simply folded the edges over to create a slightly smaller square.
• Acc+Ess (in their instruction videos) suggest fixing the switch to the plastic body, but this would have prevented taking the body off. I didn’t remove the backing paper to the switch, but used double-sided sellotape to fix the pad to the chassis block. This seemed to work perfectly well.
• However, once the real testing started on the layout I found that touching the body over the switch position was a little ‘hit and miss’. As an old model, I suspect that the Lima plastic is thicker than that for more modern models, and therefore not as responsive to the touch of a finger.
• I overcame this by cutting off a piece of copper spring, attached this to the pad, and taped some additional foil to the inside of the loco body above the position of the switch. When the body is on the spring it acts as a conductor between the foil on the body and the switch, thus overcoming any ‘gap’. I’m pleased to say that this now works first time every time.
Photograph (c) April 2016 Michael Miller

There is a light on the LCU to tell you when the unit is switched on and off. When inside the loco with the body on this cannot be seen*. You can easily tell what is happening if you have the controller on and the red light for loco A, B, C etc. is on or off. However, I decided to run a bit of optical fibre from in front of the light source on the LCU through to the cab area of the loco. This works reasonably well and if you look through the cab windows you can catch the light flashes at the end of the fibre optic cable.

The penultimate job was to tidy the various wires and, of course, ensure that they stay in place with a bit of gaffer tape!

Photograph (c) April 2016 Michael Miller

The final bit was to connect the motor wires from the LCU to those attached to the motor. I did solder these; remember to slip the heat shrink sleeves provided over the wires first!

Photograph (c) April 2016 Michael Miller

Now … just slip the body back on, fit the buffers to secure it in place … and run it. That is the fun bit.

Next project: to fit the second Protocab unit we bought to a steam loco … but that may be another story?

(*Thank you to Mike for the great write-up. - Ed)






Page last updated: 12 September 2016