Table of Contents

Dapol LMS Jinty 0-6-0T


Brian Goodhew - Gazette February 2018 (Vol 20 No.6)

Pictures by the author
Loco review

I have been gradually converting all my locomotives to battery powered radio control (BPRC) for my LMS garden railway layout to avoid the chore of track cleaning the ground level section, it’s a hands and knees job! The tender locomotives have proved straightforward, as it all goes in the tender, but I have a scratch-built brass Jinty for which the siting of the receiver and its antenna was likely to be very difficult to ensure it got a decent signal.

When I heard that Dapol were going to do a Jinty, I thought that it would be ideal for conversion to BPRC; its plastic body would have minimal effect on radio reception. As soon as the early production models were announced, I preordered a DC option version from Hattons. The Dapol rollout timetable ran a little later than originally announced but the results were worth waiting for.

The model as received

The first reaction on opening the glossy storage box is that the locomotive is surprisingly heavy. This is thanks to a metal footplate, and a heavy chassis, both die cast. The wheels have steel tyres of a decent profile, painted black, and there’s axle centre detail. The connecting rods have nice detail with working joints. The electrical pickups are made of phosphor bronze strip and make contact with the backs of all wheels. The level of detail leaves virtually nothing extra needing to be added, even the cab interior has everything in the way of pipework, controls and gauges. The firebox has LED ‘glow’ which is fun but not completely realistic. My only criticism is that some of the smaller items such as lamp irons, at least on my example, were not stuck on at all, with one actually falling off and getting lost. I would recommend that owners check their model and add a dab of superglue to these small items if necessary.

The conversion

After receiving my model and checking that it ran properly on DC, the first job was dismantle it and measure all the key spaces inside to decide where everything could be positioned. The chassis is attached to the body by two screws at each end. The vacuum pipe detail requires unclipping first before separating the chassis from the body. All main wiring is contained in the chassis unit, except for the firebox flame effect unit, and that unplugs easily.

The loco has limited space above the motor and associated circuit board, about 10mm headroom below the inside of the boiler and firebox. The smokebox/boiler front section has a nice empty space about 30mm in diameter and will accommodate five AAA-size batteries. The bunker has a nice empty space with no obstructions. The cab floor has a useful gap below it.

The receiver location

I decided the best place for the receiver was in the bunker, to keep it away from the motor and any possible electrical interference. Having standardised on the Deltang radio control system and their RX65 receiver type for all my models, I fit them with pins to allow use of a connector rather than hard wire them, as this permits interchangeability. Although over-specified for a Jinty the RX65, having a 3 Amp motor drive capability, and physically larger than other receivers in the RX6x series, will still fit nicely in the bunker, even with the additional connector seen at the left hand end.

An On/Off slide switch is also fitted in the bunker, just below the top edge. The 2in long antenna wire is left to curl around the inside of the bunker; its position is not critical.

Figure 1. The receiver's position in the bunker

Battery location

The obvious place for the batteries was inside the side tanks. The maximum dimension of the inside tank space is depth 11 mm, height 27mm and maximum overall length 75mm. I only considered cylindrical cells, but rectangular lithium-polymer types may well be found that will fit better. Any cylindrical battery must be of solder tag type for hard wiring, as there is no room for battery holders. Whatever cells are chosen, they must be mounted such that they clear the base of the tank by at least 8mm above the chassis base. This is to avoid possible contact with the centre driving wheel flange at the limits of the side play that is present on the centre axle.

Battery choices

It was difficult to decide whether to go for lithium ion cells, which would only need three or perhaps four cells in series for nominal 12V operation, or to use NiMH which would require 10 cells. The popular lithium 18650 size, 2.5 Ah cell will not fit due to its diameter. This leaves just the smaller lithium 10440 format cells, which are only 600 mAh capacity, or various capacity AAA format NiMH cells that will fit.

Using fewer cells of either type, or in parallel to increase overall capacity, in conjunction with a booster circuit was also considered. Booster circuits can be used with batteries to increase the required voltage. However these are not ‘magic’; if the battery voltage is boosted by say, a factor of two to get 12V, then the motor current draw at 12V will mean that the current from battery will be doubled, so that power in to the booster always equals power out, minus the conversion losses.

Although I have experimented with a booster on a tender locomotive, the limited space inside the Jinty would make fitting one difficult.

The consideration finally came down to using either 10440 lithium cells, one of which could be fitted in each tank with a third, and perhaps fourth, placed in the boiler, or several NiMH cells filling the tanks and elsewhere. I ultimately decided against lithium-ion cells because of the need for a ‘charge equalisation’ system, necessary in a multi-cell battery.

Equalisation ensures that the charging current shares correctly so that individual cells in a lithium battery don’t get overcharged as this can be dangerous. Whilst these sort of multi-cell batteries are used by model car enthusiasts, they are provided with a tapping to monitor each cell voltage via a multi-pin connector. This is not a problem with car batteries as they are usually removed for charging, but in a locomotive with essentially non-removable batteries it precludes this type of battery, or at the very least, it requires a complex charging connector to be mounted somewhere, or an additional internal charging control circuit board, which again can be difficult to find room for.

I therefore decided on NiMH cells. Typically two AAA cells of 800mAh could fit comfortably in each tank space, one above the other, but there is then insufficient space remaining in the rest of the loco to fit the six further batteries required to get a total of 12V. I could have fitted a total of 9 of these cells (10.8V) but decided to try for the full 12V. To get around the problem of cell numbers, shorter 2/3 AAA format 400mAh cells were chosen to give sufficient ‘voltage per tank’. 400mAh is expected to give one to two hours of continuous running time, and I am satisfied with this at present.

The shorter AAA cells are arranged in two horizontal rows, each of two cells in series, giving four cells in each tank. These are gently supported clear of the bottom on a piece of foam. This totals eight cells in the tanks; the remaining two cells of the required total of ten sit inside the smokebox, again with foam packing to keep them in place. The battery wiring is as shown in Figure 2. The wiring is slightly complicated by first bringing both end wires from each respective tank battery forwards into the smokebox. This is to avoid wires crossing over the centre space which is occupied by the motor mechanism, leaving just the final battery connector cable and connector to project back into the centre space. The individual cells in each tank battery are joined by soldering the tags together (these may need trimming for length first) and each set of four is made into a block by binding with PVC insulating tape. All wiring joints to the end tags and battery connector are covered with heat shrink tubing.

The shorter AAA cells are arranged in two horizontal rows, each of two cells in series, giving four cells in each tank. These are gently supported clear of the bottom on a piece of foam. This totals eight cells in the tanks; the remaining two cells of the required total of ten sit inside the smokebox, again with foam packing to keep them in place. The battery wiring is as shown in Figure 2. The wiring is slightly complicated by first bringing both end wires from each respective tank battery forwards into the smokebox. This is to avoid wires crossing over the centre space which is occupied by the motor mechanism, leaving just the final battery connector cable and connector to project back into the centre space. The individual cells in each tank battery are joined by soldering the tags together (these may need trimming for length first) and each set of four is made into a block by binding with PVC insulating tape. All wiring joints to the end tags and battery connector are covered with heat shrink tubing.

Figure 2. The schematic to show how the batteries are connected


Stripping the locomotive

Having decided on the position of the batteries the next job is to start stripping the locomotive. The first step was to disconnect the wiring and remove and examine the existing circuit boards (see Figure 3). This board is appears to be designed for DCC use and has the various standard connectors; these of course are unused for a DC loco.

Figure 3. The original Dapol circuit boards for DCC and DC analogue operation.


Together these boards merely act as ‘junction box’ for the various wires between the wheel pickups, a DCC decoder and the motor. The smaller board on top, via the connector, contains jumper links to join the pads for DC so that the motor connections are joined to the track pickup connection pads. It also contains diodes arranged as a bridge rectifier, the four items marked M7, which is connected into the motor circuit to supply the LED ‘firebox glow’ pulse circuit board with a variable but fixed polarity voltage regardless of motor direction. I removed the ‘firebox glow’ LED circuit board for the time being. This is not shown, but it connects via the wires on the right. These boards and the firebox glow board were retained for possible future use. I decided to follow the Dapol idea of managing all the various wiring interconnections by plugs and sockets on a new, home-made junction board. The original board is mounted on top of a plastic cradle which also holds the motor in position. This cradle and the self- tapping fixing screws are reused for mounting the new home-made junction board as shown in Figure 4.

Construction of the new circuit board This new board is made from a piece of Veroboard, copper clad stripboard, obtainable from Maplin’s, etc. A piece was cut to the same width as the original junction board, but shorter. All the connectors are cut from a length of right-angle, 0.1in pitch PCB pin header strip; matching female connectors are available in various numbers of ways. The battery connector is specially arranged to use only pins 1 and 3 of the total four pins to prevent inadvertent wrong polarity connection. The original motor and pickup wires are fairly short so they are soldered to cut down straight 0.1in pin headers arranged as through-posts, avoiding the need to solder wires on the underneath of the completed board. The diode and resistor are part of the charging arrangement (explained under ‘Battery charging’ section). The circuit is shown in Figure 5. The completed circuit and its connectors allow the upper and lower sections of the loco to be separated for servicing and subsequent reassembly without unsoldering any wires.

To avoid having to solder these wires inside the bunker, the wiring is made up first. The receiver loom is made up with the connectors at each end; the on/off switch is connector is wired and the switch soldered onto the far end of its wiring loom. These looms will then be passed through the void under the cab floor. To get access to this void and also to cut a hole in the bottom of the bunker floor for the wires, the complete cab including the cab floor and the bunker mouldings must be removed from the metal footplate.

To remove the cab from the body, take out the six screws shown arrowed in Figure 7. Note that these are a self-tapping type, so keep them separate from the four similar size machine screws that hold the body to the chassis.

The sections are partially slotted together. Carefully slide the front of the cab from under the tanks and firebox and lift all three as a unit from the footplate. The floor can then be removed carefully downwards from the main cab section, taking care not to snag the brake valve detail, reversing lever and injector pipework, etc. The main part of the cab slides upwards away from the bunker. Take care not to catch the cab doors, which are part of the bunker assembly.

With the bunker separated from the cab and the floor, the lower bunker inner floor piece requires a notch to be cut out from the edge near the left hand end. This is to allow the wires from the switch and receiver to pass through and out of the bottom.

The bunker assembly itself has an outer and inner section, joined about 10mm below the coal rails. This looks as though it is supposed to be glued all the way across so make sure these two parts are properly glued together by running some superglue into the joint all the way across. Mine was not fully glued and this would have prevented mounting the on/off switch securely.

The switch is secured to the sloping inside face of the bunker with epoxy resin so that the top of the operating slider is just below the lowest coal rail. Once set, all wires are then routed through the notch in the floor and bent to run towards the centre of the cab floor section.

The next task is to modify the rear panel of the main cab. Referring to Figure 8, note that the cab rear edge has a locating tab protruding from the lower edge of the rear cab wall which engages in a corresponding recess in the metal footplate.

The cables must pass under this locating tab once re-assembled, therefore it must have a small rectangular cutaway made in the middle and up into the rear panel of the main cab.
The cutaway needs to be of sufficient depth to provide just enough space for the wires to pass under the cab floor and through to the front. Take care not to remove too much material otherwise the cut may become visible above the cab floor.

To avoid this problem it is best to work with the cab floor placed in the normally assembled position as a depth guide. See Figure 9.

Reassemble the cab, the floor and the bunker as pictured in Figure 9. All wires are then routed through the notch towards the centre of the cab floor section as shown, keeping them as flat as possible. Secure the wires with some adhesive tape to ensure that they don’t move during reassembly and become trapped between the cab locating notch and the footplate.

Refit the complete assembly to the footplate, taking care that the end pins of the rear cab handrails engage in the corresponding holes in the footplate correctly before attempting to refit the securing screws. The cab assembly should go back into the original position without undue pressure; if this is not the case then check the depth of the notch in the cab locating tab has sufficient clearance around the wires, also make sure the wires are sitting as flat as possible. Once in position, hold the cab together on the footplate and refit the screws. This can be slightly tricky until the first couple of screws are in place.

Fit all the cables to their respective connectors on the junction board, then feed the chassis and wiring into the body aperture. Replace the four machine screws that hold the chassis in place and you're ready to go.

Figure 4. The replacement circuit board as described in the text

Figure 5. Wiring diagram for the new circuit board

Figure 6. A view of the wiring and connectors

Figure 7. Cab securing screws

Figure 8. Cab locating tab and notch

Figure 9. Cab assembly and wiring position


Battery charging

I did not want to have a separate socket for charging the batteries so decided to use the track pickups to get power into the loco. The ‘on/off’ switch is actually dual purpose as it also allows charging of the batteries. In the ‘off’ position the battery positive is connected to the right hand rail pickups via the 1N4001 diode. This prevents either an incorrect charger polarity connection from damaging the batteries, or leaking power to other conventional locos if on the same track.

I discovered that the ‘smart’ charger that I use has an interesting feature; the diode in the junction circuit initially prevented charging from taking place This caused a bit of head scratching until I found the charger program first detects battery presence and correct polarity before it applies the main charging current. With the diode present the charger was unable to detect any initial voltage from the battery and simply shut off. The solution was to add a small ‘bleed’ resistor of 3.9K Ohms in parallel with the diode; this allows the charger to ‘see’ the battery at the first step but is high enough in value to avoid any undue possibility of damaging external current flow if mis-connected.

The charger simply connects to a spare length of rail, or a section of dead track on the layout, with crocodile clips, as shown in Figure 10. Placing the loco the wrong way round is not harmful as the diode prevents mis-charging. The charging action does not heat the batteries sufficiently to worry about distorting the plastic side tanks.

Figure 10. The loco in charging position

Figure 11. The coal bunker filled and complete

Final Touches

The model conversion is completed by making a removable coal tray to conceal the receiver and switch. This is made from Plastikard, of a size to fill in the top of the bunker and is positioned just below the rim with the aid of an angled support leg. It is cut around the on/off switch outline and covered with pieces of real coal secured with PVA adhesive. The on/off switch slider is disguised by a loose piece of coal.

The Dapol Jinty before and after the operation! (…no locomotives were permanently harmed during this conversion).