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).
