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The Lilliput System

The Caley coaches use the Stones Liliput Dynamo to power the lighting. The power regulation is done by tensioning the drive belt such that it slips above a certain power output. The operation of the system is described below - this text and pictures are taken from an ancient Stone's publication. The diagrams are accessed separately through links to keep this page manageably small.
Suspension System     General Arrangement

The "Liliput" Dynamo is provided with ball bearings throughout, and designed to require the minimum of attention when running; all parts are arranged to be easily accessible for inspection or repair. The armature is of the drum type, with former wound coils, and an improved method of fitting the ball races enables it to be withdrawn from the machine, when in need of attention, without opening up or disturbing the ball races at either end; the field magnet coils are separately wound and therefore readily renewable.

A Polarity Changer, of simple form, is embodied in the dynamo; it ensures the same polarity or direction of current for both directions of running. The brush-holder, 0 (see Fig. 1), at each side of the dynamo is mounted on an arm that runs out parallel with the shaft of the machine; and this arm, carrying a contact plate, M, at its end, is attached to a rocker, D (which forms the armature of an electro-magnetic clutch), allowing it to rock through a small angle in either direction of rotation.

When the dynamo starts, the friction of the brushes on the commutator carries the rocker over until the contact plates rest against the two switchboard brushes, L (one above and one below the line of the shaft), mounted on the small switchboard, N, at the end of the dynamo; this completes the circuits of the field magnet and the clutch coil. As the speed of the dynamo increases, it excites itself and also energises the clutch coil, E, which then holds the brush rocker firmly over, and ensures good contact between the contact plates and the switchboard brushes. At the stopping of the dynamo, the clutch is not released until the field current has fallen to zero; so there is no sparking at the contacts of the automatic polarity-changer.

Standard Sizes - The following table shows the standard sizes and outputs of Stone's "Liliput" Train Lighting Dynamos; when quoting the types of dynamos, it is preferable to quote their present designation.

'Stone's Liliput'
Output in amps at 24 voltsMaximum Lamp LoadApprox. Maximum Candle Power.Equivalent Old Type
Designation.  in amps at 24 voltsWith vacuum lampsWith gas-filled lamps 
0-16 & 2493 - 580120-
11016 & 24165 - 10160240-
33016 & 243015 - 22320480AZ
43516 & 244020 - 30480720CZ
4x-245030 - 35560840-
4A-246535 - 457201100-
5502480-10040 - 60800-9001300DZ

Dynamo Suspension. - One of the principal features of the system is the method of suspending the dynamo which controls the output and prevents it exceeding the amount for which it is set no matter to what extent the speed of the train may increase. The dynamo is suspended by an adjustable link in such a manner that the dynamo is free to swing towards or away from the driving pulley on the axle. After putting the belt on, the link is adjusted so that the belt draws the dynamo out of the position in which it would naturally hang, thus putting a definite tension on the belt- just sufficient to transmit power equivalent to the amount of electricity required. This tension can be regulated by screwing or unscrewing the nuts on the tension screw, so that more or less of the weight of the dynamo is made effective. When the pull on the belt (owing to increase in speed of the train) exceeds the weight on the belt, the belt will slip, continuing to drive the armature only at its normal speed.

Dynamo Adjustable Suspension Link. - With the ordinary rigid type of dynamo suspension link, it is very often found that owing to inaccuracies in erection or the effects of vibration and wear during years of service, the dynamo is suspended out of alignment (with its armature not parallel to the axle of the wheel from which it is driven), consequently the belt does not run in the centre of the pulleys. This causes extra wear on the edge of the belt (as it will run towards one side of the pulley), decreasing its efficiency and life.

An Improved Adjustable Suspension Link has therefore been designed to permit of readily lining up the dynamo shaft parallel to the axle from which it is driven (see Fig. 2); one of the two holes in the link for the pin which passes through dynamo lug is made larger than the pin, and an adjustable plate added outside the link. This plate has a hole closely fitting the pin so that when the plate is moved towards or away from the carriage axle, by means of its adjusting screw the dynamo suspension pin is correspondingly moved at one end, thus swinging the dynamo round slightly in the desired direction.

Auto Cut-in Switch. - When the train starts and attains the requisite speed, the rising voltage of the dynamo energises the lifting, or shunt coil of, the cut-in switch, through terminals +D and -D (Fig. 3), which thereupon lifts the plunger, making connection between terminals +D and R1, through the series coil of the switch, and connects the dynamo to the accumulators. Up to this point there has been a connection between R1 and R2 through the short circuiting brush at the top, so that this first action of the switch has in effect joined up +D to R2 as well as to R1, and through these terminals the dynamo, when first connected to the accumulators, supplies part of the Iighting current through one coil of the lamp resistance. At a slightly increased train speed, the plunger of the automatic switch is drawn up right home by the increasing power of the series coil and so breaks the connection between R1 and R2; the dynamo is then directly connected only to R1, and part of the current from the dynamo goes direct to the charging battery and the remainder to the lamps, through the coils of the lamp resistance.

As the dynamo current continues to rise with the increasing speed of the train, more current will pass through the resistance coils and gradually relieve the regulating battery which thereafter acts as a balancer to steady the lamp voltage and keep it constant.

Functional diagram

The Lamp Resistance, which is an important accessory of the dynamo, is so proportioned that when the dynamo is making its normal full output the greater part of the lamp current is derived from the dynamo and passes through the lamp resistance. The regulating battery which is connected direct to the lamp circuit and controls the lamp voltage should for ideal regulation generally be allowed to discharge at a low rate, since if it receives a charge from the dynamo there will be a tendency for the lamp voltage to gradually rise rather above normal.

The perfection of lamp voltage regulation obtained by Stone's double battery system under ordinary service conditions is assured by the fact of having one battery always connected directly to the lamp circuit, and this battery, when the dynamo is generating full output, is only called on to discharge at a low rate; therefore the normal terminal voltage of the battery (and consequently the lamp voltage) is consistently maintained, and while the regulating battery does not receive any charge from the dynamo there is no tendency to rise in voltage. When the train stops the two batteries are connected in parallel by the operation of the top contact of the automatic cut-in--and-out switch, which short circuits the greater part of the lamp resistance, leaving only a short element of resistance between the two battery positive terminals.

The "Pegoud" Battery Change-over Switch reverses the relative functions of the two batteries each time the dynamo "cuts-in" again after a stop, connecting the recently charged battery direct to the lamps. Thus, during a long journey, each battery in turn for a comparatively short time serves as the regulating battery, ensuring uniformity of lamp voltage. When the lamps are turned off at the main switch, the two batteries are by the same action coupled in parallel so that both are then charged equally.

Main Switch: There are two principal classes of main controlling switches, one for use on the outside of a coach, and the other for interior use in corridor and saloon coaches etc. The standard controlling switches have contacts provided for switching on half or full lights, and controlling the half and full light resistances, and either may be fitted with extra contacts to short circuit the lamp resistance when the lights are off.