Multi Range PARMA controller:
You can convert a standard PARMA controllers to Twin Range with one 180 Ohm 3W+ resistor in parallel with the Parma resistor and one On/Off 5Amp toggle switch. 60 Ohm becomes 60/45 Ohm, or a 45 Ohm becomes 45/36 Ohm.
You can also convert to a three range model : For this you need to use one On/Off/On 5Amp toggle switch and two resistors as shown in the diagram (60/44/32 Ohm or italics: 45/35/26 Ohm)
NB2: The parallel link to the Parma resistor is the small tag (max resistance) next to the brake.
NB3: With the switch in the off position you will have a standard controller.
NB4: When using the parallel resistors the values are given as the combined max. resistance, and in parallel will give a small none linear effect of around 10% at 1/5 value (most drivers will not notice this).
NB5: Fit switch on narrow rear side above the handle so that the controller lays flat without damaging the switch.
NB6: For a 3 range use a 68 ohm 6W and 100 ohm 3W+ resistors to make up the correct values.
POWER LIMITING WITH A CONTROLLER:
You can add two additional power(voltage) limiting settings to Parma controllers, by using one On/Off/On 5Amp toggle switch and, 8 diodes (or 2 x 6.8 ohm 3W resistors) as a series connection in the power line (Pin P+). As they are carring the full current (more heat to dissipate), I recommend the use of 3 Amp Diodes to give a more consistent voltage control, in place of the resistors were voltage reduction is more affected by current. At around 0.4Amps voltage drop is approx. 1.5v and 3 v for each parallel pairs of diodes, so you need to connect 8 diodes in groups of 4 as shown as this will allow for any track were the voltage is reversed.
NB: If you use 1A diodes, you risk blowing them under extreme conditions, and 3A give better heat dissipation.
Full power / -1.2 / -2.4v resistor Power limit.
Full power / -1.5 / -3 v Diode Power limit
VARIABLE BREAK and POWER LIMITING mkIIA
At Oxford and Banbury clubs we have developed this box over the past 12 months as a means of reducing the supplied voltage for use with SlotRally and to allow younger children to build up their skills on a wide range of fixed voltage club layouts. The requirement was for a unit that would fit within the footprint of a club 3 pin 2 Amp socket for 1/32 scale cars (Ninco, NSR etc), work inline with an independent plug in controller, be compatible with forward or reversed power tracks, and provide brake adjustment.
The mkIIA box now has the following specification:
VOLTS can be switched between FULL volts, nominally -0.7v, or ADJUSTABLE(6) -1.5 to -5.2v, pairs of reversed parallel diodes allow use with normal or a reversed power supply. A GREEN LED indicates normal, or RED reversed supply (if RED not suitable for most electronic controllers), both LED’s off indicates braking not available pin E NOT connected, or NO power.
The BRAKE can be switched between FULL BRAKE, or NO BRAKE, or ADJUSTABLE reduction with 6 resistances of 1, 2, 3.5, 5.7 , 9, 16 Ohms.
The 3.5 Socket allows for a Volt meter, or an alternative Scalextric Controller to be connected.
The MDF backing can act as a locator and allows air flow for cooling.
In response to the interest shown in our inline box we have published the design with images of construction for any one to use and build or have built. The parts cost around £25 from High Street suppliers, or cheaper if purchased through the trade in bulk to build a batch of units.
NB: Only suitable for 1/32 and NOT 1/24 scale cars, also do not be tempted to use 1 Amp diodes, or single pole 12 way rotary switches for more settings as this reduces the power capacity.
NB: The latest box design now has a 3.1 Amp slow blow replaceable fuse on the power line pin 'P'.
Parts List:
2 Amp three pin plug - 2 Amp three pin socket - 25mm 1 gang pattress box
0.5M 3amp 3 core flexible cable (single cores can be used for internal wiring)
3 Watt wire wound resistors - 1 Ohm x 2 : 1.5 Ohm : 2.2 Ohm : 3.3 Ohm : 6.8 Ohm
3 Amp Diodes (1n5401) x 14
2 Pole 6 way Rotary switch x 2 + 15mm Knobs x 2 (shafts need to be cut to length for Knobs)
Toggle switches x 2 (On Off On) 3 Amp minimum
3mm low power Green LED - 3mm low power Red LED - 3.9k 0.25W resistor
11mm back spacer(MDF) cut out for plug
Sundry screws and cable clamp
3.5 Stereo Socket for Scalextric controller (or a Volt Meter with Break on Full setting : Pins E/P = Supply Volts to controller : Pins E/N= Output Volts from controller)
