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THE TRANSISTOR THROTTLES I USE

Updated July 2017




Despite having taught Systems and Technology, I do not feel that I could hold a candle to many of my peers in the electronics field. The basis of this design came from an Australian Model Railway Magazine about 1979. Although it was portrayed as an N scale throttle, I have had little problem using it for many of the locomotives I have had over the years although it does not like the higher current drawing motors such as Mantua's open frame types nor does it like locos with DCC chips running on DC. It is based on a 2N3055 type transistor and  have built it as a stand alone and as a walk around throttle for main line and switching/shunting.

You might like to change some of the values such as the capacitor and brake resistor for the inertia to suit as I like to have a fairly long braking sequence but in essence it should work well.










HOW IT WORKS

The Main throttle VR1 is fed by two variable resistors VR3 and VR4. VR4 sets the Minimum speed of your throttle control while VR3 allows you to set your maximum speed.

C2 filters the control of your circuit but your supply to the track is unfiltered and maximises your motor performance. The Minimum speed provides a "bleed" of power to the inertia capacitor so your starting is fairly instantaneous. You should get a very good pulsing effect but ensure that you have capacitor C3 in place or you may be disappointed in the output

When your throttle is turned off, your inertia capacitor will take over and start discharging through the base of TR1 and the brake VR2.

The "Braking effort"/ coasting distance can be increased/decreased by turning VR2 and bringing the train to a stop earlier.

Some people I know substitute a Resistor for VR2 and a push button  which could lead to an infinite slowdown time for the train... that is your choice!

Adjusting your throttle speeds

When first setting your throttle, turn your inertia switch (S1) OFF. Move your main throttle from its minimum speed setting about 60 degrees (I prefer to refer to it as 2 o'clock as I start with it in the 12 o'clock position) then adjust VR4 so that your light engine will just begin to move.

Then set your throttle to its maximum speed and use VR3 to set your throttles maximum speed or the desired maximum speed for your layout. This will enable you to use most of your throttle to control your train speed and provide a bit of insurance against those who want to run a train like a slot car! This is especially handy if you have a switching layout and want refined control

PARTS


VR1 BRAKING CONTROL

50 KILO OHM POTENTIOMETER

C3 FILTER CAPACITOR

220 UF 40WV CAPACITOR


VR2 BRAKING CONTROL

200 KILO OHM POTENTIOMETER

R1

560 OHM RESISTOR


VR3 & VR4 UPPER/LOWER SPEED CONTROLS

5 KILO OHM POTENTIOMETER

R2

15K OHM RESISTOR

S1& S2

SINGLE POLE SINGLE THROW ON/OFF SW

D1 AND D2

1N4004 DIODES

S3 REVERSE SWITCH

DOUBLE POLE DOUBLE THROW SWITCH

TR1

BFY50 or BC337 NPN Transistor

C1 INERTIA CAPACITOR

1000 UF 30WV CAPACITOR

TR2

2N3055 NPN TRANSISTOR

C2 FILTER CAPACITOR

470 UF 30WV CAPACITOR

POWER SUPPLY

24-30VAC 2A WITH RECTIFIER


BUILDING THE THROTTLE CIRCUIT I USE