--- In z_scale@y..., "cwsanger72" <cwsanger@h...> wrote:
> I am planning out making my own briefcase layout, but I am not sure
> how to do the power supply that runs off the 9 volt battery.
--- In z_scale@y..., "jmac_han" <jmac_han@y...>
> You're in luck, CW. Jeremy Brandon, of Joerger Systems, has just
> introduced an IC circuit that allows extraordinary slow speed
> from a 9 volt battery. The unit is designed to fit inside the
> Marklin 9v battery pack but I'm sure that you could easily find a
> to use it for your project.
> Perhaps Jeremy could explain how to adapt it to your needs. The 9v
> controller is available from Ztrack Magazine. ztrack @ aol.com
--- In z_scale@y..., John Cubbin <jcubbin@o...>
> Here's another approach for using a 9V battery as your power supply:
When we are talking about powering a layout just from a 9 volt block
battery, there seem to be three possibilities:
(1) use a 50 ohm rheostat (at least 4 watt); this produces pure/flat
DC whose level fluctuates with the load on the motor (unregulated);
it has no short-circuit protection.
(2) use the voltage regulator circuit described in the link given by
John Cubbin; this produces pure/flat DC whose level is set precisely
by the speed control (regulated); it has very good built-in short-
(3) use the unit I produce for System Joerger; this produces full
voltage pulses at 50 per second whose width depends on the speed
control; it uses a current-limiting circuit for short-circuit
For unavoidable physical reasons, (1) and (2) do not give very good
slow-running performance for many locos: as the speed control is
increased, the motor will not start until a certain critical voltage
has been reached, and then it runs fairly fast; reducing the speed
control slows the motor until a second critical voltage is reached,
then it stops. These two critical points are different for each
motor. (2) gives better performance than (1).
(3) is designed for good slow-running: as the speed control is
increased, the motor starts to turn when a certain critical pulse
width is reached (the minimum movement is "half-a-pole"), and then
turns that much at every pulse - for a 5-pole motor, 1/10 turn 50
times per second gives 5 turns per second, then through the 25:1
reduction gear means the driving wheels take 5 seconds to turn once.
As the speed control is further increased, the wider pulses turn the
motor more each time until eventually a "flywheel" mode is reached
when the momentum of the motor keeps it turning between the pulses.
Only flywheel mode is sustainable by pure/flat DC.
I have emphasised short-circuit protection because even 9 volt block
batteries can generate considerable heat when short circuited,
certainly enough to damage the plastic battery container. Fortunately
in extreme cases the battery is quickly discharged and the danger
passes. However, if a "stronger" power source is used - a mains
adapter or lead-acid accumulator for example - short-circuit
protection becomes crucial. An unprotected layout could even catch on
fire because of a short-circuit. For this reason, I do not recommend
(1) or (3) with any power source other than the 9 volt block battery.
I have designed a version of my controller specifically for briefcase
layouts and suitable for use with "stronger" power sources. It is a
small circuit board built on a standard potentiometer. The
potentiometer has a switch for turning the power on and off. The
circuit has full short-circuit protection using a positive
temperature coefficient resistor, and an appropriate capacitor for
suppressing high frequency signals from the track. It will be
available either from System Joerger or from Noch. A picture of the
prototype is here:
I hope this helps. Jeremy.