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POWERING YOUR SWITCHMASTERS
ADJUSTING THE RESISTORS FOR YOUR SITUATION
After reading the instructions consider the
following...
While a 1200 ohm resistor is supplied with
your SwitchMaster it may or may not be the right one for your installation.
In most cases we've found 1200 ohms is about
right for the typical power pack auxiliary supply. While these are often labeled
as 12 Vdc sometimes the power coming out of them is 18, 20 or more volts! 1.2k is
on the safe side. If your motor runs too fast or slow, or not at all, changing the
value of the resistor is indicated. There are so many variations from old to new,
cheap, or expensive- as well as other considerations such as your wiring (small
gauge wires going to a machine far far away) and components (old "cheap" toggles",
adding lamps or LEDs all add to the equation), the work the motor must do to throw \
the points, the scale of the turnout, and so on. So a little tweaking might be
necessary.
Beside replacing the power supply with a higher
or lower output consider changing the value of the resistors. If your turnouts are for
the smaller scales you'll likely want to turn the power down more than the larger
scales that might need more oomph.
Or maybe you have a switch in a difficult
location that requires a bell crank or other mechanical linkage that will require
more power than your other turnouts. This might mean that you'll want to change
the resistor for just this one particular motor.
We'll make this easy for you by offering a
set of 10 different resistors, our Part #1121. Use them to determine which value
is right for you. In general, once you find the right value for your set-up all
the others should follow suit. We can do this by trail and error. If the motor is
too fast that means your power supply is putting out lots of voltage. Try one of
the higher values (1.5K or 2.0K). If the motor is running slowly or not easily
starting let's try one of the middle values (1.0K, 680, 390). If your power supply
is weak then try one of the lower values (330, 270, 220). For instance, with one
power supply we tried the 1200 ohm resistor was just too much. The motor didn't
move at all. By trying different resistors we figured out 680 ohm resistor was right
for the circuit. On another power supply 1200 ohms was the right value on the same
circuit. If none of these ten resistors works then it's time to try another power
supply.
We don't sell power supplies because they are
readily available at a better price than we could offer. Besides, most model railroaders
have one or two extras lying around or could snag one at the next swap meet for next
to nothing. Old computer power supplies offer 12 Vdc, too. Who doesn't have an
extra one of those in the closet? A wall wart will also do the trick.
On another application we are actually using
alternating current (ac) to operate our switch machines. We know, we warned you
not to do that. Well, yes, we did, but we rectified the ac using diodes on SPDT
toggles to convert the ac power into direct positive or negative current. Pretty
tricky, hun? Not really, just simple electronics. The power supply is nothing more
than an 8-volt door bell transformer. For these circuits the 1200 ohm resistors was
way too much and we found that 270 ohms was just right.
Okay, if you don't have a package of assorted
resistors in hand there are some tricks you can try. If you take two 1200 ohm resistors
and tie them together in parallel (side-by-side) the result will be 600 ohms. Tie
three together and you get 400 ohms. Tie four and it's 300. The current has four
ways to travel. So it's one forth of 1200 ohms. Take two 1200 ohm resistors
and tie them together in series (nose-to-tail) and you get 2400 ohms. It's twice
as hard to pass through. You can also mix them up, for example with two tied in parallel
(600 ohms) and those in series with one by itself to get 1800 ohms. Thus, if you don't
have the particular value you need often you can build something that has the required
value.
A potentiometer is also available. Our part #1132.
It's an adjustable resistor. By turning the thumbwheel we can adjust the resistance
from 0-1000 ohms. We'll suggest you do what we have just talked about, tying the
potentiometer in parallel with the 1200 ohm resistor (or as needed) and fine tuning
the circuit with the adjustable potentiometer. We've found this very useful for
those one or two motors that might have a little more (or less) work to do than the
others.
CCC
Figure A Installed Motor
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