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POWERING YOUR SWITCHMASTERS
ADJUSTING THE RESISTORS FOR YOUR SUPPLY
A 1200 ohm resistor
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 you.
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 power supplies- as well as other considerations such as your
wiring (small gauge wires going to a machine far far away) and components (old or
"cheap" toggles", adding lamps or LEDs all add to the equation), the work the motor
must do to throw the points, the type and size 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. Consider leverage here too. Is it a short strong
throw or a longer, less powerful stroke. I told you pay attention in high school
shop class, math, physics...
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.
Our #1121 Resistor Test Pack
includes 10 different values of resistors.
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 should probably post the color code for all these but it is included in the test pack.
?POSITIVE / NEGATIVE? MORE OR LESS
It does not matter which motor lead (+ or -) the
resistor is connected to, just so long as it is conneted between the power supply and
motor so it can limit the current.
POWER SUPPLIES
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. These are really
pretty basic machines.
THE AC/DC TRICK
It is possible to use 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 (1N4001) (same as our part #1104) on SPDT toggles to convert the
AC power into direct positive or negative current (DC). Pretty tricky, hun? Not really,
just basic electronics. In our case the power supply is nothing more than an 8-volt
door bell transformer. For these circuits the 1200 ohm resistors was way too much but
we found that 270 ohms was just right.
OTHER POWER TRICKS
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. Thus, if you don't have the particular value you need often
you can build something that has the required value. They did teach you this stuff in
junior high shop class didn't they?
A 470 ohm resistor, as supplied with our LEDs
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 supplied 470 ohm resistor (or as needed) and fine tune
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.
And one last trick.
Say you have a sticky switch or two that always seem to need an extra nudge to get going.
Rather than reaching under the table each time use our part #1140 "Kick Switch" to get it going.
Here in series we are doubling up on the 1200 ohm resistor
(you may have to experiment to find the right value) thus supplying the motor with a lower "holding" voltage.
Press the momentary (on) Kick Switch bridging over one resistor so a higher "moving" voltage through just one
resistor is applied to the motor when you throw the operating toggle. Problem solved.
Yes, it is an extra step each time you throw a turnout but think of the switchman or conductor jumping on
the ground to do the same thing. Employing these will certainly add to the lifespan of your switch machines
especially if you are running them hot.
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