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To make an ARLTC to control a Tortoise or other stall motor machine, you'll need a DPDT relay, two bridge rectifiers (or 8 diodes), two diodes, and possibly a resistor. Making one for twin-coil machines is more difficult. It would be much easier to switch to a stall motor machine if having an automatic reverse loop is your goal. If you can find a DPDT relay that works with AC voltage, you can eliminate the need for one bridge rectifier. However, these are hard to find. And if you can't find a relay that operates with the voltage provided from the track power bus, you'll need an appropriate resistor. The value you'll need will depend on three things: your track voltage, the voltage needed by the relay, and the amount of current drawn by the relay's operating coil. We'll break the wiring down into two sections: relay actuation, and turnout motor wiring |
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| Relay Actuation |
The way this works is based on
the fact that only one portal is powered at a time - the other portal
is in the detection mode with no power applied. Wire the relay actuating
coil to one portal or the other - it doesn't matter which. When polarity
of the reverse section is one way, the portal will be powered and the
relay will be active. When the polarity is the other way, the portal
will not have power and the relay will relax. |
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If your relay isn't
designed for AC voltage, you'll need a bridge rectifier. If you don't
have a bridge rectifier, you can make one with four diodes, such as
four 1N4001s, as illustrated at left. |
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Because a collapsing
field from the coil will cause Back-EMF that needs to be dissipated,
another diode needs to be add as shown at right. |
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You also have to consider
the relay/track voltage difference. Most relays operate on 5 or 12 volts.
There are others, but aren't as prevalent. All you have to do to cut
the voltage down is add a resistor as shown at left. |
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The more resistance, the lower
the voltage. So if you put a resistor in that keeps the relay from activating,
you need a resistor of lower value. The key is to use a resistor of
low enough value so the relay will operate reliably, but no more. Allowing
too much voltage to the relay coils could damage the coil after some
usage. |
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Turnout Motor Wiring |
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The relay must be a DPDT device. Your relay may or may not have the same pin out as that illustrated here, so you have to go by the pin labels. Note the X between the N.C.
(normally closed) and N.O. (normally closed) terminals - the X does
not connect in the middle where they cross. These wires, which you must
install, are what reverses the polarity for the switch motor when the
relay operates. |
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Since a stall motor uses the polarity
of the power to know which way to go, you must feed DC power of the
voltage needed by the turnout machine you're using. For example, a Tortoise
needs about 12 volts, so 12 volts DC must be fed to the power-in pins. |
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If your power supply
provides AC, you can convert it to DC with another bridge rectifier
of four diodes, as shown at left. Note that when converting normal AC
this way, the voltage will go up - so it's necessary for you to check
the voltage. If the voltage is too high, you can reduce it with a resistor
as you did on the other circuit. |
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You can actually get power from
the track for this. Because DCC track voltage is AC voltage, you have
to use a bridge rectifier, or four diodes. However, because it's "square
wave", you won't get an increase in voltage. But you need to check
the voltage anyway, and use an appropriate resistor if needed. |
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Here we see it all
put together, with portal power entering the bridge rectifier (diodes)
on the right, controlling the relay's coil on the right, power input
for the turnout machine on the left (rectified if needed), and output
to the turnout machine in the middle. |
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