jonlaury
Joined: 06 Nov 2006
Posts: 336
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 Posted: Tue Oct 02, 2007 10:15 am Post subject: Diode sizing |
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In the following schematic, the entire circuit is 12VDC except for the Timer Relay Contact at the bottom which is 120VAC.
How do I size the diodes for the 12 V portions? for the the timer relay, switching 120 VAC, with a 12VDC coil?
/
+ ---+---o o---+------+----------+
| S1 | | |
| | [Relay1] |> | <-Relay
| | | | Contact
| | | +-------+
| / | | | |
+---o o---+--|<--+ | [Motor]
Park D1 | | |
| +---|<--+
| D2 |
| S2 |
Gnd -------------------+---o->o---+--+---> Trigger
| | Signal
Timer Relay Contact-> '-> | | to timer
| |
+------+
How it works: When in the park position, the park switch
and S1 are both open. Pressing S1 energizes Relay 1, its
contact closes, the motor moves and the park switch closes,
keeping Relay1 energized until the mechanism moves back
to park. When the mechanism reaches the S2 position, S2
opens and removes the (-) trigger signal to the timer.
After 30 seconds, the timer relay de-energizes and the
relay contact closes. That causes the motor to run again,
moving away from the S2 position and closing S2. That
sends the (-) trigger signal to the timer which energizes
the timer relay. The mechanism returns to the park position,
which opens the park switch and de-energizes Relay1, and the
motor stops. Diode D1 protects the switches against the
inductive spike created when power is removed from Relay1;
D2 protects against the inductive spike from the motor
when power is removed from it. The timer relay coil should
also have a diode placed across it, wired the same polarity
as the other diodes (banded end connected to the + side).
[quote][b]
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