Muggs said:
Hello All,
I wonder if someone would be kind enough to help me.
I am a designer with limited electrical experience, and I am makeing a
prototype which I need to have a switch do some dynamic braking.
What I would live to have is a rocker switch for UP/DOWN and when in the
center BRAKE.
If this is at all possible I surely would love the help, however if I'm
totally nuts (and I accecpt that I might be), please let me know.
TIA,
Muggs
You're not nuts at all. It's a simple circuit to do with
relays. Choose relays whose contacts are rated to carry
the current & voltage that your Up, Down, and Brake loads
require. See the first three diagrams and descriptions below.
(There are more diagrams after the second, but you do not
need them if you use double pole relays, and it's simpler
to understand.)
Switch wiring diagram:
Switch
Ground---A_RelayCoil----A C B-----B_RelayCoil---Ground
|
Positive-------------------+
Relay Point wiring diagram:
A B
Ground----UP---0 0-----+----0 0----Down----Ground
|
Positive---------------+
The rocker switch is double throw, center off. I've drawn it
above with an A side and a B side. Polarity does not matter -
I show it as ground (negative) connected directly to the relays,
and plus connected to the relays via the switch. You could also
use AC instead of DC, if you chose AC relays. The center (common)
contact goes to positive at the voltage source.
The relay wiring diagram shows the open and the common points
of relay A and B contacts as 0 0 When the corresponding relay
is energized there will be a path between the contacts, like
this: 0-0
See the diagram below for the following description:
A second set of contacts on each relay is used for the
brake. The closed point of the A side relay is
wired in series with the closed point of the B side
relay and then to the BRAKE, like this:
A B
Ground----Brake----0-0----------0-0-----Positive
As shown, both relays are de-energized, and there is a path
for positive to the Brake.
When either the A relay or the B relay is energized,
there is no connection through the closed point,
which is shown as 0-0 above. When the relay is
energized, the diagram looks like this 0 0 - there
is no connection from the common to the closed
point.
For the sake of completeness, I'll draw diagrams below
that show using only 1 set of points at each relay.
A_Relay B_Relay
Ground------Up---0 N--------C 0--Down---Ground
/ \
Positive----------C N---Brake---Ground
The contacts consist of a Common point C, Open point O,
and a closed point N. The line to point C can connect
either N to C or O to C, on either relay. The circuit
is shown with both relays de-energized - you can see
the path for positive to get to the Brake. The next
diagram shows the A relay energized.
A_Relay B_Relay
Ground------Up---0 N--------C 0--Down---Ground
\ \
Positive-----------C N---Brake---Ground
Note that with the A relay energized, there is a path for
positive to get to Up, but it has no path to get to
Down or Brake. The final diagram below shows the
B relay energized.
A_Relay B_Relay
Ground------Up---0 N--------C--0--Down---Ground
/
Positive----------C N---Brake---Ground
Note that with the B relay energized, there is a path
for positive to Down, but there is no path for positive
to Brake. Note also that the switch makes it impossible
for both relay A and B to be energized at the same time,
but that is shown in the first diagram, not this one.