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Maker Pro

Non Electrical person needs help!!

M

Muggs

Jan 1, 1970
0
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
 
S

SQLit

Jan 1, 1970
0
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

Center brake would be just another set of contacts on your switch. Closed
when in the center position. As for the braking your going to have to
provide that else where in your design. I have seen brakes mounted
externally on motors like elevator motors.
 
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.
 
N

Nukie Poo

Jan 1, 1970
0
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.

I think you guys missed the "dynamic braking" part mentioned by the OP
Dynamic braking is where the motor itself is used as a brake using back EMF.
We would need to know more about the type of motor used in order to give any
advice
about dynamic braking circuits. As an interesting aside, AMF 8230/70/90/XL
bowling
pinspotters all use squirel-cage induction motors and dynamic braking.
BTW, this kind of braking
will stop a large motor dead real fast, but has no holding power once
stopped. I posted a schematic of such on
alt.binaries.schematic.electronics if interested.

Also, I've seen other motors that have a separate winding that gets DC
injected for braking.
 
M

Muggs

Jan 1, 1970
0
Thanks guys,

Yes Nukie, that's exactly what I'm talking about, just like your Makita,
DeWalt "chop" saw, when you release the trigger the motor comes to
screaching halt.

What I should have probably mentioned is I will be using a 24V DC motor, and
from what I understand, I can brake this by removing power to the motor and
shorting the... Armature?

What I want to use is a simple DPDT rocker switch, so if someone could
explain to me how to wire up the switch I would be very greatful.

Muggs
 
Muggs said:
Thanks guys,

Yes Nukie, that's exactly what I'm talking about, just like your Makita,
DeWalt "chop" saw, when you release the trigger the motor comes to
screaching halt.

What I should have probably mentioned is I will be using a 24V DC motor, and
from what I understand, I can brake this by removing power to the motor and
shorting the... Armature?

What I want to use is a simple DPDT rocker switch, so if someone could
explain to me how to wire up the switch I would be very greatful.

Muggs

Assuming a simple DC motor, directly connected to the
supply (no electronics H drive or whatever) :


C--------x--Motor-y--+
/ |
Pos------0 0------Neg |
|
Neg------0 0------Pos |
\ |
C--------------------+

That's a DPDT switch, giving you direction reversal,
but no dynamic braking. Without additional components,
you can't get direction reversal and dynamic braking
with a DPDT switch. To get dynamic braking, you need
to provide a path across the motor - points z and y.
You can add a relay to do that. The coil of the relay
is wired to the points labeled C. You wire a closed
relay point and its operating point to the points
labeled x and y.
 
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