Switch terminology?

  • Thread starter Esther & Fester Bestertes
  • Start date
E

Esther & Fester Bestertes

Guest
Maybe I don't understand switch terminology, but I thought SPST means single
throw (2 positions, ie. on-off) and SPDT means double-throw (3 positions, ie.
on-off-on).

This catalog page show many switches with both terms, but mixing xST with 2-
and 3-positions. Same with xDT term.

<http://tinyurl.com/36petb>

Is my understanding incorrect? Or is this page all screwed up?

FBt
 
BTW, I'm looking for a switch that has 3 pairs of terminals and 3 positions.
Each position connects a pair of terminals together. Rocker preferred.

FBt
 
"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EF09000066D0AF01826C8@news.sf.sbcglobal.net...
BTW, I'm looking for a switch that has 3 pairs of terminals and 3
positions.
Each position connects a pair of terminals together. Rocker preferred.

FBt
Click to expand...
You're going to have to be clearer here, 3 pairs of terminals means 6
terminals.
The assumption being that your signal goes into one terminal and out the
other.

You say you wish to connect pairs of terminals together so your 3 throws
would
connect terminal 1&2 then 3&4 and finally 5&6 for example.

If that is what you desire, a double pole triple throw rotary switch would
work if
you short the two poles together. Rocker switches have only two positions
plus maybe a center off so that would not be a reasonable choice.

Another possibility is that you want two signals (stereo audio perhaps) to
go to
one of 3 destinations. A rotary switch would connect the poles to throw 1
or 2
or 3 for both the left and right signals. This would still be a double pole
triple
throw rotary switch but the poles would not be shorted together.
 
"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EEEAB0005FB58F01826C8@news.sf.sbcglobal.net...

Maybe I don't understand switch terminology, but I thought SPST means
single
throw (2 positions, ie. on-off) and SPDT means double-throw (3 positions,
ie.
on-off-on).
Click to expand...
No, ON---ON.

It's quite possible to have a SPDT switch with no center position - some
microswitches and other sna switches are like that.

You are describing SPDT center off.
 
If that is what you desire, a double pole triple throw rotary switch would
work if you short the two poles together. Rocker switches have only
two positions plus maybe a center off so that would not be a reasonable
choice.
Click to expand...
If rockers can have 3 positions:
on off on

why not:
on on on

each "on" shorting one pair of contacts.

I'm sure I've seen these before... just can't find one now.
 
"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EFD5600096B8EF04886C8@news.sf.sbcglobal.net...
If that is what you desire, a double pole triple throw rotary switch
would
work if you short the two poles together. Rocker switches have only
two positions plus maybe a center off so that would not be a reasonable
choice.

If rockers can have 3 positions:
on off on

why not:
on on on

each "on" shorting one pair of contacts.

I'm sure I've seen these before... just can't find one now.
Click to expand...
That would be a rotary switch turned on its side!
 
You are describing SPDT center off.
Click to expand...
If I want:
on - on - on

double-pole with 3 stops, what switch am I describing now?

2P3T?
 
"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21F0100000A4753F04886C8@news.sf.sbcglobal.net...
You are describing SPDT center off.

If I want:
on - on - on

double-pole with 3 stops, what switch am I describing now?

2P3T?
Click to expand...
Correct...this is most easily done with a rotary switch. Each pole
is a separate wafer attached axially to the shaft.

What is it you are trying to design? Maybe we can suggest some
all electronic ways to switch the signals.
 
Esther & Fester Bestertester wrote:

If that is what you desire, a double pole triple throw rotary switch would
work if you short the two poles together. Rocker switches have only
two positions plus maybe a center off so that would not be a reasonable
choice.

If rockers can have 3 positions:
on off on

why not:
on on on

each "on" shorting one pair of contacts.

I'm sure I've seen these before... just can't find one now.
Click to expand...
They're fabulously rare. Old style telephone swiches used to be able to do that.
Check out http://www.switchcraft.com/

Graham
 
What is it you are trying to design? Maybe we can suggest some
all electronic ways to switch the signals.
Click to expand...
Small DC motor speed control. Switching resistors or diodes or...? to provide
several speed choices.

12v motor pulls 2-4 amps.

Suggestions?

Thanks,
FBt
 
"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21F0100000A4753F04886C8@news.sf.sbcglobal.net...
You are describing SPDT center off.

If I want:
on - on - on

double-pole with 3 stops, what switch am I describing now?

2P3T?
Click to expand...
Yes.
 
"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21F291D0013AE32F01826C8@news.sf.sbcglobal.net...

Small DC motor speed control. Switching resistors or diodes or...? to
provide
several speed choices.

12v motor pulls 2-4 amps.

Suggestions?
Click to expand...
What sort of load? If your budget permits, a KB controller is a good choice.

http://www.kbelectronics.com/

Battery DC to DC: KBBC-24M 12/24 VDC, thru 40 Amps Continuous
 
"Esther & Fester Bestertester"
Maybe I don't understand switch terminology, but I thought SPST means
single
throw (2 positions, ie. on-off) and SPDT means double-throw (3 positions,
ie.
on-off-on).
Click to expand...
** Nope.

SPDT = single pole, change over

3 pos switches are specified as such.




......... Phil
 
Esther & Fester Bestertester wrote:
What is it you are trying to design? Maybe we can suggest some
all electronic ways to switch the signals.


Small DC motor speed control. Switching resistors or diodes or...? to provide
several speed choices.

12v motor pulls 2-4 amps.

Suggestions?

Thanks,
FBt
Click to expand...
One SPDT center off switch. Conceptually:

V+ ---+---[R1]---+---[R2]---+----+
| | | |
| o | |
+--------o-> | [Motor]
o----------+ |
|
Gnd -----------------------------+

Full speed with switch down, slow speed with switch
off, medium speed with switch up.

Realisticly, using resistors has problems. Reduces
torque, and they need to dissipate a *lot* of heat
at 4 amps (I^2R). Instead, use PWM - and then you
can use a pot and get the widest possible range of
speed available, avoid the heat problem, and have
better torque.

If you absolutely cannot use a pot, then you can
still get 3 speeds using the scheme above with
PWM where the resistors select the pulse width.
They won't get hot that way and can be much smaller
wattage.

Ed
 
On Thu, 15 Mar 2007 12:38:03 -0700, Esther & Fester Bestertester wrote:

Maybe I don't understand switch terminology, but I thought SPST means single
throw (2 positions, ie. on-off) and SPDT means double-throw (3 positions, ie.
on-off-on).
Click to expand...

Yes, but double-throw can also be on-on ; it depends if it has a stop
(detent) in the middle for the off position.


This catalog page show many switches with both terms, but mixing xST
with 2- and 3-positions. Same with xDT term.

http://tinyurl.com/36petb

Is my understanding incorrect? Or is this page all screwed up?
Click to expand...

What, you worry? ;-P

This might help visualize switch terminology:
http://www.kpsec.freeuk.com/symbol.htm#switches

Good Luck!
Rich
 
On Thu, 15 Mar 2007 13:40:38 -0700, Esther & Fester Bestertester wrote:

If that is what you desire, a double pole triple throw rotary switch would
work if you short the two poles together. Rocker switches have only
two positions plus maybe a center off so that would not be a reasonable
choice.

If rockers can have 3 positions:
on off on

why not:
on on on

each "on" shorting one pair of contacts.

I'm sure I've seen these before... just can't find one now.
Click to expand...
Look for "DP3T" - double-pole, three-throw.

Good Luck!
Rich
 
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