Switch terminology?

[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).

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

 

[Esther & Fester Bestertester]

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]

No momentary contacts.

FBt

 

[Lord Garth]

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

You're partially correct re SPDT excepting that if it has a center off
position,
the switch would be labeled as such. Example: Single Pole Double Throw
center off.

The poles are the armature or internal moving portion and a throw is the
non-moving contactor that receive a pole.

 

[Lord Garth]

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

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]

The poles are the armature or internal moving portion and a throw is the

non-moving contactor that receive a pole.

So the term "throw" has nothing to do with the positions, or "stops" that you
go through when moving the actuator (handle)?

FBt

 

[Lord Garth]

So the term "throw" has nothing to do with the positions, or "stops" that you
go through when moving the actuator (handle)?

FBt

The throw has only to do with the number of positions where the pole can
complete a circuit. The off positions are not counted.

 

[Homer J Simpson]

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).

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.

 

[Esther & Fester Bestertester]

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.

 

[Lord Garth]

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.

That would be a rotary switch turned on its side!

 

[Esther & Fester Bestertester]

You are describing SPDT center off.

If I want:
on - on - on

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

2P3T?

 

[Lord Garth]

If I want:
on - on - on

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

2P3T?

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.

 

[Eeyore]

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.

They're fabulously rare. Old style telephone swiches used to be able to do that.
Check out http://www.switchcraft.com/

Graham

 

[Esther & Fester Bestertester]

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

 

[Lord Garth]

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

12v motor pulls 2-4 amps.

Suggestions?

Thanks,
FBt

You'll need a pulse width modulator to control the motor speed yet maintain
good
torque. There are ways to create such a modulator with an LM555 timer IC.
You
use it output to control a power FET.

FDB603AL is such a FET and I found this one on an otherwise dead
motherboard.
It is rated to handle 33A at 30V with a Vgs of 4.5 volts and having a
Rds(on) of .036 ohms
http://www.ortodoxism.ro/datasheets/fairchild/FDB603AL.pdf

I'll drop copy of a modulator that ran in Electronics Design onto
alt.binaries.schematics.electronic

it's a Word doc...

 

[Homer J Simpson]

If I want:
on - on - on

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

2P3T?

Yes.

 

[Homer J Simpson]

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

12v motor pulls 2-4 amps.

Suggestions?

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

 

[Phil Allison]

"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).

** Nope.

SPDT = single pole, change over

3 pos switches are specified as such.




......... Phil

 

[ehsjr]

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

12v motor pulls 2-4 amps.

Suggestions?

Thanks,
FBt

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

 

[Esther & Fester Bestertester]

You'll need a pulse width modulator to control the motor speed yet maintain

good torque. There are ways to create such a modulator with an LM555
timer IC. You use it output to control a power FET.

FDB603AL is such a FET and I found this one on an otherwise dead
motherboard. It is rated to handle 33A at 30V with a Vgs of 4.5 volts
and having a Rds(on) of .036 ohms
http://www.ortodoxism.ro/datasheets/fairchild/FDB603AL.pdf

Pretty nice specs for a $1 part, especially the Rds(on). What did it power on
the moboard?

I'll drop copy of a modulator that ran in Electronics Design onto
alt.binaries.schematics.electronic

Thanks. Without doing all the math, what R & C values would you recommend?

I found a near-identical circuit here:

http://www.discovercircuits.com/PDF-FILES/SIMPLEPWM2.pdf

Any idea what function the diodes connecting to the pwm adjustment pot
perform?

Thanks again.

FBt