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.
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
No momentary contacts.
FBt
positions.
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.
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 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.
would
That would be a rotary switch turned on its side!
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.
They're fabulously rare. Old style telephone swiches used to be able to do that. Check out
Graham
Small DC motor speed control. Switching resistors or diodes or...? to provide several speed choices.
12v motor pulls 2-4 amps.Suggestions?
Thanks, FBt
Yes.
What sort of load? If your budget permits, a KB controller is a good choice.
Battery DC to DC: KBBC-24M 12/24 VDC, thru 40 Amps Continuous
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
Yes, but double-throw can also be on-on ; it depends if it has a stop (detent) in the middle for the off position.
What, you worry? ;-P
This might help visualize switch terminology:
Good Luck! Rich
Look for "DP3T" - double-pole, three-throw.
Good Luck! Rich
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