I want to create some power districts on my DCC layout and protect them with circuit breakers.
But, I would also like to install a kill switch for each power district so that I can shut off power to the district when not in use. Would a SPST toggle switch suffice? I struggle to understand the difference between a SPST and a SPDT. Would a SPDT toggle switch be appropriate to use in this situation?
What is the difference between a SPST and a SPDT and what are the circumstances in which one or the other would be used?
Thanks.
Rich
Alton Junction
Makes not a bit of difference, really. Kill one rail and the track is dead. Kill both rails, and the track is dead. it just seems 'better' to me to kill both, but is definitely isn;t necessary or even really measurably 'better'
SPDT sometimes can be harder to find, but you can use a DPDT (the kind without a center off) and it's the same thing. In fact you could wire an LED and resistor to the 'unused' pole od the DPDT so that when you turn the track off, it lights up.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy, thanks so much for that information.
I do have a bunch of DPDT switches on hand, and I would like to use a red/green LED to indicate power ON (green) and OFF (red) with that kill switch.
SPST, single pole single throw, light wall switch in your house,two term. one on top, one on btm.
SPDT, single pole double throw, similar to a 3-way switch in your house, four term. two on top, two on btm. When using a SPST for power districts, you kill the power to one rail, one rail insulated. SPDT, you kill power to both rails, + and-, both rails insulated. I prefer both rails dead. Especially on a all DC block control layout.
Frank
zstripe SPDT, single pole double throw, similar to a 3-way switch in your house, four term. two on top, two on btm.
SPDT, single pole double throw, similar to a 3-way switch in your house, four term. two on top, two on btm.
That is a bit confusing though Frank, since a household 3-way switch only has 3 terminals, not four like a conventional SPDT.
zstripe SPDT, single pole double throw, similar to a 3-way switch in your house, four term. two on top, two on btm. When using a SPST for power districts, you kill the power to one rail, one rail insulated. SPDT, you kill power to both rails, + and-, both rails insulated. I prefer both rails dead. Especially on a all DC block control layout. Frank
You have described a DPST. A SPDT switch would have 3 terminals. Single Pole Double throw. One circuit that can be thrown to two different outputs. A ST is on or off.
Dave
Lackawanna Route of the Phoebe Snow
I said similar to a three way switch. Half of the switch is controlling two poles.
How would I wire a DPDT so that ON kills power to both rails and OFF routes power to both rails while, at the same time, ON lights a bi-polar LED red to indicate no track power and OFF lights the same bi-polar LED green to indicate track power.
With a DPDT you could connect the track and a green LED with resistor to one pole, and a red LED with resistor to the other pole, so when track power is ON, the green LED is also on, and when track power is off, the red LED is on. With DCC you can finagle this with diodes to use a single red/green bicolor LED with 2 or 3 leads. The 3 lead bicolor LED makes it more obvious since there is a 'common' for the LED, but it would work the same with a 2 lead bi-color LED.
Randy, would you have the time to diagram that DPDT arrangement for me?
It is not that I am lazy, it is more about lacking the electronics skill level to diagram it myself.
Phobe Vet,
That's what I meant, but not what I typed.
Stand Corrected.
Edit: Info for anyone who may need it:
http://www.learningaboutelectronics.com/Articles/Toggle-switch-wiring.php
We all have brain cramps from time to time. It seems to happen more often as time advances. There was no judgement in my correction.
This would be how you would wire a DPDT switch to turn a single rail on/off and have corresponding red/green lighting to indicate such ....
One pole is used for the lights and one pole is used for the track. IF you want to kill the power to both rails, you would need a 3PDT switch. It would have another set of three contacts that you would wire identical as above for the other rail ....
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
There is so much mis-information in terminology in this thread !
Poles refer to the number of individual sets of contacts in the switch. SP (single pole) has one set of usable contacts. DP has two individual separate sets of contacts, 3P - three sets, etc.
ST (single throw) means the switch is either on or off. DT (double throw) means the switch is on or on selecting between two different outputs through a common input. A variance on this could also include CO (center off) where the switch actually has three positions - on/off/on.
The typical light switch in your house is a SPST, meaning it has one wire in, one wire out and that connection is either on or off.
A two way light switch is a SPDT, meaning power comes in at one point and can go out at two different points depending which way the switch is thrown. In either position, the switch is electrically termed to be "on".
Can some one help me to understand how to add a dcc decoder to a IHC mountain type engine. Where I am stump, is what to do with the wire connection that come with the engine?
Mark R. This would be how you would wire a DPDT switch to turn a single rail on/off and have corresponding red/green lighting to indicate such ....
Mark, thanks so much for your help. I very much appreciate it.
I'll see if I can draw one (not from now knowing how, but from having a decent drawing program for things like this) using a bi-color LED driven from track power. You can do a single rail with the bicolor LED using a SPDT switch, or both rails with a DPDT, no need for the extra pole just to operate the LED. The key is that a 2 lead bi-color LED is two LEDs back to back - so when the current flows one way, the green lights, when it goes the other way, the red lights. Cheap lower power diodes will block one half of the DCC signal or the other, which means only the red or green LED inside will light.