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Author Topic: Question about SPDT Slide Switch with 3 posts  (Read 2135 times)
dchampney

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« on: December 23, 2016, 10:12:52 AM »

I am installing a switch for a heater element on a DC (analog) locomotive.
What is the common post used for with this type of switch?

I am assuming i can just solder to pin 1 and 3 and be done.  Please let me know

http://media.digikey.com/photos/CK%20Comp%20Photos/MFG_JS202011CQN.jpg

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WoundedBear
A Derailed Drag Racer


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« Reply #1 on: December 23, 2016, 11:27:37 AM »

Best to use a multi-meter and sort out what is connected to what internally.

Sid
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mabloodhound


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« Reply #2 on: December 23, 2016, 12:04:28 PM »

Most likely, the center pin is the common (input) and the other ends are output.
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Dave Mason

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jbrock27

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« Reply #3 on: December 23, 2016, 12:56:47 PM »

Are you looking to do just an On/Off?  If so, reason for using SPDT switch?
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jbrock27

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« Reply #4 on: December 23, 2016, 01:08:58 PM »

PS: and would this be for the loco you had melt on you?
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richiy
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« Reply #5 on: December 23, 2016, 01:10:16 PM »

The picture shows a DPDT.
All you need is a SPST. About the same size but there are smaller.

If that is what you have now, as was said, the center is common but if you dabble in parts like this, a cheap multimeter will suffice.

richiy
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jbrock27

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« Reply #6 on: December 23, 2016, 01:22:29 PM »

a cheap multimeter will suffice

richiy

I am a big fan of the Harbor Freight multi meter you can get for free with a coupon and purchase of any other item.  richiy/G/1998/lexxon has been touting them for years and now I find that I must agree with him.  Not building space ships afterall...
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dchampney

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« Reply #7 on: December 23, 2016, 02:14:56 PM »

Are you looking to do just an On/Off?  If so, reason for using SPDT switch?

because i have one sitting here
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dchampney

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« Reply #8 on: December 23, 2016, 02:15:55 PM »

PS: and would this be for the loco you had melt on you?

NO, i took that one back!

I want to play with an older HO
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jbrock27

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« Reply #9 on: December 23, 2016, 04:44:22 PM »

Well, just bc it is what you have on hand, doesn't make it the "best tool for the job". 
 
Do you have a multi meter?  If not yet, you should.

I would follow richiy/G/1998/lexxon's advice and go with a simple On/Off micro switch instead.

I agree with Sid in that if you are resigned to use that; you need to use the meter to see which legs of the switch you have there, do what.

I also agree with bloodhound in that is likely you will want to connect to the middle leg (Common) and one of the outside legs for On/Off, but would not do so until I first confirmed the legs will operate the way I want to by doing that.

(BTW, if indeed the middle is the Common, the outside legs can also operate as inputs, depending on how you want to use the switch and how you wire it.  Not sayin that is how you want to use it here but, just sayin Wink).
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James in FL

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« Reply #10 on: December 23, 2016, 07:43:47 PM »

Just some basic electricity 101 here.

Off does not count as a “throw”.

What you appear to want is a SPST switch whereas it’s either on or off.
One input, one output, one wire.
Generally on the + side but will work equally as well as on the - side.
The switch opens the circuit.

A DPDT switch is best used as a switch that reverses polarity, and also has an off position.
That is it's intended function.
They have a two wire input and a four wire output.
              
To use a DPDT switch in a SPST application, you could solder your wire input +  to a top lug, let’s say for example to the right side lug.
Your output will be soldered to the middle lug same orientation, right side, the other four lugs are neglected, and serve no purpose.
Depending on the internals of the switch, you may need a jumper to the other paired lugs (top left to top right and middle left to middle right).
Only the switch in the middle position will work as “on” the top and bottom positions will both be “off”.
Again “off” does not count as a “throw”.

Take @WoundedBear advice and sort it out with your multi-meter.
This is the best way to educate yourself.

My reply was based on @jbrock27 suggestion that the switch can be wired in more than one way to achieve the desired outcome.
He is absolutely correct.
Yes, you also can (should) use the middle as common + and -, and then the middle will be “off” and depending which prongs you solder to (top or bottom) will be “on”.
Middle legs for input is common practice, and is “code” per se, but the switch will still function if you choose to use either top or bottom lugs as input.
The switch doesn't know, or care.
@12VDC it’s not going to hurt anything.
The position not soldered to will always be “off”.

Personally I would purchase a SPST switch which is the correct switch for the job.
We are not talking a lot of money here, 2-3 USD.  
 
A lot less if you shop eBay or Amazon.

Good luck,
« Last Edit: December 23, 2016, 08:36:32 PM by James in FL » Logged
dchampney

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« Reply #11 on: January 02, 2017, 08:59:18 AM »

Or.. Could i use the extra terminal to power an LED indicator?
obviously i can  try outside the train with a 9v battery and a resistor on the led

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jbrock27

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« Reply #12 on: January 02, 2017, 12:12:29 PM »

Which extra terminal exactly, are you asking about?
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WoundedBear
A Derailed Drag Racer


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« Reply #13 on: January 02, 2017, 12:32:09 PM »

Something tells me the OP still hasn't used the multi-meter to figure out what is connected to what.....and when.  Roll Eyes

Sid
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tiebreaker

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« Reply #14 on: January 02, 2017, 12:48:36 PM »

I save those on/off switches from kids toys and those cheap ornamental pieces of garbage that has the 4 AA batteries in them. Perfect for making separate on/off switches for lighting the layout. Quickly hidden by a shrub or in this case under the cab roof. Just incase you can not run out and get the correct switch.

like this one, when they go bad just break it open and remove the switch
https://www.seeedstudio.com/2-x-AA-Battery-Holder-with-On%26amp%3BOff-Switch-and-Slider-Cover-p-1138.html#
« Last Edit: January 02, 2017, 12:52:30 PM by tiebreaker » Logged
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