Quite Possibly The Dumbest Question About Switches Ever

briand · #1 08-29-2007, 04:38 PM

Can someone explain to me how you determine if your application requires a?:

--o/ o-- SPST (2 terminals)

OR

/o--
--o/ SPDT (3 terminals)
o--

OR

/
--o// o--
--o/ o-- DPST (4 terminals)

OR

/o--
--o//o--
--o/ DPDT (6 terminals)
o--
o--

Oh, can you provide some examples that relate to our aeroplanes too. Thanks.

Jim P · #2 08-29-2007, 04:45 PM

Aerolectric Connection has a pretty good section all about switches and examples on how different switches are leveraged in your application. If you don't have this book, it's a great reference.

Jim

MCA · #3 08-29-2007, 05:21 PM

There's a bit of explanation on page 6 of the installation manual, you can find it here http://www.verticalpower.com/documents.html . Also some other documents about connectors and contactors which may be helpful too.

Marc

lrfrey · #4 08-29-2007, 05:32 PM

As Jim said, Aeroelectric has a good explaination, but you can google spst dpdt etc and find it.

For starters, let's understand what the letters mean...

SP = single pole. One switch

DP = double pole. Two switrches, controlled by one handle

ST = Single throw... On or Off

DT = Double throw... On-On or On-Off-On if the handle has a middle position. This would be a switch with 3 terminals, the center (typically) being common. In one position it would connect to one of the end terminals, in the other to the opposite end. In the middle to neither.

Now, by pairing the names, you can get a variety of switches. DPDT for example, is two switches in one, and can be On-On or On-Off-On. Diagrams work well here, sorry I don't have any handy.

Try googeling them

Hope this gets you started.

Larry

RV6_flyer · #5 08-29-2007, 05:34 PM

Quote:

Originally Posted by briand

Can someone explain to me how you determine if your application requires a?:

--o/ o-- SPST (2 terminals)

OR

/o--
--o/ SPDT (3 terminals)
o--

OR

/
--o// o--
--o/ o-- DPST (4 terminals)

OR

/o--
--o//o--
--o/ DPDT (6 terminals)
o--
o--

Oh, can you provide some examples that relate to our aeroplanes too. Thanks.

SPST = Single Pole Single Throw = one circuit on or off

SPDT = Single Pole Double Throw = Can be A On and B Off, A Off and B On, or just On or OFF depending on how it is wired. It has a C - Common terminal, a NO - Normally Open terminal, and a NC - Normally Closed terminal depending on the switch position.

DPST = Double Pole Single Throw = Two circuits that are both on or both off. Like having two SPST switches that have the handle fastened together. A more expensive more capable SPST switch.

DPDT = Double Pole Double Throw = Like having two SPDT switches that have the same handle. Double pole as TWO circuits. Can be wired so that one circuit is on in the up position and off in down but the other circuit is off in up and on in down. There are may nore possibilities than I can write here.

Hope this helps and does not confuse. I may need to put more electrical circuit theory in for you to understand this. I am making an assumption that there is some electrical knowledge going in with the description that I am giving.

N713R · #6 08-29-2007, 08:38 PM

To further muddy the switch waters, there are maintained and momentary switches, and combinations of the like, normally noted with parenthesis.
For example, a DPDT switch might be noted on-off-on where it is maintained in whatever position it is when you let go of the handle. Whereas (on)-off-(on) would be spring loaded to return to center (or off) when you release the handle. Such as a flap switch. There are switches available that are a combination, such as (on)-off-on where one position in momentary, and the other maintained.

Not trying to add trouble, just wanting you to be informed.

briand · #7 08-29-2007, 11:10 PM

I think I get it . For example if you used a SPDT on the flaps there would be no way to reverse polarity (DP) and have an extend and retract, only one or the other. Therefore you must use a DPDT.

Thanks.

So a DPST would be used to turn two things on and off at the same time. Let me just say I don't like that. Everyone knows, the more switches you throw the cooler you look, at least to non pilot passengers.

I'm calling for a VAF wide boycott on all DPST's.

I'll start making signs for Osh 08.

Sorry, I just noticed in my first post the switch schematics got all scrambled.

johnp · #8 08-30-2007, 07:57 AM

Quote:

Originally Posted by briand

So a DPST would be used to turn two things on and off at the same time. Let me just say I don't like that. Everyone knows, the more switches you throw the cooler you look, at least to non pilot passengers.

I'm calling for a VAF wide boycott on all DPST's.

I'll start making signs for Osh 08.

oh, don't do that

you might want to use a dpst in a case where you want to control a high current device and at the same time turn on a low current/voltage annunciator. say you want a fuel pump "on" annunciator, and you want to use an led for the annunciator. you could switch the fuel pump on with one half of the switch, and a low-voltage, low-current led on with the other half. (i know you could use a resistor also, but this is just an illustration to get you started thinking.)

MCA · #9 08-30-2007, 12:13 PM

Another thing... you don't always have to match the switch type exactly to your application. For example, you can use a SPDT switch as a simple on and off switch. There will be an extra terminal, just don't use it. You could also use a DPDT for that too - it'll be bigger than necessay but will work.

This is helpful if you find a specific switch that you like, but it doesn't come in the config you want.

JonathanCook · #10 08-30-2007, 05:11 PM

Here is a link to an excerpt that Bob Nuckolls has on his website about switches. The excerpt gives great detail on switch configurations. The excerpt also graphically shows how simular configurations can differ. Note the entire chapter is 23 pages. I do recommend getting his book, "The AeroElectric Connection."

http://www.aeroelectric.com/articles/switches.pdf