A stupid relay question.

[SVSooke]

Is there a difference between a "change over" relay like this one http://www.ebay.ca/itm/CAR-AUTO-AUTO...item48487bb0a8
and a SPST like this? http://www.ebay.ca/itm/Car-Automotiv...item3cc5bcdb07

[BlackStar]

The first one is SPST and looks to have only NC normally closed contacts (closed when not energized). I cant tell if the second one's contacts are NC.

Do you need NC or NO contacts. I don't think I missed it, but you would think the ad would state what you are getting (NC or NO)

I usually just buy the SPDT relays and wire to what I need.
Like this.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=330-073

[trippivot]

those appear to be the same

common simple relays are 2 types 4 pin and 5 pin 85-86 are the power contacts and can be either polarity not specific but positive and negative.

a 4 pin is normally open between 2 of the contacts and closed when energized. 87 and 30 are the open and closing contacts

a 5 pin do both Normally open and normally cloesd when energized. and control 2 things at once

there is some debate to the resilliance of relays according to the resistance of the primary coil. 800 ohm seem to be the tough ones.

BOSCH brand -- like a chevrolet caviller lighting relay

[SVSooke]

Sorry,I didn't think to say what I was thinking of doing till after I posted and logged off.To be used for a horn relay so I would need a normally open relay

[tkent02]

Some (most) of these relays have both NO and NC contacts, you can go either way.

[Redman]

To somewhat repeat what others have said:
By change over they mean the there is a Normally Closed contact and a Normally Open contact, and when the coil is powered the normally closed contact opens and the normally open contact closes, I quess someone thought that was "changing over".

SPST: Single pole single throw. Means will be two terminals (in addition to the coil). Typically NO but could be NC.

SPDT: Single Pole double through. Means will be 3 terminals, a common and the NO and the NC. This could be concidered a "change over" I guess.

DPDT: Douple pole double through. Means will be 4 terminals, two for one set of contacts and two for other set of contacts. Each set of contacts could be NO or could be NC.