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Need help on Relays

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t_ang4

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(1) I am doing a circuit involving relay (5V SPST relay). The problem is that I am not sure how to connect the leads. My relay has 5 leads -- 3 on one side and 2 on the other side.

(2) Must i connect a diode across the relay to avoid getting an "inductive kick" ? This is because a transistor is connected to that relay and the "inductive kick" might destroy the transistor.

(3) What does the 5V means (in 5V SPST)? Does it affect the relay if I connect a diode across it?

Attached here is a section of my circuit diagram.
 

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Skyknight

New Member
Hey you! I know that circuit!!! :D Ask Gene about it! Is the clap switch, isn't it? I'm building it just now to try it before soldering the components into a PCB. Let's see what do people answer, because it's a good question :wink:
 

Skyknight

New Member
Anyway, the question about the diode has been answered to me before in this forum. Have a look at this:

http://www.electro-tech-online.com/threads/gell-cells.1380/&start=15

Although I've modified that circuit a bit, the way of connection the relay is the same. Notice the change that bogdanfirst suggests for my arrangement. Now I encourage you to do it like that. He also tells how two connect the diode.

Every relay has two parts: The control part, and the switch part. Usually, the control part works with small voltage and current, and the switch part with bigger ones. "5V" means you'll need 5V to open or to close that relay, depending on it's type.
 

Gene

New Member
Since your relay is a SPST, only 4 leads are used - the fifth lead probably has no connection. Since you are puzzled, I will assume the relay is in a sealed box, you can't see inside, and there is no manufacturer's name, part number, or data sheet.

To identify which leads go where, you will need an ohmmeter. Connect the first ohmmeter wire to one of the relay leads. Connect the second meter wire to any other relay lead - notice the reading. Move the second meter lead to another relay lead - notice the reading here. Continue with the process untill you have identified two relay wires with a resistance in the range of 50 - 1,000 ohms (these are the coil wires).

Attach the coil wires (identified above) to a suitable power source (5 volts DC?). Of the three remaining (unused) relay wires, two will have 0 resistance when the coil is powered-up and infinate resistance when the coil is not powered-up - these are your switch wires.

(2) I like to use diodes whenever I use relays.

(3) I am guessing that 5v means that the relay has a 5 volt coil.
 
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