I working with a SPST relay (Radio Shack Part Number 275-232) and I can't seem to figure it out. I've looked at the wiring diagram but it didn't help me much. Reguardless of what connections I make COM always seems to be connected to N.O. Perhaps someone could just tell me exactly what connections I should make if I'd just like to test out the relay using a 9v battery and an LED. Any help is appreciated.

 

Hi,

It's a 5 volt reed relay. With no power, the contacts should be open. I've seen them get magnetized after lots of use so they only open if they get tapped.

Since you're using a 9 volt battery, the 150 ohm coil is going to try to pull 60 ma from it. That is more than the 9 volt battery is designed for. You'd be better off using three C cells in series - the 4.5 volts will be more than enough to pull in the reed. Use a 360 ohm resistor in series with the LED so you don't burn it up.

 

Thanks for the reply. That all sounds good, but for now I can't even get the relay working. No matter what I do N.O seems to be connected to COM. I guess I'm not really sure how to hook the thing up, and the wiring diagram isn't helping any. By now it seems like I've tried all possible configurations to no aval. I sort of need to know where to make all the connections.

 

Hi,

Look at the cylinder. The two leads in line with the length are the contacts. The two extra contacts at one end are for the coil. You seem to have a meter - check the coil leads for 150 ohms. That's where you put your battery. The contact leads should check open until the battery is across the coil.

Just a guess - if the coil has a suppressor diode across it, then the coil leads will be called +5 and common. Battery - goes to the common, and + to the +5.

 

I hope you can read a schematic. See below.

 

Thank you both for the replies. I was doing it totally backwards. I only have nine volts in the house so I'll have to go grab some batteries, but at least know I somewhat know what I'm trying to do. I'll report back with my progress. Thanks again.

 

Okay so I noticed my relay is 250 ohms. When I connect the batteries to the coil the voltage across the whole circuit drops to almost nothing, and there's nothing across COM or N.O either. I have no idea what's going on. Also would I be able to use just a 9 volt battery if I had this relay (Radio Shack Part Number 275-233)?

 

Okay so I noticed my relay is 250 ohms. When I connect the batteries to the coil the voltage across the whole circuit drops to almost nothing, and there's nothing across COM or N.O either. I have no idea what's going on. Also would I be able to use just a 9 volt battery if I had this relay (Radio Shack Part Number 275-233)?

You either have it wired wrong, or your batteries are dead (at least one of them).
The 12V relay might switch with a fresh 9V battery, but I wouldn't count on it when the battery gets a little tired.

 

Thanks for the reply. The meter reads 4.5 volts before I make the connections to the relay, after I make the connection the voltage just drops. I think the batteries are fine I must still have it wired wrong. Any suggestions on a relay that might work with just a 9 volt wiring up the three AA is a pain.

 

Thanks for the reply. The meter reads 4.5 volts before I make the connections to the relay, after I make the connection the voltage just drops. I think the batteries are fine I must still have it wired wrong. Any suggestions on a relay that might work with just a 9 volt wiring up the three AA is a pain.

You can put a 200 ohm resistor in series with the relay coil (assuming it really is 250 ohms), and you can then use a 9V battery, although it will not last as long as it would if you had a 9V relay (not readily available, AFAIK). You should increase the LED's current-limiting resistor to about 1kohm.

 

Thanks again for the reply. I'm sorry to ask so many questions, but could you show me what the resistor in series with the really circuit would look like (like the schematic you gave earlier it was very helpful).

 

Thanks again for the reply. I'm sorry to ask so many questions, but could you show me what the resistor in series with the really circuit would look like (like the schematic you gave earlier it was very helpful).

It may have been helpful, but I think you got it wrong.
Here is the 9V version.

 

Heh, yeah seems like I did. I don't think the 9v version link made it up.

 

Heh, yeah seems like I did. I don't think the 9v version link made it up.

I made a mistake on the first try. Should be OK now.

 

Okay, I'm pretty sure I have a bum relay. I've wired it exactly as you specified to no aval. It didn't work with the 9 volt or the three AAs. I'm gonna go buy a new relay tomorrow. If it's not a bad really I don't know for the life of me what I'm doing wrong. Thanks for all the help.