Omron G5V-2 relay NO pins not working

relaytroubleshooting

I could swear that it was working for a while. I got back to my desk, tried it again, and it's no longer working. Could I have fried the NO pins on both sides? This is a DPDT relay. Everything works normally on the NC pins. I have never applied more than 5V. I do hear the relay click when I apply 5V to the coil. But when I measure voltage on the NO pins, I get 0V. Has anyone else seen this? I have two of these relays and I can't seem to get voltage on the NO pins with either relay. I should clarify that I'm expecting the same 5V power source to power both the coil and the common pins. If the NC pins work then I don't see why the NO pins shouldn't. In both cases the 5V is shared between the coil and any load attached to the NC/NO pins. I did try driving the entire circuit off a 9V power supply, but that did not change the results (and that does contradict my earlier statement that I've never applied more than 5V to this relay). My circuit is based on Charles Platt's "Make: Electronics", p. 59.

Here's the link to the relay product page.

http://www.omron.com/ecb/products/pry/111/g5v_2.html

Schematic I am trying to implement1

Best Answer

The relay connections in the book are wrong. The Omron datasheet for that relay shows that the connections fro the contacts are Common, NC, NO, where the book appears to use NC, common, NO.

Related Solutions

Electronic – Why did relay run when I applied half the nominal coil voltage

The simple answer is this: It is guaranteed to switch with 12v on the coil. It is guaranteed to not switch with 0v on the coil. Between those two voltages, there are no guarantees about what happens.

Or, to put it a different way: 0v=Off, 12v=On. Somewhere between 0v and 12v it must switch between off and on. It's not like it will stay off from 0v to 11.999999v and then switch on at only exactly 12.0v. Some relays might switch on at 4v. Some at 6v. Some at 8v. You might even buy a bunch of the exact same relay and some will switch on at only 4v, while others of the same relay might need 8v to switch on. But you know that it will be off at 0v, and on at 12v!

Just to confuse matters, there is the voltage at which a relay switches, and a different voltage at which it will stay on. For example, if you slowly raise the voltage the relay might turn on at 6v. But if you then reduce the voltage, the relay might not turn back off until it drops below 4v. 6v would be the switching voltage, but 4v is the holding voltage.

Of course the switching voltage and the holding voltage will vary from relay to relay and are not usually specified in the datasheet. Of course, with Radio Shack you almost never get good datasheets anyway and this is no exception.

Electronic – Do these two DPDT relays function the same

The enclosed one is definately better for the motors. Check the spec table below the description:

 Open relay:  HP @ 240V -> 1-1/2 
 Closed relay:  HP @ 240V -> 3

This means that the contacts are more rugged against the inductive feedback of switching a motor on and off, and therefore will last longer. The open relay, however would be better for the ammeter as it appears to be connected not to the motors, but only the boiler and would benefit from the extra resistive load capabilities, although the closed relay would do just as well, since it is above spec. Basically, use the enclosed relay for motor control, and the open one for resistive load if you are not concerned about spending almost $20 extra.

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