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Relay double pulsing Help!!

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Hi

To try and explain.


I have a 30 sec. PIC. based Pulse circuit that syncs to the MSF. it was purchased so not made by me.I added a relay to the output on the circuit so I could expand on what I add to it.For months the circuit as been running fine until now.Every now and then I get a double pulse on the 30 sec pulse.I'm thinking it's the relay.Why should this do this and how can I prevent it?

Also the circuit go mental when I plug in a watch timer next to it or if it's plugged near it. Why and again how do I prevent this happening?

Regards.
 
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It is hard to tell without seeing the circuit, but what you describe sounds like either switch bounce and/or lack of a pull up on your relay contacts.
 
As usual, post a schematic.
 
Hi
I don't have a schematic as I didn't build the circuit.The main part of a circuit sends out 30sec pulse this pulse goes to a relay (across the coil)the relay has a diodes across the coil.
With my question I was really asking in what circumstances might the could double bounce,

Cheers
 
Well, at least show the relay portion of the circuit. Please show on it where the signal appears to be bouncing.
 
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Hi

Here is the best I can do to represent what I have.
The 30sec output is on the 0v line. I don't have a motor connected just used that to show something, I have a slave clock with a coil

The output pulses are synchronised to the MSF. but the output is from the PIC. prog.

Cheers
 

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I would suggest putting a diode across the soleniod like you have across the relay.
Without a diode on an inductive load you can get excessive arcing on the contacts.
This would lead to premature failure of the relay contacts.
 
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The current diode does double duty to snub both the relay and the solenoid, another diode does not help.

The relay is switching a heavy load capable of causing arcing on the relay contacts.
1) Over a period of time the arcing degrades the relay contacts causing rough spots. Arcing is enhanced by the 'slow' diode snubber.
2) A high rough spot can result in a high current density and blow like a fuse. Causing an inductive spike from the solenoid. This is reverse voltage which will momentarily keep the relay coil from energising properly. After the transient the relay renergises and closes normally until the next rough spot forms. Delivering Relay chatter.
3) A rough contacter can also cause significant contact bounce with the same results as a fused rough spot.

Solution: use a better snubber than a plain diode across the relay and solenoid. A plain diode delays the decay of the transient by several hundred percent slowing relay opening and extending arcing . Use a diode plus a uni directional transorb rated at a max voltage clamp that's 20% below the max rated voltage of the relay driver.

https://www.electro-tech-online.com/custompdfs/2010/12/13c3311.pdf
 
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Most likely your relay contacts are becoming worn, You could probably replace the relay with a transistor or a mosfet.
 
Hi

Wow thanks Mosaic for the very informative reply.I will investigate the relays condition and see what we can do.
Brevor I wondered if a transistor would be a better solution seeing as it activates 2880 times per day.

Cheers

hi Mark,
Whats the contact specification of the relay and also the voltage/current the relay/s are switching.???
 
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