Relay question

[amrogers3]

Hey guys, I'm not sure if you can help me with this question. I am having some issues with a relay in the attic. I think the heat is murdering these things. I thought it was due to power surge but I've had two die this summer with no power issues. I can't really move this guy inside very easily otherwise I would do that.

I am using it to trigger an alarm from several cameras.

I've been using this one. Problem is I can't find a similar replacement. At least not one that shows the operating temperature specs.

Any suggestions on what I can replace it with?

 

[garycrist]

Did you loose these after storms? Even a couple of weeks count too.
The specs say it's good to about 150F.

 

[amrogers3]

Hello Gary, no, the last one just died today while I was home. No power fluctuations, no storms, not even raining. Just started triggering the alarm until I cut power to it.

 

[TonyR]

How many and how long would the wires have to be if you were to move it like in the garage where it's cooler?

It's it's just triggering "an alarm from several cameras" I'd think even CAT-5 would suffice.

 

[garycrist]

Generically,it sounds like too much current draw.

 

[amrogers3]

How many and how long would the wires have to be if you were to move it like in the garage where it's cooler?

looong way. 70' maybe

 

[garycrist]

Also got diodes?

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I am not familiar with your system but, kick-backs from coils unloading will cause spikes.

 

[amrogers3]

I believe the alarm_out wire on the cameras generates 300mA 12 VDC from the Dahua spec sheet. The K80 specs show it can handle 3 A. I have four cameras wired to the relay. The relay is controlling a siren so when any of the alarm_out wires on the cameras trigger, the relay will power the siren.

When this happened today, there were no alarms triggered so no power would have gone to the relay.

What you mean by coils unloading?

I do have another one of these relays near the front of the house that has not had any problems. I figured it was heat because this particular one is near where the sun beats down on the roof most of the day. Maybe there is another issue.

What do you think could be causing this and how could I test to determine what the issue could be?

 

[garycrist]

A coil, as in a relay will saturate or pull a current and pull down the contactor.
After there is no more voltage is applied, the coil un-saturates and creates a back voltage in the circuit.
This back flow voltage may be several times than the input voltage hence the diode in the circuits.
I can't remember the diode numbers anymore as I have slept since then!

 

[amrogers3]

@garycrist I appreciate your help, thank you.

I think I might have been dealing with a misconfigured camera/NVR. I have another post where a Color4K-X has been generating alerts. Come to find out, I think the smartplan/IVS on the NVR was active when it shouldnt have been and was causing the alerts and thus triggering the relay and siren. Earlier today when this happened, I tried unplugging the camera and the relay was still triggering the alarm which made me think the relay was shorted. I think the NVR has been causing the problem the whole time.

Not 100% yet, still doing some testing to try and figure this out.

 

[TonyR]

The back EMF garycrist describes is how a 12VDC automotive ignition coil can generate several thousand volts on the secondary when the points open, power is removed from the primary coil windings and the field collapses, generating much higher voltage on the secondary windings for the spark plugs.

Switching relay coils or electric locks directly with a transistor output that has no diode clamp can damage the transistor when it turns off and the coil's field collapses, causing a back EMF (a reverse electro motive force). The condenser across the points is a capacitor to dampen the arc that occurs when they open so as to prolong their life.

We used 1N4004 rectifier diodes across the coils of 24VDC relays with its anode to the negative and the cathode (the white band on the diode) connected to the positive side of the DC control circuit.