Magnetic Contacts - Expiry date? - False Alarms years later!

[alarmbenjy]

Magnetic Contacts.

Plain white, standard surface mount, cater for four wires, but only use two just for trigger.

One set on one building, other on different system in another building.

After 3 years with no alarms, get false alarms "door", happens again, then again. No wind, no door movement.

2nd building about the same age alarm triggered "door"

Is it me, but as they have been working for years why now?

Does the magnet get weaker, do they degrade after so long or is it my method of mounting (even after all these years).

Do they have to be placed side by side screws facing outward, or can you have the one on the frame mount screws facing forward and the non wired magnet side mount screws facing inward towards wired side. During tests and years of service it has always worked. As the contacts are very nearly touching each other.

Again with the other setup, wired side is on the frame, mount screws facing forward and the magnet part still the same vertical and inline, but at a slight angle on the curved trim on the upvc door.

Any idea's, are there stronger, or more reliable contacts.

Many thanks.

 

[bernardgreen]

Some magnets do degrade of time. Though three years seems rather short life time for a magnet unless it was a very cheap / low quality material used.

 

[EightyTwo]

No, they don't have expiry dates.

Yes, you can mount them that way. So long as they are even side-to-side and roughly parallel with <10mm of gap, they should be fine.

Check that the connections are tight and not showing signs of corrosion or water ingress. Grab a magnifying glass or your best reading glasses and check that the sealed glass ends of the reed switch aren't broken.

If all this is okay, I have come across one other strange failing on old contacts: they go high resistance. You can check this with a multimeter set to the lowest ohms range. Disconnect the contact and measure the resistance as you bring it slowly up to the magnet. The contact should switch from infinite to zero ohms (or a couple) straight away. I have seen some contacts that show a couple of hundred ohms just as they switch - and you can hold them there. This is not good! In fact, it's a nightmare if you're using EOL on a Galaxy.

Change the contacts if they're giving you trouble - they're cheap enough!

 

[alarmbenjy]

No, they don't have expiry dates.

Yes, you can mount them that way. So long as they are even side-to-side and roughly parallel with <10mm of gap, they should be fine.

Check that the connections are tight and not showing signs of corrosion or water ingress. Grab a magnifying glass or your best reading glasses and check that the sealed glass ends of the reed switch aren't broken.

If all this is okay, I have come across one other strange failing on old contacts: they go high resistance. You can check this with a multimeter set to the lowest ohms range. Disconnect the contact and measure the resistance as you bring it slowly up to the magnet. The contact should switch from infinite to zero ohms (or a couple) straight away. I have seen some contacts that show a couple of hundred ohms just as they switch - and you can hold them there. This is not good! In fact, it's a nightmare if you're using EOL on a Galaxy.

Change the contacts if they're giving you trouble - they're cheap enough!

Thanks for the above info, main worry was buying too cheap. But looking at more expensive ones online and they look identical to the cheap maplin ones. Can't find any branded ones.

Its happened to me before on an outbuilding, replaced then fine for a couple of years then same problem. Then for it to happen on another system and keep triggering on another set of contacts a few years old, just knocked my confidence. lol

 

[bernardgreen]

If all this is okay, I have come across one other strange failing on old contacts: they go high resistance. You can check this with a multimeter set to the lowest ohms range.

That is the more likely reason for a door sensor to stop working. the most common cause is the glass to metal seal allows air to enter the tube and contact corrosion occurs. Ironically some reed switches fail because the current switched is too small and the contacts are not properly wetted when switching and develop an insulating surface. In theory wetting is not needed for a reed switch filled with an inert gas but over time leaky seals allow air into the tube and the un wetted contacts begin to fail. And not all reeds are filled with inert gas when manufactured. These do have a minimum switching current requirement if long life is to be achieved.

( mercury wetting is something entirely different )

 

[JM2]

I think you'll find mercury wetting is for that exact senario - little or no current, so use mg wetted contacts.

 

[scott1980]

Next to batteries, we replace more contacts than anything else. It could also be an intermittent cable fault or a dodgy join in the cable somewhere. Providing the cable is OK, then I recommend the CQR SC550 heavy duty contact. They have a much wider operating gap and a nice big magnet. They're about £3 or so. They're quite large though so check the dimensions before you purchase to make sure they'll fit on your doors.

 

[EightyTwo]

I'll go along with Scott1980. We usually fit the SC550 heavy duty contact in barns, outbuildings, sheds, etc.. Steer clear of the grade 3 contacts - they're expensive and the range is much lower. I've replaced a higher proportion of these compared with the ungraded ones.

 

[Europlex]

Steer clear of the grade 3 contacts - they're expensive and the range is much lower. I've replaced a higher proportion of these compared with the ungraded ones.

I hope you replace 'like with like'

 

[EightyTwo]

Magnetic Contacts.

Plain white, standard surface mount, cater for four wires, but only use two just for trigger.

Not grade 3 then...

You can always replace an ungraded/grade 1 device with a higher grade. In this case, I wouldn't recommend it. A DIYer might think that a more expensive, grade 3 product is "better" - which it isn't!

 

[bernardgreen]

A DIYer might think that a more expensive, grade 3 product is "better" - which it isn't!

But it might be better, might be a lot better, for example it could be a Hall effect device which can be far more reliable and longer lasting than a "cheap" reed switch.

 

[Europlex]

A DIYer might think that a more expensive, grade 3 product is "better" - which it isn't!

But it might be better, might be a lot better, for example it could be a Hall effect device which can be far more reliable and longer lasting than a "cheap" reed switch.

But Bernard, it isn't any better, it's the way it is configured that makes it G3.

The 'contact' (reed switch) is exactly the same.

 

[redpis]

Cool alternative to reeds

http://www.magnasphere.com/downloads/technology-overview.pdf

 

[JM2]

Reminds me of those trembler switches.

All packaged up and ready to install - I wonder how much they'll come in at.

 

[alarmbenjy]

Unbelievably I am still having trouble with the magnetic contacts on what is a small shed door. I have the heavy duty ones "CQR SC550" as suggested in an above reply to see if that would stop the false alarms. I had the contact omitted for the rest of winter until late spring and ever since it has been perfect, however it wasn't over winter. What is it about cold nights that triggers these contacts. It has now been replaced 4 times in less than 10 years. The alarm panel is Accenta G4. The cable to the contact is less than 2 metres from the panel, the contact is connected by the 2 wires without tamper, the wires are and always have been securely screwed down on the terminals with no cable thread breaks or fraying. I'm now thinking forget magnetic contacts and wish I could find a physical switch that is held shut to complete the circuit when the door is closed in the same way a magnetic switch works but surely more reliable. Any idea's are still greatly appreciated.