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Latching Relays

David Birchall

Oct 2, 2017
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I am an Electrician, but have little experience of working with electronics. I am in the process of installing a very simple hard wired 12 volt DC alarm, consisting of 8 door and window reed switches and 2 personal attack buttons in my friends motorhome.

I am struggling with connecting up a Latched Relay, I understand how the relay and latch connections work, but I am unsure as how to connect the external strobe flashing light and a Sound Bomb once the alarm been activated. I have been looking at relays SPST, DPDT, TPDT and various changeover relays. However there are many types on the market from £1:20 to £11:00 plus and some refer to auto relays for large loads and other to telecommunications. Also I have read that the collapsing coil in the relay can cause spikes and damage other electronic components (strobe, sound bomb). I believe I would need to connect suitable capacitors at certain points in the circuit.

I also need to buy/build a very simple timer circuit to cut the alarm off after 10 minutes max and would need to how to connect it into the overall circuit. Any help would be really appreciated.

Rational behind a simple circuit.

MY friend tells me many motorhomes have alarm systems and are basically small household alarms systems or simple shed type alarms, some even have vibration detectors and are wireless/wifi connected, But one thing they all have in common, is they are 100% electronic control and when a problem occurs they are far away from home and, like my friend are away for the winter in Spain or Portugal, for the sake of a small fault the complete system has to be switched off. The motorhomes suffer like any road vehicle from a terrific amount of vibration.

I said to my friend I would install a very simple, reliable system, that would enable him to carry out some simple fault finding and possible repairs to the system, that is why I have choosen fixed hard wired contacts, use of well proven relays able to cope with vibration. The use of suitable strobe and sound bomb/horn will be trail and error


Hope someone can help/suggest or advise on the project.

David Birchall
 

73's de Edd

Aug 21, 2015
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Paging . . . . . . . .Most Honnable . . . . . . .ChosunOne . . . . .Come in pls . . .Come in pls.
 

Minder

Apr 24, 2015
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Also I have read that the collapsing coil in the relay can cause spikes and damage other electronic components (strobe, sound bomb). I believe I would need to connect suitable capacitors at certain points in the circuit.

David Birchall
Google Free wheeling Diode.
M.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Here's a simple (Closed Loop Alarm) latch using a DPDT relay.

Chris
upload_2017-10-4_11-26-38.png
 

David Birchall

Oct 2, 2017
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Oct 2, 2017
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Morning Chris,

Thank you for taking the time to reply As I said, I am an electrician and in our trade we only have 3 wires (Brown, Blue, Green/Yellow) keeps it very simple.

1. Can you clarify what the 3 bar triangular symbol refers to. To me it refers to an Earth, in your diagram it appears to refer to an Negative

2. Are all the components (excluding the S1/S2/S3) included in the Latched Relay

3. I understand how how a basic relay works, and I understand how the latch is connected, however the diagram with internal components and connections, with some appearing to go from a positive 12 volt to a negative 12 with no resistance (dead short).

4. I understand how a DPDT switch works, but the diagram has me a little confused, the 12 volt latch appears to come from nowhere.

5. yes, it's hard work talking to an electrician, but please bear with me.

To help simplify matters, could you a) suggest a suitable relay type and then identify the appropriate connections.

I want the complete circuit to operate as follows.

Set/Arm

When the alarm is activated the relay then connects the external sound and strobe light

I am also looking to incorporate a very simple time device (max upto 10 minutes) after which time the alarm is switched off.

Note. I do not want a time delay for entry/exit

Any advise, suggestions will be welcomed

DaveB
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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I drew that circuit some years ago. It was primarily intended to demonstrate how a relay with spare contacts could be wired to latch. Tomorrow I'll post an updated version with a full explanation. I'll also do my best to answer all your questions.

Chris
 

David Birchall

Oct 2, 2017
3
Joined
Oct 2, 2017
Messages
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I drew that circuit some years ago. It was primarily intended to demonstrate how a relay with spare contacts could be wired to latch. Tomorrow I'll post an updated version with a full explanation. I'll also do my best to answer all your questions.

Chris
Morning Chris,

Thank you for taking time to help out, it really is appreciated and as we say over here "I owe you one".

Cheers Dave B
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Dave, I'm very sorry for not replying when I said I would. I have a long list of excuses but I'll spare you of the details.

Before you spend time and money fabricating a burglar alarm have you searched through Amazon and Ebay? The Chinese have totally changed the electronics market to the point of making it impossible to DIY cheaper than buying an off the shelf complete system.

Here's some Ebay links that make my point.
https://www.ebay.com/sch/i.html?_fr...H1.Xburglar+.TRS0&_nkw=burglar+alarm&_sacat=0

http://www.ebay.com/itm/Wireless-GS...964851?hash=item1a05d48a73:g:UOIAAOSwc49Y8G~Q

Don't be fooled by the supplier's shipping location. China is known for its factory direct free shipping on most items, which are usually small E-Packets. My guess is that since an alarm system is larger than an e-packet they find it cheaper to ship in bulk to a distribution point in the U.S, UK, etc. location. So despite the listed shipping location I'd bet my left nut that it's a Chinese seller. In fact, you will find identical products sold under different product names or part numbers.

Cheers,
Chris
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Dave, I forgot to mention that if you're hell bent on a partially home brewed hack take a look at this link..
http://www.ebay.com/itm/DC-5V-12V-2...Relay-ON-OFF-Switch-Loop-Module-/191909501362

Take note of the push button N/O switch in the product photo of this timer. A closed security loop interfaced to that switch input can be adapted. It can be accomplished with a single transistor and one resistor. If solid state is not your bag then a small (low coil current) SPST(N/C) control relay can replace the transistor and resistor. Reed Relay's are well suited for this.

Cheers,
Chris
 
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