Siren hold-off, the easy way?

[Pgordon]

Now that all the flash parts are available for Comfort G2, it’s likely that I’ll be doing[font=\"Times New Roman\"] [/font]some major work on the panel again soon. As ever, the biggest PITA with this is that as soon as I power-down the system, my main siren goes off. Clearly I therefore need to provide a 12V hold-off to the siren to shut it up whilst I’m working on the panel. Normally, I frig some Heath-Robinson-esque arrangement that involves disconnecting the siren cable from the SIREN terminals on the mainboard, and twisting the bare wire-ends round a temporary supply (usually a wall-wart, since I don’t usually have enough slack cable to pull them down to reach the battery)...

Frankly, this is pants.... it takes a couple of minutes to complete the above bodge, during which the siren is blaring, and it  almost always[font=\"Times New Roman\"] [/font]“falls off” during the work in progress, setting it off again... (and It takes a minute or two to reverse the bodge at the end as well).... Net result, - my neighbours aren’t very happy with me!

Therefore, before I embark on the next round of work on the panel, I want to sort out an easy, reliable, and[font=\"Times New Roman\"] [/font]straightforward way of[font=\"Times New Roman\"] [/font]managing the siren hold-off. I’m envisaging something that just involves flicking a switch mounted somewhere inside the main enclosure.

When work commences, the requirements always include:

-      [font=\"Times New Roman\"] [/font]cutting the mains power

-      [font=\"Times New Roman\"] [/font]disconnecting the battery from the mainboard

-      [font=\"Times New Roman\"] [/font]connecting a hold-off supply to the siren

Clearly, it would be a simple matter to break the cable from the battery, & insert a switch to cut the input to the mainboard.[font=\"Times New Roman\"] [/font]I also want it to switch the battery terminals over to supplying the hold-off to the siren...[font=\"Times New Roman\"] [/font]– Presumably, I shouldn’t connect the battery to the siren cables whilst they’re still connected to the SIREN terminals on the mainboard, - as otherwise I’ll be pumping 12V INTO the mainboard on those siren terminals...[font=\"Times New Roman\"] [/font]– not sure what the effect of that might be....

So I’m after suggestions how to achieve this easily... – I’d need to supply both + and – to the siren, so I guess I’d need to switch *both* battery terminals, even though I’d only need to cut one of them to remove battery power from the mainboard.... so I guess at least I need a DPDT switch on the battery output leads  to switch them both from the mainboard to the siren... – what about the issue of the 12V then being connected to the SIREN outputs? – could I just put a diode in the + lead between the switch & the SIREN connection?

The layout I'm contemplating is shown in the attached JPG. The 12V FROM the battery is connected to the centre poles in this diagram, - the BAT & SIREN points are the terminals on the mainboard[font=\"Times New Roman\"] [/font]where the battery & siren are connected to Comfort.[font=\"Times New Roman\"] [/font] When switch is in[font=\"Times New Roman\"] [/font]position 1 (leftmost), the + and[font=\"Times New Roman\"] [/font]– terminals from the battery are connected to the usual battery in terminals on the mainboard, as per normal. When switched to position 2 (rightmost), the battery is disconnected from the battery in terminals on the mainboard (thus achieving 1 of the 3 requirements), the 12V battery supply[font=\"Times New Roman\"] [/font]is instead rerouted to the cable going off to the siren, thus providing the hold-off required to keep it silent. The diode is inserted[font=\"Times New Roman\"] [/font]in the cable[font=\"Times New Roman\"] [/font]before it enters the SIREN terminal such that current is able to flow OUT of the terminal, but not IN to it.....

Does this make sense?[font=\"Times New Roman\"] [/font]– would this be feasible?[font=\"Times New Roman\"] [/font]– any thoughts?[font=\"Times New Roman\"] [/font]– alternative suggestions?

TIA

Paul G.

 

[Pgordon]

Also had another idea, just using a 3PDT switch, conected as per the amended JPG below...

[slychiu]

Both these schemes should work

It wont comply to the new EN50131 which you Europeans have introduced though - the burglar would be able to do the same thing

[Pgordon]

Thanks Chiu.

The toggle switch will be inside the main panel enclosure though, so methinks that by the time a burglar has access to the siren hold-off switch, I would already have a few more pressing things to worry about!

Can I take it that, with the 3PDT switch method, it is OK to just break the SIREN+ line (or whatever it\'s called) to the siren when the switch is thrown, and not bother to also break the other line... - It wouldn\'t be hard to break both lines to the siren terminals, but obviously I\'d then have to use a 4PDT switch instead...

Paul G.

 

[ident]

There should be no problems with breaking the SRN+ to the siren only

[Pgordon]

[user=86]ident[/user] wrote:

There should be no problems with breaking the SRN+ to the siren only

Cool. Thanks.  3PDT switch now ordered. I\'ll mount it on a piece of stripboard with some terminal blocks just like the ones on the main board, and mount it on some pillars inside the enclosure on one of the available mounting positions.

I\'ll let you know how it works.

Paul G.

[Pgordon]

Got the bits in front of me, - just wondering before I start assembly, is there any particular gauge wire I should use? - I ask because the battery connection cable from the spades on the battery to the BATT connector on the mainboard (JP52 is it?) are a fair bit chunkier than any of the other 12V cables in the case....

I think given the length of this existing battery cable, and the spaces available in the case where I can mount this board, I *may* need to extend them slightly... in so doing should I be concerned about what gauge wire I use?

Cheers.

Paul G.

 

[ident]

The siren may take about 1 Amp, hence the cable needs to be able to take that current without melting. The gauge of the battery cable is more than enough for several times that current.
However the function of the siren hold off is to charge the internal siren battery not to drive the siren, so the wire gauge should not be an issue. The siren sounds only when you remove the voltage.
Make sure the wire does not become warm in normal operation

[Pgordon]

Well, Ive constructed the board, will get round to fitting it tomorrow hopefully... I\'ve made it as small as I possibly could, and I\'ve mounted it \"double-decker\" style using tall pillars over the top of an ADM01.

I\'ve attached a small photo of it in case anyone\'s remotely interested!

Cheers.

Paul G.

 

[Pgordon]

OK, first problem! - after installing & testing the switch, it didn\'t work... - everything is 100% hunky-dory with the switch in normal mode, but when in \"hold\" position, with the panel powered down, the siren still went off... - couldn\'t immediately see why, - I measured the voltage across the SRN+ and SRN- terminals in this state, and I was getting the 12V from the battery, via my switch (actually, I\'m measuring 13.8VDC from the battery...) so what gives?

Well, I returned everything to the normal state, measured across the SRN terminals again, and I see that the Comfort Mobo is only providing 3.8V to the siren....

So my question is; Is the voltage difference what is causing this not to work? - I guess I could test this by rigging up  a variable PSU set to as close to 3.8 as I can get (I think 3.5 is available) - will this be close enough?

One thing that kinda makes me think the voltage difference is at least having some effect is that I got 2 entirely different siren sounds between when I was giving it 13.8V and when I was giving it nothing at all... My next thought is to use a little DC-DC converter allied to my switch. - I have one lying around here, but it only offers 3.0V and 4.5V output settings, which are fairly close, but not exact...

Any thoughts / advice anyone?

Cheers.

Paul G.