Hi,

 

I'm looking to install an alarm system for a steel shed with no windows. Alarms are all very new to me so I'd appreciate some advice. What I want to achieve is:

 

- An audible alarm activated when the door is opened.

- A system that runs on mains power, but which has a battery backup of at least 2 weeks.

- Preferably some way of disabling the alarm before entering the shed, avoiding the need to have a period to allow for a code/key to be used to disable the alarrm once the door is open.

- Surface contact sensors on the door.

 

Is this achievable, or am I looking for something that doesn't exist? I'm open to other suggestions if anyone has any. All advice gratefully received.

 

Thanks in advance.

it is achievable but batteries for alarms are designed for standby use. If you regularly have long powerfails it will damage the battery but you basically need to calculate your standby time from your normal quiesant current for example

 

assume your system has a day mode current of 0.2A

2 weeks = 336 hours

.2A * 336 hours = 67.20 Amps

Thats a big battery

 

even if you got the day current to .1A thats still 34 A/h battery

 

The largest battery a galaxy (for example)  will charge is 17A/h

 

Its doable but i think you may need to rethink or build something that is very low power (ie a relay)

is using a 17 A/h battery and a .2A day mode current the best you will get is 85 hours standby.

 

And you will have to derate your battery for teh colder weather.

Thanks for your advice. I'm not expecting regular power outages, but wanted to do my best to maintain cover if I was on holiday and for some reason the power failed or was interrupted. As you say, I think I'll have to scale back my ambition for battery backup. I suppose I could always use a DIY-style set-up as a back-up for those times.

 

Battery aside, is there a mains powered system that fits the bill that anyone is aware of and would recommend?

As long as your caling back your backup requirements then id look at an optima in a large poly case.

 

Basic panel but will do your requirements

 

you could always add a dialler/text unit to report ac fails