Converting fire alarms to an external DC supply. - Page 1
Forum section: electronics / projects

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 14, 2012, 09:46:32 am
content: In our house, of which we are the owners, I want to run DC for most of the low load house wiring.This includes fire alarms. I could also supply a DC backup power supply, so I don't have to change the backup batteries.Does anybody know of any DC fire alarms available in Australia? Maybe I could buy ones designed for caravans.Or may I should convert my existing alarms to wired DC.It would probably be best using the battery powered ones and just supply 9V externally. Rather than the 240v ones which are more expensive anyway.Then there is the question of obeying the rules, I assume because fire alarms are not mandatory in old homes that I can rework as I wish, but who knows what the authorities think.Also I seem to have a lot of trouble with false alarms on my AC powered alarms. Anybody got any brands or types they recommend Ionisation, Photodetector, Dual or other.

author: GeoffS
author_rank: Unknown
timestamp: October 14, 2012, 10:03:10 am
content: Depends on what Australian state you're in, but I think you'll find that hard wired smoke detectors must be 240V with a 9V battery backup.Wiring must comply with AS3000 and be installed by a 'suitable licensed person'.I don't know about a home you own requiring a smoke detector, I do know that rental properties are required to have at least one.

author: SeanB
author_rank: Super Contributor
timestamp: October 14, 2012, 10:48:16 am
content: Buy the battery powered ones, and buy long life 9V lithium batteries for them. These should last 10 years in the alarm at least.

author: Unknown
author_rank: Unknown
timestamp: October 14, 2012, 11:42:17 am
content: In the UK depending on the category you fall into is to the type you are required to install. The more complex ones are the multi-zone addressable types. The detectors can be set to one of few different detector modes like....QuoteWhere I live I just use battery ones, and I test them from time to time by burning my toast. ;-)

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 14, 2012, 12:26:24 pm
content: I'm in Tassie, and I have a sparky licence.AS 3000 is mainly about Low voltage wiring: 50ac and 120dc and up.there are rules on selling electrical goods.There are rules on telco and data wiring.There are rules on building safety. Which I know nothing about.QuoteAny idea who's rule that is?Jucole: it seems we don't have those categories here, I wish we did.Sometimes I think the nuisance alarms are from tiny bits of dust, or maybe from mains.The most problematic alarms I have are photodetector( they were cheap).QuoteThat seems a good idea, you mean buy the normal battery ones and put in your own lithium don't you?They also sell 10 year lithium battery powered smoke detectors with sealed non replaceable batteries. But in not the photodetector type.

author: GeoffS
author_rank: Unknown
timestamp: October 14, 2012, 12:40:40 pm
content: Information I had on smoke alarms was all on 240V units hence the AS3000 reference in them.The only low voltage hard wired units I ever had anything to do with (a long time ago!) were part of a fire detection system and were heat, rather than smoke detectors. Different set of rules back then as I was allowed to work on them and I'm not a sparkie! Touch a wire these days and you'd better have a license for itMy reference to 240V with 9V backup was in reference to a property I had in NSW so may well have been local rules.(What part of Tassie? I'm at Port Huon)

author: SeanB
author_rank: Super Contributor
timestamp: October 14, 2012, 01:44:03 pm
content: Duracell has a 9V lithium cell specially made for both long life and high current, perfect for smoke detectors.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 14, 2012, 02:28:45 pm
content: Quote from: HackedFridgeMagnet on October 14, 2012, 09:46:32 amWhy? What voltage? This seems like a lot of trouble and expense to go through unless you have good reason. Only thing I can think of is that you are off-grid solar powered with batteries and you don't want to pay the efficiency cost of DC->AC->DC. That isn't to say there aren't other reasons, I am just curious what yours are.

author: bilko
author_rank: Frequent Contributor
timestamp: October 14, 2012, 03:04:09 pm
content: Quote from: SeanB on October 14, 2012, 01:44:03 pmLots of info on these forums about shoddy duracell products. I wouldn't trust their products in a kids toy, never mind a product to alert me to danger.

author: G7PSK
author_rank: Super Contributor
timestamp: October 14, 2012, 05:07:33 pm
content: I would look at fire and smoke detectors that are intended for burglar alarm systems they are powered by 12 volts.Something along the lines of this unit.http://www.tlc-direct.co.uk/Products/EI100R.htmlFound an Aus. one.http://www.psaproducts.com.au/12V-DC-PINKERTON-SMOKE-ALARM.aspx

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 14, 2012, 10:38:41 pm
content: Thanks for the linkQuoteHopefully they are a reasonable price.One smoke detector went off at 1-2am last night, no smoke, no fire. It cost about $70 dollars. I have about 3 different brands in the house. The one in my sons room goes off so regularly that I leave it disconnected. That was a cheapie, but AS approved.@Bilko, yes i think battery quality is an important point, my feeling is if I have a centralised 9-12v supply, Lead acid battery backed. then I can be sure that If the lights of the smoke alarm are on then the wiring is ok. Then I can monitor the battery fairly easily. Maybe a micro with a webserver.the advantage of SeanBs system is it is so simple and so standardised. whereas as my system would be unique and therefore introducing a whole new range of other risks.QuoteIt was initially about safety, also now about aesthetics ( which is hard ) and making stuff that is a bit arty, and also I think that in this day and age that we dont need mains power for lighting, I am trying to prove it. Maybe one day I can make a business out of it.It started because I have an old house that is wired very strangely, by the previous owner, one roome has 5 lights and 5 switches that each turn off all the 5 lights. Therefore I have masses of TPS cable up in my roof. I also have 32pair running back to Telstra, and a 48 way cat 5 patchbay. The previous owners were eccentric and ran an ISP in the pre ADSL modem days.But the worst of it is they have run separate earths for some of the mains cables, some of the older light fittings are not even earthed, and are difficult to get too as they have a skillion roofs. Add to that my fear of mains power and I am a sparky.Then the LED s came along an I thought I would run the lighting in house as DC. I made some 24 volt constant current drivers which work fine but my light fittings are still coming along. So I am running at 24v but thinking of either 36 or 48 volts.I also ordered one of Doug Fords flat panels.I know you are thinking that voltage drop will be an issue, but it really isn't at 24 volts using leds, higher voltages will be even less.I will have 2-3 sub distribution boards for the DC voltages in different spots in the house. These will also keep the DC cable runs short. I am currently using one of the more efficient MeanWell supples for the 24 volts.Doing all this DIY lighting stuff means my fire detectors are of paramount importance.GeoffS I am from Margate, Port Huon is a nice spot.

author: johnwa
author_rank: Frequent Contributor
timestamp: October 16, 2012, 07:53:32 am
content: I remember Colin Mitchell had a circuit for this in one of his books. It fed an external supply to the smoke detector, and monitored the current using an SCR, causing an alarm output to latch on when the horn was activated. I had a quick look on his website and couldn't see it, but it may be up on there somewhere.

author: ptricks
author_rank: Frequent Contributor
timestamp: October 16, 2012, 01:42:56 pm
content: One of the good things about having the battery in the smoke detector is what will happen when your DC power supply catches fire ?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 16, 2012, 11:19:10 pm
content: Quotegood point. In fact comments like this are one of the key reasons I threw this question out.I knew going away from conventional solutions on a safety matter requires a lot of care and thought.It relates back to the general question of centralised control vs decentralised control. Both have issues.I guess it is coming down to 2 optionsBattery powered smoke alarms using lithium 9v.or Running 9V to the smoke alarms (about 6) and maintaining the battery centrally. I could add on to this option an extra battery powered smoke alarm.I might just go with option 1.I have enough unconventional stuff in the house, and the main points are covered.ie. Not 240v and not changing batteries every 6 months.thanks for the thoughts

author: ColinA
author_rank: Contributor
timestamp: October 17, 2012, 11:21:15 pm
content: I've been in the fire alarm industry for over 20 years so here is a little info. Keep in mind I'm in the USA and do not know any code requirements for your country.There several types of smokes for security/fire alarm systems. I will skip the big addressable commercial type systems. But for most residential applications photoelectric is used over ionization. Each type has its benefits depending on the site and type of protection needed.On the circuit end of it there are also a few types, 2-wire, 4-wire, and addressable. Most of these devices are only listed for use on power limiting circuits and a voltage of either 12 or 24vdc. The 2-wire is designed for use on a circuit designed for that type of smoke, basically when the detector activates it sinks the circuit leaving enough to drive an led/sounder. The 4-wire requires a voltage input and provides a short across a dry relay upon activation. Code requires that these circuits be supervised by the use of end-of-line resistors and power supervision for 4-wire circuits. With the resistor one is able to detect an open, short, and or loss of power on the wiring.Of all the advice, I highly recommend you fully understand what your doing and review the local fire codes. Smoke detectors save lives when installed correctly.