How to use a smoke detector as a breaking circuit - Page 1
Forum section: electronics / beginners

author: axero
author_rank: Regular Contributor
timestamp: June 07, 2016, 11:29:54 am
content: I want to put a smoke detector inside a machine that operates on mains voltage. I want the smoke detector to break the supply to the mains input of the machine as soon as it detects smoke inside the machine and keep the circuit open until a user comes and resets it manually.What types of components should I look for? Can I use a regular smoke detector and rebuild it for above mentioned purpose? If so, that models of such detectors would you recommend for such purposes?

author: botcrusher
author_rank: Regular Contributor
timestamp: June 07, 2016, 11:35:34 am
content: Many industrial alarm systems work on the normally closed premise. You'd have to look for one that latches until power to it is reset.

author: Muttley Snickers
author_rank: Unknown
timestamp: June 07, 2016, 12:37:36 pm
content: Simply switching off mains power to a machine by means of a smoke detector not only sounds like a bad idea but is potentially very dangerous and if this modification is necessary then it should be properly and professionally implemented. You would not switch mains power directly through a device that was not specifically designed or approved for that purpose and you would first need to know the maximum draw including inrush or startup current of the machine in question and then select an appropriate mains rated relay or contactor.I don't know the full application you are intending to modify but ideally a possible scenario could be a smoke sensor which may be utilised to trigger a controller or system which inturn notifies the operator of an issue and perhaps a pending manual or automated shutdown sequence. Once triggered a simple manual reset may be more difficult than you might imagine because the smoke must first be completely evacuated from the area before a clean reset can be accomplished otherwise it will re-trigger again.There are smoke detectors and PE beams with C/O alarm contacts (not mains) but they are designed to be used as an input trigger to a controller or system which then performs additional functions such as generating an alert, alarm or in your case control a relay or contactor, these types of sensors may not be suitable anyway and may be affected by the machines normal operation with generated fumes or vibration, in addition you may need to liaise with the site electrician to ensure appropriate approvals and methods.Also you may need to incorporate a bypass feature should the smoke detector become faulty or problematic which could then lead to a number of other problem scenarios such as machine down time, frustrated operators and even unqualified people tampering with mains wiring because the work is backing up and the boss is screaming.Over

author: axero
author_rank: Regular Contributor
timestamp: June 07, 2016, 05:24:47 pm
content: I don't see the the danger in adding an extra circuit that shuts the power down in case of a smoke detection.It's a computer system that started burning after a faulty cable short circuited due to poor manufacturing. So if I put a smoke or co detector near a fan outlet that is quite sensitive and let it trip a fuse should smoke be detected, then what's the problem with that?I think I can take apart a simple fire alarm device or whatever it's called and feed the siren output to a tripping relay or something.

author: Muttley Snickers
author_rank: Unknown
timestamp: June 07, 2016, 05:34:32 pm
content: Of course you can, the fact that you made mention of a machine and an operator I mistakenly assumed it was perhaps an industrial application which happens to be my primary environment, I can delete the post if you so wish.

author: axero
author_rank: Regular Contributor
timestamp: June 07, 2016, 07:08:47 pm
content: The system has a 1500W power supply and it doesn't seem to understand short circuits very well. It's essentially a piece of welding equipment that simply burns the metal and keeps feeding the Amps should there be a short circuit.So if there is a circuit telling it that smoke is coming out of whatever it is feeding power to, then I think it would be quite handy.Now since there are cooling fans, I'm not sure that the smoke detectors would be very good at detecting development of smoke or CO. There is quite a bit of airflow that may prevent buildup of high enough concentrations of smoke or CO to trip common smoke detectors.

author: Delta
author_rank: Super Contributor
timestamp: June 07, 2016, 08:59:18 pm
content: You are sounding like your meddlings will cause far more danger than they will prevent.

author: bitslice
author_rank: Frequent Contributor
timestamp: June 07, 2016, 10:40:21 pm
content: You could use some kind of air sampling system to feed a gas sensorhttps://www.seeedstudio.com/depot/datasheet/MQ-2.pdfor if there are particles produced from the short, then you could use a laser dust sensorvarious modules are on ebay, you don't have to modify an existing smoke unit.

author: axero
author_rank: Regular Contributor
timestamp: June 08, 2016, 01:32:06 am
content: A laser dust sensor sounds interesting, or even a gas detector. The laser modules I just found on eBay can be connected to USB that would make a less intrusive solution be possible where I can write a small program that tells the computer to shut down upon smoke detection.It's just that if I make the sensor trig on too small a level it may yield false positives. I don't know the particle size of smoke, wonder if it is sensitive enough to detect smoke particles. I dare not to think about a situation where the window is open and someone happens to have a cigarette break outside. I wonder how a reliable air sampling could be done inside a computer case, or outside...A reliable protection system that gives a proper fire protection may be difficult to achieve but at least it might be better than no protection at all.There is no particular danger in what I'm doing, just happen to have bought some of the beefier stuff off of Newegg and running it 24/7 for long and demanding computations for my science project. I don't like to have to babysit the computer all day in case a fire would happen. Perhaps a fuse box could help. If I know that certain portions of the system don't consume more than a certain number of watts, then I could yield some short-circuit protection by fusing them off with lower amperage fuses. But then again, a fuse won't prevent fire from a bad/glitchy cable connector. I'm only using the "high quality brand" stuff but that didn't appear to be enough. So it would be nice to have some kind of smoke detection or fire detection system instead.

author: Brumby
author_rank: Unknown
timestamp: June 08, 2016, 01:38:33 am
content: How widespread is this problem?

author: axero
author_rank: Regular Contributor
timestamp: June 08, 2016, 01:44:43 am
content: I don't know. Fires in server rooms are apparently not that common but they also have quite sophisticated fire extinguishing equipment to boot. The most dangerous parts of server rooms appear to be where the UPS equipment is located. I'd assume however that as power supplies get stronger the more dangers come with them.