Connect with us

Powering an old smoke detector

Discussion in 'General Electronics Discussion' started by Pharaday, Feb 27, 2016.

Scroll to continue with content
  1. Pharaday

    Pharaday

    125
    4
    Jan 18, 2016
    So I got this old style doorbell. Might be broke. It has 3 wires coming out of a plug that can have 4. When I power the black and one of the white wires, the LED lights up. But I cant make it ring. Tried powering the other wire already. Do I need the 4th wire to that plug? Help

    P.S. why is the transformer radioactive?! Oh, its ok cause its filtered through asbestos.

    2012-10-30_00-48-16_304.jpg
     
  2. ChosunOne

    ChosunOne

    379
    98
    Jun 20, 2010
    Gee, your radioactive doorbell looks an awful lot like an ionization-type smoke alarm with a speck of americium at its core. But if you want to wire 120VAC into it, I don't see why you can't wire it as a doorbell.


    You only need one set of white & black to power it up--the other pair is to carry the circuit to the next smoke alarm. There will be a button or switch somewhere on the PCB to make it sound a test. It may even be a reed switch, activated by a magnet. I can't see the PCB well enough to tell. Soldering a pair of wires where the button/switch is now, then running that wire to your doorbell button should do the trick. I doubt the button terminals carry 120VAC, but I'd check to see what voltage they do carry.

    It'll make one raucous doorbell, though.

    PS: I doubt there's any asbestos involved here. The americium radioactive particle is to ionize the air in the metal chamber. The level of ionization is affected by the amount of particulate matter (smoke or dust) in the chamber, which is how it detects smoke.
    Btw, a lot of those old smoke alarms were replaced for one of two reasons: Either they stop detecting, or they start false-alarming. If this one is generating false alarms, then expect to hear your "doorbell" sound non-stop at odd hours when no one's at the door.

    Let us know how it goes.
     
    Last edited: Feb 27, 2016
    davenn likes this.
  3. Pharaday

    Pharaday

    125
    4
    Jan 18, 2016
    oh wow its a smoke detector. yep, found the button. thing must be old it sounds like a jackhammer. not for fire or doorbell. I'm going through a noisemaker phase. but I like good noises!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    The radioactive source is safe as it is, and is designed to be safe if involved in a fire.

    However I wouldn't be tempted to pull it apart and try to find the alpha source as that most definitely IS NOT safe.
     
  5. hevans1944

    hevans1944 Hop - AC8NS

    4,543
    2,116
    Jun 21, 2012
    I have several of these that I salvaged for the alpha source. Years ago we mounted a much more powerful alpha source (it was registered with the AEC) in place of a pen on an analog X-Y plotter. With a clever circuit to drive the plotter in a raster pattern, we measured the current between the alpha source and an aluminum target plate hoping to find micro-cracks in the surface. I don't think that worked, but it was an interesting experiment. I am collecting the alpha sources for use as a possible no-contact replacement for brushes in an electrostatic generator, specifically a Voss electrostatic generator.
     
    davenn likes this.
  6. Alec_t

    Alec_t

    2,904
    784
    Jul 7, 2015
    If you do tinker with that smoke alarm, don't forget it's mains powered and not isolated from the mains, so any part of it should be treated as LIVE and potentially LETHAL.
     
  7. Anon_LG

    Anon_LG

    453
    117
    Jun 24, 2014
    Take out the americium from a few of these and build yourself a fission reactor! Ensure you keep a safe distance though and have some control rods ready.

    *Edit: And an escape plan for when the authorities find this out. If you get caught, act crazy and they may let you off easy.
     
  8. hevans1944

    hevans1944 Hop - AC8NS

    4,543
    2,116
    Jun 21, 2012
    It is not necessary or even possible to build a fission reactor from americium. You need to collect a goodly quantity of yellow-cake or uranium oxide (U3O8) and process it chemically into uranium trioxide (UO3). Then you need to convert, again through a chemical process, the uranium trioxide to uranium dioxide (UO2). Next, you need a few hundred thousand gallons of deturium oxide, AKA "heavy water" and plans for the Canadian CANDU heavy-water nuclear reactor. Besides the huge stack of uranium bricks used to build the first atomic reactor for the Manhattan Project, this is the only fission reactor that will fission with un-enriched uranium.

    But you are right, going down this road will draw considerable attention. Acting crazy will not be a defense, it would be a given, and you would not get off easy. On the bright side, three hots and cot for life at government expense is a likely outcome.
     
  9. Anon_LG

    Anon_LG

    453
    117
    Jun 24, 2014
    You may also get skin lesions.

    As it turns out, the ESA sees it as an alternative in radioactive thermoelectric generators see here.
     
    Last edited: Feb 28, 2016
  10. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    I think the Manhatten Project used natural uranium metal fuel elements with graphite moderating blocks. This was certainly the case with the Magnox power reactors which I worked on in the 50s. The fuel elements were devilishly heavy, you did not want to drop one on your toe.:)
     
  11. hevans1944

    hevans1944 Hop - AC8NS

    4,543
    2,116
    Jun 21, 2012
    According to Wikipedia, it was constructed with "45,000 graphite blocks weighing 400 short tons (360 t) used as a neutron moderator, and was fueled by 6 short tons (5.4 t) of uranium metal and 50 short tons (45 t) of uranium oxide." IIRC, the natural ratio of U235 to U237 and U238 is too small to allow a compact fission reactor.

    You need to "moderate" the neutrons, cooling "fast" neutrons emitted during spontaneous decay of the uranium isotopes to much slower "thermal" neutrons that will be captured by the U235 isotope and cause fission with the release of more high-energy neutrons. There is a square-cube law at work here: the volume of the reacting nucleii increases as the cube of the radius while the surface area for escaping neutrons increases as the square of that radius. So, if you make the "pile" big enough, fewer neutrons per unit volume will escape the surface. Escaping neutrons contribute nothing to the fission reaction inside.

    You still need to moderate the neutrons that do remain inside the "pile" so they will interact with the U235 nucleii and cause a chain-reaction fission, and that is where the graphite enters the picture. IIRC, the Chicago pile also used cadmium foil-covered rods to quickly dampen the fission reaction by absorbing (rather than just moderating) the neutrons. These rods were allegedly held up out of the pile by manila ropes and a large fireman's axe was stationed nearby to chop the ropes and release the dampers into the core of the pile. Hence the expression, SCRAM the reactor meaning Super-Critical Reactor, Axe Manila! Or so I have heard. Actually, this is no-doubt a back acronym invented after SCRAM become common usage for a fast shutdown of nuclear reactors. See this NRC article for perhaps a more factual history. The more likely explanation is the control rods were motor driven and a large red button was used to electrically drop them quickly into the reactor. Someone saw this and asked, "What do we do after pressing the button?" The answer: "Scram the hell out of here!" I think that is as likely as any other explanation for the origin of the "acronym" SCRAM.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-