A Few Quick Questions:

1: I recently got a heat detector. It’s an Edwards 281A, and it’s 135F fixed temperature & rate-of-rise. Does this mean if I try to test it the disc will pop out? And also, could I hook this up in a circuit (Without a panel) to some alarms and heat it up and have it trip the alarms?

2: I also recently got a BRK Model 1812 ionization smoke detector. It is rated at 12 volts DC. Is there any way I would be able use it in a 24VDC system? (Like off a panel) And, the same question as the last one: Could I hook this up in a circuit (Without a panel) to some alarms and get some smoke and have it trip the alarms?



Really ccs46? No. 24 volts is way out of the range of any device listed at 12V, especially a smoke detector due to their extreme sensitivity. The general rule is +/-10% of the listed voltage is acceptable, but this rule is more commonly used in AC systems. For testing the detector, it will require a compatible panel if it is two wire. If it is four wire, theoretically it can be powered by an external current-limited 12V power supply and connected like a pull station.

For your heat detector, you can test the rate-of-rise device if you are careful. Rate-of-rise detects an increase of heat to a threshold in a certain amount of time, usually around 15F in one minute. If the heat exceeds 135F then you are correct; the fusible link within the detector will melt, the disc will fall out and the detector will be latched permanently into alarm. These can be wired just like a pull station and do not require power, unless it is an intelligent device, which your model is not.

The smoke has about 16 screws, but only 2 are actually usable. (The others are glued shut)

Also, how could I test the heat without popping the disc?

I would either use a hair dryer or a stick lighter to heat the disc, as soon as the rate-of-rise trips stop heating it and let the disc cool.

Ok, and the rate of rise will activate alarms without a panel?

1. Use a heat source that doesn’t go above 110 or 120 degree’s to test the rate-of-rise heat, then you won’t ever pop the fixed sensor. If the detector is at a room temperature of say 70 degrees, you just have to heat it up to 85 or 90 in a minute. Shouldn’t get anywhere near 135. This is safer to do with a heat gun or a hair dryer than a lighter, a lighter can shoot it up pretty fast if you aren’t careful. It’s a 2-wire heat detector, it needs to be powered by a zone module to work. You’re better off getting a conventional heat detector if you want to rig up a circuit to activate an alarm without a panel.

2. There are 3 different versions of the BRK smoke you have, the 1806 powered by 6vdc, the 1812 powered by 12vdc, and the 1824 powered by 24vdc. You need 12vdc to power it. How you get 12vdc is up to you, you can always use a separate power source from your main FACP. It has NO/NC/COM relay contacts that you can use to drive anything, including a signal. Simply take the positive lead from your power source and hook it directly into the positive side of the signal, then take the negative lead from your power source and connect it to the COM contact on your smoke. Then take another wire and connect it from the NO contact on your smoke to the negative side of the signal.

The NO/NC/COM acts like a light switch, connecting to the NO contacts is like connecting to a light switch that’s normally off. When the smoke detector activates, it flips that light switch, effectively completing the circuit and letting power pass through to the signal.

Also from <LINK_TEXT text=“https://www.systemsensor.com/en-us/Docu … 56-156.pdf”>https://www.systemsensor.com/en-us/Documents/2812_2824_Manual_I56-156.pdf</LINK_TEXT> , the maximum allowed voltage for powering your detector is 17.3 volts. DO NOT CONNECT 24VDC TO IT!!!

edit: I should also note that activating a signal with an unsupervised relay like that isn’t up to code and shouldn’t be used in a real world application. For whatever hobby thing you have going on though it should be just fine.

What would set off the smoke detector? Hairspray?

Hair spray is a lacquer type product that will leave a residue that will contaminate your smoke detector. Use a spray designed for smoke detector testing. Alternatively use a smoke source like an old fashioned punk stick like is used to light fireworks or an incense stick.

Anything else other that canned smoke I can spray into it? (It’s sitting on the ground)

Light a match and blow it out close to the detector. You may have to pick the detector up and hold it close to the (extinguished) match so that the smoke can waft in.


Still, you should never attempt to power 12V devices with 24, even if you wire them in series. In fact, doing so makes you have to activate both in order to initiate an alarm. They won’t be supervised if you try that on a panel, either. It’s generally a good idea to stick to 24V devices, or if he really wants to use it, use a separate power supply for the power going into the detector and the zone terminals like normal. Again, that’ll only work if it’s a four-wire detector, and it will not be supervised.

I’m not a tech, but I know a potential problem when I see one.

The 1812 smoke detector you have is a 4-wire device, you need two wires for voltage, and two wires for the alarm contacts. If the only source of power you have available is 24VDC, you can get a voltage converter like the Altronix VR5T Voltage Converter, which will take 24VDC in and give you 12VDC out. Of course the VR5T is around $40, so may not be practical. Plus it is NOT listed for use on fire alarm devices - will it work, yes - should you rely on it to operate correctly for life safety purposes, no. Your best bet would be to drive it right off a 12VDC power supply or lead acid battery. It will work just fine powered by a 12V burglar panel also.

With this being a 4-wire device, you need to provide your own means of power supervision - an “end of line power supervision relay” wired to the 12V power source and in series with the detection circuit is appropriate.

That all being said, you should really only use this for hobby or experimental use only. Use newer and listed devices for the safety of you and your family.

HOLD HEAT FOR ONLY A COUPLE SECONDS! I have killed my 5601p because it didn’t instantly go off…

This is a good point, the rate-of-rise device will still measure the heat increase on the disc without direct heat being applied, and due to the time component of the alarm thresholds, waiting for it to trip could cause the temperature to surpass the fixed-temperature point. Thanks Brandon.

No problem! :wink: