FWR and DC

Does anyone know any alarms that will work perfectly on DC and FWR. My panel puts out FWR but my homemade one puts out DC &’ I’m thinking about linking them together and using my homemade one as a NAC extender for DC alarms. (I plan on using integrity h/s’s, strobes, and horn in my new system.

From my experience, any electronic device will work fine. (correct me if I’m wrong)

It’s the mechanical alarms (34T, 9838, etc.) that sound horrible.



Do you know the difference between the two?

Yes; DC is direct current meaning its current that stays at one voltage and is why DC horns sound smooth on DC and AC is Alternating Current meaning it jumps around at different voltages (?) and AC alternates at 60 times per second which is the reason why the 9838 makes a hi-lo sound similar to the 7002T just slower.

Do not use ANY Simplex-branded fire alarm signals made since the mid 1990s on full wave rectified power! They are not designed for that and they will die.

What how do they die? And as for that. Does a 4001/4002 put out DC when there are no batteries?

Here’s the difference:



AC current constantly alternates, at a frequency of 60 Hz in North America and 50 Hz in Europe. It switches from “forward moving” voltage to no voltage to “backward moving” voltage at a rate of sixty times per second. Also, the flow of electrons actually changes every time the current alternates. The advantage with AC is it can travel over extremely long distances with negligible voltage drop.



DC current flows in one direction, and stays constant. The advantage with DC is the electricity is constant and has more “kick” to it, but it cannot travel as far as AC without severe voltage drop.



A rectifier’s function of converting AC to DC is it only allows the current to flow in one direction. Since AC is constantly switching between two directions, it changes both the “forward” and “backward” flowing electrons to only “forward” flowing. Because of the brief time between the alternations where there is no voltage at all, this is what produces full wave rectified power.



Full Wave Rectified (FWR) DC is unfiltered, and is the result of the rectifier which converts AC to DC. Instead of a constant flow, it instead pulses at an extremely fast rate (which is why mechanical horns on FWR sound raspy) because it still has the sine wave from the AC current.



Filtered DC voltage is linear, where it stays at voltage constantly. The filtering is achieved by a rather large capacitor, which for those who do not know, is like a rechargeable battery that lasts an extremely short time. In this application, less than a second. The capacitor’s function is to hold some of the voltage for the brief time no voltage is present. Capacitors are why sometimes when you turn something off it seems to stay running for a second or two, or “fading out” instead of completely turning off.



Regulated DC is one step further. It takes the filtered DC and passes it through a semiconductor called a regulator, which ensures the output stays at a constant voltage. Electrical fluctuations in a power line can cause the voltage to rise slightly for a brief time, and the regulator compensates for this by resisting the extra voltage increase.



The problem with Simplex alarms is they do not contain a capacitor to compensate for the constant electrical current switching from rectified current. This constant switching can damage the delicate circuitry used in strobe lights and some horns.


The voltage stays the same. The jumping is the flow switching directions.

I’ve only had an issue once and that was when I set off my TrueAlert SmartSync remote strobe on my 4001 w/o realizing the batteries were in the panel - the strobe ended up flashing 8x per second! Now whenever the strobe flashes, it emits a “smoldering” odor & hissing noise, which is why I don’t use it anymore. But the rest of my experiences show as long as the batteries are in the 4001, ANY signal that I hook up to it operates just fine.

How can you fix this on a simplex 4001? I have batteries in the panel but this is still happening

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