Finding AC NAC Power Supplies

I’m a little confused on how I would power a Simplex 4050 on for example an MS-5ud considering the NAC’s give off 24vdc? The 4050 I have would need 12VAC. I’ve looked into transformers and inverters but I would need something to trip the inverter/transformer if the panel goes into alarm. The school I go to has a mix of Spectralert Classics and Honeywell SC808a (Simplex 4050) in one building. I think the panels are Deltanet fs9 but not too sure. How would they or a fire alarm technician go about it? Maybe some vintage NAC extenders could help? I apologize if this has already been discussed a while back.

In every instance of this scenario I’ve seen, there were two entirely separate systems tied together to trip one another. The older/original panel powers the AC devices (either 120V or a low voltage series configuration), while a newer panel from an addition or retrofit powers the modern 24V devices. An alarm on either panel would trip the other through relays, so they would still function as a coherent system, but other than that the AC and DC lines do not interact.

I know they have AC transformers. Edwards Signaling sells some for this purpose. However is there a way that the NAC can connect to a normally open circuit that’s connected to the power supply so it can do coded blasts as well? I’m sure they exist just not sure where to look. What about power inverters from 24vdc to 12vac? Is that plausible? I’m new to AC alarms since all today are DC. Maybe any old panels that supply AC power that could be found on ebay? I can’t think of any AC panels off the top of my head.

Keep in mind that the old systems using low voltage AC horns had them wired in series. For example, a circuit of six 12 VAC 1.8 Amp horns would need 72 volts applied to it. In the real old days (4245, 4246, 4247 systems) this was accomplished using a big resistor in the panel to drop the voltage from 120 VAC. Slightly newer systems (4208, retrofit 2001) used a signal module with an autotransformer to adjust the output voltage.



The last Simplex system normally sold with AC signal modules was the 4208. That would have one or more H1 or H2 modules in it. Those had one or two circuits respectively. Manufacturing ended on those around 1978. There was a series signal module (2001-2077) for the 2001 system so a 2001 could replace an old panel and still operate the series AC horns. As far as I know no new install 2001 systems used AC horns so the series module is very rare.

Thanks. I found the Edwards 88-50 Transformer that provides 12-24VAC output for signaling. This particular model is designed for large buildings for AC alarm horns/bells. How would this be wired to a Firelite MS-5ud or any similar panel? Somehow it needs to activate only when the panel goes into alarm.

Here is the link: http://edwards-signals.com/index.cfm?pid=105

Yesterday I have received several 4050 fire alarms that run on 12vac. As of right now I cannot buy a 12vac power supply until later this week. I will be receiving a 24vac transformer with the appropriate amperage tomorrow. I couldn’t acquire a 12vac as I ordered from a local warehouse that doesn’t carry 12vac ones. The Home Depot or Lowe’s doesn’t carry a transformer with enough amps. Plus I had very little cash. Just a little impatient to test my alarms. Can you run 24vac on a 12vac fire alarm without causing a fire or component damage. I have seen some people run 24vac on 12vac fire alarms without a problem. Maybe if I keep it to a minimum I won’t overheat or burn the coil? What are your inputs?

I recommend against applying 24 volts to a 12 volt horn. While a few seconds probably would not overheat the coil it could damage the mechanical parts by over flexing the diaphragm.



Since you say you have several horns, two 12 volt horns in series will work on 24 volts. Be sure the current rating (amps) on the horns is the same.



All my 4050s are 1.5 amps and the transformer gives off 1.6 amps. If I wire the two horns up in series like you said, they’ll both work fine? Or will the second horn eat up the amps? I’ve read that with DC alarms that if each alarm is 0.2 amps and the power supply gives of 3 amps, you can only wire up about 15 alarms on that power supply. Would the same apply for the 4050 or am I misunderstanding amps and voltages?


DC notification appliances are wired in parallel. In that circuit you are correct that each added appliance will increase the total current drawn from the power supply. The drawing I made is a series circuit. One of the basic laws of electrical circuits is that the current is the same at all points in a series circuit. Two 12 volt 1.5 amp horns in wired in series with 24 volts applied the total current in the circuit will be 1.5 amps. With 1.5 amps flowing each horn will have 12 volts across it.


Awesome! Thanks for clarifying

I saw that listing on eBay. Did you buy those 4251-20s that were AC rated too? I had my eye on those.