So I got a nice Simplex Vibratone 4040 for a good price on Ebay except I ran into a problem. I don’t know how to safely power it with 12VAC. I have searched the internet but I can’t find any affordable solution. Any help will be appreciated.
A transformer would be the safest option IMO. But somebody probably has a cheaper and better way then mine so I would wait to see who answers next.
Well, what else are you going to use instead of a transformer? lol
I saw someone said in another thread could use a resistor. Although it’s not the safest option.
That is inefficient, especially diving the voltage in 10 to get the right amount. Not to mention the power consumption of one of those horns…
Resistors are for current…
Wouldn’t work on AC devices.
Not necessarily… you can make a voltage divider with some.
You can create a voltage divider circuit with a resistor network. Completely valid way to do things in electronics, just not a good idea for fire alarm systems, inefficient with the current draws.
You are much better off using a transformer. Good old radio Shack has a 12 volt 3 amp transformer for about $12. Plus the transformer isolates the horn from the 120 volt circuit, so is much safer.
The 12 volt fire alarm horn it should have a current rating of about 1.6 amps. Using ohm’s law to figure out the resistor needed goes like this.
E = Voltage in volts.
I = Current in amps.
R = Resistance in ohms.
120 - 12 = 108 volts. So the resistor has to drop 108 volts to end up with 12 volts across the horn.
The resistor needed would be R=E/I so 108/1.6 = 67.5 ohms.
Now for the power dissipation. P= E X I. So 108 X 1.6 = 172.8 watts. That is a big (physically) resistor.
As an example, the Simplex 4246 fire alarm panel used series AC horns and had a compensating resistor that the installer had to adjust to match the number of horns. That resistor is 100 ohms at 160 watts. They are about 1.5 inches in diameter and about 10 inches long.
Get a transformer!
Would this be a good idea:
http://www.ebay.com/itm/Ademco-Pittway-Honeywell-Basler-AC-Adapter-PRI-120V-0-25A-SEC-12V-AC-20VA-/251726163454
low amp rating on that, might not work well.
Something like:
screw terminals make it easier.
I would take the thing to RadioShack so they can look at it and help you exactly. Now instead of using 9v battery’s for my Spectra classic I use a transformer to power it.
You do realize that transformers output AC, not DC?
Maybe he means a power supply.
No the 4040 is a AC horn so it needs a tranformer…
No, I meant that you can’t use just a transformer to power a Spectralert Classic. The AC would likely kill it. You’d need a 24VDC power supply. I was referring to you.
Well, since it does have a diode, it could (in theory) work on A/C, but it would be inefficient because you would only be using half of the wave, and might fry something if you aren’t extremely careful. I would just use DC to power it, it’s the only practical way.
Ah ok Yah I did mean power supply.