Relay for Car Alarm Siren Output

The npn you use will need to be able to support the voltage and ampage on the base which is something I don't know. You have to consider that the transitor base will need to take the chirps as well as the 12v full siren.

lurch228 wrote: The npn you use will need to be able to support the voltage and ampage on the base which is something I don't know. You have to consider that the transitor base will need to take the chirps as well as the 12v full siren.

You got a point there. I hadn't taken on account the fact that the base should take both voltages.

Most of my experience is with diodes and resistors so I can't be of much more help but I'm trying to learn what I can about transistors as I go. If you figure it out give me a heads up. If I figure anything more I'll post back.

lurch228 wrote: Most of my experience is with diodes and resistors so I can't be of much more help but I'm trying to learn what I can about transistors as I go. If you figure it out give me a heads up. If I figure anything more I'll post back.

That's a big 10-4 buddy.

A FET is supposed to work in reverse of a transistor coupled with a resistor(s) to clamp back the voltage might work. Prior to the npn of course.

lurch228 wrote: A FET is supposed to work in reverse of a transistor coupled with a resistor(s) to clamp back the voltage might work.

Those are good news, buddy. I'ma put myself into your suggestion, let me see what I can find about it.

Also found this info on a forum: The transistor method is perfectly fine if you insert a current limiting resistor to 12v. Transistors are, after all, current operated devices - it's ok to pull the base up to hundreds of volts as long as the resistor limits the current to something in the low milliamp range. Something in the range of 10k to 100k would work for 12V with most small transistors.

lurch228 wrote: Also found this info on a forum: The transistor method is perfectly fine if you insert a current limiting resistor to 12v. Transistors are, after all, current operated devices - it's ok to pull the base up to hundreds of volts as long as the resistor limits the current to something in the low milliamp range. Something in the range of 10k to 100k would work for 12V with most small transistors.

That's pretty logical. It looks like I might as well "protect" the transistor's base and collector with some resistors to avoid burning it, as long as it shoots 12v out of that emitter. Then it's just a matter of calculating with the ohm's law to limit the input voltages and currents to base and collector, depending on the transistor's behavior, since I've read that some of them amplify the voltage on the collector depending on the voltage they receive on the base, pretty much like this: collector voltage + base voltage = emitter voltage. Just as you, I ain't too familiar with transistors.

Best that I can figure this should work. With a 100ohm resistor on the base. npn KSC5402DTTU link below. npn

Question? If each siren is working fine with one direct to the alarm and 2 aren't working, have you confirmed your grounds are solid for both and good ground to the alarm brain? If you take the positive and negative wires from both sirens and test them together direct to the battery or another known good 12v and ground location, do the sirens work fine? If the alarm brain is capable of running one siren (which draws about 1-2 amps), it should be able to push a relay (that only draws about 300mA) to then make both sirens work. I have 3 sirens in my car (2 under the hood and 1 hidden inside) all running off a relay attached to the siren wire and work flawlessly. Did I miss anything?