How can I test to find out what is the required voltage of a certain device? For example, a horn? This will make it easier for me to know if I need a relay to increase the voltage output.


PS. I already have a digital multimeter...

 

relays are usually for switching larger amounts of current. Or if you are using a low voltage to switch on a high voltage. A relay will not increase voltage.

So what are you using to switch on the horn? Is this a 12v horn?

 

Yeah, that's what I meant to do...I guess I didn't describe it correctly.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">So what are you using to switch on the horn? Is this a 12v horn?</TD></TR></TABLE>

That's the thing I want to find out. I have no idea what kind of a horn it is, therefore, I want to test the required voltage for it. The horn will be switched with the horn output of the alarm...but don't tell me: yeah, you'll need a relay...I want to know how to test for these things, so I could figure it out all by myself.

 

There really isn't a way to "measure" the required voltage of the horn. This is what datasheets are for. A horn will more then likely work under and over the recommened voltage. Where did you get the horn from?

 

Oh, it's a factory/normal horn of a Prelude. The one you honk when you see retard-drivers on the road


But if the horn requires a relay, that means there is a factory relay somewhere in the car already? Or they send a high output right away?

 

Then its a 12 volt horn. And yes there is a horn relay in the car already.

Typically a car use a low current contact switch for the horn. Basically two pieces of metal that touch when you press the horn. This powers the coil of the relay, which uses low current and keeps arcing to a minimum. When the coil is charged it causes a mechanical switch to switch on an this allows a larger amount of current to flow. So basically your relay is an inline switch to turn your horn on and off. Instead of using your finger to switch it on it uses voltage and low current.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Odessa &raquo;</TD></TR><TR><TD CLASS="quote">How can I test to find out what is the required voltage of a certain device? For example, a horn? This will make it easier for me to know if I need a relay to increase the voltage output.


PS. I already have a digital multimeter...</TD></TR></TABLE> Get yourself some fuses a 20 amp, 15,10,7.5,5,3,2,1 start with the 20 amp inline on power to horn, honk horn, a nice long one, move down to 15 amp, same thing, keep going down till fuse blows, not perfect, but fuse size above one that blows is going to be very close to amp draw of horn.
If running off an alarm, you will need a relay. 94

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fcm &raquo;</TD></TR><TR><TD CLASS="quote"> Get yourself some fuses a 20 amp, 15,10,7.5,5,3,2,1 start with the 20 amp inline on power to horn, honk horn, a nice long one, move down to 15 amp, same thing, keep going down till fuse blows, not perfect, but fuse size above one that blows is going to be very close to amp draw of horn.
If running off an alarm, you will need a relay. 94</TD></TR></TABLE>

He has a multimeter just plug it in an measure it. The current the device is using can be measured, the voltage a device will require can not.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

He has a multimeter just plug it in an measure it. The current the device is using can be measured, the voltage a device will require can not.</TD></TR></TABLE> We already know its a 12v horn, he wanted to know if he could run it with the output of his alarm, and as most multimeters have a 10amp max for current, I guess you could test down to 10amps and then use the meter 94

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fcm &raquo;</TD></TR><TR><TD CLASS="quote"> We already know its a 12v horn, he wanted to know if he could run it with the output of his alarm, and as most multimeters have a 10amp max for current, I guess you could test down to 10amps and then use the meter 94</TD></TR></TABLE>
I really don't think a stock horn uses 10 amps thats 144 watts thats one serious horn.

I would not use an alarm out to power a horn I would use a relay.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">
I really don't think a stock horn uses 10 amps thats 144 watts thats one serious horn..</TD></TR></TABLE> better to be safe than sorry, better to blow a fuse outside then the one inside the multimeter.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">

I would not use an alarm out to power a horn I would use a relay.</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fcm &raquo;</TD></TR><TR><TD CLASS="quote">
If running off an alarm, you will need a relay. 94</TD></TR></TABLE>

94

 

I don't know, I didn't use a relay for my horn and is working fine for some reason.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fcm &raquo;</TD></TR><TR><TD CLASS="quote"> better to be safe than sorry, better to blow a fuse outside then the one inside the multimeter.





94</TD></TR></TABLE>

Check your alarm's manual. If it's referred to as a Low Current output, then no it will not drive the horn its self. If you're using the horn already installed in the car, and tag the wires in the steering column, then yes, it should be able to run it as long as they are the same polarity (IE&gt; a negitive output from the brain and a negitive trigger for the horn wire). If you aren't sure, the safest way is to just use a relay

 

"I want to know how to test for these things, so I could figure it out all by myself."


If you wanna figure out if you need a relay for something without knowing what the specs of the device is, you need to do some testing. First locate the device. Then probe the wires with a multimeter. Find out how much voltage is being used. Most times when you are dealing with things such as horns, lights etc. it will be 12v. Newer car use multiplex wiring which means that the device it being controlled by one wire at 2 different voltages. For example. Newer dodge vans' door locks use ONE wire to lock and unlock the doors. The wire may sit at 5 volts. When you hit lock, the current is passed through a resistor and drops down to say 1.5 volts. when that happens, the doors lock. When you hit unlock, the voltage may rise to 10.5 volts. Then the door unlocks. For what you are doing, this isn't the case. Just sharing some extra info. So test your wires and see how much voltage is passed thru. If you see that it is 12v. then you know you need at least this amount to operate the device. Next, there are many ways to do this but here's one way. Test the device and find out how much resistance it has. Once you have that info, you can use the formula, Volts divided by resistance = amperage. So say you have a 12v horn, it shows a resistance of 6 ohms, you come out with 2A. reference this against your alarm manual to see how much current the wire puts out and that will tell you if u need a relay or not.

 

Ok, this is very strange...or may be not. Yesterday I was bypassing my clutch with the Status output wire of the Compustar. It outputs only 250 mA. I tested the clutch switch output and it read 12v on my dmm. I still wanted to give it a try to hook it up without a relay, so I simpy stripped the Status wire and inserted in the clutch switch plug. Tried to remotely start the car without manually depressing the clutch and what do you know?? It worked!! So no need a relay for this, even though people told me I do need one. What I'm thinking is the signal that this clutch outputs goes to a device which requires a small input in order to determine the position of the clutch...so it just gives it more than it needs...that's my guess.