How powerful of a relay do I need....

**kibble** · 06-23-2008, 11:14 PM

Originally Posted by JonnieBlaze

So I've got some questions about Relays. I went to radioshack to ask but no one there new the answers, so I figured I'd come here and ask.

As a former Radioshack employee, I can tell you that no matter what store you go to now days, you won't find anyone who knows anything about electronic components. Pretty much everyone went the way of the dodo. When I was working there, all the other employees sent their customers to me that needed help with anything technical. The company has moved from the more DIY side to the retail side and most of the people that are employed don't know squat. So much for their "You got questions, We got answers" slogan.

Anyway, I believe it only takes about 100ma at 12v to get an amplifier to turn on. 5V won't do it as I learned by experimenting.

**HiJackZX1** · 06-24-2008, 04:47 AM

Originally Posted by kibble

As a former Radioshack employee, I can tell you that no matter what store you go to now days, you won't find anyone who knows anything about electronic components. Pretty much everyone went the way of the dodo. When I was working there, all the other employees sent their customers to me that needed help with anything technical. The company has moved from the more DIY side to the retail side and most of the people that are employed don't know squat. So much for their "You got questions, We got answers" slogan.

Anyway, I believe it only takes about 100ma at 12v to get an amplifier to turn on. 5V won't do it as I learned by experimenting.

Are you sure? I have my remote wire connected to pin 4 of my serial port, and that has 3 amps connected to it. I really dont think 12V is going through pin 4. Maybe as long as there is a signal period, it will turn on.

**kibble** · 06-24-2008, 12:50 PM

Originally Posted by HiJackZX1

Are you sure? I have my remote wire connected to pin 4 of my serial port, and that has 3 amps connected to it. I really dont think 12V is going through pin 4. Maybe as long as there is a signal period, it will turn on.

Pin #4, DTR should be putting out +12V. Serial port communications use +12V and -12V, which is why when you're interfacing 5V electronics to a serial port you need an RS232 converter.

**JonnieBlaze** · 06-24-2008, 02:12 PM

Originally Posted by HiJackZX1

I decided to go with a program called AMPCTRL that you connect the AMPS remote wire to pin number 4 on your serial port. Once the program sees that something is producing a stream of sound it turns on the amps.

I'll probably be using an M-Audio Transit USB soundcard. So maybe I could do it this way to avoid that "thump". But, since I'll be using a laptop on a docking station, and keeping my headunit for the radio functionality, I would not be able to turn on my amps without the laptop being in the dock correct? (say I was making a quick trip down the street and didnt take the laptop with me but I will wanted to listen to the radio...)

**HiJackZX1** · 06-24-2008, 02:59 PM

Originally Posted by kibble

Pin #4, DTR should be putting out +12V. Serial port communications use +12V and -12V, which is why when you're interfacing 5V electronics to a serial port you need an RS232 converter.

AHHHHH, ok I learned something new, I didnt think 12V could run safetly through such a small wire......

**kibble** · 06-24-2008, 03:22 PM

I would feel safer putting some sort of transistor driver on the line though to boost the amperage that it can drive. The serial port outputs really aren't made to source or sink much current.

**Rob Withey** · 06-24-2008, 03:31 PM

Originally Posted by HiJackZX1

AHHHHH, ok I learned something new, I didnt think 12V could run safetly through such a small wire......

The current has more to do with the size of the wire than the voltage.

**HiJackZX1** · 06-24-2008, 04:01 PM

Originally Posted by Rob Withey

The current has more to do with the size of the wire than the voltage.

I think I agree, I just started noticing that when I turn on the PC with AMPCTRL it takes almost a minute for the amps to come on, and when it does it fades in as though the amps are fighting for the wire to send the signal to power them on. On my setup I have a thin wire coming from the MoBo serial header, then connecting to a distrubution block then the amps connecting to that. I have a total of 4 amps, and I think this may be the issue. In that case, can I simply add a relay that has a 12v signal and the serial port simply triggers the relay, which all 4 amps will be connected to?

**kibble** · 06-24-2008, 07:37 PM

I don't think the serial port puts out enough current to activate the coil in the relay. Best bet would be to have a transistor being switched on by the DTR line and have that running the relay. A solid state relay would probably eliminate having to use a transistor as they're made to use low currents to turn on, they're usually more expensive though.

**HiJackZX1** · 06-25-2008, 04:09 PM

Originally Posted by kibble

I don't think the serial port puts out enough current to activate the coil in the relay. Best bet would be to have a transistor being switched on by the DTR line and have that running the relay. A solid state relay would probably eliminate having to use a transistor as they're made to use low currents to turn on, they're usually more expensive though.

I think ill go that route and use a solid state relay....