What relays do I need?

[Nothadoth]

Hey.

I've been given conflicting advice as to what size relays I'm using so id like some help.

I'm going to be running the following in my car:

1800w (600rms) subwoofer amp built in off a 4 gauge cable

2400w (not sure rms) amp off a 4 gauge cable to run:

4x420w speakers (150w rms)

I want a relay on each power cable and a relay on each speaker. When I flick a switch the amp and sub become live and the speakers swap over to the amp. When I turn it off it kills everything and swaps the speakers back to the stereo.

I have everything installed and working but how big do I need my relays to be? I currently have 2x 12V SPST 40A relays (for power) and 4x 12V 5A relays (for speakers).

Thanks in advance

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[trumpet 5,000+ posts]

First tip: stop referring to max or peak power ratings for your equipment. Second, if you're switching speaker wires with relays the 5A capacity per relay should be adequate. I haven't built a switching setup like you described but speakers are voltage devices, not current devices, so the current should be very low on speaker wires. Measure it to be sure.

 

[rfmayhem 10+ year member]

why do you want to switch between radio and amp power.that's alot of work for low ended audio

 

[Nothadoth]

Ok thanks.

Well I don't know too much about electronics myself. I'm going off what my brother has told me as he's training to be an electrical engineer. He says the relays I have are good enough, but everyone I've spoke to in shops have said I need bigger relays. And the calculators tell me I need bigger ones.

 

[Nothadoth]

why do you want to switch between radio and amp power.that's alot of work for low ended audio

Just means I can swap between using my amp or my stereo when the car isn't turning over. Save battery. It wouldn't suffer any audio loss if it's just going through 1 relay which can handle it surely?

 

[bubbagumper6 5,000+ posts]

Don't put the relays on the power cable for the amplifier, there's far too much current going through there and it's unnecessary considering the amp has a built in relay for turning it on/off. Put your relay on the Remote Turn On input, that's what it's there for.

 

[Nothadoth]

I have been using a remote wire from the switch input for the stereo. The car battery kept dying I can't understand why. :-S

 

[bubbagumper6 5,000+ posts]

I have been using a remote wire from the switch input for the stereo. The car battery kept dying I can't understand why. :-S

Doesn't matter where you get the source from, just put the relay between the source and amp. Then your toggle switch will make/break that connection turning the amp on/off (if the source is off the amp will turn off regardless of the toggle switch state).