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Thread: Use relay to tun on amp?

  1. #1
    Variable Bitrate
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    Use relay to tun on amp?

    I fired up the complete carputer install today. Using M1000, full size DVD and HD, and a 150w AC PSU. Im using the 12v rail to power the xenarc. I decided I would use the same wire supplying 12v to the Xenarc to power the amp. When I booted up, the Xenarc worked fine, but the amp would not power up. When I put a voltmeter on the remote line, I only got 8v. Is the Xenarc drawing too much power to turn on the amp? I guess so the amp runs fine when I connect the remote line directly to battery.

    Would the best way to deal with this be simply using a relay connected to the 12v of the PSU and the battery? Id use the power supplied here to power the Xenarc and turn on the amp. any thoughts?
    Is this where the witty comment goes?
    97 Black pearl Mazda Miata MX-5 Carpc V2? maybee..

  2. #2
    Registered User belezeebub's Avatar
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    Use the 12V rail to turn on a relay and the relay to power the amp

  3. #3
    Variable Bitrate
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    I think I figured it out after reading this thread. I was using an AC extension cord to the house to power the system, I havent hooked up the inverter yet. When I made the voltage measurement, I did not measure voltage across the wiring to the Xenarc, I measured it across the 12+v of the xenarc to the ground of the battery. that would explain the low voltage, and why the amp did not turn on. I'll bet if I measured accross the wiring to the Xenarc, I'd get 12v. If there was only 6v across those two wires, the monitor sure as hell would not have been on.

    The power, coming from the AC in the house had really no path to get to the ground in the car. Automotive grounds are not always 0v anyway.

    Im certainly not connecting the amp ground to the PSU, so I will try an inverter tomorrow, if it still does not power up I will just use the 12v to power a relay.
    Is this where the witty comment goes?
    97 Black pearl Mazda Miata MX-5 Carpc V2? maybee..

  4. #4
    Variable Bitrate
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    Quote Originally Posted by belezeebub
    Use the 12V rail to turn on a relay and the relay to power the amp
    thats the best bet. I will pick up a relay tonight.
    Is this where the witty comment goes?
    97 Black pearl Mazda Miata MX-5 Carpc V2? maybee..

  5. #5
    Variable Bitrate
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    found a nice relay pinout diagram in this post.

    I'll wire as follows

    85 to -12v of psu
    86 to +12 of psu
    30 to batterey (duh)
    87 will provide +12v from battery to power whatever when the computer boots.

    Is this correct? I dont feel like letting any smoke out of anything. TIA
    Is this where the witty comment goes?
    97 Black pearl Mazda Miata MX-5 Carpc V2? maybee..

  6. #6
    Constant Bitrate accentsound's Avatar
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    If you are getting 8V accessory voltage on the remote from the cars system a relay will not help you. The relay needs 12v to close. Put in a 6v relay and you just end up burning it.

    You seem to have a wireing error. The Acc voltage in a car is 12v when the key is in the on position. Check your wiring and don't muck with the relay. You should be connecting the amp remote to the Acc of the car not the psu 12v. Only of your PSU has a lead specifically for remote out do you connect it. In either case yoou have a problem if you are seeing 8v. that a relay is not going to fix.

  7. #7
    Maximum Bitrate starfox's Avatar
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    I'm a bit confused about what's going on in this thread, can I just check a few things?

    You're switching your amp on with the 12V lead from your ATX power supply that's running off an inverter? And your Xenarc's also running off this 12V supply?

    If you're getting 8V at the Xenarc's end, you might want to run a thicker cable from the ATX 12V line to your Xenarc because you're probably draining too much current for the cable that you're using.

    You're fine to use the relay in this situation (try to buy a good quality 12V relay so you don't burn the coil out running it at specced latch voltage all the time). Check what voltage you're getting at the relay's connection, if it's too low it won't latch (as someone said before).

    There's an error in your pin wiring, make sure that 86 goes to the ATX PSU's ground (the pins leading from the black wires on your standard ATX power connectors) and not to -12V. 12V to -12V is 24V, and you'll break the relay.

  8. #8
    Variable Bitrate
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    You're switching your amp on with the 12V lead from your ATX power supply that's running off an inverter? And your Xenarc's also running off this 12V supply?
    thats right.

    It works fine now. the voltage reading I took was not measured properly. I had an extension cord running from the house powering the computer for testing purposes. I measured the voltage from the +12v going from the PSU to the xenarc to the ground of the battery.

    If I was really only seeing 8v on my 12v rail the PC would be much bigger problems. The relay will be fired up by the psu, as It needs to be on when the computer is on, not just when the car is on. This is a show car, and I want to be able to turn on the system with the key off.

    thanks guys. for your help. Its working now with the relay. PC boots, then amp comes on.
    Is this where the witty comment goes?
    97 Black pearl Mazda Miata MX-5 Carpc V2? maybee..

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