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  • Relays..

    I have a specific question about relays. First of all will this work? I will have 2 amps and my computer that all need to be switched when the car is started. SO:

    I was thinking relay from, battery and switched from the remote lead on my Head Unit. Then the relay feeding into a distro block, and the distro block feeding the "switched" line into the amps remote turn-on terminals, and then powering my inverter.

    Will that work?? and what amp relay would I need?

    thanks, I hope i explained that well...

  • #2
    why not just tie them all together off of the remote out on your head unit? these devices take very little power on the remote line itself, you probably don't even need a relay.

    However if you wanted to use one, just get any SPST or SPDT 12V relay (you only need < 1A contact current, so any relay will do), and then just hook it up like you described.

    As I reread your post, I see that you also want to power an inverter off of this. How big is your inverter? You can probably just get any SPST or SPDT 12V relay at 20A or 30A which will power a 240W or 360W inverter, respectively. Use the remote line from your head unit to switch this relay as well. I prefer using the head unit because the computer is only on when the radio is on (which really is always) and then I have an easy method of turning it off from the front while keeping the ACC line high, but you could just as easily power it off of the ACC line from the car.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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    • #3
      so your saying with the 2 amps and inverter I should set it up as I described??

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      • #4
        as I understand your description, yes.

        But you'll need a rather high current relay, which can be expensive (or several lower current ones in parallel).

        Actually if you head down to your neighbourhood automotive wrecker or shop you can probably buy used automotive relays that are like 30-60A for $4-5 each if they are nice to you. These are ones used for your air conditioner, fuel pump, etc and are found in your engine compartment in a fuse panel. One of those will work perfect for what you need.
        IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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        • #5
          would 40A be enough?

          http://www.partsexpress.com/pe/showd...ID=15175&DID=7


          And what gauge wire do you think I should run to the inverter, and from the battery?

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          • #6
            40 amps will be perfect, provided that your inverter is less than 450W.

            8 guage (~80-100A) or 10 guage (~60-80A) will do fine for your installation. I wouldn't recommend going down to 12 guage though, you might cut it close and then you won't be able to expand in the future either.

            Just get a good length of 8 guage and run it properly through the underside of the car and into the trunk, then you'll be able to have future expansion as well.
            IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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            • #7
              yeah just hook them all up to your head unit's "remote" lead. This turns on once the head unit turns on, it is a built-in relay. It is more than adequate to turn on some amps an an inverter - just don't use it as your primary 12v source..

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              • #8
                The problem is that the inverter doesn't have a remote-in lead, which is why he'd need to use a relay to power it.
                IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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                • #9
                  hey, you wouldnt happen to know another good store that sells relays would you?? partsexpress rapes you on shipping.. $9 to ship a stupid little relay to me!

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                  • #10
                    http://www.digikey.com
                    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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                    • #11
                      Originally posted by unrealer33
                      hey, you wouldnt happen to know another good store that sells relays would you?? partsexpress rapes you on shipping.. $9 to ship a stupid little relay to me!
                      Why don't you just buy one from a local electronics store? Don't go to Radio Shack, they suck. They would probably have a relay that would work, but I like to support my local geeks instead.

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                      • #12
                        try going to a local auto shop, they have automotive relays that they'll probably sell to you for $2 a pop or something. that's where I got all of mine.
                        IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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                        • #13
                          Yep, even in overprices Britain, a generic 4 connector 30AMP headlight/Foglight/driving light relay is only about 5-6gbp from a motorfactor.

                          And that is convenient when I'm going to be runnign a 300watt inverter which should draw about 25AMPS hopefully.

                          If need be, I can always add a bigger relay.
                          4x4 in a turbo stylee.

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                          • #14
                            Got my inverter running off a relay that I picked up at Maplins. It's all fine (turns off when the ignition goes etc) apart from when I crank the engine again the Inverter then complains about not getting enough power (constant beep and nothing turns on).

                            If I then flick the inverter off at it's switch and turn it back on, it's fine.

                            Very strange. Anyone have any ideas on that... my initial reaction was to put a capacitor of some description in there so it could draw a bit of juice from there when i've cranked the engine?
                            Celica VVTi
                            EPIA M10000 Nehemiah, 160Gb HDD, 7" Lilliput VGA Touchscreen, Opus 150Watt PSU, Slimline DVD/CDRW, Road Runner

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                            • #15
                              Originally posted by Magma
                              Got my inverter running off a relay that I picked up at Maplins. It's all fine (turns off when the ignition goes etc) apart from when I crank the engine again the Inverter then complains about not getting enough power (constant beep and nothing turns on).

                              If I then flick the inverter off at it's switch and turn it back on, it's fine.

                              Very strange. Anyone have any ideas on that... my initial reaction was to put a capacitor of some description in there so it could draw a bit of juice from there when i've cranked the engine?
                              Yep, what you need is a power cap somewhere.

                              What source are you using for the switch signal for the relay?

                              That might make a difference?
                              4x4 in a turbo stylee.

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