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Kill Switch...because I believe in over kill.

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  • Kill Switch...because I believe in over kill.

    I am looking for a switch that I can put inline on my 2 gauge power line. has anyone every done it?

  • #2
    I never have, but I just seen a car battery cutoff switch at Harbor Freight that would do the job.

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    • #3
      use a circuit breaker, the resettable kind... you can trip it at any time to open the circuit, like a switch. this is the most compact way to switch this, and it also adds the necessary protection that you would have otherwise had to use a big fuse holder anyway

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      • #4
        Big rigs and heavy equipment use a master disconnect switch. I think you will need something like that for that 2 gauge wire. SNO
        Click image for larger version

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        • #5
          Originally posted by turbocad6 View Post
          use a circuit breaker, the resettable kind... you can trip it at any time to open the circuit, like a switch. this is the most compact way to switch this, and it also adds the necessary protection that you would have otherwise had to use a big fuse holder anyway

          I have one of these up under the fender. It's not easy to get to per say, but it works
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          • #6
            Ah - a favorite topic... of mine.

            Do you mean kill switch, or isolation switch? The two are very different and cannot be combined (safely) with a single switch.


            I assume you mean an isolation switch.
            The best is a switch in the battery's -ve/ GND lead. That's best because it can be located anywhere on/in the vehicle without safety issues if the battery cable gets pinched and shorts to chassis or the bonnet shorts to the battery +ve terminal. (That's an important issue for competitive vehicles that require isolation switches in case of accident. Most are required to be cabin mounted in reach of the driver, and some require an additional switch at one rear corner of the vehicle. And I note with amusement that few prohibit +ve isolation LOL!)

            For non-competition purposes there are more options. Because the starter or alternator an other loads may be acceptably left connected, a smaller switch can be used in whatever +ve feeds are desired.
            The -ve/ground version is generally only suitable to switch ALL -ve/gnds from in the battery -ve terminal. It hence has to be rated for starter motor currents plus other loads. (You never want to break just one ground in a multi-grounded system - eg, battery -ve to engine to body, amplifier of HU power GND, CPU GND etc. Alternate ground paths with blow circuits, burn cables & tracks, fuse throttle cables, etc.)

            For +ve switches, I like the thought of the circuit-breaker types.
            For GND and competition use, it's usually the plain $20 isolator switch.


            Now, as for kill switches....

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            • #7
              I would like to have the ability to shut of the power to that line completely is what I am looking to do

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              • #8
                Ok, an isolation switch, for specific loads, hence +12V switching.

                There are lot to choose from including those pictured above. Even relays could be used (especially for automated or timed or low-voltage-cutout disconnection).

                A common type of switch used for competitions is:

                .. but many variants exist.


                The main thing is that the switch has a current rating higher than the fuse your are using for that line (I assume 150A - 200A for 2G?).
                And beware peak current ratings as opposed to constant current capability.

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                • #9
                  You don't want to put a switch that you physically flip directly in line with the main power. That is just bad mojo waiting to go wrong.

                  Put a switch that controls the coil of a relay. The extra 20mA of current draw is well worth the protection of the switch. And if you are planning on using the switch as a plug/unplug, then you could wire it so that the normally closed powers your system and when you flick the switch it disconnects and the relay conducts. That would be the best in terms of power saving, but backwards from what people would expect.

                  This also gives you the ability to use a good high quality relay and and cheap crappy switch. The benefit is that the switch can be a very small but awesome looking switch instead of one of the very few able to switch the power required for your whole system.
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                  • #10
                    Not that I disagree - I too usually always suggest relays hence eliminating big switches and minimising voltage drops as well as have a large selection of switches, and inputs (FusionBrains, PCs etc).

                    IMO it comes down to the application. Presumably it's for audio or other accessories, a suitable relay/contactor.is appropriate (no matter how it is controlled).
                    But if to isolate a main supply (as in competition) or to disconnect something normally powered, then a switch is probably more appropriate - eg, manual switch(es) to isolate parallel batteries instead of battery isolator relays.
                    (Al I know is it's a 2G cable, not it's function.)

                    But a switch is advised (read: is used except in complex redundant relay implementations) where relay opening or failure is critical (eg, main power; maybe beams).

                    If it's audio that does not have to be isolated frequently, then a switch. If power is only required when in operation, then a relay.

                    FYI - relays can bounce. Hence not used for "competitive" main-power isolation except when considered reliable enough; usually requiring redundancy and known-spec components (G-forces etc).
                    Last edited by OldSpark; 04-14-2013, 03:08 AM. Reason: Tidied up a bit.

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                    • #11
                      Originally posted by OldSpark View Post
                      Not that I disagree - I too usually always suggest relays and hence eliminating big switches and minimising voltage drops as well as have a large selection of switches, and inputs (FusionBrains, PCs etc).

                      It comes down to the application. Presumably it's for audio or other accessories, a suitable relay/contactor.is appropriate (no matter how it is controlled).
                      But if to isolate a main supply (as in competition) or to disconnect something normally powered, then a switch is probably more appropriate - eg, manual switch(es) to isolate parallel batteries instead of battery isolator relays.

                      But a switch is advised (read: is used except in complex redundant relay implementations) where relay opening or failure is critical (eg, main power; maybe beams).

                      If it's audio that does not have to be isolated frequently, then a switch. If power is only required when in operation, then a relay.

                      FYI - relays can bounce. Hence not used for "competitive" main-power isolation except when considered reliable enough; usually requiring redundancy and known-spec components (G-forces etc).
                      Agree but for a CarPC, I don't see a relay as a problem.

                      Relays are a great way to make isolation, and to take care of surges you can use multiple relays with current limiting R's. For instance one of vehicles is a Prius and the main traction battery is completely disconnected from the system when not in READY. When the car boots 3 relays are turned on that connects the main traction battery to the inverter and spins up the engine using one of the two electric motors. The sequence is the HV- relay, followed by the HV+ (180VDC to 260VDC) through a 1 ohm power resistor, a delay, then another HV+ relay with no current limiting resistor is thrown, and then the 1R limiting resistor is turned off. This sequence is very reliable and safe and allows complete isolation of the main pack from the vehicle. Even when in use, the battery is completely isolated from the chassis in any way.
                      Fusion Brain Version 6 Released!
                      1.9in x 2.9in -- 47mm x 73mm
                      30 Digital Outputs -- Directly drive a relay
                      15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                      Buy now in the MP3Car.com Store

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                      • #12
                        We are in total agreement.

                        Thanks for the Prius confirmation. I was sure they used total isolation - IMO you have no choice. It's no different to AC UPS batteries - hundreds of DC volts with lot of Amps - not exactly human or crowbar friendly, but they were often required to be isolatable into battery strings not exceeding 120V for maintenance purposes. [The how was not specified - ie, if undoing normal a bolted battery connection; manual switch; remote contactor) - except for REPO (Remote Emergency Power Off) applications.]
                        And I looked at the Prius set up wrt supplying ~200VDC to an audio amp, as well as arguing that that Swedish 4kW or whatever amped audio took its power direct from the HV batts, not via 12VDC, extra 12V batteries, and often a second alternator. I never did contact those Swedes... Must reinvestigate...

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                        • #13
                          Originally posted by OldSpark View Post
                          We are in total agreement.

                          Thanks for the Prius confirmation. I was sure they used total isolation - IMO you have no choice. It's no different to AC UPS batteries - hundreds of DC volts with lot of Amps - not exactly human or crowbar friendly, but they were often required to be isolatable into battery strings not exceeding 120V for maintenance purposes. [The how was not specified - ie, if undoing normal a bolted battery connection; manual switch; remote contactor) - except for REPO (Remote Emergency Power Off) applications.]
                          And I looked at the Prius set up wrt supplying ~200VDC to an audio amp, as well as arguing that that Swedish 4kW or whatever amped audio took its power direct from the HV batts, not via 12VDC, extra 12V batteries, and often a second alternator. I never did contact those Swedes... Must reinvestigate...
                          That's one of the beauties of the Prius. It has a 1KW 12v rail that doesn't depend on engine speed (or even it being on) that is always ready. And then another 4KW+ that can be drawn from the HV lines tapped at the battery. When my electrical panel in my house was being upgraded, the mains grid power was off from sunup to about 7pm at night. I just hooked up my inverter to the Prius, put it in READY, and my whole house was powered off of the car burning almost no fuel.

                          For high power applications, it just can't be beat.

                          That's one of the beauties of the Prius. No alternator, and a 1KW 12v rail that does not depend on engine speed (or it even being on). When my house's electrical panel was being re-wired the mains grid power was off for 12
                          Fusion Brain Version 6 Released!
                          1.9in x 2.9in -- 47mm x 73mm
                          30 Digital Outputs -- Directly drive a relay
                          15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                          Buy now in the MP3Car.com Store

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                          • #14
                            I thought maybe a relay but I would like to have something definite. A switch is a definite on off. Kind of like unplugging it. To me a relay would be relying on electronics which is what I don't want to do so I can have a I know its turned off in cases when I need it.

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