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

  1. #11
    Fusion Brain Creator 2k1Toaster's Avatar
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    Quote 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

  2. #12
    Raw Wave
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    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...

  3. #13
    Fusion Brain Creator 2k1Toaster's Avatar
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    Quote 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

  4. #14
    Constant Bitrate
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    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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