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Thread: Using a relay to auto-power on HDD and power inverter

  1. #31
    Constant Bitrate Startingline13's Avatar
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    Well knowing that I would surmise that the yellow would go to one end of the switch (the top perhaps) and the blue would go to the other end (the bottom), on the inverter, similar to how I have the switch created for the laptop to turn on and off which I mounted in my arm rest.

    But as far as the black and white go, I'm not quite sure.

  2. #32
    Constant Bitrate Startingline13's Avatar
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    On second though, the black is grounded, so the white would be IGN then, correct?

  3. #33
    What can I say? I like serial. Curiosity's Avatar
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    You got it!

  4. #34
    Constant Bitrate Startingline13's Avatar
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    It works!

    Thanks again everyone for the assistance, especially you Curiosity. It may not seem like much to you, but the little help you offered went a long way for me and helped solve a problem I've been having for months. Once again, thank you.

  5. #35
    Raw Wave
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    Congrats SL13! Yep - he's good isn't he!
    FWIW - IMO it "ain't much", but I (we?) understand how HUGE it can be for others. It's often so easy in hindsight. But that's what these forums are for - problems, solutions, brainstorming, teaching/learning etc.
    Many of your big "problems" today are our problems from yesteryear. Hopefully though, these days you will learn more easily than we did.... (like if we didn't have a good source or teacher, or worse - one that was wrong or bad!).


    Anyhow, I added a "non-hijacking" reply earlier that got wiped off (maybe my new Firefox v3.6 - lots of forum posts not posting first time...?). It was intended for a later discussion, or discussion elsewhere...

    Anyhow, now that the thread has "ended"...


    It looked to me like that inverter does not have an earth-pin connection (the wall-socket's 3rd pin), and I suspect from its other 2 AC-output wires that its AC output is NOT isolated from its 12V DC input (aka floating).

    These are generally not major issues, but can cause problems.
    Safety can be one issue (ie - whereby touching one output wire can cause a serious shock if AC is not floating; in some cases (no pun) equipment (cases) have been live!).
    But moreso the ability of loads to clear faults - ie, blow their own fuses etc.

    Though not a problem in double-insulated (un-earthed) equipment, it can be when used for domestic earthed equipment.
    Not that I'm saying the output should be grounded or earthed - that actually created a hazard (not that that stopped some authority from insisting on its implementation )!.

    But it seems to be an issue at times.
    I have even seen people post that they would NEVER use an inverter in a vehicle because if their dangers.... quote: "as if house AC isn't dangerous enough.... (Yet a DC inverter can be safer than normal AC supplies, and the same protection can be used - eg, RCDs (Residual Current Devices) also misnomered as "Earth Leakage" switches/breakers or detectors or "Safety Switches".

    So, does the topic have any interest?
    Should it be started elsewhere (if so where - I never initiate threads lol!) or maybe start here and can then be transferred (cut&paste & edited) to a new thread.....?

  6. #36
    What can I say? I like serial. Curiosity's Avatar
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    Well, working with high voltage electronics and not knowing the basics is a bad combination, but some poeple don't want to learn the simple stuff, and that's fine. It just doesn't make sense.

    That ground pin not being connected could be common. Not sure. Ground should be wired to a long rod shoved into the ground but you can't do that in a car. That's the path of least resistance when lightning strikes or there's a short. Plus an inverter doesn't expect devices grounded to the car's chassis. The transformer in the AC/DC of the device plugged in usually isolates the whole AC circuit so it still works, hopefully. In a short being a human fuse, there's no neutral/hot and no certainty that grounding one side or the other will even blow a fuse. Shorting the 2 wires together would though.

  7. #37
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    In relation to the inverter grounding issues, while i know that it must change from model to model of coarse the ones i have dealt with have the earth AC terminal go to a wing nut bolt mounted in close to the DC input

    the reason for that is dependent on the use and mounting of the inverter, if in a solar house design the inverter would the staked with an iron pole into the ground, as mention not exactly possible in a car, thanks to our friends, the tire :P in an automotive situation it is recommend by the manufacture that you connect the wing nut to the ground of the DC, which for 3 prong AC devices is a must but as mention earlier to with most PC related things being 2 prong items only it is completely unused so is irrelevant.

    hope this adds something useful

    ---
    pyro

  8. #38
    Raw Wave
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    Yet again Pyro..... (useful).

    That hits on one issue regarding inverters - the output ground/earth pin is NOT for grounding, but to clear equipment faults.
    It can also be for EMI interference, but let's KIS.

    [ FYI: Here in Aus - earth is earth, ground might be earth or chassis; and chassis is chassis (and body!).
    We use an earthed AC distribution system with designated Active and Neutral conductors - the Neutral being earth connected at the generator(s) and then (in general) only at the end-building's fuse/distribution box - hence "MEN" meaning a Mains Earth-Neutral connection at the source (ie, fusebox).
    Hence an Active fault to the earthed equipment chassis blows a fuse. ]


    Therefore the AC ground pin should be used if using "grounded" (earthed) loads.
    However, that may then reference the system...

    In a floating system like an isolated inverter's AC output, if you touch either AC conductor you will be fine - you will NOT get a shock (except maybe for a small "static" equalising zap).
    In a referenced (non-isolated etc) system - say where one side (Neutral) is ground connected - touching the Neutral is harmless, but touching the other side (Active) is quite shocking and often fatal.

    So why do we create a hazardous referenced system? That gets a bit complicated.... Maybe I'll offer the observation that the world has gradually moved from a 2-wire AC system to a 3-wire earthed/grounded AC system. (I need to keep this reply short & sweet....)
    It can have to do with EMI and shielding - ie, earth/ground the chassis so it doesn't act as an antenna.
    But it did have a lot to do with safety and unintended referencing....

    If you touch BOTH AC wires, you get zapped (electrocuted) - it doesn't matter if it's isolated or earth/ground referenced.
    If a tree falls across an isolated system's wire, or some carbonised rodent or water or conductor does the same, then it becomes a referenced system.
    If you then touch the wrong conductor, you get zapped.

    Hence we make the system "safe" by connecting equipment chassis to earth/ground. Then it doesn't matter if there is any internal fault - you won't get zapped. A Neutral to chassis fault probably won't do anything, but the Active to chassis fault will blow a fuse.

    Now if reliable RCDs aka Residual Current Devices or Earth Leak Detectors were available a few decades ago, we could have kept our 2-wire isolated AC system - though that is more from the safety point of view; it doesn't factor in the need for EMI shielding which is more important today (hello GSM!).

    BTW - RCDs operate by detecting any DIFFERENCE in the 2-wire AC currents. If they are not the same, then current must be leaking off somewhere - maybe through you! Hence they should trip and break the supply.
    The DO NOT detect earth or ground leaks as such, merely the current difference in its two conductors.
    The so-called leak could be to heaven (and it probably will be if you are the conductor), hence why Earth- or Ground-leakage detector isn't such a good name.

    Our Standards Association also frowned on the term "Safety Switch" as they figured people would think they were safe and hence maybe become careless else deliberately touch active conductors (it's a cheaper buzz than deliberately crashing air-bagged cars).
    Alas like airbags, RCDs (Safety Switches) may fail to operate. Components blow and mechanisms fail. And many do not regularly test their system and hence relays and circuit breakers etc may seize. (Ever seen a $multi-million site go down because nobody had tested their UPS (Uninterruptible Power Supply) for years - the batteries and everything were fine, but the contactors had seized. LOL!)
    Hence why RCDs have a test button with a notice like "test every x months".


    Anyhow, whilst an inverter output need not or should not be "earthed", its earth/ground pin could or should be connected to its Neutral output, or - for shielding purposes - the DC ground.
    Or (and?) an RCD could be used PROVIDED the RCD switches BOTH conductors.
    If an RCD only switches ONE conductor (as may be done with cheaper RCDs in dedicated wiring), then you might still be getting zapped from the other conductor.


    So, whatchas reckon.... should I write something about these issues...?
    Oh poo - I just did.

    Note however that the above excludes inverters with a bypass supply - ie, like a UPS where there is a mains connection (ie - a wall socket AC supply). That requires a local MEN point and dual-pole switching (the inverter supplies the Neutral-Earth connection WHEN the inverter (DC) is supplying the load, and the mains Active and Neutral must both be switched, and of course the inverter chassis is AC/mains-earthed - all in accordance with Australian Standards (LOL!)) - but that's another story.....

  9. #39
    What can I say? I like serial. Curiosity's Avatar
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    Right. As far as I know an inverter is the same as a UPS. They just pump +60 on one side and -60 on the other, and flip it 60 times per second as a square wave. There's no A pole-neutral-B pole or the 240V wave from a generator, unless it's switching +/-120 on one side? Which I mean, either way would produce the same result but I'd assume whatever is cheaper.

  10. #40
    Raw Wave
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    Yes - though it isn't +/-60V and it isn't a square wave - the minimum these days is modified square/sine wave which is a 3-step each way - ie, +40, +80, +40, -40, -80, -40, +40V etc - the actual voltages selected for whatever peak or RMS value they decide to emulate.

    But unlike an ac-ac UPS which is usually ground referenced, and inverter doesn't have to be.
    Viz: AC powered equipment that connects to Utility power usually has to conform to some Standard. In Australia it is AS-3000 which is legislated and hence mandatory. It defines the earthed system that we have - similar to the British but I'm unsure about USA and the other "former" 2-pin or double insulated countries.
    In Australia, a mains-AC UPS must therefore be earthed and its output must also be similarly earthed, and the UPS should supply the MEN when on inverter supply if dual-pole switching is used. (I am unsure of recent progress. Alas AS-3000 is intended for AC loads, whereas inverters, generators and UPS are generators - not loads per se. I was once accused of breaching AS3000 because I specified dual-pole switching for inverters, and AS3000 stated that "the Neutral shall not be switched". However the Electricity Authority approved it and added that "to NOT switch the Neutral would be hazardous". But there was a later IT-equipment standard that went against that..... )


    Anyhow, as you say, the inverter output is floating as with a UPS.
    Hence if you touch either conductor, you will not get a shock (the -60V or whatever becomes 0V and the other side then becomes "live" 120VAC).
    But for UPS, one side will probably be tied to earth or ground.

    An inverter does not have to be referenced - that's what makes them "safer" in cars than wall outlets etc.
    But early inverters that were marketed for cars did often have a common ground for input and output - and this was a hazard. I still see advertising notes stating "these are NOT the old hazardous type....".

    The output isolation doesn't effect cost that much. The biggest cost factor is the mod-square versus true sinewave outputs. There there is the usual protection costs - like overloads, transients, reverse polarity etc.
    An isolated inverter cannot use an auto-transformer so that may add cost, but who uses them anyhow (not even modern car ignition coils LOL!). Hence an isolated output saves on the copper used to connect to the input DC power.

    And even though the inverter's 3rd ground/earth pin may be tied to the DC ground for EMI etc suppression, that doesn't mean the AC output has to be related to it. But that's were Standards can be confusing, and there are many misunderstandings out there (like the guy that insisted on an earth stake for the inverter output so that an Earth Leak Detector (RCD) could be used. Fail x 2! But what would I know - I only got my AS3000 breach approved and endorsed).

    But do you need the inverter AC ground connection to blow equipment fuses? (Probably not - when you plug the active to chassis shorted faulty equipment into a wall or mains socket, the fuse will blow then.)
    I usually set up my distributed outlet permanent inverters with their gnd/earth connected to the "neutral" output so that my system is the same as a domestic supply.
    But for self-contained loose inverters, I just ensure they are isolated from the DC supply. No point setting up a non-isolated hazard.

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