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3 prong AC for main cabin

Discussion in 'Gen 5 Prius Main Forum' started by Will B, Aug 22, 2023.

  1. Will B

    Will B Active Member

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    Hi there, I just got my 2023 Prime and still in the throws of getting it set up. Fun times! It replaced my 2003 Gen1 Prius, so a huge step up in technology.

    The built-in AC adapter is big for me. We go on road trips and my wife is usually using her laptop so we've been using a stand-alone inverter. The weird thing is the AC outlet in the main cabin is only 2-prong. Laptops clearly need 3-prong and running an extension to the trunk doesn't seem great. I have a ground "cheater", but curious what solutions others have used for ground connection. I'm thinking of running a ground wire to one of the bolts holding down the driver or passenger seats. Does anyone have a better idea?

    will
     
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  2. Tom_06

    Tom_06 Active Member

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    Don't loosen seat mounting bolts unless you have a torque wrench and the specs to properly retighten them. Seat mounting bolt tightness is part of the safety restraint system.

    I'm surprised your laptop has a 3 prong plug. The ones I have had over the years (HP, Sony, Apple) have all been two prong adaptors. If your inverter plugs into a cigarette lighter outlet and offers a 3 prong outlet, it is just BS. That "ground" is just connected to the same thing as the neutral wire inside the little box as the cigarette lighter is just a two wire DC supply.
     
  3. Trollbait

    Trollbait It's a D&D thing

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    Not every lap top charger has a 3 prong plug. There is even 12 volt ones available. Look into the specific lap top. Maybe it will be safe without a grounded charger, and you can use the adapter without grounding it.
     
  4. aforkosh

    aforkosh Active Member

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    Apple laptop charger bricks have been 2-pronged from time immemorial. Modern laptops that charge via USB-C can use any USB-C charger of the appropriate wattage. The bricks are usually 2-pronged.
     
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  5. Will B

    Will B Active Member

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    Tom_06: Ugh, good point on not messing with that bolt. That seemed the easiest access to something grounded. Over the decades all my laptop power cords have been 3-prong, so just assumed they were all that way. Maybe it is because I get "desktop replacement" class laptops with heftier power supplies. If neutral is indeed hooked up to chassis ground, then life is good. I've never had an in-car inverter before, so not sure how it is wired up. I guess I could (VERY CAREFULLY) try to measure resistance between neutral and chassis ground and see if they are connected. I'm pretty sure that is how my stand-alone inverter is wired. I do want it grounded somehow.

    will
     
  6. Will B

    Will B Active Member

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    Aforkosh: Thanks. As mentioned to Tom, interesting that I've only ever seen three-prong cords for my laptops. I'll do some poking around to see if neutral is indeed connected to chassis ground. I feared it may be kind of like the "double insulated" setup you see on some equipment that just isolates everything.
     
  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Some laptops still have a power brick with a ground pin, but I haven't noticed any that actually needed it, electrically speaking.

    My most recent Apple and Dell machines both came with 3-prong power bricks, which I leave unused in a drawer at home. On the go, I run both on a USB-C brick that has a folding 2-prong connector.
     
  8. ChapmanF

    ChapmanF Senior Member

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    Years before USB-C and -PD and -PPS, when every laptop and gadget had its own shape of power jack and its own voltage requirement, third-party accessory outfit Kensington had a kind of cool product: a power brick with a multiconductor output cable and a whole bunch of different tips you could buy to fit different laptop and other device power jacks. Each tip contained a tiny bit of circuitry that would work, over the extra wires in the cable, to program the brick for the right voltage output. Kind of like what somebody would have to invent after seeing a prophetic vision of USB-PPS but being stuck in the 2000s.

    Apparently their brick (which is quite compact) was a tiny bit lacking in the isolation department. The cable on the input side, plugging into the wall, lacks the usual wider prong for neutral, so it can be plugged in either way. And I have this HP laptop with a stylish metallic top, and depending on which way I plugged that brick into the wall, my typing on the laptop can come with an extra zesty zing.

    I eventually carved a mark on the neutral side of that plug, so I'd remember which way to plug it in.
     
  9. Trollbait

    Trollbait It's a D&D thing

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    I was surprised my little 13in lap top had a three prong charger brick.
    Just saw a similar lap top charger on Amazon, but it plugged into the 12 volt outlet of a car.

    Saw a comment looking into this that a lap top with metal case originally had a sleek, 2 prong charger, but customers reported getting tingles while charging. So they started using a grounded charger. That's why suggest looking into the specific lap top.
     
  10. sam spade 2

    sam spade 2 Senior Member

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    Why ?
    Serious question.

    The entire outer shell of the laptop likely is plastic.
    That should effectively make it "double insulated".

    The body of your car very likely is NOT used as one side of the AC service like
    commercial power is.

    I think you should buy a "cheater" and not worry about it.
     
  11. Will B

    Will B Active Member

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    Sam:

    Fair question. As mentioned earlier about some folk getting a tingling feeling on a double-insulated device. Even with a plastic case, there is probably some metal somewhere and certainly metal if you plug something in like USB. I worked for a satellite TV company until retiring and we made the move from 3-prong to 2 prongs for some set-top boxes and without ground having the chassis float to half-way between live and neutral was "just how it works" and you did what you could to make sure it was safe. That just seemed not great to me, so must admit decent grounding is more a preference than a necessity.

    The car itself clearly isn't grounded, but better to be at the same potential as the chassis while you are inside it at least! :)

    will
     
  12. ChapmanF

    ChapmanF Senior Member

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    I think the issue with my tingly laptop was I was using the third-party power brick that falls, shall we say, a wee bit short of being double-insulated.

    The laptop is tingle-free on the brick that HP supplied with it.

    It's also tingle-free on the aftermarket power brick, if I remember to look for the mark I made showing which prong goes to neutral. :)
     
  13. Will B

    Will B Active Member

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    Chapman: Yea, I'm probably being a bit overly paranoid! :)

    In other news:
    - I measured resistance between chassis ground and live and neutral coming out of the socket in the center console. No measurable connectivity for either. Kinda makes sense, it is whatever the source equivalent of "double insulated" is. I also measured between chassis ground and the USB plug grounds and those are near-zero ohms.
    - I measured resistance between the mains ground and ground on the laptop-side plug and get *exactly* 1Mohm. That rings a bell, zero ohms is bad in case there is a failure of some kind with hot, a dead short can make lots of smoke. Again, makes sense after realizing that.
    - I measured resistance on my old external 12V-120V inverter and that was zero ohms from the 12V ground to the AC ground plug.

    Armed with that, I figured I just needed a "light ground" for the ground pin, so resorting to just an alligator clip that I'll attach to the chair rail when traveling. With that, TADAA! :) My solution below. The wire is trimmed to be just long enough to as not to snaggable.
    Prime Ground.jpg

    will
     
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  14. sam spade 2

    sam spade 2 Senior Member

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    The whole reason for GFI with commercial AC power is that
    you are real close to the potential of the earth ground any time your body
    is touching the ground......even through shoes.
    IF you are standing in water or touching a good ground, then
    you are connected to one side of the power line.

    And that earth "ground" also is the "neutral" side of the AC power line.

    The AC power from an inverter or transformer brick does NOT use earth ground
    as part of it's distribution circuit.......or the chassis of the vehicle either.

    Thus you might get a little "tickle" if you come in direct contact with one
    of it's wires.......but you will not complete a circuit through your body like
    with commercial AC.

    I hope your little green wire fix makes you feel better.......
    but it accomplishes exactly.......NOTHING useful.
     
  15. Will B

    Will B Active Member

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    Sam:

    It DOES make me feel better! :) Given a three-prong cord and a two-prong outlet I have to do something and grounding a chassis the designers intended to be grounded seems a good thing even if in the absolute sense the failure conditions where it matters are even more obscure than with real mains. So not COMPLETELY useless, but agree the value is pretty minimal. It is as good a solution as an extension cord to the outlet in the baggage area without needing an extension cord.

    But mostly it makes me feel better! :)

    will
     
  16. Gokhan

    Gokhan Senior Member

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    That is odd. I thought two-hole outlets were obsolete—not that you would need a three-hole plug for an AC/DC adaptor. Just remove the plug of a computer power cord and install a two-prong plug by not connecting the yellow–green ground wire. Black wire connects to the narrow prong, and the white/gray wire connects to the wide prong.
     
  17. Gokhan

    Gokhan Senior Member

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    No, definitely do not do this! This is very dangerous. You do not want to connect the ground cable unless you have an earth ground. If there is a short, you could get an electric shock if you do this. Electrical ground only works if there is an earth ground, and grounded connections can be more dangerous than ungrounded connections if the earth ground fails.

    Now, reflecting on my previous post, this is probably exactly why Toyota used a two-hole outlet instead of a grounded outlet.

    Simply use your two-to-three-terminal adaptor without any ground cable, and you will be OK.
     
    #17 Gokhan, Aug 23, 2023
    Last edited: Aug 23, 2023
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  18. Will B

    Will B Active Member

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    Gokhan: Alas it isn't that simple. Even Toyota has a three-prong plug in the back! Just two prong in the center console. Ground is there only for when things (and in general multiple things) go wrong. The odds of truly needing it are nearly but not exactly zero so I agree mostly with Sam Spade. To me, if a device was designed to assume it is grounded I want to support it. The ground "cheaters" aren't intended to disconnect ground, they are officially to connect ground to the plate screw they say should be grounded. Yea, not how people use it, but none of us speed either, right? It clearly isn't earth ground, but in a car, chassis ground is your ground reference. The difference as best I can tell is for the built-in inverter, both live and neutral look to be floating, so not presenting the same hazard you'd get with house mains.

    To be clear, we're going down rabbit holes here, the practical side of our differences are minor if non-existent. For giggles tomorrow I'm going to confirm the ground pin in the back plug is indeed connected to chassis ground as I suspect. I also have a mains tester that also can test for GFCI. If the car trips on the GFCI test (which I suspect it will), that is even better support the ground pin being superfluous. Since Neutral and Ground are not connected, I think it will get grumpy about that though.

    will
     
  19. ChapmanF

    ChapmanF Senior Member

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    The Xantrex inverter I have in the back came with a separate stud on the rear panel to bond the inverter chassis to the car, and a screw on the bottom that can be removed or inserted depending on whether you want neutral bonded to that. It also has a GFCI on the output, which struck me as a good idea, and I retrofit(ted?) a GFCI into an AIMS inverter lying around, too.

    [​IMG]
     
  20. Will B

    Will B Active Member

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    ChapmanF: Interesting and that seems along the lines of what I would have expected as at least an option, grounding the inverter chassis to the car chassis.

    I got two expected and one very unexpected result from the Prius though!
    - In the back, the plugs ground pin is indeed hooked up to chassis ground (no surprise)
    - With the mains tester I get an "open ground" error indication. This is expected too given that the car is floating neutral relative to chassis ground. Just the center light in the pic below for this test.
    - The weird thing was when I hit the GFCI test button. Nothing tripped (a definite bummer), but the Not/Neutral reverse light lit??!!

    I need to think about this a bit more. The way I understand the GFCI test button is it makes a relatively high resistance connection from hot to ground. If there is a GFCI breaker, it detects a current mismatch between hot and neutral and trips. It didn't, so wondering if that light is just a natural consequence of the GFCI test failing. By pressing the test button, hot is "slightly" connected to ground. Since both hot and neutral are floating, if hot gets referenced to ground via the test button, then neutral will then look hot relative to ground and that lights the red light??? It certainly does so with enough current to light the neon bulb.

    The car not tripping based on the GFCI test is definitely a disappointment. Can anyone else check this just to see if it's maybe a one-off error with Tester.jpg my car? That seems odd. How this plays into the original discussion on the importance of ground I'm not sure yet.

    Definitely learning new things! :)

    will