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help wiring an inverter into a campervan

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  • help wiring an inverter into a campervan

    Hi people,

    I'd like to get a power inverter to power a Wii in my campervan. The van has mains sockets inside which can be used when the van is hooked up to a site power outlet.

    I was wondering if there's a way to wire the inverter into these sockets so that they can be run off the battery, but so that when you plug the van into the mains, the inverter won't be fried. (Would that even happen? What would happen if you plugged an inverter's outputs into the mains?!) I'm thinking that some kind of relay might do the trick, but I really don't know the first thing about relays...

    Thanks for any help.

  • #2
    Get a licensed electrician to do it. (That's the usual legal requirement.)

    Usually connecting inverters to the mains is quite illegal, and it will fry your inverter - hopefully without too much of an explosion and damage to neighboring electrics (which you will be liable for).


    • #3
      Are you looking to simply connect the battery terminals from the invert to your vehicles 12/24volt lines? If this is the case, Its low voltage and can be done by most people... not a high voltage job in this case unless you are reboxing the inverter or something..

      I could be wrong,
      2004 Holden WL Caprice Auto GENIII
      Base System = Raspberry Pi
      Everything else is pending for now as switched from a Mini-ITX setup


      • #4
        Sorry, I took that to be apparent.
        It's the AC side that is Regulated (by law, as well as voltage etc).

        It's different if proposing unplugging the power outlet and plugging the inverter output in its place.
        But interconnected switching is regulated, plus it can be hazardous - it should use dual pole switching (active and neutral) - and arguably the AC power outlet's earth/ground.

        And appliances other than "double insulated" usually depend on an earth or ground to Neutral connection for safety fusing (ie, to prevent electric shocks), but that should be provided by the inverter in any situation.
        [ IE - even if not connected to the planet Earth's earth/ground (which I don't recommend for safety reasons for battery powered "earth/ground-stake isolated" inverters), any 3rd-pin earth/ground should be connected to the inverter's Neutral line. If such loads are connected to domestic/commercial AC power outlets, then that must supply that earth/ground to Neutral connection - NOT the inverter! Hence in part why dual-pole switching is required. ]
        Mind you, I have met some electricians that seem totally unaware of such issues. Luckily the last was in a mower shop and I simply showed him the "safety sticker" on a generator. and then....

        Of course if vans etc are not effected by such regulations, there is a simple way to achieve what the OP wants.
        But understanding what I have said provides the required knowledge and responsibility to the reader for implementation.

        And I'd suggest RCDs (residual Current Devices, aka here as "Safety Switches"(sic)) for any inverter output and power outlet is safety is a concern.


        • #5
          Thanks for the replies. I've got no problems connecting the inverter to the van's leisure battery, what I wanted to do was connect the inverter's power output to the existing plugs which normally only provide power when connected to the mains (i.e. when plugged in at a camp site).

          The van has one of these in it:
          Click image for larger version

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          As I understand from your reply, OldSpark, I should wire up the inverter's live, neutral and earth to the socket (or is neutral and earth the same thing in this case? - earth for the inverter will be the van chassis). Then I should include a dual pole switch to disconnect the inverter's live and neutral when power is supplied from the mains in a site. The plug will then be earthed to planet Earth through the camp site's earth at the power supply.

          How do I make this dual pole switch automatically disconnect the inverter when AC power from a site is plugged into the van?

          Thanks again.


          • #6
            Thanks OldSpark. I understand what you have said. So, basically, connect the inverter's live to the socket live pin, and the inverter's neutral to the socket's neutral and earth pins, and set up a dual pole switch so that when I connect to domestic/commercial AC power outlets, both connections are immediately broken so that the socket's earth pin is now earthed to Planet Earth instead of the inverter's neutral.

            Is this right? Are there relay switches available that can achieve this simply?


            • #7
              Would something like this 10A DPDT relay do the trick?


              • #8
                Rats, I though the PMS3 had all you needed, but it does not cater for an inverter. (IMO, that's strange!!)
                After all, it handles incoming mains AC and the vehicle's DC (including aux battery) and hence should be "Authority Approved".

                But it appears to simply be a battery charger that uses mains AC to power the 12V DC loads else AC loads with no provision for a battery to power AC loads...

                I'll have to look into it later, but I think the PMS3 will complicate things. I suspect you (still) have to switch the PMS3 mains input (which probably requires a License) but then disable its internal charger.

                There should be a PMS model that handles an onboard inverter (surely?).
                Again, later...

                Ideally we'd get inside the PMS3 to do the switching and the addition of the inverter (with its subsequent disabling of the PMS3's "charger"). Of course, that's probably illegal unless Licensed etc.

                As to earth = neutral, they are VERY different wrt Legislation and Regulations. Although they may be interconnected a various points, it is WHERE and when such interconnections exists that is crucial. Incorrect or no interconnection can be fatal, as well as equipment & system damaging.


                • #9
                  FYI - I found the following diagrams from an old telco spec.

                  The first shows a battery powered inverter supplying the MEN connection, ie, the "Mains Earth-Neutral" bond to enable "3-wire" AC loads to clear (blow) their fuse in case of an active to (earthed) case fault.

                  To hopefully preempt confusion, its Earth is NOT terra-firma - it merely refers to the labeling used for Aussie etc wiring.
                  Also, an inverter has L1 & L2 outputs which are "floating" (assuming it is an "isolated" inverter, but non-isolated inverters should never be used; I think they are illegal in Australia). The Active and Neutral labels are assigned to L1 & L2 depending on which AC pin they are connected to.
                  In the cases below, the inverter output that is bridged to the "Earth" output must be the Neutral. (Or rather, it becomes the neutral.)

                  Click image for larger version

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                  This 2nd pic below shows a similar inverter with a "bypass" mains AC supply.
                  The inverter is the same as the diagram above - ie, it has an output "Earth" which is taken from the inverter's "Neutral" output.
                  However, if the mains AC is supplying the load, it is illegal to bond Earth to Neutral (MEN) other than at the MSB (Main Switch Board) that supplies the mains AC. (There are some exceptions to that AS3000 Rule, but they are not relevant here.)

                  Hence dual-pole switching is required.
                  When the inverter supplies the load, the inverter supplies the MEN.
                  When the inverter is in bypass mode and the AC is supplied by the mains AC, the mains supplies the MEN (ie, at the switchboard etc).
                  [ Dual pole switching is also used to prevent inverter-generated AC feeding back to the mains. That can be hazardous for electricians and firefighters that have isolated the mains at the MSB and therefore believe there to be no downstream AC. 240VAC inverters can inductively or capacitively couple 120VAC to the mains supply. That is a separate issue to providing the inverter output MEN. ]

                  Notice too the Earth to the inverter chassis. That's because these particular inverters have an internal mains-inverter changeover relay, and since the inverter is connected to a mains AC supply, its chassis must therefore be earthed (AS3000 regulations).
                  [ IE - the DC supply is "isolated". The DC input has no relevance to Earth except whatever Earthing is applied to the battery. (FYI it's normally +ve for traditional "land line" exchanges, and -ve for "mobile" (cell phone) exchanges.) ]

                  Click image for larger version

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                  Though somewhat preliminary info for now...
                  An RCD can be used on the inverter output (irrespective of whether they have an Earth output), though an Earth is required for the RCD's self-test
                  Since any work in the inverter and relay etc should only be done with both the DC and AC mains disconnected, the RCD can be placed after the dual-pole switch.
                  An (additional) RCD can also placed at the mains AC input. Though unnecessary in this instance (since it's "all internal" and the mains is disconnected during maintenance), it may be desirable depending on other things connected to the mains - eg, battery chargers etc.

                  Hopefully the figs are reasonably easy to understand if not the RCD comments.
                  But it's meshing the above into a PMS system that gets tricky.

                  And if you got your PMS3 image from, you should have seen its footnote:
                  Important:- Please note that all Mains Electrical appliances Must be fitted by a suitably qualified engineer
                  If Appliance Is Diy Installed The Electrical Installation Must Be Inspected For Safety by a suitably qualified engineer

                  Note too that EXCEPT for the mains connection (whereby there is a terra-firma Earth), there is no terra-firma Earth involved.
                  Whether to "earth-stake" an inverter system's "earth" to terra-firma is somewhat contentious.
                  I argue that it introduces a hazard in normal mobile inverter use and should only be done in certain circumstanced (eg, if interconnecting to other eathed equipment).
                  But that's where RCDs should provide adequate protection.

                  Simple isn't it?

                  A final solution will be simpler. It's working forward to that final diagram that a PITA - especially if trying to use existing equipment like the PMS3.

                  PS - terra-firma earth is represented by the 2 "earth" (or chassis or GND) symbols in the 2nd fig.
                  Last edited by OldSpark; 04-21-2012, 01:06 PM. Reason: PS...


                  • #10
                    Thanks so much, OldSpark. The second diagram is very useful.

                    So, if I cut the power cable between the PMS3 and the socket, and splice it and the inverter's outputs into a double-pole double-throw relay that defaults to the inverter side, but which switches to the mains side when mains is plugged in then everything should be fine. The inverter would not supply any AC to the PMS3 because it is isolated from it by the relay.

                    Is is possible to use 240V AC to switch a relay?


                    • #11
                      Make sure that (2nd) diagram isn't controversial. (Nor the first for that matter.)
                      It caused a great stir down here a few decades back. (Industry people said it was "illegal".)

                      Yes, there are 240VAC relays (as in 240VAC coils/solenoids).

                      And I presume you mean the relay at the AC output of the DMS3... (At the input should be illegal.)
                      If so, no cutting should be necessary - the DMS3 AC supply passes thru, else the inverter is powering the loads and supplies the MEN.
                      IE - the APPROVED and Licensed-wired 240VAC relay coil is across the mains input of the DMS3 so that when energised, its contacts at the DMS3 AC output bypasses the inverter. [ POST EDIT - can now probably ignore this original addition... "as well as cutting the inverter's DC supply. (How is another issue.)" ]
                      When the mains AC drops, the inverter relay drops out, hence changing over to the inverter's AC & MEN point. That involves [ POST EDIT - can likewise probably ignore this original text... "DC connection and inverter start-up, and" ] a break of at least the relay changeover time (plus inverter start-up).

                      If mains is available, the batteries are being charged thru the PMS3 so the inverter overhead (idling or stand-by current) isn't an issue.
                      So forget that mains disconnecting the inverter's DC statement earlier. (Sorry, I should have thought about this...)

                      Whilst the mains is stable, you might manually switch off the inverter.

                      FYI regarding the 2nd diagram...
                      It is essentially an ac-ac UPS but without the rectifier aka charger.
                      It was from a telco spec for powering "essential" AC equipment off 48V exchange batteries that powered all the comms gear.
                      It was also an "on-line" system, ie, it was the inverter that normally supplied the load. (Unlike off-line UPS which switch to the inverter ONLY if there is no mains AC. In fact typical domestic PC UPS etc have a combined rectifier(charger) and inverter so it can only either charge, else invert. (LOL.... How do you know when the inverter has failed?))
                      Hence it would only switch-over if the DC failed or the inverter failed or was overloaded, ie, no switching delay due to loss of the mains AC.

                      However, the inverter would track the incoming mains and would allow a manual transfer if it was in sync.
                      It was the inverter that energised the "bypass" (mains-changeover) relay. (Energise when the inverter supplied the load.)
                      To cut a long story short, it was defined as a "no break" system where "no-break" was defined as "up to a 5ms break" (ie, for relay switching time, and- in theory - sensing time).
                      That was because under typical standards, a 5mS break could be tolerated by typical loads like PCs (... LOL... but not the IBM-XTs with the Mexican-made power supplies with brown rivets - like Sodium lamps etc they only tolerated a 1mS break if that! Oh - the memories... )
                      And if you wanted to force a break when the inverter wouldn't allow it (because the mains was not there or out of voltage/frequency tolerance or not in-sync), then you simply flipped the inverter's input DC breaker (and prepared an explanation if its loads blew up! )

                      Why did I recite the above?
                      Firstly because that's the way I'm used to thinking and you application is sort of inverted... ooops, opposite to that.
                      Hence I need to be careful and you need and others to check my sanity.

                      It also includes important issues such as what if the loads are switched over to an out-of-phase supply?

                      And I shall reiterate the universal Riot Act that you SHALL not perform any work that is Mandated to be done by qualified and Licensed personnel.
                      And that extends to 240VAC etc work that is NOT covered by such mandates.

                      I did try to investigate the DMS3 and your desire in more detail, but didn't get far.
                      However during this reply's "discussion", it seems the answer may be fairly straight forward. But it can't be that easy can it?

                      But hold back any implementation lest you die or get gaoled or kill someone else or cause damage etc.

                      Was what I outlined what you were thinking?
                      And are you UK based? (Or yUK LOL.)

                      Meanwhile I'll break and try a fresh look...


                      • #12
                        Originally posted by OldSpark View Post
                        It also includes important issues such as what if the loads are switched over to an out-of-phase supply?
                        That's a really good question, say you switch in less than 5ms, then what happens if AC mains are 90, or even 180 degrees out of phase with the inverter output? 60hz is 16milliseconds per phase, so if you switched at the wrong point in both phases, you could potentially have up to 32ms between voltage peaks for a single cycle. What would that do to a power supply? Not sure!
                        "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
                        My Shop


                        • #13
                          Ah yes, a fun question.

                          It can happen. F.ex, the North Island of New Zealand is (or was?) fed by a DC link from the South Island. Occasionally its phase could instantaneously change due to its DC-AC conversion. (It used to be about twice power year. I found out because AC-AC UPS would drop the mains.)
                          I'm not sure if Vancouver suffers the same. (It's undersea AC feeds were converted to DC decades ago to carry more power.)

                          And anyone with a typical PC UPS is likely to experience the same during a power outage.

                          Chances are that modern SMPS power supplies (used in PCs & TVs and most newer things like phone chargers etc) don't care - they just need a certain voltage of any shape.

                          Transformers etc won't like it, but they too are probably ok.

                          Plus if it's with a 4-5mS break (a typical relay or contactor switch-over time), that's about a 1/4 cycle or 90° break for 50-60Hz AC. It's not as if you have an instantaneous voltage change as I described above (where worst case maybe it could go from a peak -√2 x 240 = -340V to +340 within a milli-second. though I'd consider that extreme unlikely).

                          Alas I'm trying to delve deep in my memory banks... But all I see is brown rivets!

                          But even if it's a tracking in-sync inverter or UPS, a switching delay of ~5ms is ~ 90°, hence on average some 100V for a 240V AC supply. (Would it be the "average" of half the peak?)

                          And that's just the switching delay. How long does it take to sense and decide to switch? IE - the voltage difference could be greater...
                          [ That was never defined in aforementioned inverter nor UPS specs, mainly because being on-line, it was not that important an issue. (READ: too hard to define!) ]

                          Now and again when switching on power outlets you might here a crackle or an arc. From what I recall, that was sometimes due to the switch-on being near the peak voltage whilst the transformer etc load was magnetised in the opposite phase. (Other times due to bad switches or slow turn-ons, hence arcing.)
                          Last edited by OldSpark; 04-24-2012, 10:19 AM.


                          • #14
                            We have a zantrex inverter on our boat - it has 2 inputs - 12v and 110 a/c - it automatically knows to turn the inverter on if there is no a/c coming in (and use the 12v power source).