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Thread: help wiring an inverter into a campervan

  1. #1
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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. #2
    Raw Wave
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    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. #3
    Variable Bitrate mayhembdm666's Avatar
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    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. #4
    Raw Wave
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    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. #5
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    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:
    Name:  PMS-3.jpg
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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. #6
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    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. #7
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    Would something like this 10A DPDT relay do the trick?

  8. #8
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    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. #9
    Raw Wave
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    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.)

    Name:  inverterwiringtype0noma.gif
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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.) ]

    Name:  inverterwiringtype12mai.gif
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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 jaccampers.co.uk, 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 at 01:06 PM. Reason: PS...

  10. #10
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    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?

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