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I have the setup below in my cabin. Currently I have to manually turn off the inverter for the 220V as well as the main switch when leaving the cabin. I would like the main switch to control both, by somehow having a relay open the inverter circuit when the circuit from the batteries to the fuse box is open (i.e. toggled to "off").

I am totally open to changing the setup/layout by introducing new components.

I have not dabbled in relays before, but whatever the solution is, it needs to handle the fact that the inverter draws up to 180A, and most relays I have found max out at 100A.

            ┌────────────┐
            │  PV array  │
            └──────┬─────┘
                   │
             ┌─────┴───┐
             │ Charger │
           ┌─┴─────────┘
           │
           │
  ┌────────┴──┐         ┌─────────┐
  │ Batteries ├─────────┤Inverter ├────────────┐
  └────────┬──┘         └─────────┘            │
           │                                   │
           │                          ┌────────┴─────┐
           │                          │220V circuit  │
       ┌───┴───────────────┐          │  w/appliances│
Has    │ Fuse box          │          └──────────────┘
on/off │ / 12v distribution│
switch!└───────────────────┘


        ┌──────────────┐
        │12V appliances│
        └──────────────┘

Additional info to answer comments

  • The batteries are 12V. Most of the cabin (lights, stereo, fan, Wallas kerosene burner, USB-chargers) runs off 12V and I don't want the hassle of changing it all. They all draw small currents (typically 4-5A in total @12V).
  • The inverter is not a fancy Victron high-end one, but some "China brand" I do not know the name off, bought off Ali Express or BangGood, cabable of 1000W continuous, 2000W peak. No remote control option or anything.
  • Yes, I have a professional crimp tool for large gauge cables (used to create the existing cables)
  • Yes, I do have a boat style switch that handles big loads (which is not installed, yet). power switch
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    What's your battery voltage? That may affect what options you have. Is it actually 12V or do you have a higher voltage setup and voltage converter for our 12V circuits?
    – Chris H
    Nov 2, 2023 at 9:13
  • 1
    What make and model is the inverter? Also, what are you using for your 12V distribution shutoff? Nov 2, 2023 at 11:45
  • I would have a nice beefy contactor between the battery and the inverter + 12V fuse box. And I do hope there is a properly sized fuse between the batteries and the inverter as well. You can get a "battery switch" as used on, e.g.,boats, that can handle 1000A or more and have it disconnect the battery from everything.
    – Jon Custer
    Nov 2, 2023 at 12:39
  • @JonCuster I suspect they don't want to disconnect the charge circuit
    – Chris H
    Nov 2, 2023 at 13:06
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    @ChrisH - The OP needs to handle 250A loads for the inverter, and who knows how much for his 12V loads. As one example, I have a 100A cable (fused and switched) going to the back of the truck to charge beefy trailer batteries and run an air compressor. Yes, a professional crimp tool for large gauge cables (0/2/4/6) was a good investment.
    – Jon Custer
    Nov 2, 2023 at 14:00

2 Answers 2

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The word you may be looking for isn't "relay" but "contactor". These are more often used for switching mains, but definitely exist to switch high DC currents.

Note that when selecting relays, contactors or even switches, it's important - essential at high currents - to ensure the DC rating is within spec. That's because arcing across the contacts is a real issue, and AC arcs self extinguish while DC arcs don't. So relay contact current and voltage specs are likely to be lower for DC than AC.

You'd also want a 12V coil rating. That's quite easy, but check that the "12V" on your 12V circuit isn't too high; especially when charging it can get nearly to 15V - and when drawing a lot of current the voltage can sag. You may need a power supply taking in 12-ish V and giving 12V ± 0.5V or something similar. These are readily avilable for powering sensitive kit in cars.

Contactors for this sort of DC current look to start at around £/$/€200-300. I'm not saying any of these are right, or available where you are, but here are some examples.

Also check your inverter's documentation for its own shutdown procedures. It might not like you cutting the input if there's a load on the output. Mine (3kW peak, 1500W continuous) specifically tells me to turn it off with its own switch, which is far too small to switch the incoming current, and thus must instruct it to shut down. I'd risk cutting the input if the output was unloaded or very lightly loaded.

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    Also check your inverter's documentation for its own shutdown. It might not like you cutting the input if there's a load on the output. Mine (3kW peak, 1500W continuous) specifically tells me to turn it off with its own switch, which is far too small to switch the incoming current, and thus must instruct it to shut down. I'd risk cutting the input if the output was unloaded or very lightly loaded.
    – Chris H
    Nov 2, 2023 at 10:08
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    that comment seems worthy of adding to the answer itself...
    – FreeMan
    Nov 2, 2023 at 12:55
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    Thanks a lot. A contactor seems like the theoretically right thing, but the price is getting a bit steep with power supplies to give a even voltage in addition to the pricey contactor for this kind of current. It seems I might just need to introduce an additional set of bus bars with a switch in between them to break power, so that both the distribution panel and the inverter can be cut simultaneously. Having that contactor, on the other, would open up for turning everything on/off remotely (using Arduinos), which is entising. Thanks a bunch!
    – oligofren
    Nov 2, 2023 at 22:09
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However if that distribution panel can be setup to switch and supply that high total current then you could power the inverter from the panel.

If not the keyword you are looking for is "contactor" those imply high current applications. If you search for a 200A DC contactor you should find some that will fit your needs.

Put the contactor (rated for the current and the DC voltage) between the inverter and the batteries and power the coil (make sure it matches your battery voltage) from the distribution box controlled by the main switch.

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    I was assuming that you'd want to keep the wires to the inverter as short and uninterrupted by extraneous connections as possible. And 12V distribution panels tend to be built for 10s of A max
    – Chris H
    Nov 2, 2023 at 10:07
  • @ChrisH AFAIK you just need a tiny trickle of power to the contactor from the distribution panel. That just controls the on/off (closed/open) state of the contactor, which has the big current from the battery running through it. Am I right, ratchet freak?
    – oligofren
    Nov 2, 2023 at 21:58
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    @oligofren yes, the bit I didn't think would work was the first paragraph, switching the high current with the panel
    – Chris H
    Nov 2, 2023 at 22:13

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