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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
oligofren
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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 02 '23 at 09:13
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    What make and model is the inverter? Also, what are you using for your 12V distribution shutoff? – ThreePhaseEel Nov 02 '23 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 02 '23 at 12:39
  • @JonCuster I suspect they don't want to disconnect the charge circuit – Chris H Nov 02 '23 at 13:06
  • @ChrisH - sorry, meant disconnect the load downstream of the battery, not between the battery and the charge circuit. Doing both loads at once is fairly easy with a pretty small switch. – Jon Custer Nov 02 '23 at 13:09
  • @JonCuster OK, just extra cabling then. I know in my campervan I have very short fat leads to the inverter, and far thinner leads to the 12V systems; I rely on the inverter's own input fuses and control switch, disconnecting the leads mechanically for long periods of downtime. I haven't worked on quite such thick cables and don't have the tools to terminate them, but the OP might need to obtain such tools anyway – Chris H Nov 02 '23 at 13:55
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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 02 '23 at 14:00
  • If the inverter supports higher voltage input, reconfiguring the batteries to a higher voltage bank makes this much, much easier than sticking to 12V. the 12V loads can be either a completely separate bank, or run from a 48V->12V converter (switch-mode power supply.) – Ecnerwal Nov 02 '23 at 14:14
  • @JonCuster, yes, that's why I stick to an approach that uses only factory-terminated cables for my inverter. The crimp tool might be the most expensive part of the job. I haven't handled mine in a while, but I reckon they're thicker than 0, as well. – Chris H Nov 02 '23 at 14:17
  • @Ecnerwal of course there are multi-input inverters, but they're specialist enough it would probably be more cost-effective to replace the one that's there. Plus the cost of the SMPS and a new solar charger setup for the rewired panels (dual 12/24V is quite common, anything higher, again, is a separate product) – Chris H Nov 02 '23 at 14:19
  • One other point (partly @JonCuster) is that 12V fridges (which the OP may well have) are very sensitive to voltage drop. Other appliances too, if they have low battery detection circuits. I had to run separate cables for mine, with a single non-shared fuse instead of a shared main fuse plus one serving the fridge, and avoiding the undersize, overlength cable in my distribution panel. Otherwise the inrush current to the compressor tripped its low battery circuit (and there were no sensible mods I could make to the fridge as everything is sealed) – Chris H Nov 02 '23 at 14:23
  • @ChrisH Many (but not all) 12V inverters are actually 12/24V or 12/24/36/48V - the 12/24 are fairly common, since larger trucks (lorries) tend to use 24V systems. So it's not uncommon for someone to set up a 12V system using equipment that could support higher voltage. – Ecnerwal Nov 02 '23 at 14:30
  • @Ecnerwal I know mine is specifically 12V only, as are the others I can see in mine browser history from when I bought it. – Chris H Nov 02 '23 at 14:38
  • Are you looking at a marine switch because that's all you can find that can switch DC at the currents you're looking at? (You may not be able to use that switch for a fixed mains application.) Also, are there *auxiliary contact* kits available for the switch you've been looking at? – ThreePhaseEel Nov 03 '23 at 02:21
  • @ThreePhaseEel Yes to the first question. I have no idea what the second one means :) – oligofren Nov 03 '23 at 02:42
  • @oligofren -- second one means that the switch has a kit for it that allows you to add extra switch contacts for switching small signals – ThreePhaseEel Nov 03 '23 at 03:25

2 Answers2

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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.

Chris H
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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 02 '23 at 10:08
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    that comment seems worthy of adding to the answer itself... – FreeMan Nov 02 '23 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 02 '23 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.

ratchet freak
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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 02 '23 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 02 '23 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 02 '23 at 22:13