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Can I use mains as backup for off-grid solar system?

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  1. #1
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    Default Can I use mains as backup for off-grid solar system?

    G'day electrical pros,


    I want to run 6 freezers/fridges (10kWh/day) with a 4kW array of solar panels, 4x 300Ah 12v LiFePO4 batteries, and a 2kW 12V Projecta Intelli-Wave Pure Sine Inverter.


    Instead of using a generator as backup for consecutive cloudy or rainy days, can I just use household mains instead? Ideally it would be nice to just somehow plug my inverter into an outlet permanently, and have the mains power automatically take over if batteries fall below a certain charge (e.g. 30%). Does such a connection exist?


    Australian sun is supposed to give 8-20kW daily for 4kW of solar panels, depending on season. And batteries can power all the freezers for a day without sun. But sometimes we like to power other things as well, or we might get a few rainy days and it's too much hassle to start up the generator all the time.


    Australia has 240V 10A household outlets as standard.


    Many thanks to any electrical genius who can help.
    Cheers,
    Ryan

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    I can't see why not. I'm not an electrician tho. I think the thing you are looking for is a changeover switch. Maybe you should be asking a off grid installer, they do this stuff all the time.

    BTW, Phild will be along shortly to ask you to change your listed location. State should be a minimum.

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    Quote Originally Posted by Uncle Bob View Post

    BTW, Phild will be along shortly to ask you to change your listed location. State should be a minimum.
    Yes indeed, the profile location helps keep member's advice locality relevant.

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    Thank you, any recommendations appreciated. For an Australian suitable changeover switch that for both ways is automatic (no human turning of knobs) and seamless (instant transfer so no micro delays when switching). Would it be as simple as wiring my battery source into the grid slot, and wiring the grid source into the backup slot? - kinda just exactly the opposite way you would think it is designed to be wired. Like most people would want solar batteries as a backup to the grid, but I'm that weird one that wants grid backup to my solar batteries haha!

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    Not an electrician so I could be completely wrong but I suspect that the supply authorities will not permit an “off grid” solar system to be connected to their supply network.
    IE if you have mains supply to the property any solar system must be grid connected.

    I would check with your local supply authorities.

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    Cheers droog. I'm not wanting to reverse send electricity to the grid though, would there be a gadget that prevents that happening? If still it isn't permitted even then, would there be such a gadget that allows me to simply plug my projecta inverter directly into any 240V 10a household outlet. In such a way that it only draws backup power from that outlet when my solar batteries are low (70% depleted)?

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    Are you using a generator now, if so how do you connect it to the house?

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    My projecta inverter has an input connection slot on the back of it to wire up a generator to it. For outputs, the inverter has 2 standard AU outlets, so I can just plug in the 6 freezers directly with a couple of powerboards. Not wanting to power the whole house, just the freezers, and occassionally some other tools or computers.

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    Reading between the lines I assume it is some sort of fishing shack or some such other building and it will not have someone there permanently to use a manual change over switch and you need something automatic.
    If I'm correct you proberbly would not be allowed to use an auto changeover to mains however you would be able to have a manual changeover with a three position switch which is no different to using a generator as a backup.

  10. #10
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    Droog is right. If you're generating and using your own power and that same 240V distribution system is also connected (or can be connected) to the public electricity grid, this will attract the interest of the energy companies and compliance issues. They're called "hybrid grid connected", which is solar + battery + grid connection and they have a particular way of being setup.

    What happens when the public grid fails gets complicated. Conventional grid-connected solar with battery storage is required to automatically isolate your system by shutting off the inverter when the grid goes down to prevent back-feeding into the lines and electrocuting linesmen trying to restore power. In other words.... great having a battery to use on normal nights, but you still get the blackouts! A step ahead of this is a battery bank that has a backup function to power one or two essential circuits, with the rest being disconnected from the grid during blackouts. Then there is hybrid with UPS, which can power your home with the grid down, but the design and safeguards are more complicated.

    So doable yes..... but only with proper design and installation, because the mere fact that you "can" plug your normally solar powered circuits into mains power if you need to makes it "grid connected". Your panels and batteries may be able to integrated into such a system saving you $$ (batteries being the most expensive component by far). Your inverter.... I have doubts.

    Not a sparky, but speaking from 10 years experience with an off-grid system and having explored many alternatives.

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    Basically yeah, needs to be automatically switching between solar/battery power and mains power, whenever the batteries cross the 30% mark, without a person being present. I don't really need to modify anything the grid box if unnecessary - if there is an option to just hook my inverter up to any household outlet? Surely the authorities wouldn't mind you plugging something into a regular household outlet to draw power - for all they care, you've probably just plugged a 2000W toaster into an outlet. What difference would it be to plug in an inverter instead of a toaster?

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    Quote Originally Posted by countrybloke View Post
    What difference would it be to plug in an inverter instead of a toaster?
    A very big difference, an inverter generates power an toaster consumes power to put it simply. How would you plug your inverter into a power outlet by a lead with 2 male plugs or connect the house that has to comply with AS 3000 and have a caravan inlet supply.
    If your installation never had any connection to the grid things would be much easier.

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    I was just reading the manual of the inverter and the mains connection is normal operation the via the mains if the mains fail then it drops over to battery a normal method of backup supply but as you said you want to reverse this so it becomes a bit more complicated.

    Am I right in assuming in addition the the inverter you also have a solar charger for the batteries?

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    Quote Originally Posted by Bros View Post
    I was just reading the manual of the inverter and the mains connection is normal operation the via the mains if the mains fail then it drops over to battery a normal method of backup supply but as you said you want to reverse this so it becomes a bit more complicated.

    Am I right in assuming in addition the the inverter you also have a solar charger for the batteries?
    I got a few dirt cheap charge controllers, but no, I would need to go and buy a decent one - maybe paralleling a couple of Renogy Rover Li 100A would do the trick yeah? I also have a PIP-5048MG which is a decent offbrand charger/inverter combined all in one. But for these freezers, I would rather put my projecta inverter to use, especially being left unattended a better brand inverter like Projecta seems a more solid option.

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    There is a reference to connection of inverters in another AS which I don't have. This is a copy of the entry.

    inverter.jpg

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    Default Can I use mains as backup for off-grid solar system?

    What if you had a PowerPoint or two connected to mains permanently. These power points had chargers that would on.y be used when the voltage dropped below some predefined level.


    Sent from my iPad using Tapatalk Pro

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    Quote Originally Posted by Bros View Post
    There is a reference to connection of inverters in another AS which I don't have. This is a copy of the entry.

    What if there is perhaps some super super advanced type of automatic physical circuit breaker/isolator, in such a way that it physically cuts off the inverter power completely, before then allowing power to be drawn from the outlet into the inverter, all done within milliseconds for a seamless transition. Technically on those terms of automatic physical disconnection, the inverter would not be considered "grid-connected"?

    Quote Originally Posted by Forrestmount View Post
    What if you had a PowerPoint or two connected to mains permanently. These power points had chargers that would on.y be used when the voltage dropped below some predefined level.
    Do you mean plug a smart battery charger into a regular household outlet, and have that battery charger programmed so that it only charges when the battery bank falls below a certain voltage (equivalent to 70% discharge)? That way the inverter can continue to draw battery power, while the outlet replenishes the batteries charge? Seems like a great workaround.

  18. #18
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    Not sure it's been mentioned, but if there is any chance at all of a non-grid system outputting to the grid during a grid power outage, you could kill the grid repair team. Just saying

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    Quote Originally Posted by r3nov8or View Post
    Not sure it's been mentioned, but if there is any chance at all of a non-grid system outputting to the grid during a grid power outage, you could kill the grid repair team. Just saying
    Yeah I would think though that a physical circuit breaker/isolator is the industry standard of completely eliminating that chance of any electricution. Currently, the only thing stopping most Australian houses from sending their solar through the grid during an outage is a simple solar isolator I think. That's pretty much it. We have one on the wall for our grid-tie solar of the main house. Whenever we have an outage, the isolator switches off automatically and just cuts the solar power to the gridtie inverter. When the outage ends, the isolator switch automatically switches back on and solar resumes. So if an isolator switch is considered "enough protection" for the grid repair team, why can't a similar switch be installed between my projecta inverter and house outlet. Surely there must be such a gadget.

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    Quote Originally Posted by r3nov8or View Post
    Not sure it's been mentioned, but if there is any chance at all of a non-grid system outputting to the grid during a grid power outage, you could kill the grid repair team. Just saying
    Also my Projecta inverter is a well known brand in Australia and apparently already comes with an AC transfer switch built in to it. On page 3 of my inverter manual https://www.projecta.com.au/ts164920...ion+Manual.pdf it says "The built in automatic transfer switch ensures a quick transfer of power when switching between mains and battery power. The automatictic change over function eliminates the need to manually swap over AC plugs or be switching dials between the two power sources. When mains power is available, mains power passes through the inverter to power the accessories directly. When the mains power is disconnected the appliance automatically switches across to inverter power." I don't understand why Projecta would make an illegal product that risks electrocution to grid repair teams in an outage?

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    I think Tesla battery drawing from solar and mains never feeds back to grid. If you had a black out and battery was low and no sun out, having a genset with ATS and relay to inhibit genset starting unless it’s a blackout, then genset feeds battery and battery feeds the house. When battery is full, or sun comes out, Tesla cuts 240 in, genset stops. Tesla on a clients site is set up to not feed back to grid, not sure if that is standard.

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    ...yep, solutions out there, been looking at something simular (Grid tied but battery/solar backup on outages) but not easy to find anyone that either knows or is interested including my original solar installer...short of spending 15k on a Tesla battery backup setup which isnt an option.

    Id double check with your electricity retailer that they dont have an issue with what you propose - an islanded solar system that will connect the grid when the batteries get to 30%. There are strict network rules for obvious reasons and the distribution companies record what addresses have a network connect solar for a multitude of reasons.

    Enphase make a auto changeover switch designed to work with its "Ensemble" system but is not available in Aus yet...meant to have been available some 18 months ago but is also very expensive >$3k not including labor ....and hard to work out if it can be programed for your requirement to switch to the grid

    There is an invertor (sunnyboy I think???) - check the web site "Solar Quotes" as read about it the other day, that is set up to be mains connected with a backup outlet to keep using solar/batteries. By the way it reads I dont think it will go the other way ie: rely on battery and switch to mains on a specified trigger point.

    Seen a couple of setups with different inverters in the US but still more around switching to battery backup when the grid is out. Be interesting on what you can find as a cost effictive solution.

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    Hmm the simplest/cheapest way to go might be something like the Enerdrive 12V 60A battery charger, permanently hooked up to the battery bank and just let it keep running 24/7 from any household wall outlet. Program it to only charge when batteries fall below 30%, and stop charging around 80% or so. Hopefully the solar charger can also be permanently connected to the battery bank simultaneously without conflicting with the Enerdrive charger? I think you can also hook up a generator to the Enerdrive charger as a last resort if both outages and cloudy days persist.

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    https://www.youtube.com/watch?v=WVM0...nnel=altEStore

    Has some good info and easy explained for the general person.

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    Quote Originally Posted by countrybloke View Post
    Also my Projecta inverter is a well known brand in Australia and apparently already comes with an AC transfer switch built in to it. On page 3 of my inverter manual https://www.projecta.com.au/ts164920...ion+Manual.pdf it says "The built in automatic transfer switch ensures a quick transfer of power when switching between mains and battery power. The automatictic change over function eliminates the need to manually swap over AC plugs or be switching dials between the two power sources. When mains power is available, mains power passes through the inverter to power the accessories directly. When the mains power is disconnected the appliance automatically switches across to inverter power." I don't understand why Projecta would make an illegal product that risks electrocution to grid repair teams in an outage?
    I'm not understanding why there is a problem , you are going to feed the inverter which will charge the batteries, the inverter will regulate the supply to the batteries which will in turn power a separate 240v system, the separate supply to the inverter could be a genset or whatever, it isn't going to back feed 240v out that way, if it did a lead plugged into it would be live at the male end.
    inter

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    What he said.
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    my-system-setup.jpg
    Here is a picture of my setup. My 4kW off-grid system needs to be completely separate from the house 3kW solar system, and also cannot touch the Energex meter box at all, otherwise it could void the 44c feed-in rate, would that be correct for the Queensland coast area? I am searching for the mystery gadget shown on my picture, if such a thing exists out there. Programmable to automatically switch between drawing inverter power or outlet power, depending on time of day, or special programmed inputs, such as a relay of battery bank voltage that triggers a switchover.

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    There are a few semi-remote properties around here that use a changeover switch to connect the house supply to either the grid or a generator (but not both at the same time). This is a fairly simple and common setup. I haven't completely digested exactly what you want but the various replies seem to be getting a bit complicated. Working on the KISS principle, although such a setup might not exactly suit your situation would it good enough?

    Any electrical contractor can set this up for you. Have a look at AS3000 7.3.8.1 and in particular Fig 7.5

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    Quote Originally Posted by chalkyt View Post
    use a changeover switch to connect the house supply to either the grid or a generator
    I don't want to connect the house to the grid. I just want to connect 1 plug to 1 outlet, simply by physically plugging it in, just like you would plug in any appliance such as a toaster. I can physically plug it in to the outlet, then physically unplug and replug into my inverter. It takes 2 seconds to manually do. Now I just want a device that does it automatically instead. My inverter has the same outlet just like any random household wall outlet, you can plug a toaster into my inverter, just as you do a wall outlet.

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    Technically what you want to do isn't difficult. The hard part might be getting the supply authority to allow it.

    An automated version of Fig 7.5 for one outlet could be done with a simple 10A two pole changeover relay with the changeover contacts connected such that the supply to the outlet can only be mains or inverter but not both at any one time. These relays (or contactors) come with a variety of operating coil voltages from around 12V DC to 240V AC and are usually less than $50. The tricky bit would be some device that tells the relay to operate (or release depending on how you configure the changeover) when the battery charge falls below some nominated level.

    A suggested above, spend a dollar or two with a contractor or engineer who is experienced in off-grid installations then take what they suggest to your supply authority for approval.

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    Quote Originally Posted by chalkyt View Post
    Technically what you want to do isn't difficult. The hard part might be getting the supply authority to allow it.
    That will be the most difficult part as supply authorities are in the business of selling power and not be made a standby supply.

    My experience which is 10 yrs old was using Plasmatronice PL60 controllers that had a generator start feature. These were good controllers as everything was configurable.

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    Quote Originally Posted by John2b View Post
    Thanks. Taking everyone's suggestions, I did some research and I think we may have hit the jackpot with this "Moes ATS" here: https://www.youtube.com/watch?v=eO9dVJM2ik8 and can buy it here for $150 https://www.aliexpress.com/item/1005004334426850.html and Will Prowse also recommends it here: https://www.youtube.com/watch?v=ni0A_ZdH7aU

    Quote Originally Posted by chalkyt View Post
    The hard part might be getting the supply authority to allow it.
    I would prefer to avoid (legally) needing the supply authority's permission. Surely there must be a legitimate way. For a completely off-grid system, permission is not needed, it doesn't even touch their meter box. Also, I don't think permission is needed for plugging into any random household outlet things like a UPS (https://www.ebay.com.au/itm/172718452986) or a laptop charger, yet both of these have batteries and inverters built-in, so how are these allowed to be plugged into a wall outlet, if theoretically they can generate power and feed it back into the wall socket, thereby electrocuting the repair team in a blackout. Should UPS appliances be banned in that case? If this is true, UPS and all laptop chargers should be banned. Isn't there some kind of isolation/bypass system in UPS appliances and laptop chargers, that prevents backfeed into the wall socket? If I wire up my system with the Moes ATS like in my picture attached here, would this be allowed without permission? The Moes should have some kind of isolation to prevent backfeed surely.
    setup-moes-switch.jpg

  34. #34
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    Quote Originally Posted by countrybloke View Post
    Thanks. Taking everyone's suggestions, I did some research and I think we may have hit the jackpot with this "Moes ATS" here: https://www.youtube.com/watch?v=eO9dVJM2ik8 and can buy it here for $150 https://www.aliexpress.com/item/1005004334426850.html and Will Prowse also recommends it here: https://www.youtube.com/watch?v=ni0A_ZdH7aU
    Buy that at your peril as it would not meet Australian standards and cannot be used on the mains supply in any form.

    UPS connected to the supply would be certified to Australian Standards and would be isolated from the mains when supply is lost.

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    The Automatic ATS Dual Power Transfer Switch your link references sold on AliExpress may or may not be approved for connection to the Australian electricity supply, but otherwise has the same function as the Australian made Latronics ACTS40 Automatic Ac Transfer Switch which I linked to in the post above.

    I feel I need to say that I question whether you should be playing around with lethal power systems when your questions imply your understanding of how they work (and hence the dangers involved) is quite limited. Stay safe!
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    Quote Originally Posted by Bros View Post
    UPS connected to the supply would be certified to Australian Standards and would be isolated from the mains when supply is lost.
    I agree. I want something certified to Australian Standards and isolated from mains when supply is lost, and I want that for my system. Would you think that John2b's recommended Latronics ACTS40 is certified and isolated and approved for connection to Australian electricity supply? If so, I will buy it. But it seems as though everybody is still saying that even with the Latronics ACTS40, you still need to get permission from Energex? If it's already approved, why is permission still needed? Just like the UPS - it is already approved, so you can just plug it in, no permission needed. If no permission is needed, I will buy the Latronics ACTS40.

    Quote Originally Posted by John2b View Post
    The Automatic ATS Dual Power Transfer Switch your link references sold on AliExpress may or may not be approved for connection to the Australian electricity supply, but otherwise has the same function as the Australian made Latronics ACTS40 Automatic Ac Transfer Switch which I linked to in the post above. I feel I need to say that I question whether you should be playing around with lethal power systems when your questions imply your understanding of how they work (and hence the dangers involved) is quite limited. Stay safe!
    Yes I want the Latronics ACTS40 you recommended. I only saw more potential in the Moes because it seemed to be perfect since it also had the battery voltage trigger. Pity it won't be allowed. Alright then. So it will have to be the Latronics ACTS40, but now I also need some kind of extra device to cut off inverter draw when voltage hits a certain point (for 30% SOC). Otherwise, the Latronics ACTS40 will wait for the battery to fall completely flat down to 0% before switching, which ruins the batteries life severely?

    I can certainly get an electrician to connect everything, but first I need to buy all the right gadgets ready to go, or otherwise they will have no clue what to do. You'd be suprised at how many electricians I've brought this to, and they have no idea what specific parts to buy. They all say "talk to a solar specialist or Energex". And all the solar specialists say "talk to an electrician or Energex". And Energex says "talk to an electrician or solar specialist" And then I'm in an endless loop of phone tag.

    Funnily enough, I finally found a licened electrician, his name is Gary, who is also a solar specialist and knows Energex requirements, and he said: "
    Use an Auto-Transfer Switch something like this: https://www.ebay.com.au/itm/304518006320 to transfer to over from Inverter to Wall Socket." Well, I wonder what Bros and John2b would have to say about that recommendation! I guess I would be buying that at my peril, against Australian standards, and in violation of supply rules. Thanks Gary - what a disaster of a recommendation from an expert.

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    I see there are 2 parts to this idea.
    a) detecting when the batteries are nearly flat (low State of Charge - SOC) as an initiating event for any AC changeover and, coupled with that, detecting when the batteries have returned to a higher (SOC) and returning the AC situation to normal.
    b) the actual AC changeover function.

    I think all of the discussion here has focused on b) and, to me, have missed the need for the changeover to be initiated by something other than the loss of AC voltage (which most discussion has focused on but will not be the case if I read the requirements correctly)..
    I also think there has been no thought given to a)
    The two go hand in hand.

    As for a)
    There needs to be a method of detecting the SOC of the batteries to provide a trigger signal to effect a change of AC source for the freezers. Ideally, this same SOC detector will also be able to sense a higher SOC and provide a trigger to return the AC source for the freezers to the "normal" source. Ideally, this detection system should be able to be configured to enable to operator to set the trigger points at different SOC levels as the user may require.

    Such systems are readily available in the RV industry where SOC display devices have smart shunts which measure the current in/out of the batteries associated with them, and which in turn have relay contacts available to provide a trigger source to whatever the use wants to control. A common usage is for a low battery SOC to trigger a relay to disconnect all 12v loads from the battery and not reconnect those loads until the SOC has returned to a higher level
    This is exactly the situation the OP is looking for, only the control is of AC loads, not 12v DC loads.
    Such devices are manufactured/supplied by Enerdive, Victron and other 12v specialists to the 12v/RV industry. Look at the Victon 712 monitor and smart shunt or the Enerdrive Epro monitor. (Essentially the the same device.). Also investigate other manufacturers.
    With these devices, they can be programmed to close or open its internal relay contactat at any SOC the user wants to programme in to it. So, (say) a SOC of 30% to close the relay (and hence initiate a change over of AC supply to the freezers to the mains) and release of the relay at (say) a SOC of 90% to return the AC supply to the freezers to the solar panel sourced AC.
    Most systems use the batteries own 12v to supply, via the relay contacts, 12v to some sort of relay device to effect the high power switching of the loads.

    And b)
    We now have a need to switch the freezers AC supply from one AC source to another, triggered by a 12v signal from the monitor.
    I see 2 methods of achieving this.

    1) By including in the battery system a 240v/12v battery charger, permanently connected to the batteries, in parallel with the solar panel controller. The 240V to this charger would be fed via a 240v contactor (relay), triggered by the 12v signal (relay contacts) from the monitor.
    In this case. the charger would be doing nothing until the monitor detects a low SOC and causes the AC chargers 240V to be switched on via the contactor. Once the SOC builds up via the 240v charger to the required higher SOC the monitor will then disconnect the AC to the AC charger and the batteries will return to being being charged solely from solar.
    The freezers would always be supplied 240v from the existing inverter irrespective of the SOC of the batteries.

    2) By incorporating an AC changeover contactor between a mains point on the wall and the AC generated by the existing inverter which changes the AC source for the freezers from a solar source (via the inverter) and the mains source (via the wall) and supplied from the house/grid. Again, the trigger signal for this contactor would be a 12v DC from the contacts of the battery monitor.
    This is perhaps a little more intricate to design and install as it involves more 240v wiring and control. Change-over 240v contactors specifically manufactured for this type of use (Changer-over from supply source A to supply source B) are common in the industrial scene. Most come with 240V trigger coils or 24V AC coils, but there are 12v DC coil contactors available.


    I would consider option 1) to be the simplest to install. The main difficulty will be getting an AC sparkie to source the contactor and integrate it into some sort of arrangement for the monitor, set-up with the assistance of an Auto sparkie.

    The monitor suggested is a true SOC monitor that measures the current in and out of the batteries to determine the actual SOC. It is not a voltage type meter that just looks at the battery voltage to determine the SOC. I assume the batteries are one of the lead/acid types (open cell/AGM/Sealed). These monitors will also work with Lithium batteries. In fact, it is the only type of monitor that gives an accurate SOC with Lithium batteries and also L/A batteries.
    An advantage of the monitor is that the OP will also be able to know the actual SOC at any time by referencing the display.

    Not a recommendation from personal experience, but from along association with the RV industry I often read references to Springer Solar & RV (something like that), somewhere in QLD, where the OP is. I would suggest giving them a call as they seem to be experienced in both the 12v and 240v fields.

  38. #38
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    Can I also suggest you do some research on social media and dedicated forums.
    There are hundreds of people with DIY solar who have a similar situation like you have (but it just does not seem as if they are the same.)

    Ity may be that someone may want to run their house off solar, but auto switch over to a generator when the batteries are low.
    No different to you who wants to run your freezers off of solar and auto switch over to mains when the batteries are low.

    Look up "DIY Solar" and similar on Facebook
    Google something similar on the net and look for solar forums.

    What you wish to do is not new. There are many people who have done it before and are all too willing to share their expertise and experiences.
    There is no need to re-invert the wheel.

  39. #39
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    Quote Originally Posted by countrybloke View Post
    Otherwise, the Latronics ACTS40 will wait for the battery to fall completely flat down to 0% before switching, which ruins the batteries life severely?
    No, the inverter has a cut-off voltage setting, which is set to suit the duty cycle from 10% to 100% to whatever you want for the batteries by setting the cut-off voltage. When the inverter cuts out the auto changeover will switch to mains because it senses the loss of inverter output. When the batteries regain charge to the volts you set in the inverter for restarting, the inverter will start up again and the auto changeover switch will switch back to batteries.

    Funnily enough, I finally found a licened electrician, his name is Gary, who is also a solar specialist and knows Energex requirements, and he said: "Use an Auto-Transfer Switch something like this: https://www.ebay.com.au/itm/304518006320 to transfer to over from Inverter to Wall Socket."
    You are lucky to have Gary so use what your licensed solar specialist recommends. Many sparkies have little experience of solar, and then usually only bog standard mains connected systems. Custom off-grid is a whole different world, and adding custom mains interactivity to off-grid is more specialised again.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

  40. #40
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    thank heavens for Gary!

  41. #41
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    Quote Originally Posted by r3nov8or View Post
    thank heavens for Gary!
    I agree now we can go back to electric cars.

  42. #42
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    Apart from the technicalities of how to do it all, it occurred to me (as also suggested somewhere above) that you can simply plug any "appliance" into a socket outlet (i.e. a powerpoint).

    So, if the whole arrangement was assembled as an "appliance" that just plugs into the nearest socket outlet it may overcome any supply authority concerns about anything permanently connected to the mains.

    Obviously this would need to get the O.K. from your supply authority, but generally their world ends at the output of the socket outlet. Might be worth looking into.

    Good luck!

  43. #43
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    Can I offer a third possible solution.

    Option c)
    - Place an ATS (Auto Transfer Switch - look them up) in the 240v connection between the existing inverter, the mains and the freezer supply.
    They are a non-electronic relay device that automatically switches AC supply to a load (your freezers) from input (source = inverter) A to input (source = mains) B and returns once input A is present again. They normally are mounted in switch boards to handle power failures but can be free mounted on a board.
    :Wire the existing inverter 240v to the "normal" input A and the mains 240v to the "auxiliary" input B (note - in some situations B would often/normally be wired to a generator or some such device)
    :Wire the output of the ATS to the freezer 240v supply cord.
    - Also place a high current relay/contactor in the 12v supply line between the battery and the existing inverter.
    - Use the battery monitoring as described above and connect its trigger relay contacts to the coil of the contactor.

    In use,
    - the monitor will detect a low SOC and close its rely contact.
    - This in turn will actuate the contactor in the 12v supply to the existing inverter, removing its 12v supply and stop it from working.
    - The loss of 240v from (input terminal A) of the ATS will cause it to auto switch to input terminal B -( the mains).
    :The battery is protected from further degradation from the lack of standby current draw of the inverter and is able to be recharged from the solar as fast or as slow as the weather allows.
    - When the batteries recharge and return to a predetermined, higher, SOC the monitor will open its contact
    :the 12v contactor will release
    :12v will be applied to the inverter again and it will start producing 240v again
    :the ATS will sense the presence of 240v again at its input A and switch back to connecting the inverter to the freezers

    The only thing to watch out for in this option is the current rating of the contactor which will be handling the 12v supply to the inverter.
    Contactors (infact virtually all relays - unless specifically made for DC switching) rate the current of their switching capability in AC amps.
    Switch DC current is much more destructive and "sparkie" than AC switching. When switching DC amps, the current is not self-arc-extinguishing as AC current switching is as a consequence of the AC constantly varying between (+) voltage, zero, and (-) voltage as is the nature of AC. The constant voltage of DC will draw a large arc when switching off. This causes deep pitting of the contactor contacts and a much shorter life (even welded contacts) of the contactiot.
    In choosing a contactor, ensure you seek out the DC current rating of the contacts - which can be up to only 1/10th of the AC current rating, and hence chose one that will handle at least twice the DC current of the inverter.
    Better still, seek out a contactor specifically designed for DC switching. It will have built-in arc suppression and heavier duty contacts.

  44. #44
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    It's an off grid system, the inverter or system will have a facility for generator backup for charging the batteries, all the OP wants to do is replace the generator with a lead from the grid system, no rocket science needs to be engaged.
    inter

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    So for this system, I'm going to take all of your advices, so between inverter AC output / wall outlet / freezer powerboard, will use Latronics ACTS40 $448 (https://www.sunergysolar.com.au/latronics-acts40pm-40-amp-automatic-transfer-switc), since being Australian-made and certified, should appease supply companies as a valid full isolation from the Projecta inverter, and should satisfy as a regular "appliance" when switched to the position of supplying freezers from wall outlet power. Will use $314.50 Victron BMV-712 with shunt (https://www.outbackmarine.com.au/vic...-bluetooth-gre).

    I would probably avoid Gary's suggestion for a non-certified cheap Chinese brand ATS $51 + $80 shipping (https://www.ebay.com.au/itm/304518006320), which would still require the Victron BMV & shunt as well anyway. And I would also probably avoid the Moes brand ATS $142.92 (https://www.aliexpress.com/item/4000051790713.html), even though it does both combined jobs of Latronics and Victron ($762.50), because I guess those are are better brands, even if over 5x times pricier (ouch). Victron is actually Chinese made nowadays, but I guess it still holds its reputation. Do you think the BMV-712 with shunt has a contactor and wiring that is beefy enough to handle the 12V 1200A battery bank? Or would I need to buy something additional?

    The option for using a battery charger permanently plugged into a wall outlet to charge the battery bank won't work anymore, since I have come to realise that there is no such battery charger that exists to be able to connect to a battery bank of that kind of amperage. Unless one that costs maybe several thousands.

    I have also come to realise that paralleling solar and batteries makes everything difficult and expensive. But I guess it is too late for this system. So for my next two additional offgrid systems, I am intending to do the following (copied below from new thread https://www.renovateforum.com/f223/v...#post1139315):

    Two identical 4kW systems (one for upstairs, and one for downstairs), each having 16x 250W 12V (22.5voc, 13.41A) panels in series, which run directly into each MPPSolar 5048MG inverter http://www.mppsolar.com/manual/PIP-M...l-20211006.pdf or https://mppsolar.com.au/product/u564...high-pv-450vdc (or Growatt 5kW Offgrid SPF5000ES is a similar inverter that I could swap out for if need be).

    Each 48V battery bank is 4x 300Ah 12V LiFePO4 in series, which also plugs directly into inverter. Each battery has internal BMS built-in apparently. Optional backup generator/grid AC bypass can also plug directly into each inverter. Across both $7k systems ($14k total cost), we would have 8kW panels, 28.8kWh batteries, 10kW total power draw capability, 30-50kWh daily generation (winter-summer). No combiner box, no complex wiring, no charge controllers, no BMS, no displays. Just panels, inverter, and battery bank.

    I think I still need PV isolator, battery DC disconnect & fuse, and inverter AC breaker, but that's about it maybe? Keen for any advice if I missed something. Haven't set it all up yet, but have already bought the batteries/inverter/panels a couple years ago all still unopened in boxes. Discussion can be made on new thread here (https://www.renovateforum.com/f223/v...5/#post1139315) to be separate from this old thread.
    Last edited by Bros; 4th Aug 2022 at 04:45 PM. Reason: Paragraphs for ease of reading

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