Combining low wattage Victron Phoenix with Growatt 12K inverter

[timselectric]

Its all the same thing it's just how you describe it. Two 120V sine waves 180 degrees out of phase add to form a single 240V sine wave. Since you have access to the two individual 120V sine waves it makes more sense to me to call them 180 degrees out of phase but I'm an analog engineer and maybe that's not the lingo that electricians use.

The point is that the two 120v legs are not 180 degrees out of phase. They are in phase. They are two halves of the same phase. If they were out of phase, you couldn't get 240v between them.

 

[eemarty]

The point is that the two 120v legs are not 180 degrees out of phase.

Yes....they are. What does 180 degrees out of phase mean to you? On a 240V system, one leg is an inverted version of the other when measured with respect to ground/neutral. Go ahead and measure it on an oscilloscope. One is exactly 180 degrees out of phase with the other. Am I taking crazy pills here?

 

[timselectric]

Yes....they are. What does 180 degrees out of phase mean to you? On a 240V system, one leg is an inverted version of the other when measured with respect to ground/neutral. Go ahead and measure it on an oscilloscope. One is exactly 180 degrees out of phase with the other. Am I taking crazy pills here?

It's a single phase. If you measure from the center, it will appear to be inverted. But, in reality it's not. If the two legs weren't in phase, you wouldn't be able to get 240v combined.
To clarify
The legs aren't inverted, your test points are.

 

[timselectric]

Maybe this will help.

 

[McRod]

To be clear, I know the left/right side doesn't matter. The idea I took from this is that the inverter is feeding power "backwards" through the breaker, something I hadn't thought of. Didn't realize that would work for one, and not 100% if that would be "up to code" now that I know it would work. Currently in my own panel, with only the Growatt wired, it does come into the mains. Adding the Phoenix though, maybe I could have it come in through a breaker, as opposed to wiring BOTH into the mains?


Yeah, I'm fully convinced that running both of these at the same time is a bad idea. I had already thought that...a little unfortunate it couldn't work as that would make an easier install, but that's reality.

That's what I'd love to do! Assuming only one inverter will ever be on at a time, I'll have to go out to the shed (200ft away) multiple times a day to toggle between them. Any setup that can have this done automatically, or even via a switch in my house would be incredible. Currently my best idea here is a networked arduino that can push the buttons, lol. The transfer switches are new to me, and so is remotely controlling the Growatt unit. Going to do a bit of research on this and get back to you. Thank you so much for your comments, you hit the nail on the button.


Right - currrently I have the Growatt wired into a subpanel that accepts both hots. For the phoenix, my plan is to just split the single hot into two and wire them into their own smaller breaker and "backfeed" or have them come in through the mains with the Growatt. And not run any 240V/split-phase appliances while the Growatt is off.

You can designate a breaker within a main panel to feed a subpanel. I don't think that's called "back feeding". But it does require a sub panel, which you said earlier that you didn't want to do. And if you build out a sub panel, there is no reason to feed it from your main, because it will be powered from your other inverter. Basically a separate system.

 

[McRod]

Maybe this will help.

Damn, that's a good video. ? Makes me feel like I slept in a Holiday Inn Express!

 

[eemarty]

Yes I understand how transformers work. I have a masters degree in electrical engineering. I watched the video. I agree it depends on your reference point which he mentions. I don't really understand his logic though: he's saying that you should choose a different reference for each leg and then you can call them in phase? My reference point is ground. A scope's reference point is usually ground. If you put the two hots of a split phase circuit on two channels of a scope with ground as the reference point, you will see two sine waves that are 180 degrees out of phase from each other and each measures 120VRMS with reference to ground.

If the two sine waves were perfectly in phase with each other then there wouldn't be voltage between them! In fact that is what the OP is proposing to do. Connect the hot from a 120V inverter to both legs of a split phase system. This will give perfectly in phase sine waves on both legs. So you will get 120V between each leg and ground but if you measure voltage between the two legs you will get 0V because the two sine waves are coming from the same 120V inverter. They are "in-phase".

I'm not sure why electricians are so adamant that people not call the two legs in a split phase system 180 degrees out of phase. They have to develop all these complicated explanations about how you just need to change the reference point and then it's in phase. I think there is a scientific definition of the phase of a sine wave and then there's the electrician's colloquial definition of "phase" and these aren't the same. So I think we just have to agree to disagree here.

 

[timselectric]

if you measure voltage between the two legs you will get 0V because the two sine waves are coming from the same 120V inverter. They are "in-phase".

It's not two legs. It's one leg, feeding both bus bars.

I'm not sure why electricians are so adamant that people not call the two legs in a split phase system 180 degrees out of phase.

Because they're not.

I think there is a scientific definition of the phase of a sine wave and then there's the electrician's colloquial definition of "phase" and these aren't the same.

They are the same. There's only one phase.
And only one sine wave.
Connecting the scope leads 180 degrees from each other, doesn't change the sine wave. It only changes what you see on the scope.

 

[timselectric]

I think we just have to agree to disagree here.

Agreed

 

[Mattb4]

This would probably involve a lot of complicated rewiring. I have a 200ft 6/3 cable running from the shed to a standard split phase box in my house which powers everything in the house. Not even sure how I'd begin splitting the loads, and the load would basically be "everything 120V" anyways. All my lights, electronics, etc. The only thing the Growatt will really be powering is the range and heat pump, and my higher 120V usage (maybe power tools and heavy kitchen appliances like a high powered blender).

Yes, I know this is possible. I cannot use the DC switch though because the Growatt AIO would not charge the batteries while I'm using the Phoenix in that case. I think I'd have to use an AC switch on their outputs to control which one is powering the panel.

I guess my questions are:
1) How should I wire the AC outputs of the inverters for a nice clean, safe, setup? Since currently the Growatt output goes into the shed breaker box as the "mains" and out through a breaker, I imagine I'd also want the Pheonix to be wired into the "mains", somehow connected before the box so only one set of mains wires. Maybe there is a better way to do this?
2) What would happen if I had both inverters on at the same time delivering AC to the house - would that ruin the 240V split phase? My suspicion is yes unless the Phoenix distributed its power perfectly across both legs, which is very unlikely, but still an interesting theoretical thing to know.
3) How might my 240V appliances react if I'm sending single-phase 120V down both legs? I'd rather not have to make sure I physically disconnect them when switching between inverters, but that is my current accepted reality. I also don't really want to "test" this on my 2k range in case I damage it...but maybe. I'll be sure to report back to those interested if I do.
4) Any unintended consequences of wiring the inverters together like this that I might not be aware of?

I also thought this idea might be interesting to some members struggling with the idle draw of a larger inverter - and that maybe someone knew of someone already building a setup like this.

1. There is no really easy way to accomplish without creating a critical load sub-panel with transfer switch. Since you can not ever parallel the two inverter outputs combining them in the same main panel is a recipe for problems.
2. Nothing happens if you run 2 inverters at the same time from the same battery bank so long as they never connect their outputs. You do however take a hit from now having the idle load of two inverters.
3. If you have a 240v breaker where both inputs are the same leg of a 120v source you get zero volts between the two lugs. It is like measuring one wire with a volt meter by using both leads to measure the same test point. But if you ever go either to neutral or ground they they will give you 120v. Depending on your 240v appliance it might have some circuits that use 120v and you will see that portion have power.
4. Unintended consequences is keeping it all straight and simple to operate.

My advice is to simply accept that you have power draw from your system even if it is not powering loads. It takes power to make power. Plan for it by having sufficient supply.

ETA: Just talking now and not pointed at the OP.

One thing people who rely on batteries tend to have a hard time accepting is just how limited of a power source they are. We hardly think of powering a few hundred watts on grid power as any big thing especially since grid powered is measured in kilowatt-hr. But when powering that from a battery it is a whole different kettle of fish.

 

[l00semarble]

Just thinking out loud here. I would have done something different from the start but if you are stuck with the Growatt and you want to make something work like you are thinking you could *MAYBE* consider this. NOTE: I have not thought this through entirely - just brainstorming:

2nd inverter could be an inverter/charger wired in series with 1st inverter.

Growatt split phase output 120v/240v goes into the input of a Victron Multiplus-II 2x120. Output of Multiplus goes to house main AC panel wired normal 120/240v split phase.

User would simply turn off Growatt inverter and immediately (UPS fast) Multiplus would invert single phase 120v into BOTH sides of panel. All 120v loads would work, all 240v loads would see 0v and not work (and also not be damaged.). When user wants 240v HVAC he turns on Growatt, Multiplus recognizes 120/240v split phase input, in synchronizes itself to L1 of new split phase input, and transfers split phase through to panel. The integrated transfer switch is rated for 50a. In this scenario the Victron PowerControl and PowerAssist functions will work on L1 only but technically the help the Mulitplus gives to L1 could make it easier for the Growatt to start the HVAC or other heavy loads. I would be sure that if there is a 120v phase that has more loads than the other I would be put that as L1.

They are used this will all the time in RVs with 50a split phase "shorepower" service to "pass through" split phase when available and then energize both sides of 120v with one phase when inverting.

Standby consumption of Multiplus is 4w-15w depending on version and mode.

Well....I just thought of the gotcha...they are only available in 12/24v and OP has a 48v battery. Still...maybe food for thought on a series inverter rather than parallel like OP was originally thinking.


For those not familiar here is a description of function:

MultiPlus-II 2x 120V​

​

The MultiPlus-II 2 x120V is the perfect one-box mobile solution for standard North American 50A 120/240VAC split-phase applications. Whether it is supplied from shore power or a generator, the MultiPlus-II 2x120V can accept and passthrough both lines of a 120/240V supply, with the capability to utilize the full 50A for charging and AC loads. When connecting to a single phase 120V supply, the L1 input of the MultiPlus-II 2x120V will accept incoming power for charging and passthrough, while combining the L1 and L2 outputs for single-phase 120V on each line.

The MultiPlus switches to inverter operation when no AC source is available. The inverter output is also 120V single phase. In inverter mode, the MultiPlus-II 2x120V internally connects both lines L1 and L2 together to provide 120VAC to loads on either output. Therefore, in all connection circumstances, both sides of a distribution panel will be supplied with 120V. However, 240VAC is only available when the MultiPlus is supplied by a split phase 120/240VAC source. This prevents heavy loads such as water heaters or 240V air conditioners from discharging the battery.
The MultiPlus-II 2x 120V has all of the expected features of our versatile inverter/charger range, including PowerControl, PowerAssist, Input Current Limit, two AC outputs, as well as parallel and 3ph configuration for larger capacity VE.Bus systems. Suitable for LiFePO4 batteries and a variety of other battery technologies.

 

[timselectric]

Just thinking out loud here. I would have done something different from the start but if you are stuck with the Growatt and you want to make something work like you are thinking you could *MAYBE* consider this. NOTE: I have not thought this through entirely - just brainstorming:

2nd inverter could be an inverter/charger wired in series with 1st inverter.

Growatt split phase output 120v/240v goes into the input of a Victron Multiplus-II 2x120. Output of Multiplus goes to house main AC panel wired normal 120/240v split phase.

User would simply turn off Growatt inverter and immediately (UPS fast) Multiplus would invert single phase 120v into BOTH sides of panel. All 120v loads would work, all 240v loads would see 0v and not work (and also not be damaged.). When user wants 240v HVAC he turns on Growatt, Multiplus recognizes 120/240v split phase input, in synchronizes itself to L1 of new split phase input, and transfers split phase through to panel. The integrated transfer switch is rated for 50a. In this scenario the Victron PowerControl and PowerAssist functions will work on L1 only but technically the help the Mulitplus gives to L1 could make it easier for the Growatt to start the HVAC or other heavy loads. I would be sure that if there is a 120v phase that has more loads than the other I would be put that as L1.

They are used this will all the time in RVs with 50a split phase "shorepower" service to "pass through" split phase when available and then energize both sides of 120v with one phase when inverting.

Standby consumption of Multiplus is 4w-15w depending on version and mode.

Well....I just thought of the gotcha...they are only available in 12/24v and OP has a 48v battery. Still...maybe food for thought on a series inverter rather than parallel like OP was originally thinking.


For those not familiar here is a description of function:

MultiPlus-II 2x 120V​

​

The MultiPlus-II 2 x120V is the perfect one-box mobile solution for standard North American 50A 120/240VAC split-phase applications. Whether it is supplied from shore power or a generator, the MultiPlus-II 2x120V can accept and passthrough both lines of a 120/240V supply, with the capability to utilize the full 50A for charging and AC loads. When connecting to a single phase 120V supply, the L1 input of the MultiPlus-II 2x120V will accept incoming power for charging and passthrough, while combining the L1 and L2 outputs for single-phase 120V on each line.

The MultiPlus switches to inverter operation when no AC source is available. The inverter output is also 120V single phase. In inverter mode, the MultiPlus-II 2x120V internally connects both lines L1 and L2 together to provide 120VAC to loads on either output. Therefore, in all connection circumstances, both sides of a distribution panel will be supplied with 120V. However, 240VAC is only available when the MultiPlus is supplied by a split phase 120/240VAC source. This prevents heavy loads such as water heaters or 240V air conditioners from discharging the battery.
The MultiPlus-II 2x 120V has all of the expected features of our versatile inverter/charger range, including PowerControl, PowerAssist, Input Current Limit, two AC outputs, as well as parallel and 3ph configuration for larger capacity VE.Bus systems. Suitable for LiFePO4 batteries and a variety of other battery technologies.

View attachment 124451

That sounds like a good solution for the OP.
I wasn't aware of this function on that unit.

 

[CubesAreShapes]

Thank you so much for the comments everyone. It is hard to address them all individually now.

I really like the idea of the Multiplus II 2x120V in series for many reasons - but am concerned about the upfront cost (3-4x) and it has a 3x more idle draw when compared with the Phoenix (though, provides much more usable power, also an advantage). Also could not find one available to me in 48V. It seems the power draw is around 20-30W? Though the spec sheet lists only 11W (https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-3kVA-2x120V-EN-.pdf). 2nd issue is that it indeed does not come in a 48V model, such a shame!

I'm open to trying to sell off the Growatt for a much better setup, but I'm not so sure what that setup would be, and for anything from Victron to come anywhere near the power of 12kW split-phase I would be spending a huge amount of money. 4 multiplus'?

I think the "best" solution here might be to have them both in power saver mode with a remote automatic transfer switch - or at least have the Growatt on in power saver mode and remotely turn on/off the Phoenix with a switch prioritizing the Phoenix. That way only one is connected at a time, I have the major power savings of the Phoenix for the majority of the usage, and can use the power of the Growatt whenever needed (without having to go to the shed). Re: wiring - I could do a "manual transfer switch" using the breakers and panel I already have, lowering the cost and making a future upgrade to an automatic transfer switch possible. I'm thinking, instead of the Growatt coming into the mains, it would come into a 2 pole breaker, and I could have the phoenix come into its own smaller 2 pole breaker (with a jumper cable to connect both legs to the same 120V input). The mains would then be the output to the house. To switch between them I just flip the breakers (only one being on at a time).

I'm running a huge 225ft 6/3 cable from the shed to the house, any sub panel idea in my understanding would involve another one of these $2k cables, no? I think that makes it feel a little prohibitive.

I'm still doing research and lots of thinking on this. I haven't found a suitable transfer switch and tbh I'm not sure what I'm looking for here with the 120V and split-phase coming in. Would a standard 240V transfer switch work? Looking at https://www.victronenergy.com/transfer-switches/ve-transfer-switch or

12 Best Automatic Transfer Switches Reviewed and Rated in 2024

Find the best automatic transfer switch for you here. I review the 12 models I used before and discover the best option.

www.galvinpower.org

. This switch looks like it'd work but if I understand correctly, I'd have to wait a pretty long time for the power to come after switching the Pheonix on? 30 seconds?! https://www.amazon.com/dp/B00F4620OO

I like the low upfront cost of the Phoenix, $600 on Amazon but hate how it can't be expanded in the future. I think I might be better off with a Multiplus II, but the 2x120V model doesn't seem to be available, and not sure how I'd make the standard Multiplus II work well for this setup. I could expand in the future and maybe one day ditch the Growatt though. The growatt does its job but is kind of annoying (e.g. have never got the shine server stick to work, says its connected and online but have never seen any data!). I don't like having to buy a transfer switch with the Pheonix, a pretty decent added cost ($300-$400?) that could be better spent on a Multiplus II. But with only one input on the Multiplus II, I think I'm still looking at needing a transfer switch or doing things manually. It's a lot to consider.

Found this video:

, which is neat, would be cool to replace his Phoenix (an older model? this is not the same Pheonix Im looking at - which is https://www.amazon.ca/gp/product/B076T5N9V8) with my Growatt in this setup - but this is all 120V AFAIK. Maybe if I had two Multiplus IIs, each taking one 120V leg of the Growatt...but then my idle is ~60W compared to ~10W of the Pheonix alone...and my upfront cost is probably closer to $5k than $1k.

@ l00semarble, I'm curious what you would have done different from the start. Very open to substantial improvements to this, even if it means eating the cost on the Growatt.

Of course I want to have this solved asap but jumping into another purchase that long-term won't work for me is not what I want to do. The small Phoenix 1200VA inverter solves my immediate issue at a low cost, but might not do me justice in the long-term especially with it not being expandable.

 

[CubesAreShapes]

I wonder if it makes sense to have something reduce the 48V to 24V for the input of a multiplus II 2x120? I also wonder why on earth Victron wouldn't make a 48V model of this. It does seem perfect, the pass through also being 50A! It literally seems perfectly designed for this purpose. The fact that it also comes with a very fast 50A transfer switch is definitely worth $$.

Pass through only seems to be 32A on the smaller Multiplus (not 2x120V) models, jumping to 50A when you go to 48/5000 - but still not split phase (It supports 240V - which I think does NOT work for me on split-phase unless it had a 3 wire connection, but would love to be corrected)

Re: eating the cost of the Growatt idle...My major problem here is probably my location in northern ontario. I have 3.6kW of panels (8x450W panels, probably going to add 4 more since I have one more slot in my box to parallel them and the Growatt is happy with the extra current) and 20kWH (4x100AH 48V batteries) which seem to work when it's sunny. Even every 3 days or so. But I'm getting a week of clouds here, and adding enough batteries and solar panels to charge them up in a day would be a HUGE expense. I'm running my generator way more than I'd like, and using gas to do it (expensive and non-renewable). So thinking if I had a Phoenix I could get through a week of clouds without running the generator. I am completely off-grid, or else I'd maybe be happy just using the AC charger on the Growatt.

 

[CubesAreShapes]

What about Sigineer APC3048D? Seems to output 3000W split-phase out of the box and has a built in transfer switch. I could wire the Growatt into it, I think. Seems to be comparable units from Sungoldpower and AIMS. Would still have to manually turn on/off the Growatt, but maybe I could keep it in power saver mode. Sigineer probably uses more idle power than it might be worth, 60W according to the specs. Will look into the others.

Edit for link: https://www.sigineer.com/product/30...48-volt-120v-240v-split-phase-pure-sine-wave/