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timmtoolman avatar image
timmtoolman asked

Can you paralell two MultiPlus, one charging from grid, the other from generator?

Hi everyone,

Hopefully the title explains it all, but if not...

I've read through the manuals and some online articles looking for specific clarification on this, but the information on Multiplus/VEWhatever is very fragmented and poorly organized, and the search function here isn't much better. I'd like a definitive answer before we outlay such a premium price.

We're looking at buying one Multiplus (24v 3000VA) for now, due to budget limitations, to serve as our inverter and the primary 'bad weather' charge source from our generator. But when grid connection becomes available at the property in the next few years, we'd like to add a second Multiplus to the same battery bank, outputs in parallel (single phase) just to boost general inverter capacity, but also to enable grid-charging/passthrough via one Multiplus, while keeping generator charging/passthrough on the other. Ideally, so that we can charge the batteries and/or pass through power to loads from either generator, or grid, or both, depending on circumstances. No plans/interest in feedback to grid.

Is this possible? If so, do we NEED a GX device to manage this?

Thanks

multiplus ve.bus
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7 Answers
porcini avatar image
porcini answered ·

Hello,

yes, this is possible, but you can't use both sources simultaneously. You have to chose which one should be prefered.

regards,

Porcini

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timmtoolman avatar image timmtoolman commented ·
You mean that It cannot use both grid and generator power at the same time? Why is this? And do you have a reference/document where this is outlined in more detail? Thanks
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porcini avatar image porcini timmtoolman commented ·
you cannot sync the genset with the grid
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timmtoolman avatar image timmtoolman porcini commented ·

Ah right, so you mean I cannot use both grid and generator AC passthough? That makes sense.


But surely one MP can pass through power from grid, while the genny is used to charge tha batteries? Or alternatively, one can bpass thru from grid/gen, and the other can invert and sync to the grid/genny (whichever is in use)?



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porcini avatar image porcini timmtoolman commented ·

it wouldn't be possible in a split phase system, but as they are paralleled, I think so. But it's not possible to charge from generator while using the grid.

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timmtoolman avatar image timmtoolman porcini commented ·
Thanks. Can I ask - where did you get this information from? ANy specific documents?
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marekp avatar image
marekp answered ·

You can do something like that, but it is better to buy a Quatro to get the same result.

Power of this system will be equal to the power of one MP.


screen-shot-2021-09-24-at-43513-pm.png


screen-shot-2021-09-24-at-43513-pm.png (127.1 KiB)
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timmtoolman avatar image timmtoolman commented ·

Thanks. But why is the power not summed? The capacity is there surely?


Do you have a reference document I can read further? Where did this image come from?

Thankyou again



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marekp avatar image marekp timmtoolman commented ·

https://professional.victronenergy.com/online-training/20/

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timmtoolman avatar image timmtoolman marekp commented ·

Can you please outline more what you mean by "Power of this system will be equal to the power of one MP."

Even you diagram seems to indicate the output is equal to that of 'shore/genset plus BOTH inverters'


What is the point of syncronising and linked functionality, if it then wont combine power outputs?

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marekp avatar image marekp timmtoolman commented ·

You can register for free and listen to all the professional lectures.

When there is no grid or genset, you will get power from both MPs.

When running from the grid or from genset power will be limited by input relay of one MP.

Also charging current is limited to the one MP capability.

This is how I understand that setup.


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timmtoolman avatar image timmtoolman marekp commented ·
That seems to be a login service I cannot access....



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timmtoolman avatar image timmtoolman marekp commented ·

I've just found this thread, which also seems to contradic what you're saying, in that it says 'two 5000va Multis would be equivalent to a 10000VA Quattro'.


https://community.victronenergy.com/questions/59584/can-two-multiplus-provide-the-same-functionality-o.html




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marekp avatar image marekp timmtoolman commented ·
But one MP will provide power from the grid and the other from the battery.

Only one MP can charge the battery at the rate of 1.7kW only if its capacity is available for charging.

If you draw 4.8kW (two MP/3000 in parallel) the battery will be limiting the time the system will provide this power even when you have AC from the grid.

You could set your genset to charge the battery at the same time, but not through one of MPs.

It would have to be separate charger.

MPPT could be used to charge battery but only when the sun is up.

Again, this is as I understand this setup. I could be wrong. :)


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timmtoolman avatar image timmtoolman marekp commented ·

"If you draw 4.8kW (two MP/3000 in parallel) the battery will be limiting the time the system will provide this power even when you have AC from the grid."

I understand the batteries will be the limiting factor - after all, its just two inverters in tandem. But you said 'the power of this system will be the power of one MP". Why would it not be the power of 2 x 3000VA?

"But one MP will provide power from the grid and the other from the battery. Only one MP can charge the battery at the rate of 1.7kW only if its capacity is available for charging."

Why? Where is this said? Why can't one unit charge from AC and the other from genset, to provide double the charge to the batteries? It's just two DC charge currents. Obviously this would entail there is no inverter/AC power available when doing this, but I dont see why they cant simultaneously act as chargers.


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marekp avatar image marekp timmtoolman commented ·

If you connect AC-out of both MPs together, they are synchronized on each AC-in as well.

So you cannot connect unsynchronized genset to the second AC-in when first AC-in is powered..

This is why you can feed AC to this system only through one MP's AC-in.




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timmtoolman avatar image timmtoolman marekp commented ·
Okay, I think I get what you mean...


So youre saying that with two Multis connected in parallel, once it detects the 'first' AC input on the 'first' MP, it will set up BOTH to sync with that waveform. This way, if the second MP was to start inverting off the batteries to supplement the AC input, the waveform would match.

Thus, when the 'second' unit detects an AC signal on its inout, and finds it's out of phase/sync, it will simple reject that input as it obviously cannot control that waveform? Ergo, it cannot use it to start charging.

Is that correct?

Thanks


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marekp avatar image marekp timmtoolman commented ·
That is correct.
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iand avatar image iand timmtoolman commented ·
IIRC you can think of the Multiplus as having one bidirectional AC<==>DC converter inside, which can charge the battery (ACin==>DC), act as an inverter (DC==>ACout) if there's no ACin, or act as a power boost (ACout=ACin+DC==>ACout).


In power boost mode the Multiplus adjusts its internal DC<==>AC converter to match the frequency and amplitude of ACin; depending on how its controlled, it can either take power from ACin and pass it to the batteries (charging) or take power from the batteries and add it to ACout (power boost) by adding it to ACin.


So if the two ACout are connected together, then so are the two ACin if each Multiplus is connected to an AC source. If the ACin sources are identical both Multiplus work in parallel with double the power. If the ACin sources are different and both are turned on then either one of the Multiplus will refuse to connect to it (best case) or the two will fight each other and something will die (worst case).

I don't know for sure what happens, but even in the best case you will only be able to use one Multiplus at a time to charge the batteries.


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timmtoolman avatar image timmtoolman iand commented ·
Noted. Am replying to your answer below
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marekp avatar image marekp timmtoolman commented ·

The way I set-up my system is as follows.

System is based on 48V battery. (when you listen to the lectures you will know why)

I have 3 phase system build on 6 MP-II/48/3000.

My genset is charging battery directly. This way is the most economical way since genset is running at max efficiency until battery is full. When you connect genset to the AC-in, it is not loaded with the constant power because your house load is changing and it is not economical.

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timmtoolman avatar image timmtoolman marekp commented ·
Thanks. Where in that lecture are the points re. choosing 48v? Or just the usualy concerns about efficiency of transmission with lower currents?
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marekp avatar image marekp timmtoolman commented ·

Try reading this first.

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

and other materials here:

https://www.victronenergy.com/support-and-downloads/technical-information


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timmtoolman avatar image timmtoolman marekp commented ·
thanks
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s3w47m88 avatar image s3w47m88 timmtoolman commented ·

@Timm.Toolman in your comments above you mentioned you don't know for sure what would happen if you put two AC in's that may, or may not, have the same waveform.


I had the same question, so I tried it.

Nothing happened, the system was smart enough to protect from any hazardous results (sparks, overheating wires, etc...)

I had a generator, I don't remember which one but it was probably my Campion Dual Fuel 5000 watt generator. Which has a 30 amp and a 20 amp outlet. I tried by running just the 30 amp first to the main "L1", and the system charged. Then I ran the 20 amp to the second "L2". Nothing changed, L1 continued to charge

Then I reversed them. Again, L1 charged, not L2.

I also tried this with a smaller generator I have, from both it's 20 amp ports. Assuming their wavelength was the same and it would be allowed. It was not. L1 charged, not L2.

Eventually, as I mentioned in my previous comment, I purchased a separate inverter, non-Victron brand, and used that to charge the system with a second generator. I don't think I have tried to draw the power through the non-Victron inverter AND the main (first) MultiPlus at the same time yet. If I did, the generator stalled (the larger 5000 watt one) but I don't remember.

I hope this information is helpful to someone on the struggle bus!

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iand avatar image
iand answered ·

The downside is that though both Multiplus together can provide 6kW/230Vac from the batteries (discharge), the battery charging current from shore or genset is limited to 70A/1.7kW by the fact that you can only use one or the other at a time. A single Quattro 24/5000 can charge at 120A/2.9kW, costs almost as much as two Multiplus but you don't have the parallel/control problems.

NB. Multiplus II is newer/cheaper/smaller and there's a Quattro II coming, see here https://www.victronenergy.com/media/pricelist/Web_PricelistVictron-EURO_2021-Q3.pdf

Multiplus 24/3000/70 EUR1570

Multiplus II 24/3000/70 EUR1342

Quattro II 24/5000/120 EUR2700

Note that at these power levels 48V is cheaper, if you have the choice:

Multiplus II 48/3000/35 EUR1060

Quattro II 48/5000/120 EUR2200

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timmtoolman avatar image timmtoolman commented ·
This contradicts what @MarekP said above. He says the output is for some reason only equal that of one MP ie 3000VA.


Where are you getting your information from, may I ask? Also - why can onle one MP charge at a time? If each MP has its own independant AC input, why can they not both charge at once?


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marekp avatar image marekp timmtoolman commented ·
AC-in and genset are not synchronized and this is why you cannot have both AC sources feeding at the same time, and this is why only one MP can be charging. The one connected to AC.
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timmtoolman avatar image timmtoolman marekp commented ·
why would they need to be synchronised? Theyre the same frequency in the first place, and theyve both converting to **DC** to charge the battery.


This explanation still makes no sense., and nobody can apparently reference any material to back it up.It's not mentioned in that video you linked either.



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marekp avatar image marekp timmtoolman commented ·
If you do not believe us, do the experiment.

Start your genset and plug it into the live AC socket.

Only do it from the distance and buy insurance for your house before doing it. :)


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timmtoolman avatar image timmtoolman commented ·
Where does it say you can only charge from one Multi at a time?


I dont understand why two cant just act like two independant chargers. Nor can I find that written anywhrre.


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iand avatar image
iand answered ·

You can't have 2 independent AC sources connected to the two Multiplus at the same time, because when you connect an AC input to the Multiplus the AC output follows it to allow power boosting. So if (for example) the shore is 220V 50Hz and the generator is 230V 51Hz, the AC outputs of the inverters fight each other if they're connected together.

If you have two separate AC output buses then you can use both at once, but then you have to partition the loads across the two buses.

If you have one AC input source connected to both in parallel, then you can parallel both outputs. But not for the case you want, if the AC inputs are separate (shore and genset) then the AC outputs have to be separate too.

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timmtoolman avatar image timmtoolman commented ·
Why does the diagram above fropm the Victron training material contradict this, then? If both AC sources are the same frequency, surely there is no issue?



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iand avatar image iand timmtoolman commented ·

The two AC sources will not be the same frequency. The shore power will be at the frequency of the grid (e.g. 50Hz +/-1%). The generator will run at its own frequency (e.g. 50Hz +/-5%). Each Multiplus can only see its own AC input, and synchronises its AC output to this (same voltage and frequency) to allow power boosting. If you connect the AC outputs of both Multiplus together and have both AC inputs active, there may be magic smoke...

The Victron manual says that if Multiplus are to be connected in parallel, the voltages at all three ports (AC in, DC battery, AC out) must be closely matched, with identical cable resistance and identical models of Multiplus, because the AC==>DC and DC==>AC circuits inside need to share current equally.

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porcini avatar image porcini timmtoolman commented ·

If there are two active inputs, the unit will sync and connect to the prefered one. This means only one input will be used, the other one will be ignored.

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marekp avatar image marekp timmtoolman commented ·
Not only frequency needs to be the same.

Phase also needs to be the same.


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iand avatar image iand marekp commented ·
And voltage.
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marekp avatar image marekp iand commented ·
And all harmonics. :)
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timmtoolman avatar image timmtoolman marekp commented ·
And its belt and shoes.
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marekp avatar image marekp timmtoolman commented ·
Harmonics are not a joke.

Try to connect in parallel square wave (infinite number of harmonics) and sine wave (one harmonic)

This is why some gensets are impossible to use on AC-in.

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timmtoolman avatar image timmtoolman timmtoolman commented ·

Okay I think i get whats being said here - jsut to repeat in case it's missed above


So youre saying that with two Multis connected in parallel, once the 'first' MP detects an AC input, it will set up its own output (obviously) but also the output of any other paralell units to sync with that waveform. This way, if the second (or third etc) MP was to start inverting off the batteries to supplement the original AC passthrough, the waveforms would match.

Thus, when the 'second' unit detects an AC signal on its input, and finds it's out of phase/sync, it will simple reject that input as it obviously cannot control that waveform? Ergo, it cannot use it to start charging.

Is that correct?

Thanks

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timmtoolman avatar image timmtoolman commented ·
So as a corollary of this:


If one ACout is isolated from the other (or indeed not even in use), then it would indeed be possible charger batteries both off grid and genset, using both MPs simultaneously as chargers? The critical factor here being isolating the respective ac outputs.


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iand avatar image iand timmtoolman commented ·
Yes, that's what I said earlier -- if ACin and Acout are *both* separate for both Multiplus then only the DC (battery) ports are in parallel, so they act as two independent units. You then have to split the AC loads between the two units, no more than 3kW each.
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timmtoolman avatar image timmtoolman iand commented ·
Gotcha.


I assume this is all the same for the Quattros?

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iand avatar image iand timmtoolman commented ·
Yes, a Quattro can only select one AC input at a time, but it can switch between the two inputs depending on the rules that are applied.
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timmtoolman avatar image
timmtoolman answered ·

I'm trying to reply to comments, but suddenly it's saying they're 'awaiting moderation?'

From what I'm reading though, my understanding now is:


So youre saying that with two Multis connected in parallel, once it detects the 'first' AC input on the 'first' MP, it will set up its own passthrough with this waveform, and signal the outputs on any other parallel MPs to match this waveform. This way, if the second (or so on) MP was to start inverting off the batteries to supplement the AC passthrough from the 'first' MP', the waveform would match.

Thus, when the 'second' unit detects a different AC signal on its input, and finds it's out of phase/sync, it will reject that input as it obviously cannot control that waveform and sync it? Ergo, it also cannot use it to start charging.

Is that correct?

Thanks

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porcini avatar image porcini commented ·

More or less it's correct.

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timmtoolman avatar image timmtoolman porcini commented ·
'More or less'?


Have I misunderstood something?



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timmtoolman avatar image timmtoolman timmtoolman commented ·
oh and now i can comment again apparently



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porcini avatar image porcini timmtoolman commented ·

The second unit can charge from the power it gets from the output (which is basically the input of the first multi)

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timmtoolman avatar image timmtoolman porcini commented ·
Hm, okay.....


So ...wouldn't that imply a total charge of MORE than just one MP then?

Couldn't one MP take its 70A charge from the selected AC input, then pass through the rest of the power to Acout, and on to the next MP, which then uses that to charge as well?


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porcini avatar image porcini timmtoolman commented ·

Yes, that's all I tried to tell. But consider transfer capacity, there is a 16A and 50A model.

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timmtoolman avatar image timmtoolman porcini commented ·
Noted, thankyou



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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

I'm trying to reply to comments, but suddenly it's saying they're 'awaiting moderation?'

I looked into that.
The reason is because you "@mention" to much users in one comment.

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mrhappy avatar image
mrhappy answered ·

Combining DC power from different sources is easy, it's just voltage. AC is voltage, frequency, phase, DC offset etc. that have to be exactly in sync to combine power sources the way the multiplus and quattro do it when using AC input. When one multiplus have locked in to the grid and follows these variables with its inverter, there is no way for another un-changeable AC input source to enter the party.

A Quattro already have two AC inputs and can be programmed to use either one under chosen conditions. If you get a quattro 24/3000 now and add a second one in the future to parallell them, you would be using the units the way they are designed to be used. Be aware, though, that the electronic hardware design updates continually and to sync two units they have to be very close or the same when it comes to hardware, so the longer the time goes, the harder it (might) will be to get one that is compatible with the one you buy now.

I would wait for the Quattro II, I myself have a Multiplus-II which I am very pleased with and the coming Quattro-II is probably the same but with another AC input for the kind of application you are questioning about.

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timmtoolman avatar image timmtoolman commented ·
The issue is price. Where I am, a 24/3000 Multi is about half the price of a Quattro.


I understand the quattro also has dual inputs....but when you say 'adding a second in the future is the way they are designed to be used' - it would still have the same restriciton regarding different AC inputs, no? If two parallel quattros share an AC output, I still wont be able to draw AC in from both generator AND grid, correct?


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mrhappy avatar image mrhappy timmtoolman commented ·
correct
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marekp avatar image marekp timmtoolman commented ·
Those two identical Quatros can be connected in true parallel fashion.

Inputs are connected and outputs are connected.


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timmtoolman avatar image timmtoolman marekp commented ·
What do you mean 'true' paralell? How does this differ to the Multis? You mean that as they have two inputs each, you can have both units set up to bnoth be connected to the same genny on one input, and the same grid on the other, so when they switch, they are still on the same 'syncd' input?



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marekp avatar image marekp timmtoolman commented ·
Correct, and both can charge battery at the same time, they share the load.
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mastercatz avatar image
mastercatz answered ·

just wondering if its possible to have the grid connected to all the multiplus AC input 1 or can it only be connected to 1 unit ? if not I guess large battery charger is needed to allow parallel to provide needed combined AC output power?

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nickdb avatar image nickdb ♦♦ commented ·
All the inverters need to be connected. You can get creative (unsupported) with multi-phase systems, but in a parallel set, they all need to share the grid connection.
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mastercatz avatar image mastercatz nickdb ♦♦ commented ·
ok thanks , I was getting mixed info some places were saying Only 1x of the Inputs would be used and only that multiplus would be doing the loads leaving the others in standby as only the battery banks could be used to share loads , what I am wanting to do is have another 24v inverter supply its load and was going to feed that into AC1 and then use 48v victrons in paralel with their own new battery bank as the old inverter can not supply the loads needed and still have not gotten $'s worth out of the existing 24v bank yet to just throw away , assuming someway to set a import limit so it will not overload the other inverter's output ? I have had other inverters before when you could set % grid , battery and solar that is used , I might just throw the generator onto a battery charger
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