question

erkel avatar image
erkel asked

48/5000 Quattro II and Multiplus II parallel

Hi,

From some pictures, I am seeing that the 48/5000 230v Quattro II and Multiplus II are the same design, with a slight BOM difference being the extra AC input connector relay etc.

Is there any reason why paralleling them would be any different than paralleling two Multiplus II's
Sure I know it is unsupported, but given that it is only a marketing / product segment differentiation difference and the design down to the PCB is the same why would it not work.

Do the inverters check anything other sync signals etc when powering up in parallel?

I already have a 48/5000 Quattro II, but I can get the Multiplus II for half the price.


Thanks


Stephen


MultiPlus Quattro Inverter Charger
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2 Answers
Alexandra avatar image
Alexandra answered ·

@Erkel

Because they self identify as something different.

it is also about relay synchronization and the input resistance would be different. So while 'essentially the same' are actually quite different as well.

The control board is different.- the chip is mentioned in the documentation as a factor and the hardware revision matters as well. There are small but significant changes even in the same models.

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erkel avatar image
erkel answered ·

Looking at the VE.BUS pin out and skimming the VE.BUS protocol doc, I am not seeing any synchronization signaling, There is a RS485 bus over VE.BUS for coms but nothing dedicated for sync that I can see.

I take it that sync in achieved by each multiplus / quattro via sensing and synchronizing on the AC output?
Ie The master turns on first and then the slaves sync to the AC output from the master then the slaves turn on once they are in sync.

Reading through the parallel docs there is no power balancing logic either, you need to match the output wiring resistance and not use large wiring as per docs, as you are using the output wiring as as load balancing resistors, to balance the load between the inverters.

If there is no model checking with the other devices on the VE.BUS in parallel systems on startup, assuming one unit is configured as master and another configured as slave, it should work regardless of what regardless of what multiplus II / quattro II model it is I would think?
Sure I know that is bad from a business prospective and is "unsupported" as you are opening a can of worms.

But surely if we can ask nicely matching output models in the multiplus II / quattro II range ie 48/5000 II models can be paralleled, it is business decision that may need some tweaks in the software to indicated that it is an allowed configuration?



4 comments
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Kevin Windrem avatar image Kevin Windrem commented ·

Parallel operation relies on equal impedances in all AC and DC paths of all units in parallel. Rather than each unit operating on its own, the master tells the slaves what inverter duty cycle to use. This and frequency/phase synchronization are all handled by careful, mission critical communication over the RS-485 connection between the units. If impedances differ between units, then one unit will produce more current than the others. This is the main reason for "same model, same vintage" requirement exists. Even tiny resistance variations inside the units will unbalance the currents.

Let's not also forget the obvious difference that a Multi has only a single AC input and a Quattro has two AC inputs. So you would not be able to cable them up the same anyway.

System configuration tool does not permit selecting devices of different types (I tried it in demo mode.)

The only way this could work if it were allowed in the configuration tool is through experimentation and trimming cable lengths to compensate for internal impedance differences.

The amount of system engineering to pull this off would far exceed the price difference between Multi IIs and Quattro IIs.


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trepsig avatar image trepsig Kevin Windrem commented ·

From what I understand from your comment, if I plan to use multiple units in parallel, do they need to be purchased and set up at the same time? Therefore, would it not be possible to plan an infrastructure to which more Quattro II units can be added as the need for energy consumption increases?

I recently bought a house in the countryside and wanted to start experimenting with the Quattro II by purchasing one, with the idea of being able to add more in the future as energy needs increase. For example, currently, the car is a PHEV charging at 3.5kW with a 17kWh battery, but in the future, we will likely have an EV with a much larger battery and charging at 7kW which can't be handled by a single Quattro II.


Thanks in advance for any guidance or insights you can provide.

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nickdb avatar image nickdb ♦♦ trepsig commented ·
A frequently discussed topic.

If they are too old then you may struggle to get them balanced.

Even if the units are identical, the wear alone affects the internals and how well they will pair.

Occasionally there are hardware changes which can really affect this, your supplier should be able to advise you, but generally, it is best to parallel them upfront or soon after.


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Alexandra avatar image Alexandra ♦ nickdb ♦♦ commented ·
@trepsig

You can plan it like that, but have a definite time period. And this does depend how hard you are running the system.

But in 6 months hard service you will notice a definite difference.

It matters a little less with three phase so the bigger EV scenario I would switch to. Three phase system rather than try parrallel.

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