Adding a generator to a grid tied Victron system


I currently have a grid tied Multiplus 2 at my house.

I want to add a generator for backup, but it seem the Multiplus 2 can be a bit finicky with generators and it is tricky to set up. I was thinking of replacing the Multiplus 2 with one of these options…

  1. Quattro + anti-islanding device and then use generator on second AC input.
  2. New Quattro 2 and then use generator on second AC input

I understand that there are some restrictions on using the above 2 options while still also grid tied?
What would be the best solution?

What do you mean by this exactly?
Additional generation capability that will be used a fair amount but isn’t absolutely critical?
Or is an emergency generation that is fail-safe available anytime and rarely used?
How long (hours) must this standby generation last when you use it?

There are many options at different price points with subtle differences in suitability and convenience.

The two mentioned options are equivalent. A Quattro-II should cost less.

You would not use the anti-islanding on the generator. It would trip way too often. So if you used a Quattro, you’d put the anti-islanding on the grid input, and the generator would be tied directly.

With the both options, you can set the grid code of the second input to something other than NRS097, and you can use this to better support the generator.

Also, can I suggest putting the generator on AC-in-1? The reason is simple. When both sources are available, the Quattro gives AC-in-1 priority. That means that with the generator on AC-in-1, simply starting the generator automatically uses it, without having to throw a breaker. With AC-in-2, if the grid is also on (eg during a test run), the Quattro will not use the generator input unless you turn off the grid. And in systems where you have auto start/stop with a test run option (where the generator is started a few minutes a week to test it), that’s obviously suboptimal.

What I learned from my cousin with his MPII setup and a cheaper gennie, MPII refused to connect to the gennie, was that one needs to remove the NRS grid code, set it to other or whatnot, on the MPII, and his gennie happily ran with 3 x 3kva MPII’s in parallel.

Once Eskom comes back, he puts the NRS grid code back.

He was happy with that as the gennie only came into play when there were extended LS events and bad weather and a low SOC.

My 2 cents.

As an emergency generation that is a fail-safe; available anytime and rarely used…

I expect the standby generation will last 2-4 hours to just top up the batteries again.

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Thanks, that makes sense…I will definitely do that.

I understand you can set a charge limit on the generators AC input into the inverter so that the generator does not get overloaded…

The installer that installed my current system says if the loads are greater than the generator can supply, the inverter will switch the AC out off.

I understand that this might happen if there is zero battery charge, but if you still have charge in the battery will the Powerassist feature in the Victron inverter not just take charge from the battery as well, without switching the AC outputs off?

More than that. It allows the generator to be properly loaded. A generator is most efficient when it is loaded down to around 75% capacity. I was looking at some numbers yesterday, how much fuel a Diesel generator uses. Petrol will be similar.

Lightly loaded, it makes around 2.5kWh per liter. Properly loaded you can get this up to 3.5kWh per liter of fuel. That’s literally a difference of 20% vs 30% efficiency. So other than preventing overload, it also ensures that if there is little load, whatever is left is used to charge the battery.

Not quite. It takes the difference out of the battery in this case (if you enable PowerAssist, which I recommend you do), thereby allowing larger intermittent loads to run with a smaller generator.

Ok thanks, that makes sense.

Great info, thanks.

Another question:
I use the Multiplus 2 mqtt interface to pull data into node red.
Does the Quattro also have an mqtt interface or do you need a separate GX device?
I presume the Quattro 2 does have the mqtt interface like the Multiplus 2?

Uuuuuh, is that a trick question? Of course the Quattro is supported just as well as the Multi :slight_smile:

It is the GX device (Cerbo/Venus, etc) that enables MQTT and ModBus communication. I use ModBus.

Whilst the Quatro has a dedicated input, this could be overcome with a manual chop-over that could select a generator supply on the Multiplus input.
However, I think when it comes to the unit accepting the quality of the chosen generator’s supply I would expect the Quatro and the Multiplus to be equally finicky.

There seems to be many inconsistent versions of what brand and model of generator works. There is also the issue that the cheaper portable generators are mostly centre-tap earth. (V-0-V)

When I go off-grid, I’ll have a big battery bank capable of supporting me for several days.
However, I am not under the illusion that there I will never, ever require a generator.

Although I have not heard of anyone using the following solution.
What I intend to do is have a 96V DC generator supplying my batteries through an MPPT. This will allow me to control the load on the generator as well as control the dc voltage during the charging cycle. I can control the generator load by setting the MPPT max current.
However, it should overcome the problems of the inverter unit being finicky about accepting the AC waveform and the V-0-V issue.
I will install a dedicated MPPT, but there is no reason an existing MPPT and a chop-over couldn’t be used.

I haven’t shopped around yet so I just included this link for a quick google example:

Yes and no. With the Quattro, you can set one AC-input to be NRS097 compliant, and the other one to be “Other” with a nice wide input range. With the Multi, and a manual changeover, you may have to reconfigure the grid code every time you want to use the generator (as TTT says his friend does). There are, as far as I know, more improvements in the pipeline for the Quattro firmware too, but such improvements will never help you with the Multi as you have only that one input… which must be set to the relevant grid code to be compliant.

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OK, understood, I didn’t think of that (and I have Quatros)
The V-0-V thing will still present an issue though as that is non-compliant anyway.

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Ok, so it seems that to connect a generator to a Victron inverter the way to go so far:

  • Quattro with GRID on AC2 and GENERATOR on AC1
  • Enable PowerAssist
  • AC2 with GRID on anti-islanding and grid code NRS097
  • AC1 with GENERATOR not any anti-islanding and a grid code something other than NRS097 and wide input range
  • Rate limit generator current on AC1 to about 75% of the generators capacity.

Is there anything else that will be best practice to connect a generator to a Victron inverter?

More generically (for all generators)…

Generator needs to be earthed and TN bonded (South African regulation, otherwise you are not allowed to connect it to a house installation).

If possible, try not to use the smallest crapiest petrol generator, it works much better if you have something larger and stabler, eg a Diesel engine running at 1500RPM with a 4-pole alternator is always better than a petrol droning away at 3000RPM with a 2-pole alternator.

Ok. Is there any advantage to the so-called inverter generators.

Like this for example:
Inverter generator

As @plonkster stated:

That one is not a T-N generator. It is a V-0-V portable generator, which has two live wires with a centre-tapped Neutral. The live wires are 110V higher and lower than the neutral respectively giving a 220V total between the two lives. This is done because it is recognised that this is a portable generator that will not be used with earth leakage so there will only ever be a maximum voltage of 110V between live and earth.
It is designed to be used the double insulated portable tools.

It can be a V-0-V generator regardless of whether it is an inverter-based generator or not.

A standby generator which is a fixed installation generator will be 220V L -N and designed with the purpose you want to use it in mind. It is also more expensive.

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Additionally, I would avoid inverter-generators altogether when using with an inverter. Well… as always “it depends”, but certainly if you’re going to use ESS on the Multi, I would not put an inverter generator in front of it.

The reason is simply that an inverter generator already has a built-in inverter. They typically have a 3-phase alternator running at whatever speed is needed for the required power, this 3-phase “wild” AC is turned into DC and then changed back into 50Hz AC. Exactly 50Hz AC. And therein the issue…

With an older mechanical-style generator, the frequency is coupled to the engine RPM. Your typical hardware store petrol generator has the engine running at 3000RPM, which if you divide by 60 (to get revolutions per second) gives you 50Hz. That is not an accident. That’s why generators will always run at 3000RPM or 1500RPM (unless it is belt coupled, in which case you have to work in the pulley ratios). Now there is an interesting thing that happens with mechanical generators: If you accidentally feed energy into them, they turn into “motors” and they push the engine speed up, which can be detected and used to prevent this from happening. With your inverter generator… it was never designed to work like that.

So I would advise staying away from fancy inverter-generators. What you’re looking for is a good conventional Diesel generator… if the budget allows of course.


Thanks for the info…so a 1500rpm, diesel generator with 4 poles it is.

Just so that I can get the full picture, though…

I am thinking of installing the old style Quattro that it seems does not do a check for centre tapped generators that might be attached to it.

Besides the regulations forbidding connecting a centre tapped generator to a house installation, are there electrical dangers to doing this…i.e will something get damaged, blown up or someone electrocuted?