allaboutsolar avatar image
allaboutsolar asked

Reverse Power to Generator in AC Coupled Off grid System

How is reverse power flow to generator controlled in AC Coupled off grid Multi and Quattro Systems?

Generatorac coupling
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5 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Allaboutsolar,

Please have a read of this previous Question, and come back here if you still need further answers;

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allaboutsolar avatar image
allaboutsolar answered ·

Thanks Guy,

No that does not appropriately answer the question at all.

My expectation when seeking technical support would be to find clear references to installation and programming manuals (including clause numbers) and detailed wiring diagrams as required to ensure compliance with warranty requirements, not anecdotal experience from third parties.

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Hi @AllAboutSolar,

In that case you would be best to attend a Victron technical training program.

I explain in some detail why this is the case in this answer:

I do give the following technical description:

If you are worried about the surplus AC PV potentially back feeding into the Generator, it is possible. In this case it can be an option to modify the configuration of generator on AC2 input and AC PV inverter on AC2 output of the Quattro and program them via assistants to only be available during states of charge or voltage ranges where there is no chance of reaching full charge simultaneously while both are connected, or it must only be one or the other connected at all.

Stand Alone system design is a complex interaction of many components. User requirements will need to be interpreted based on many variables, and is the domain of a specialist, and specific to that installation.

Some systems will require full isolation of a generator and AC solar, others will require none.

If you are unable to attend training yourself, please contact a Trained Victron Dealer who has attended training which includes more advanced documentation and diagrams.

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allaboutsolar avatar image allaboutsolar Guy Stewart (Victron Community Manager) ♦♦ commented ·

Thanks Guy, yes that is who I originally contacted and they said they had no idea and to try here, in the mean time I've quoted out the job using products from a company that provided on the phone technical support yesterday.

Thanks though for your time.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ allaboutsolar commented ·

Would you mind sharing those?

It would help me to improve things on Victron’s end to see the example of the kind of resources that you were looking for.

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andreww avatar image
andreww answered ·

I agree with @AllAboutSolar that this is not an entirely satisfactory answer.

I hesitate to join in because I am a third party with an "anecdote".... but for what it's worth...

I am in the scenario you describe: off-grid with a solar inverter feeding into the AC side of a Victron Multiplus, and a diesel generator feeding into the generator input.

I have a system that continuously monitors the flow of power (true RMS power) through various points in the system and I can confirm that absolutely definitely you do sometimes get reverse power being fed to the generator. The Victron limits the battery voltage, and the maximum current into the battery. You can therefore get a situation where the solar generation (minus loads) is putting more power into the Victron than it can use. If the generator is off, then the Victron will frequency-shift and this will reduce the solar power output. However, if the generator is on, the Victron cannot frequency shift because the frequency is controlled by the rotation speed of the generator engine in this situation. In this scenario it feeds the excess power back to the generator. I have graphs that show this very clearly.

What Guy Stewart is saying (I think) is that if you are worried about this, then you can configure the Victron so that it doesn't turn the generator on in the first place in this scenario. But I agree with you that this isn't really a satisfactory answer. My generator has a 3-position switch: (a) manual off (b) auto (ie controlled by the Victron / CCGX and (c) manual on. If it is switched to "manual on" then the Victron cannot turn it off. (I do occasionally have reasons to put it manually on, and anyway it is something that can happen, so it should be allowed for).

It would be better if the Victron could be configured to simply open its generator input relay in this situation, ie open-circuit the generator so that the load is zero rather than negative.

My own generator does not seem to be harmed at all by the occasional episode of reverse power, but I agree with you I would prefer not to have it at all.

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Hi @AndrewW,

In your circumstance, I would suggest perhaps to attach your AC solar to the AC-2 output of your Multi, and use the programmable relay assistant or Generator Assistant so that the AC-input relay is opened when the AC2-output relay is closed, and when AC-input relay is closed, AC2-output relay is opened.

There is some further documentation for this use case here:

This will prevent the possibility of AC-Solar back feeding to the generator. In effect, inverting the default behaviour (where AC-2 out relay is closed when AC-input also is).

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andreww avatar image andreww Guy Stewart (Victron Community Manager) ♦♦ commented ·

Thanks Guy. I hadn't intended to hijack @AllAboutSolar's thread with my own issue - but I'm afriad I'm now more confused that when I started. The documentation at is somewhat confusing. The first paragraph discourages you from using the Self-consumption Hub-2 v3 assistant ("this is now depreciated") but then the second paragraph seems to suggest that pretty much the only reason you might use the "AC ignore" solution would be if you had an old-type microprocessor.

Secondly, I don't want to merely "ignore AC input": I want the Victron to start and stop my real generator. The only time I would want to ignore AC input is in the situation where there is negative power to the generator.

It sounds as though in your solution I could either have generator power or solar power at any given moment but not both. But I don't want to turn solar off merely because generator is on - but only under the fairly rare circumstances that there is reverse power to the generator.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ andreww commented ·

It would be valuable to bring together a few of these various resources under the one heading now that AC coupled systems seem to be increasingly common.

Your example perfectly demonstrates some of the difficulties with hard design rules.

Though I agree the public documentation around the options available and implications could be improved.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ Guy Stewart (Victron Community Manager) ♦♦ commented ·

I have created an additional AC Coupled PV Training in Victron Professional Online Training.

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clubbers avatar image
clubbers answered ·

It's kinda mindboggling that a company of Victron's size cannot supply a complete list of instructions on how the product is supposed to be used. The information should be available, and only if you can't understand it (the text/pictures) should you have to attend the training.

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Hi @Clubbers

There are a lot of options to do this, what is the best solution depends on the installation.

Because of all the options, we recommend to use an experienced installer for these systems. If your installer cannot set this up, than you might be better of with another installer.

One of the simplest solutions is to use DC-solar chargers

When using AC coupled solar, you can shut down the PV. how to shut down the PV inverters depends on the situation, easiest option is to put them on AC-out2 and disconnect the relay when charging with a generator.

A very simple way: set the generator to run at 52-53 Hz, so the PV shuts down when the generator is running.

You can set the generator to stop before the battery is charged fully, preventing feed-in. But in this case, again, total PV power shouldn't exceed inverters charge capacity.

And then something else: most (bigger) generators don't mind if there is a little feed-in, the rpm will raise a bit (52-53Hz?) and PV will throttle back to zero.

So there's your answers. Please understand that due to all the possible configurations, it's not easy to just learn this from any documentation (although everything can be found online). You also need experience to correctly setup and dial in the systems, prevent oscillations, etc.

Also, read:

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clubbers avatar image clubbers Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

My point is, that you shouldn't have to search through the site, different manuals etc. Lot's of the info is spread out in various places, and you have to read one manual, then apply that knowledge in another etc. It's not good.
If you buy an appliance, it should come with one manual, or at least all manuals colletcted.
Also, in many of the manuals there are errors, 120/230 is mixed, different models are mentioned completely mixed in the text, jumping from one to the other (for example Quattro and MultiPlus is often mixed).

For example, if you go to the quattro, and click on manuals, you get this link.

But that link is not the same as this one!

Why on earth, isn't all those manuals linked in the 1st link???

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ clubbers commented ·

Hi @Clubbers,

I like to fix these things when I can,

On my computer I clicked both of those links and see the exact same identical list as I would expect.

What are you seeing on your computer that is different?

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daymie avatar image
daymie answered ·

Hi Guy,

What if the feedback is going to the Grid and not the generator? How can this be stopped?

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