franck47 avatar image
franck47 asked

actually have Multiplus want to add Fronius prime

Hello Friends at Victron !

I actually have an off grid system that runs with a recent (2018 I think) Victron Multiplus charger/inverter 5000VA (24/5000/120), a battery bank 1500Ah 24V and a Victron Blue Solar charger 2000W fed with 3kWp PV array.

I have installer another 10 kWp PV array and I'm looking for obtaining the best from it.

Picture here under is the actual configuration , and the new part to add : it was imagined as the addition of a band new fromius primo 8.2kW to feed the microgrid. I've been told the actual fronius Primo and my actual Multiplus should work together perfectly.

My questions are :

-will the multiplus charge the battery using the ac provided to it on its output ?

-could the multiplus be unhappy of this configuration as the Primo is overpassing the 1-1 rule, means are the problems related here are they still relevant to 2018 multiplus and Primo use ? as they are supposed to be very well fit together by Victron & Fronius ??

-if breaking this rule would be a problem , if have a setting at the Primo inverter to let him produce AC standalone and then install the Primo at Multiplus AC in , instead ? supposed no more rule 1-1 problem then ?

-otherwise if I purchase a primo 8.2kVA, I may be obliged to set software limitations to example 5kVa maybe ? And then make trials with oscilloscope switch on/off loads and see how behave frequencies and voltage when shut off to confirm the settings in the particuliar setup ?

I used to be a solar installer, but no more commercial now, and the technology improvement require us to update. Not easy, many manufacturers. I decided to keep using the victron, nice manufacturing, but feels a bit sad to see the new blue solar charger full of gel, cannot be repaired anymore.

The Victron products can be used in so diverse situations, it's an enormous Job you are doing at Victron. Thanks a lot for your help !

I am wishing to bring an interesting question that may interest many. Haven't found related equivalent in history.

Also thanks to anyone that who agrees to help !


MultiPlus Quattro Inverter ChargerFronius
img-0388.jpg (56.3 KiB)
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

3 Answers
Vangelis Beligiannis avatar image
Vangelis Beligiannis answered ·

Hi, I am an installer too and I have had a very similar system with yours for 2 years. The Fronius will charge the battery through the Victron.

The 1-1 rule is essential for avoiding overcharge of the battery and overloading the Victron as well when charging through it. I had installed 5000Wp panels on a 3000W Primo in order to follow the rule.

If you install the Fronius on the Ac in the 1-1 rule does not exist but on an off grid system the fronius Will not work on the Ac in.

If you install the Fronius on Ac out and regulate the output you will be fine.

Have in mind that if your batteries need equalisation, the Victron cannot do it with the Fronius. It can only be done with the Mppt.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

franck47 avatar image
franck47 answered ·

Hello Vangelis.

Thanks for your help and experience report ! Where you also using a Multiplus 5kVA ?

So when the Primo will inject AC, when an AC load suddenly OFF, the Multiplus will be obliged to feed the excess voltage into the battery ?

And in normal regulated operation (AC loads under control, Multiplus on & Primo injecting as necessary) then the multiplus is it able to normally monitor control the charge of battery thru itself in a normal manner ? (3 steps charging)

What about if the primo was able to run solely (not tie grid) , then we would feed multiplus AC in with Primo, and the Multiplus would act in power assist mode ?

Power assist has no 1-1 rule requirement I think ?

idea :would it be possible to detect these events (surge energy battery charge from a sudden load released on AC) and immediatly clamp AC with a power resistor ?

Or if the event is also noticeable as AC overvoltage, simply make a precise voltage-limiter load that would take all the excess energy ? I have noticed, not yet measured, in normal operation a multiplus does produce overvoltage when we release a significant load.

Have no setup like this existing ?

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.


The Fronius is instantly regulated to reduce its power if the Loads get less. This is done by elevating the AC frequency. The Fronius has a derating algorithm and will even go to 0W if necessary to comply with the Multi demand. No overload has ever occured to me.

0 Likes 0 ·
franck47 avatar image franck47 Vangelis Beligiannis ·

hi !

I see on your other post, you have a quattro 8KVA, so it should work without risk with the fronius 3kWp if you have big enough batteries...

I know the fronius and Multi would have regulations to prevent overcharge, but reading at victron document the problem maybe the regulation can't be intantaneous , while overload can be, I can understand that, regulation system should not be immediate, if it was it could introduce some malfunction of another over-reacting type, efficient way to cool the stuff is not having the things too reactive.

For the moment I think I would purchase a fronius 8.2 but derating it @ 3kW (I think could be done on it's software) . This way I can install on it my 10 kWp panels, it will cope with max peak Amps from the panels.

And I will try to study voltage limiting device, because I think if have transitory overload from the fronius it would create an overvoltage that could be limited by a load that becomes active only at these overvoltage events. To give a mechanical example, just like a centifugal brake would do.

0 Likes 0 ·

On a much more Advanced level, you can program the Fronius to reduce its output when the battery is almost charged and on the other hand, use the full output of the fronius when the battery is far away from 100% SOC. I am a certified Fronius Service Partner and I can give you details how to achive this with absolutelly no risk for your battery. On the bottom line you can use the Fronius as an 5 kw inverter until 95% SOC is reached and then reduce the Fronius output to 3kw until SOC reached 100%. Let me know if you want the details

0 Likes 0 ·
franck47 avatar image
franck47 answered ·

Yes Vangelis I am interested !

But I haven't receive the fronius yet. Where are you located ? No MP here I think

(you wrote "On the bottom line you can use the Fronius as an 5 kw inverter until 95% SOC is reached and then reduce the Fronius output to 3kw until SOC reached 100%. Let me know if you want the details)

1 comment
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Hi. Sorry for the delay. You can use a power output limit on the Fronius to never go over 5000 KW. It is in the PROFI menu of the Fronius. After that you need to use a relay (from your GX device) to give the Fronius an order to reduce the output further if SOC is above 95%.This is done by Using the I/O input on the datamanager of the Fronius and with some parametets that must be entered in the Energy Management menu of the Fronius.

If you need further assistant Let me know

0 Likes 0 ·