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Vangelis Beligiannis avatar image

Equalization not possible for Victron off-grid AC coupled and DC coupled systems.

Hello!

I have spent many hours and days to make my offgrid system to perform an equalization charge on my OPZS batteries. I am now almost absolutely certain that my system will never manage to perform it properly unless Victron makes changes to the process. To be more specific.

I have a Multiplus 24/5000 an MPPT 150/70 (2000W panels installed) and a fronius 3.0 (5000W panels installed) on the ac out.

If I programm the MPPT to perform an automatic equalization, it will start the process after it has finished the absorption face. But as soon as the voltage increases the ac coupled Fronius dicreases its output to 0W and stops taking care of the AC loads of the house. So the MPPT power is distributed to the AC loads and what is left tries to equalize the battery. If the ac loads increase the things get even worse! The Fronius continues to give 0W an the the demand of the AC load comes from the MPPT and from the battery! So although there is plenty of solar power to manage the load and perform the equalization the fronius stays closed and the battery starts to discharge! Even if the volatge of the battery drops bellow the float voltage, the fronius stll stays closed!

If I manually start an equalization on the Multiplus together with the MPPT, thing are better, but the Fronius only gives a small percentage of the loads and does not give its full power.

If on the other hand I try to start an equalization only on the Multiplus from the CCGX, then the MPPT switches of and the fronius has to take care of the loads and the equalization at the same time.


This is very disappointing ! Practically my batteries will never equalize and they will be finally damaged.

Is there any change that Victron will improve the firmware of the Multiplus so it can take care of the loads when the MPPT is trying to equalize?

In the pictures below you can see that the MPPT is trying to cover the loads and the equalization while Fronius is closed. img-20201229-124350.jpg


MPPT - Solar Charge Controlleroffgrid
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3 Answers
Vangelis Beligiannis avatar image
Vangelis Beligiannis answered ·

Finally there is no answer to the my question. Equalizing on an off grid ac coupled system is not possible. The Multiplus will keep the frequency locked above 52.7HZ and the Fronius will never give power to make the equalization possible.

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As I was informed by Daniël Boekel (Victron Energy Staff) , on another post :

"Our PV inverter assistant (also in ESS assistant) uses the configured absorption voltage (in the Multi).
As a safety feature, when battery voltage is above absorption voltage * 103%, the output frequency is locked until voltage lowers to float-voltage -3,2 volt (48V system)."


So this is probably the reason the equalization will not work on an off-grid system with an ac coupled inverter. When the inverter tries to increase the voltage to make the equalization, the frequency locks.

michelg avatar image
michelg answered ·

Hi Vangelis ! As far as I understand the situation, the issue is coming from the Fronius which detects the increasing power and disables its own production. I see two ways of having a workaround : perform manually the equalization AND disable the connection from the battery bank to the Fronius, so it will continue using its own power coming from the PV array.

Or, look if there is a switch / physical or software to enable a higher voltage arriving at the Fronius and still letting it using its own power.

May be there is a trick, but not owning a Fronius makes me difficult to see if there is another option available. You will probably get an answer from the VE Staff on the forum.

Michel.

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Thank you for your reply. I cannot disconnect the battery from the multiplus because it will shut down. The only trick I can do is reconfigure the Absorption voltage in the Multiplus to meet the equalization voltage of the MPPT. This way it will work as if in absorption. I then have to also regulate the DVCC charge current so it does not damage the battery.

This can be done but it is difficult and ofcourse it cannot be done by everybody. I am an installer and I can do it but I can never explain to a simple end user how to do it.

Lets hope somebody from the victron staff will help


michelg avatar image
michelg answered ·

May be there is an option using a Battery Protect, you could disable the power arriving to the Fronius from the battery bank, so it will continue to work and provide AC.

Michel

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The Fronius inverter is AC coupled, so it is not connected to the battery bank.


You can see in the picture thet the DC bus is not connected to the Fronius.