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lonesom avatar image
lonesom asked

ESS + DVCC - MPPTs overcharging battery when feed-in limit is reached.

Hi there,

I have a DC coupled system:

2x 150/70 Smart Solar MPPT

1x MP 48/5000/50-70 II

15kWh LFP (Polarium).

7.2kW PV array.

ESS and DVCC are active.

There is some anomalous behaviour, when the grid max feed-in rate is reached (~4200w), excess PV power is dumped into the battery beyond the absorption/float voltage, causing overcharging of the battery.

I understand the MPPTs are externally controlled by the Multi, and go to maximum power when controlled by ESS feed-in, but it seems like an oversight for the Multi to allow the MPPTs to dump excess PV into the Batteries when the feed-in is at it's maximum rate?

I understand I can throttle the MPPTs manually using max charge limit to stop this behaviour, but that wastes PV potential when I have to charge the battery and have AC loads also.

Am I doing something wrong here?

Advice much appreciated.

MPPT ControllersESSDVCC
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3 Answers
Alexandra avatar image
Alexandra answered ·

@Lonesom

ESS on feedback ignites the DVCC charge current limit it is in the manual.

with DVCC and non intelligent batteries (at least that is what i am assuming is happening here as your batteries are not on the compatible list), each mppt relies on its own internal algorithms.

Try using the charge voltage limit there to cap what is sent to the battery in DVCC Do you have a BMV in the system? This will help the system differentiate what is passing over the ve bus and what is going to the battery.

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lonesom avatar image lonesom commented ·
Hi Alexandra,

Thanks for your input.

The DVCC CVL is already enabled, and matched to the absorption voltage. The MPPT's still just blast past this and without intervention the batteries hit their over voltage protection.

Your assumption is correct, the batteries are not in comms with the victron system.

I have a smart shunt in the loop but no BMV.

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lonesom avatar image
lonesom answered ·

Update:

After trying a few things, I've isolated the issue down to the Feed-in limit function. If this is enabled (I had it set to 4000W), the MPPT's just continually push excess energy into the battery above and beyond the stated ABS and FLT voltages set. However, with this function disabled (no feed-in limit), the MPPT's behave appropriately, holding the Battery voltage at 0.4v above the set float voltage, even where there is certainly additional PV power to be used, it constrains output to the max potential of the Multiplus.

Is this a bug?


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larsea-dk avatar image larsea-dk commented ·
If it was a bug, it might be sorted. I have tried to run with the "limit system feed-in" under ESS activated and it seems also to hold at approx. 0.4v above the max voltage of the battery. I haven't yet tested it in days with shifting cloud/sun. I just expect it works, since the MPPT do react fast. Hopefully I remember to update on this later :-)
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tranzorb avatar image
tranzorb answered ·

Seems like the problem I stated today : https://community.victronenergy.com/questions/203452/ess-with-dvcc-and-dc-coupled-pv-surplus-injection.html

I would be great if Victron could add some options to let (even more) choice to users on the behaviour of the system..

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