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PeterM avatar image
PeterM asked

Charge voltage just slowly increasing beyond given values

Recently updated firmmare on MP1 5 kva 230V from 433 to 497. Its a grid connected system ESS with SMA PV inverter and BMV 702 battery monitor. Recently having good weather so battery was fully charged by midday and charger went from absorb mode to float mode ( 54.4V ABS and 53.8V float ) however voltge just crept up to 55 V by the end of the day . Current was very small around 0.3 A, however its enough to increase voltage on a fully charged battery ( 600AH lithium ) . I have DVCC on using the BMV as a reference voltage . Voltage sense lines currently not connected. Any ideas ? 1661273460125.png


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MultiPlus Quattro Inverter Charger
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6 Answers
Alexandra avatar image
Alexandra answered ·

@merle.peter@gmail.com

Use DVCC to limit the charged voltage.

It may be there are cells are unbalanced in your pack. Just guessing, in my experience this is when I have seen that weird rise in voltage.

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PeterM avatar image PeterM commented ·

Hi Alexandra, no it has nothing to do with an unbalanced pack - the pack is not managed by the Victron - no CanBus. It is a DIY battery with a JK BMS - its perfectly balanced delta less than 5 mV

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Alexandra avatar image Alexandra ♦ PeterM commented ·
Try the DVCC setting then.
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zoneblue avatar image
zoneblue answered ·

Is it temp compensating? Should be disabled for lithium.

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PeterM avatar image PeterM commented ·

No , batteries are set to lithium . This never happened with V433 on the Multi, Only thing thats changed is v497 on the multi and have removed sense wires ( did some rewiring - might reintroduce the sense wires again )


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Alexandra avatar image
Alexandra answered ·

@merle.peter@gmail.com

In getting some feedback from various sources, the solution discussed is to enable 'feed in excess' for DC-coupled in the ESS menu of the GX device, and then set the Limit Feed in maximum to 0 W.

This should allow any of those small excess overshoot currents (a couple of amps) to go to the grid instead of into the battery and keep the battery voltage stable.


The voltage rise situation in my case happened grid at night with a keep batteries charged so not the same as your situation.

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PeterM avatar image
PeterM answered ·

I do full export to to grid - no limit ,. Do not have any mppts - Solar is SMA GT inverter . As I said previously the only change was a change from V433 to v497 on the multi. I noted that the V497 uses different algorithms to calculate AC consumption. It seems to have a dead band between -2 and +2 Amps where internally I think current in that range is considered "zero " . I have also seen that when DVCC was on ( now removed it to check if its a DVCC issue ), setting current charge limit to zero the charge current drifts between -2 and +2 amps even when you have surplus PV and system is exporting to grid . Previously the 0 current was tightly managed managed +- 0.5 A .

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Alexandra avatar image Alexandra ♦ commented ·

If you are feeding back DVCC is supposed to be ignored. Especially the CCL.

But I have seen users on the forum utilize the 0A CCL in DVCC to prevent their system charging from the AC PV. And make sure they are only DC mppt charging.

But you did make 2 changes to the system, I guess putting the voltage sense wires back will help work out which one made the difference.

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johanndo avatar image
johanndo answered ·

I doubt there is any charging what you see, it is the resting Voltage of the cells, they discharge from Absorption until they hit the float setting. The voltage fluctuation comes from loads and variable voltage drops / increases resulting from the currents involved. It will not overcharge your battery. 3.4V cell voltage for Absorption (16 cells 54.4V) is way too low any way, battery may be not even 90% full.

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PeterM avatar image
PeterM answered ·

Iss is related to DVCC. Disabled DVCC and the problem has resolved. There is obviously a different way that DVCC works with V433 and V497. I used DVCC to syncronise my BMV 702 voltage which is accurate to the multiplus internal voltage which is horribly inaccurate

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