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chrisawp asked

Maximum Charge Voltage (DVCC - Limit Managed Charge Voltage)

Good morning Victron Community,


I've noticed the addition in DVCC the ability to limit the managed battery charge voltage to a value of your liking. The way I understand it is the ability to override the BMS CAN CVL (charge voltage limit) value from the battery and to charge at the selected voltage specified in DVCC.


1619248571504.png


For this particular site we are using 2x Revov R100 batteries which are set up with CAN comms between the battery pack and Multiplus-II 5kVA. The battery's parameters are set up to charge at a CVL value of 55.5V as seen below


1619248694990.pnghowever as a test I've lowered it to 54V in DVCC (and KEEP BATTERIES CHARGED) BUT I see that although it is trying to be close to 54V charging it still goes above that at 54.51V and triggers a High Voltage alarm on VRM (see below):


1619248448215.png


2021-04-24-090239.jpg


VEConfig file is also set up to charge at 54V for both absorption and float for this test (just noting as extra information).


Question for this post: Any ideas why this 54V limit is not holding?


Although the end result doesn't affect the batteries (safe voltages) the alarms in VRM are the problems.


Thanks!

Multiplus-IIbattery chargingDVCC
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2 Answers
Vangelis Beligiannis avatar image
Vangelis Beligiannis answered ·

The over voltage is due to the fact that the PV inverter has a slow response with the frequency swifting.

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chrisawp avatar image chrisawp commented ·

@Vangelis Beligiannis - I specifically switched off the PV inverter for this to eliminate it as possible cause, the only production was from a Smart Solar 250/100. Also, frequency shifting is only applicable in off-grid mode.

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Alexandra avatar image
Alexandra answered ·

@ChrisAWP

It is also possible the BMS is getting a bit of a runaway issue in cell management. Where one or two cells in the battery are needing to have their charge bled down but the balancing boards are not quick enough so the whole bank is rising.

I have a local brand that does that.

You SOC is in absorption phase there so it is most likely overshooting internally. The problem is particularly bad with repeat absorption when keeping it at full charge - had the bank rise over 62V once causing mppt shutdowns and everything. Have found letting it cycle at down to 95% helpful.

It is a can bus generated warning so it suggests the batteries are gving the warning even though the battery itself is designed to allow the higher voltage? If you set it back to its recommended voltges does the error stop?

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chrisawp avatar image chrisawp commented ·

Hi @Alexandra, valuable points made! Worthwhile to completely discharge and charge it back up again.

Setting back to recommended voltages renders the same issue also.

What I did find yesterday was that if I used Optimized (with or without battery life) and kept the SOC at 100% then it actually charged at the set voltage in DVCC (54V in this case) without overshooting. Using keep batteries charged makes it overshoot, which makes me think about your point of the cell management issue.

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Alexandra avatar image Alexandra ♦ chrisawp commented ·

Hi @ChrisAWP

Excellent, glad you managed to zero in on the issue.

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