question

Hendrik Coetzee avatar image
Hendrik Coetzee asked

Battery "trickle" discharging while scheduled charging active

System details :

  • Victron MultiPlus 2
  • DC MPTT coupled
  • BYD battery
  • Grid-tied
  • Grid feedback NOT allowed
  • DVCC enabled

I am using Scheduled Charging to prevent battery discharge during certain times of the day. "Stop on SOC" set to 50%.

As I understand the documentation, battery discharge is not allowed while the schedule is active.

And this is mostly true - I do not see "large" discharges from the batery.

However, I do observe a continuous, fluctuating "trickle" discharge while charge schedule is active. I easily lose 5% SOC to this in a +-6 hour period.

In the attached screenshot you can observe a 10W draw, while Scheduled Charging is active.

I do NOT see this when min SOC has been reached - then battery draw is zero, as expected.

So my question is, is this:

  1. a software bug? (venus, mp2, byd BMS)
  2. misconfiguration?
  3. harware issue of some sort?
  4. documentation omission?

Anybody else experiencing same? Not?

ESS
screenshot-20190809-161600.png (200.9 KiB)
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Jaco Reinecke avatar image Jaco Reinecke commented ·

Jip, also seen it. No idea why it is slowly discharging.

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3 Answers
Justin Cook avatar image
Justin Cook answered ·

@Hendrik Coetzee, the Multiplus-II has a zero-load draw of between 13W and 18W depending on your exact model, so I suspect that this is what you're seeing.


multi-ii.png (86.1 KiB)
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Hendrik Coetzee avatar image Hendrik Coetzee commented ·

Thanks @justin - initially I thought so too, but it seems it is more complicated than that.

Seems scheduled charging had some unintended side effects in v2.20, which was fixed in v2.30.

BUT the fix essentially necessitates that some small discharge still be allowed from the battery.

Details here: https://powerforum.co.za/topic/4094-victron-multiplus-2-ess-scheduled-charging-battery-trickle-discharge/?tab=comments#comment-59268

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Alexander Bartash avatar image
Alexander Bartash answered ·

I see the same behavior on Quattro II 5kva + BMV 702. It discharges slowly until hits minimum allowed SOC value in ESS.

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johnone avatar image
johnone answered ·

I'm also seeing "a continuous, fluctuating "trickle" discharge while charge schedule is active" when an SOC target is set during a scheduled charge. If no SOC target is set, the batteries reach 100% and reliably go into 'Idle' state until the end of the schedule charge period. System is M-P II 48/5000 FW 500 and 4x 3.5kWh Pylontech batteries.

I see this has been an issue in the past with Victron's software configuration - e.g. https://github.com/victronenergy/dbus-systemcalc-py/commit/0067057c52858edeaf26256e9d2be10d4519b78a

My concern is that the batteries are not equally discharging, they fluctuate between one, two, three or all batteries discharging. End of scheduled period SOC ends up being 2-3% below the SOC when setting the target to 80 or 85%.

As per the above linked to thread, I'm guessing that with the ESS Manual, "the docs glossed over some of the ugly details."??

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