Lynx Shunt not resetting to 100%

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andybierlair asked Feb 24, '23

Lynx Shunt not resetting to 100%

I am having struggles to getting my Lynx Shunt reset the SOC to 100%.

My battery is full, hardly accepting any more Amps BUT the criteria for the shunt to reset to SOC are not met, as it does very small micro cycles, each time resetting the "Charge detection time".

Even setting this to as low as 1 minute does not help as the battery is constantly going from charging to idle to discharging and back.

My settings:

* Lynx Shunt:

Charged Voltage: 55.0V

Tail current: 0.70% (Total Ah of battery: 840Ah)

Charged Detection Time: 1 min

* All the MPPTs (5x 450/100):

Float & Absorption: 55.4V

* Multiplus II (3x 5000 / 3 phase):

Float & Absorption: 55.2V

I am feeding excess energy to the grid (ESS). Disabling this does not prevent the battery from doing these micro cycles.

The AC Loads on the Multiplus are constant. Initially I thought spikes might cause those micro cycles, but it's not that.

The battery is DIY with a JK BMS, no communication with Victron, no DVCC. I would like to keep it that way. Balancing happens at 3.45V and all cells are balanced with < 10mV deviation.

Any clues how I can prevent those micro cycles so that my shunt actually trips to 100% SOC?

Here a view of the battery, just a few seconds apart:

SmartShunt SOC

screenshot-2023-02-24-at-132252.png (217.7 KiB)

screenshot-2023-02-24-at-132214.png (220.0 KiB)

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klim8skeptic answered · Feb 24, 2023 at 05:56 PM

* Lynx Shunt:

Charged Voltage: 55.0V

Tail current: 0.70% (Total Ah of battery: 840Ah)

Charged Detection Time: 1 min

Your tail current seems low at 0.7%. 2 - 4% would be the normal range.

Charged detection time 5 min should suit.

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andybierlair commented · Feb 24, 2023 at 06:22 PM

I don't think my tail current is that low. 0.7% out of 840Ah is still about 6A going into the battery.

I will try to increase the tail current a bit to see if it has a better effect. At this stage I am not sure if the battery goes into constant charge/discharge state when the tail current is slightly higher, but it's worth a shot. If it works, then I would increase Charged detection time accordingly.
I will have to wait for tomorrow's sunshine to give it a shot :)

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klim8skeptic ♦ andybierlair commented · Feb 24, 2023 at 06:45 PM

Keep an eye on the current the batt takes during the absorp time, it really tapers off quickly.

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andybierlair commented · Feb 25, 2023 at 12:23 PM

Increasing the Tail Current to 2% solved my issue. At the same time I was able to increase the Charged detection time to 5 minutes, which I feel is much better as well.

Thank you for those hints!

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Answer 1 · 2023-02-24T12:59:19Z

JohnC answered · Feb 24, 2023 at 12:59 PM

Hi @andybierlair

Your Charged Voltage is set too high. Just lower it enough so your 'microcycles' don't reach it.

They may not be microcycles anyway, just the lack of application of a charge V.

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andybierlair commented · Feb 24, 2023 at 01:05 PM

The charged voltage seems OK to me. When I monitor the situation, it never goes under 55.0. It usually stays between 55.05 and 55.15, which is within the boundaries for the Shunt's "Charged Voltage" Criteria.

Each time there is a little discharge of just a few Amps, the charged detection time counter is being reset. And in my case, this going back and forth happens in very short intervals (less than 1 min).

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JohnC ♦ andybierlair commented · Feb 24, 2023 at 01:20 PM

Sounds like your BMS switching, possibly set too high? Either V or A is spiking past the limits, perhaps of too short a duration to detect, at least with standard monitoring means.

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andybierlair JohnC ♦ commented · Feb 24, 2023 at 01:27 PM

BMS Switching as in overvoltage protection? This is set to 3.65V and I'm quite far from that, as all the cells are balanced to 3.45V

Other than that, the BMS is sitting quiet not doing anything abnormal.

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