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Victron shunt vs battery BMS SOC

lotsofyoda

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Joined
Sep 19, 2022
Messages
8
My setup:
(1) battery bank: 120kwh (2400 Ah) - 24 x Lifepower (5.12kwh/100 Ah)
(2) inverters: Growatt 5000es x 6 in parallel
(3) panels: 6kw strings x 6 = 36kw solar input
(4) Victron Lynx shunt
(5) Solar Assistant monitoring, connected to 16 of my batteries in the bank, getting real time SOC from each of these batteries.
(6) Cummins 20kw propane backup generator with auto-start and auto shutting off.
(7) equipment all in garage at 50F/14C, generator outside.
(8) shunt controls generator start SOC 20%) and off (SOC 50%)
(9) 3 more inverters Growatt 5000es that are only wired between generator and battery bank to charge battery bank on “the back side”

My problems:
(1) Victron shunt SOC almost never matches battery SOC as read from battery BMS.
(2) if I have a full battery and synched Victron shunt to 100%, I can get both values to match almost throughout discharge to 20%, the first time only. For this to work, I have to set the capacity of my battery bank in the shunt to 2000 Ah, not the actual 2400. (20% not useable, batteries are only 12 months old)
(3) when charging the bank, the shunt may show 10-20% higher. I’m talking about SOC reading 50% on the shunt and turning off my generator. When the battery BMS is reading 35-40% SOC. This compounds with multiple charge/discharge cycles.
(4) my battery BMS has shown critically low SOC <5% when my shunt still thinks I have 25% left and generator didn’t fire.
(5) I’ve tried all combinations of settings. Currently peukert at 1.0 (off) which seems to give me most accurate discharge on first discharge. I’ve reduced my charging efficiency to 85%. Not sure what I’m missing

My current conclusions:
(1) Victron shunt completely inaccurate/almost worthless
(2) battery BMS most accurate
(3) may switch to using home assistant o communicate with Solar Assistant to get BMS SOC and try that quote for triggering generator.

Any thoughts/suggestions?
 
Last edited:
My setup:
(1) battery bank: 120kwh (2400 Ah) - 24 x Lifepower (5.12kwh/100 Ah)
(2) inverters: Growatt 5000es x 6 in parallel
(3) panels: 6kw strings x 6 = 36kw solar input
(4) Victron Lynx shunt
(5) Solar Assistant monitoring, connected to 16 of my batteries in the bank, getting real time SOC from each of these batteries.
(6) Cummins 20kw propane backup generator with auto-start and auto shutting off.
(7) equipment all in garage at 50F/14C, generator outside.
(8) shunt controls generator start SOC 20%) and off (SOC 50%)
(9) 3 more inverters Growatt 5000es that are only wired between generator and battery bank to charge battery bank on “the back side”

My problems:
(1) Victron shunt SOC almost never matches battery SOC as read from battery BMS.

Common. Though it shouldn't be as bad as you describe.

My Batrium and BMV drift a few % points, but always in the same direction, and I just re-synch them periodically - maybe once a month.

(2) if I have a full battery and synched Victron shunt to 100%, I can get both values to match almost throughout discharge to 20%, the first time only. For this to work, I have to set the capacity of my battery bank in the shunt to 2000 Ah, not the actual 2400. (20% not useable, batteries are only 12 months old)
(3) when charging the bank, the shunt may show 10-20% higher. I’m talking about SOC reading 50% on the shunt and turning off my generator. When the battery BMS is reading 35-40% SOC. This compounds with multiple charge/discharge cycles.
(4) my battery BMS has shown critically low SOC <5% when my shunt still thinks I have 25% left and generator didn’t fire.
(5) I’ve tried all combinations of settings. Currently peukert at 1.0 (off) which seems to give me most accurate discharge on first discharge. I’ve reduced my charging efficiency to 85%. Not sure what I’m missing

My current conclusions:
(1) Victron shunt completely inaccurate/almost worthless

Do the amps reported by the shunt match the BMS and match a check with a DC clamp ammeter, i.e., are all three measurements the same?

(2) battery BMS most accurate

Generally speaking, I don't put cheap Chinese stuff ahead of Victron stuff by default.

Does the BMS report Ah consumed in addition to SoC?
 
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